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8/19/2015 MODULE 12.1 OVERVIEW OF THE CENTRAL NERVOUS SYSTEM ERIN C. AMERMAN FLORIDA STATE COLLEGE AT JACKSONVILLE Lecture Presentation by Suzanne Pundt University of Texas at Tyler © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. CENTRAL NERVOUS SYSTEM OVERVIEW OF CNS FUNCTIONS • Central nervous system (CNS) – includes brain and • Functions of nervous system can be broken down into spinal cord; involved in movement, interpreting sensory information, maintaining homeostasis, and functions relating to mind three categories: Motor functions – include stimulation of a muscle cell contraction or a gland secretion; function of peripheral nervous system (PNS) Sensory functions – detection of sensations within and outside body; also is a function of PNS © 2016 Pearson Education, Inc. OVERVIEW OF CNS FUNCTIONS Integrative functions – include decision-making processes; exclusive function of CNS; includes a wide variety of functions: o o o BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • • Functions of nervous system (continued): o © 2016 Pearson Education, Inc. Interpretation of sensory information Planning and monitoring movement Maintenance of homeostasis Higher mental functions such as language and learning Brain – soft, whitish-gray organ, anatomically continuous with spinal cord; resides in cranial cavity and directly or indirectly controls most of body’s functions Weighs between 1250 and 1450 grams; made of mostly nervous tissue; contains epithelial and connective tissues as well Internal cavities called ventricles; filled with cerebrospinal fluid Receives about 20% of total blood flow during periods of rest; reflects its requirements for huge amounts of oxygen, glucose, and nutrients © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 1 8/19/2015 BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • Brain consists of four divisions, each distinct in type of • Cerebrum – enlarged superior portion of brain; input it receives and where it sends its output: Cerebrum divided into left and right cerebral hemispheres Each cerebral hemisphere is further divided into five lobes containing groups of neurons that perform specific tasks Diencephalon Cerebellum Responsible for higher mental function such as learning, memory, personality, cognition (thinking), language, and conscience Brainstem Performs major roles in sensation and movement as well Figure 12.1 Divisions of the brain (lateral view). © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • Diencephalon – deep underneath cerebral • Cerebellum – posterior and inferior portion of brain hemispheres; central core of brain Divided into left and right hemispheres Consists of four distinct structural and functional parts Responsible for processing, integrating, and relaying information to different parts of brain, homeostatic functions, regulation of movement, and biological rhythms Heavily involved in planning and coordination of movement, especially complex activities such as playing a sport or an instrument © 2016 Pearson Education, Inc. BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD © 2016 Pearson Education, Inc. BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • Brainstem – connects brain to spinal cord Involved in basic involuntary homeostatic functions Control of certain reflexes Monitoring movement Integrating and relaying information to other parts of nervous system Figure 12.1 Divisions of the brain (lateral view). © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 2 8/19/2015 BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • Spinal cord – long tubular organ enclosed within • White matter – found in both brain and spinal cord; protective vertebral cavity; blends with inferior portion of brainstem; ends between first and second lumbar vertebrae 43–46 cm (17–18 inches) in length and only ranges from 0.65–1.25 cm (0.25–0.5 inches) in diameter Central canal – an internal cavity within spinal cord that is continuous with brain’s ventricles; filled with cerebrospinal fluid consists of myelinated axons Each lobe of cerebrum contains bundles of white matter called tracts; receives input from and sends output to clusters of cell bodies and dendrites in cerebral gray matter called nuclei (Figure 12.2a) Spinal cord contains white matter tracts that shuttle information processed by nuclei in spinal gray matter (Figure 12.2b) © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD • Gray matter – found in both brain and spinal cord; • Communication between gray and white matter consists of neuron cell bodies, dendrites, and unmyelinated axons Outer few millimeters of cerebrum is gray matter; deeper portions of brain are mostly white matter with some gray matter scattered throughout Spinal cord is mostly gray matter that processes connects different regions of brain and spinal cord with one another; myelinated axons enable near instantaneous communication between locations • Make note – organization of gray and white matter in brain and spinal cord is reversed; spinal white matter is superficial while it is deep in brain information (in cord center); surrounded by tracts of white matter (outside); relays information to and from brain © 2016 Pearson Education, Inc. BASIC STRUCTURE OF THE BRAIN AND SPINAL CORD © 2016 Pearson Education, Inc. OVERVIEW OF CNS DEVELOPMENT • Brain and spinal cord develop from a tube with an enlarged end in embryo and fetus (Figure 12.3) Neural tube – hollow tube from which nervous tissue develops; completely developed by fourth week of gestation Caudal end of neural tube forms spinal cord; cranial end forms three saclike structures (primary brain vesicles) which include forebrain, midbrain, and hindbrain Cavity within hollow neural tube becomes ventricles in brain and central canal in spinal cord Figure 12.2 White and gray matter in the CNS. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 3 8/19/2015 OVERVIEW OF CNS DEVELOPMENT OVERVIEW OF CNS DEVELOPMENT • Primary brain vesicles give rise to five secondary brain vesicles by fifth week of development • Secondary brain vesicles create four divisions of mature brain (continued): • Secondary brain vesicles create four divisions of Midbrain expands into secondary brain vesicle called mesencephalon; develops into mature midbrain mature brain: Forebrain expands into two secondary brain vesicles (telencephalon and diencephalon); two lobes of telencephalon become cerebral hemispheres; diencephalon retains its name in mature brain Hindbrain develops into two secondary brain vesicles (metencephalon and myelencephalon), both of which develop into remainder of brainstem; metencephalon also matures to become cerebellum © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. OVERVIEW OF CNS DEVELOPMENT MODULE 12.2 THE BRAIN Figure 12.3 Development of the brain. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE CEREBRUM THE CEREBRUM • Cerebrum – structure responsible for higher mental functions (Figures 12.4–12.9, Table 12.1) Gross anatomical features of cerebrum include: o Sulci – shallow grooves on surface of cerebrum; gyri – elevated ridges found between sulci; together increase surface area of brain; maximizing limited space within confines of skull; example of Structure-Function Core Principle Gross anatomical features (continued): o Fissures – deep grooves found on surface of cerebrum o Longitudinal fissure – long deep groove that separates left and right cerebral hemispheres o A cavity is found deep within each cerebral hemisphere; right hemisphere surrounds right lateral ventricle; left hemisphere surrounds left lateral ventricle Figure 12.4 Structure of the cerebrum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 4 8/19/2015 THE CEREBRUM THE CEREBRUM • Five lobes are found in each hemisphere of cerebrum (Figure 12.4): Frontal lobe Parietal lobe Temporal lobe Occipital lobe Insula Figure 12.4b Structure of the cerebrum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE CEREBRUM THE CEREBRUM • Five lobes of cerebrum (continued): Frontal lobes – most anterior lobes o Posterior border – called central sulcus; sits just behind precentral gyrus o Neurons in these lobes are responsible for planning and executing movement and complex mental functions such as behavior, conscience, and personality Figure 12.4a Structure of the cerebrum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE CEREBRUM THE CEREBRUM • Five lobes of cerebrum (continued): • Five lobes of cerebrum (continued): Parietal lobes – just posterior to frontal lobes o Contains postcentral gyrus posterior to central sulcus o Neurons in these lobes are responsible for processing and integrating sensory information and function in attention © 2016 Pearson Education, Inc. Temporal lobes – form lateral surfaces of each cerebral hemisphere o Separated from parietal and frontal lobes by lateral fissure o Neurons in these lobes are involved in hearing, language, memory, and emotions © 2016 Pearson Education, Inc. 5 8/19/2015 THE CEREBRUM THE CEREBRUM • Five lobes of cerebrum (continued): • Five lobes of cerebrum (continued): Occipital lobes make up posterior aspect of each cerebral hemisphere o Separated from parietal lobe by parieto-occipital sulcus o Neurons in these lobes process all information related to vision Insulas – deep underneath lateral fissures; neurons in these lobes are currently thought to be involved in functions related to taste and viscera (internal organs) © 2016 Pearson Education, Inc. THE CEREBRUM © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER • Gray Matter: Cerebral Cortex – functionally most complex part of cortex; covers underlying cerebral hemispheres Most of cerebral cortex is neocortex (most recently evolved region of brain); has a huge surface area Composed of 6 layers (of neurons and neuroglia) of variable widths (Figure 12.5) All neurons in cortex are interneurons Figure 12.4c Structure of the cerebrum. © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER • Gray Matter: Cerebral Cortex (continued): Functions of neocortex revolve around conscious processes such as planning movement, interpreting incoming sensory information, and complex higher functions © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER • Gray Matter: Cerebral Cortex (continued): Neocortex is divided into three areas: primary motor cortex, primary sensory cortices, and association areas (continued): o Neocortex is divided into three areas: primary motor o cortex, primary sensory cortices, and association areas (next slide) o © 2016 Pearson Education, Inc. Primary motor cortex – plans and executes movement Primary sensory cortices – first regions to receive and process sensory input Association areas integrate different types of information: • Unimodal areas integrate one specific type of information • Multimodal areas integrate information from multiple different sources and carry out many higher mental functions © 2016 Pearson Education, Inc. 6 8/19/2015 THE CEREBRUM-GRAY MATTER THE CEREBRUM-GRAY MATTER Motor areas – most are located in frontal lobe; contain upper motor neurons which are interneurons that connect to other neurons (not skeletal muscle) • Primary motor cortex; involved in conscious planning of movement; located in precentral gyrus of frontal lobe • Upper motor neurons of each cerebral hemisphere Figure 12.5 Structure of the cerebral cortex (left hemisphere, lateral view). control motor activity of opposite side of body via PNS neurons called lower motor neurons; execute order to move © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER • Movement requires input from many motor association areas such as large premotor cortex located anterior to primary motor cortex • Motor association areas are unimodal areas involved in planning, guidance, coordination, and execution of movement • Frontal eye fields – paired motor association areas; one on each side of brain anterior to premotor cortex; involved in back and forth eye movements as in reading © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER Sensory Cortices • Two main somatosensory areas in cerebral cortex; deal with somatic senses; information about temperature, touch, vibration, pressure, stretch, and joint position Primary somatosensory area (S1) – in postcentral gyrus of parietal lobe Somatosensory association cortex (S2) – posterior to S1 © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER Sensory Cortices (continued): Sensory Cortices (continued): • Special senses – touch, vision, hearing, smell, and taste • Special senses (continued): each have a primary and a unimodal association area as does sense of equilibrium (balance); found in all lobes of cortex except frontal lobe Primary visual cortex – at posterior end of occipital Primary auditory cortex – in superior temporal lobe; first to receive auditory information; input is transferred to nearby auditory association cortex and other multimodal association areas for further processing lobe; first area to receive visual input; transferred to visual association area which processes color, object movement, and depth © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 7 8/19/2015 THE CEREBRUM-GRAY MATTER THE CEREBRUM-GRAY MATTER Sensory Cortices (continued): Sensory Cortices (continued): • Special senses (continued): • Special senses (continued): Gustatory cortex – taste information processing; scattered throughout both insula and parietal lobes Vestibular areas – deal with equilibrium and Olfactory cortex – processes sense of smell; in evolutionarily older regions of brain; consists of several areas in limbic and medial temporal lobes positional sensations; located in parietal and temporal lobes © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER Multimodal association areas – regions of cortex that allow us to perform complex mental functions: • Language – processed in two areas of cortex: Broca’s area – in anterolateral frontal lobe; premotor area responsible for ability to produce speech sounds Wernicke’s area (integrative speech area) – in temporal and parietal lobes; responsible for ability to understand language Figure 12.5 Structure of the cerebral cortex (left hemisphere, lateral view). © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER Multimodal association areas (continued): Multimodal association areas (continued): • Prefrontal cortex occupies most of frontal lobe; • Parietal and temporal association areas – occupy communicates with diencephalon, other regions of cerebral gray matter, and association areas located in other lobes; many functions including modulating behavior, personality, learning, memory, and an individual’s personality state © 2016 Pearson Education, Inc. most of their respective lobes; perform multiple functions including integration of sensory information, language, maintaining attention, recognition, and spatial awareness © 2016 Pearson Education, Inc. 8 8/19/2015 THE CEREBRUM-GRAY MATTER THE CEREBRUM-GRAY MATTER • Basal nuclei, found deep within each cerebral hemisphere; cluster of neuron cell bodies, involved in movement; separated from diencephalon by a region of white matter called internal capsule; includes (Figure 12.6): Caudate nuclei Putamen Globus pallidus Table 12.1 Motor, Sensory, and Association Areas of the Cerebral Cortex. © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER © 2016 Pearson Education, Inc. THE CEREBRUM-GRAY MATTER • Basal nuclei (continued): Caudate nuclei – C-shaped rings of gray matter; lateral to lateral ventricle of each hemisphere with anteriorly oriented tail Putamen – posterior and inferior to caudate nucleus; connected to caudate nucleus by small bridges of gray matter; combination of putamen and caudate are sometimes called corpus striatum Globus pallidus sits medial to putamen; contains more myelinated fibers than other regions Figure 12.6 Structure of the basal nuclei (anterolateral view). © 2016 Pearson Education, Inc. THE CEREBRUM-WHITE MATTER • © 2016 Pearson Education, Inc. THE CEREBRUM-WHITE MATTER Cerebral white matter can be classified as one of three types (Figure 12.7): Commissural fibers – connect right and left hemispheres; corpus callosum, largest of four groups in this category, lies in middle of brain at base of longitudinal fissure Projection fibers – connect cerebral cortex of one hemisphere with other areas of same hemisphere, other parts of brain, and spinal cord; corona radiata are fibers that spread out in a radiating pattern; condense around diencephalon to form two V-shaped bands called internal capsules Association fibers – restricted to a single hemisphere; connect gray matter of cortical gyri with one another © 2016 Pearson Education, Inc. Figure 12.7 Structure of cerebral white matter. © 2016 Pearson Education, Inc. 9 8/19/2015 THE CEREBRUM-LIMBIC SYSTEM • THE CEREBRUM-LIMBIC SYSTEM Possible pathway for information transferred by conduction of an action potential from one region of brain to another (Figure 12.8): 1. Action potential originates in gray matter 2. Action potential is sent to another area of gray matter by projection fibers 3. Second (new) action potential is generated by gray matter; spreads to neighboring gray matter by association fibers 4. Lastly, a third action potential is generated; can be sent to other cerebral hemisphere by commissural fibers Figure 12.8 A possible pathway for conduction of an action potential in the brain. © 2016 Pearson Education, Inc. THE CEREBRUM-LIMBIC SYSTEM • Limbic system – important functional brain system, includes limbic lobe (region of medial cerebrum), hippocampus, amygdala, and pathways; connect each of these regions of gray matter with rest of brain (Figure 12.9) Found only within mammalian brains Involved in memory, learning, emotion, and behavior © 2016 Pearson Education, Inc. THE CEREBRUM-LIMBIC SYSTEM • Limbic system (continued): Limbic lobe and associated structures form a ring on medial side of cerebral hemisphere; contain two main gyri: cingulate gyrus and parahippocampal gyrus Hippocampus – in temporal lobe; connected to a prominent C-shaped ring of white matter (fornix) which is its main output tract; involved in memory and learning Amygdala – anterior to hippocampus; involved in behavior and expression of emotion, especially fear © 2016 Pearson Education, Inc. THE CEREBRUM-LIMBIC SYSTEM © 2016 Pearson Education, Inc. THE DIENCEPHALON Diencephalon – at physical center of brain; composed of four components, each with its own nuclei that receive specific input and send output to other brain regions (Figure 12.10): • Thalamus • Hypothalamus • Epithalamus • Subthalamus Figure 12.9 Structures of the limbic system (anterolateral view). © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 10 8/19/2015 THE DIENCEPHALON THE DIENCEPHALON • Thalamus – main entry route of sensory data into cerebral cortex (Figure 12.10a, b) Consists of two egg-shaped regions of gray matter; make up about 80% of diencephalon Third ventricle is found between these two regions Thalamic nuclei receive afferent fibers from many other regions of nervous system excluding information about the sense of smell Figure 12.10a, b Structure of the diencephalon. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE DIENCEPHALON THE DIENCEPHALON • Thalamus (continued): • Thalamus (continued): Regulates cortical activity by controlling which input should continue to cerebral cortex Association nuclei o Each half of thalamus has three main groups of nuclei separated by thin layers of white matter o o Specific nuclei function as relay stations that receive Receive input from variety of sources Process information related to emotions, memory, and integration of sensory information Processed information is sent on to appropriate association areas of cerebral cortex input, integrate information, then send information to specific motor or sensory areas in cerebral cortex © 2016 Pearson Education, Inc. THE DIENCEPHALON THE DIENCEPHALON • Thalamus (continued): • Hypothalamus – collection of nuclei anterior and inferior to larger thalamus Nonspecific nuclei o o o © 2016 Pearson Education, Inc. Receive information from basal nuclei, cerebellum, and motor cortex Send information to a wide range of locations including cerebral cortex and other brain regions Involved in controlling arousal, consciousness, and level of responsiveness and excitability of cerebral cortex © 2016 Pearson Education, Inc. Neurons perform several vital functions critical to survival; include regulation of autonomic nervous system, sleep/wake cycle, thirst and hunger, and body temperature © 2016 Pearson Education, Inc. 11 8/19/2015 THE DIENCEPHALON THE DIENCEPHALON • Hypothalamus (continued): • Hypothalamus (continued): Inferior hypothalamus – anatomically and functionally Antidiuretic hormone and oxytocin, hypothalamic linked to pituitary gland by an extension called infundibulum; hypothalamic tissue makes up posterior portion of this endocrine gland hormones that do not affect pituitary gland, have their effect on water balance and stimulation of uterine contraction during childbirth, respectively Hypothalamus secretes a number of different releasing Input to hypothalamus arrives from many sources and inhibiting hormones; affect function of pituitary gland; in turn, pituitary gland secretes hormones that affect activities of other endocrine glands throughout body including cortex and basal nuclei © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE DIENCEPHALON THE DIENCEPHALON • Hypothalamus (continued): • Epithalamus – superior to thalamus; most of its posterosuperior bulk is an endocrine gland called pineal gland; secretes melatonin; hormone involved in sleep/wake cycle Mammillary bodies – connect hypothalamus with limbic system; receive input from hippocampus; involved in memory regulation and behavior Input from outside nervous system; endocrine system • Subthalamus – inferior to thalamus; functionally connected with basal nuclei; together, they control movement (among others) provides information from receptors that detect changes in body temperature and receptors that detect changes in osmotic concentration of blood © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE DIENCEPHALON CEREBELLUM Cerebellum – makes up posterior and inferior portion of brain; functionally connected with cerebral cortex, basal nuclei, brainstem, and spinal cord; interactions between these regions together coordinate movement (Figure 12.11) • Anatomically, divided into two cerebellar hemispheres connected by structure called vermis (Figure 12.11a) • Ridges called folia cover exterior cerebellar surface; separated by shallow sulci; increases surface area of region Figure 12.10c Structure of the diencephalon. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 12 8/19/2015 CEREBELLUM CEREBELLUM Cerebellum (continued): • Divided into three lobes: anterior, posterior, and flocculonodular lobes (Figure 12.11b) • Cerebellar cortex – outer layer of gray matter • Cortex is extremely folded and branching white matter is called arbor vitae because it resembles tree branches Figure 12.11a Structure of the cerebellum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. CEREBELLUM CEREBELLUM Cerebellum (continued): • Inner white matter contains clusters of gray matter (deep cerebellar nuclei) scattered throughout • White matter converges into three large tracts called cerebellar peduncles; only connection between cerebellum and brainstem Figure 12.11b Structure of the cerebellum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. CEREBELLUM THE BRAINSTEM Brainstem – one of oldest components of brain; vital to our immediate survival as its nuclei control many basic homeostatic functions such as heart rate and breathing rhythms (Figures 12.12–12.15) • Controls many reflexes (programmed, automatic responses to stimuli); functions in movement, sensation, and maintaining alertness Figure 12.11c, d Structure of the cerebellum. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 13 8/19/2015 THE BRAINSTEM THE BRAINSTEM Brainstem (continued): • Located inferior to diencephalon, anterior to cerebellum, and superior to spinal cord, on midsagittal section of brain (Figure 12.12) • Extends to level of foramen magnum; along with fourth ventricle (deep within brainstem), continuous with spinal cord and its central canal Figure 12.12a Midsagittal section of the brain showing the brainstem. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BRAINSTEM THE BRAINSTEM Brainstem (continued): • Three subdivisions; superior midbrain, middle pons, and inferior medulla oblongata, where following structures reside: Fibers of cerebellum and related nuclei travel through portions of brainstem where they either synapse with nuclei found there or progress on to other destinations in cerebral cortex or spinal cord Figure 12.12b Midsagittal section of the brain showing the brainstem. © 2016 Pearson Education, Inc. THE BRAINSTEM © 2016 Pearson Education, Inc. THE BRAINSTEM Brainstem (continued): Nuclei of reticular formation – group of connected nuclei scattered throughout brainstem, many functions including regulation of respiration, blood pressure, sleep/wake cycle, pain perception, and consciousness Tracts of white matter between spinal cord and brain – nearly all pathways to and from brain and spinal cord travel through brainstem Cranial nerve nuclei – many cranial nerves originate in brainstem; their nuclei have many sensory, motor, and autonomic responsibilities © 2016 Pearson Education, Inc. Figure 12.13 External anatomy of the brainstem. © 2016 Pearson Education, Inc. 14 8/19/2015 THE BRAINSTEM THE BRAINSTEM • Midbrain • Midbrain (continued): Inferior to diencephalon; surrounds cerebral aqueduct (connects third and fourth ventricles) (Figure 12.14b) Includes following structures: o Also known as mesencephalon; shortest and most superior brainstem region o Superior and inferior colliculi, protrude from posterior surface of brainstem; two paired projections that form roof of midbrain (tectum); involved in visual and auditory functions respectively; project to thalamus Descending tracts – white matter tracts that originate in cerebrum and form anteriormost portion of midbrain; called crus cerebri © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BRAINSTEM THE BRAINSTEM • Midbrain (continued): • Midbrain (continued): Includes following structures (continued): o o Includes following structures (continued): Substantia nigra – posterior to crus cerebri, is a darkly pigmented region whose neurons work with basal nuclei to control movement Red nucleus – posterior to substantia nigra; communicates with cerebellum, spinal cord, and other regions involved in regulating movement; role in humans not yet understood o o Many cranial nerve nuclei are found in midbrain Midbrain tegmentum – region of midbrain between cerebral aqueduct and substantia nigra; contains numerous nuclei, many of which are components of reticular formation; both ascending and descending white matter tracts are found in this region as well © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BRAINSTEM THE BRAINSTEM • Pons – inferior to midbrain; has a prominent anterior surface that contains descending motor tracts from crus cerebri, some of which pass through pons en route to spinal cord Other tracts enter cerebellum by way of middle cerebellar peduncle • Pons (continued): Pontine tegmentum – surrounded by middle cerebellar peduncles Pontine nuclei have many roles including: regulation of movement, breathing, reflexes, and complex functions associated with sleep and arousal Reticular formation and cranial nerve nuclei are located posterior to these tracts © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 15 8/19/2015 THE BRAINSTEM THE BRAINSTEM • Medulla oblongata – most inferior structure of brainstem; continuous with spinal cord at foramen magnum (Figure 12.14c) Pyramids – on anterior surface of medulla, contain upper motor neuron fibers of corticospinal tract (also called the pyramidal tract) as they travel from cerebral cortex to spinal cord • Medulla oblongata (continued): Right and left corticospinal fibers decussate (crossover) within pyramids; motor fibers originating from right side of cerebral cortex descend through left side of spinal cord and vice versa Posterior columns – paired tracts of white matter found on medulla’s posterior surface; carry sensory information from spinal cord to nucleus gracilis and nucleus cuneatus © 2016 Pearson Education, Inc. THE BRAINSTEM © 2016 Pearson Education, Inc. THE BRAINSTEM • Medulla oblongata (continued): Posterior columns also decussate within medulla so sensory information from right side of spinal cord is processed by left side of cerebral cortex and vice versa Olive – lateral to each pyramid; protuberance that contains inferior olivary nucleus; receives sensory fibers from spinal cord and directs information to cerebellum Several cranial nerve and reticular formation nuclei are found in medulla Figure 12.14 Internal anatomy of brainstem divisions. © 2016 Pearson Education, Inc. LOCKED-IN SYNDROME • • • Caused by damage to motor tracts of pons; cerebral cortex is unable to communicate with spinal cord; no purposeful movement is possible, but sensory pathways to brain remain intact (as do other cortical functions) Patients are therefore literally “locked in” their bodies; yet fully aware of everything going on around them; some can communicate using eye movements controlled by midbrain Small number of patients recover some motor functions but most do not; overall prognosis is poor; most succumb to infections or other paralytic complications © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BRAINSTEM • Reticular formation – collection of over 100 nuclei found in central core of three brainstem subdivisions making this one of most complex regions of brain (Figure 12.15) Input is received from multiple sources including: cerebral cortex, limbic system, and sensory stimuli Output is sent throughout entire brain and spinal cord © 2016 Pearson Education, Inc. 16 8/19/2015 THE BRAINSTEM THE BRAINSTEM • Reticular formation (continued): Central nuclei (center of reticular formation) function in sleep, pain transmission, and mood Nuclei surrounding central nuclei serve motor functions for both skeletal muscles and autonomic nervous system Other nuclei are instrumental in homeostasis of breathing and blood pressure Lateral nuclei play a role in sensation and in alertness and activity levels of cerebral cortex Figure 12.15 The reticular formation. © 2016 Pearson Education, Inc. THE BIG PICTURE OF MAJOR BRAIN STRUCTURES AND THEIR FUNCTIONS Figure 12.16 The Big Picture of Major Brain Structures and Their Functions. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BIG PICTURE OF MAJOR BRAIN STRUCTURES AND THEIR FUNCTIONS Figure 12.17 The Big Picture of Major Brain Structures and Their Functions. © 2016 Pearson Education, Inc. THE BIG PICTURE OF MAJOR BRAIN STRUCTURES AND THEIR FUNCTIONS MODULE 12.3 PROTECTION OF THE BRAIN Figure 12.17 The Big Picture of Major Brain Structures and Their Functions. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 17 8/19/2015 BRAIN PROTECTION BRAIN PROTECTION Three features within protective shell of skull provide additional shelter for delicate brain tissue: • Cranial meninges – three layers of membranes that • Cranial meninges – composed of three protective membrane layers of mostly dense irregular collagenous tissue Structural arrangement from superficial to deep: surround brain • Cerebrospinal fluid (CSF) – fluid that bathes brain epidural space, dura mater, subdural space, arachnoid mater, subarachnoid space, and pia mater (Figure 12.18) and fills cavities • Blood-brain barrier – prevents many substances from entering brain and its cells from blood © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BRAIN PROTECTION BRAIN PROTECTION • Cranial meninges (continued): • Cranial meninges (continued): Epidural space – between inner surface of cranial bones and outer surface of dura mater; only a potential space as dura is normally tightly bound to bone only allowing for passage of blood vessels Dura mater (dura) (continued): o Dura mater (dura) – outermost meninx; thickest and most durable of three meningeal layers; double-layered membrane composed mostly of collagen fibers with few elastic fibers Two layers of dura (Figure 12.18a): • Periosteal dura – outer layer; attached to inner surface of bones of cranial cavity; functions as periosteum with extensive blood supply in epidural space • Meningeal dura – inner layer; avascular and lies superficial to arachnoid mater • Mostly fused, creating a single inelastic membrane except in regions where cavities called dural sinuses are found © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BRAIN PROTECTION BRAIN PROTECTION • Cranial meninges (continued): • Cranial meninges (continued): Dura mater (dura) (continued): o Dura mater (dura) (continued): Dural sinuses – venous channels; drain CSF and deoxygenated blood from brain’s extensive network of veins; also found where meningeal dura folds over itself and courses between structures in brain © 2016 Pearson Education, Inc. o Dural folds include falx cerebri, tentorium cerebelli, and falx cerebelli (Figure 12.14b) • Falx cerebri – within longitudinal fissure; forms partition between left and right cerebral hemispheres; superior sagittal sinus (large dural sinus) found superior to falx cerebri • Tentorium cerebelli – partition between cerebellum and occipital lobe of cerebrum • Falx cerebelli – partition between left and right hemispheres of cerebellum © 2016 Pearson Education, Inc. 18 8/19/2015 BRAIN PROTECTION BRAIN PROTECTION • Cranial meninges (continued): • Cranial meninges (continued): Subdural space – serous fluid-filled space; found deep to dura mater and superficial to arachnoid mater; houses veins that drain blood from brain Arachnoid mater – second meningeal layer deep to Arachnoid mater (continued): o Arachnoid trabeculae – composed of collagen fiber bundles and fibroblasts; anchor arachnoid to deep pia mater o Arachnoid granulations (villi) – small bundles of arachnoid; project superficially through meningeal dura into the dural sinuses; allow for return of CSF to bloodstream subdural space; thin weblike membrane composed of dense irregular collagenous tissue with some degree of elasticity (Figure 12.18c) © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BRAIN PROTECTION BRAIN PROTECTION • Cranial meninges (continued): • Cranial meninges (continued): Subarachnoid space – found deep to arachnoid mater and superficial to pia mater; contains major blood vessels of brain; filled with CSF Pia mater – deepest meningeal layer; only meninx in physical contact with brain tissue Pia mater (continued): o Follows contour of brain, covering delicate tissue of every sulcus and fissure o Permeable to substances in brain extracellular fluid and CSF; allows for substances to move between these two fluid compartments; helps to balance concentration of different solutes found in each fluid © 2016 Pearson Education, Inc. BRAIN PROTECTION © 2016 Pearson Education, Inc. BRAIN PROTECTION Figure 12.18a, b Structure of the cranial meninges and dural sinuses. Figure 12.18c Structure of the cranial meninges and dural sinuses. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 19 8/19/2015 THE VENTRICLES AND CEREBROSPINAL FLUID • Four ventricles within brain are linked cavities that are continuous with central canal of spinal cord (Figures 12.19, 12.20) THE VENTRICLES AND CEREBROSPINAL FLUID • Right and left lateral ventricles (first and second ventricles); within their respective cerebral hemisphere (Figure 12.19): Resemble ram’s horns when observed in anterior view; Lined with ependymal cells horseshoe-shaped appearance in lateral view Filled with cerebrospinal fluid Three regions: anterior horn, inferior horn, and posterior horn © 2016 Pearson Education, Inc. THE VENTRICLES AND CEREBROSPINAL FLUID © 2016 Pearson Education, Inc. THE VENTRICLES AND CEREBROSPINAL FLUID • Third ventricle – narrow cavity found between two lobes of diencephalon; connected to lateral ventricles by interventricular foramen • Fourth ventricle – between pons and cerebellum; connected to third ventricle by cerebral aqueduct (small passageway through midbrain) Continuous with central canal of spinal cord Contains several posterior openings that allow CSF in ventricles to flow into subarachnoid space (Figure 12.19a) © 2016 Pearson Education, Inc. THE VENTRICLES AND CEREBROSPINAL FLUID • Cerebrospinal fluid (CSF) – clear, colorless liquid similar in composition to blood plasma; protects brain in following ways: Cushions brain and maintains a constant temperature Figure 12.19 Ventricles of the brain. © 2016 Pearson Education, Inc. THE VENTRICLES AND CEREBROSPINAL FLUID • Choroid plexuses – where majority of CSF is manufactured; found in each of four ventricles where blood vessels come into direct contact with ependymal cells (also produce some CSF themselves) Fenestrated capillaries have gaps between endothelial within cranial cavity Removes wastes and increases buoyancy of brain; keeps brain from collapsing under its own weight © 2016 Pearson Education, Inc. cells; allow fluids and electrolytes to exit from blood plasma to enter extracellular fluid (ECF) © 2016 Pearson Education, Inc. 20 8/19/2015 THE VENTRICLES AND CEREBROSPINAL FLUID THE VENTRICLES AND CEREBROSPINAL FLUID • • Choroid plexuses (continued): About 150 ml (2/3 cup) of CSF circulates through brain Pathway for formation, circulation, and reabsorption of CSF (Figure 12.20): Fluid and electrolytes leak out of capillaries of choroid and spinal cord plexuses into ECF of ventricles 750–800 ml of CSF is produced daily so old CSF must Taken up into ependymal cells; then secreted into ventricles be removed as choroid plexuses make new CSF as CSF Process of CSF production and removal occurs Circulated through and around brain and spinal cord in constantly; CSF is completely replaced every 5–6 hours subarachnoid space; assisted by movement of ependymal cell cilia Some CSF is reabsorbed into venous blood in dural sinuses via arachnoid granulations © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE VENTRICLES AND CEREBROSPINAL FLUID THE BLOOD-BRAIN BARRIER Blood-brain barrier – protective safeguard that separates CSF and brain ECF from chemicals and disease-causing organisms sometimes found in blood plasma (Figure 12.21) • Consists mainly of simple squamous epithelial cells (endothelial cells) of blood capillaries, their basal laminae, and astrocytes Figure 12.20 Formation and flow of cerebrospinal fluid (CSF). © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE BLOOD-BRAIN BARRIER THE BLOOD-BRAIN BARRIER • Unique features of endothelial cells found in barrier: • Substances that easily pass through plasma membranes Neighboring endothelial cells are bound together by many tight junctions; prevent fluids and molecules from passing between them; influenced by activity of astrocytes on developing brain Limited capacity for movement of molecules and substances into and out of cell by endocytosis and exocytosis © 2016 Pearson Education, Inc. are able to pass through blood-brain barrier; include water, oxygen, carbon dioxide, and nonpolar, lipidbased molecules • Protein channels or carriers allow for passage of other essential molecules across blood-brain barrier; include glucose, amino acids, and ions • Most large, polar molecules are effectively prevented from crossing blood-brain barrier in any significant amount; while barrier is protective, it can hinder access of medications into brain © 2016 Pearson Education, Inc. 21 8/19/2015 THE BLOOD-BRAIN BARRIER CONCEPT BOOST: WHERE EXACTLY IS BLOOD-BRAIN BARRIER? • No single structure is labeled “blood-brain barrier” on any figure because blood-brain barrier isn’t around brain; it’s within brain • Not located in one distinct place but found throughout entire brain • To understand this, we must first understand body’s tiniest blood vessels; capillaries are vessels that deliver oxygen and nutrients to body’s cells and remove any wastes produced by cells Figure 12.21 The blood-brain barrier. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. CONCEPT BOOST: WHERE EXACTLY IS BLOOD-BRAIN BARRIER? • Capillaries found in most organs and tissues are fairly INFECTIOUS MENINGITIS • Potentially life-threatening infection of meninges in subarachnoid space; inflammation occurs, causing classic signs: headache, lethargy, stiff neck, fever • Diagnosis – examination of CSF for infectious agents and white blood cells (cells of immune system); bacteria and viruses are most common causative agents: leaky; allow a wide variety of substances to move from blood to extracellular fluid (and vice versa) • Capillaries of brain are specialized to allow only selected substances to enter its extracellular fluid; effectively act as a “barrier”; prevents other substances from doing so (Figure 12.21) • Blood-brain barrier, therefore, is actually a property of capillaries found throughout brain rather than a distinct physical barrier Viral – generally mild; resolves in 1–2 weeks Bacterial – can rapidly progress to brain involvement and death; aggressive antibiotic treatment necessary; some most common forms are preventable with vaccines © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. THE SPINAL CORD • Spinal cord – composed primarily of nervous tissue; MODULE 12.4 THE SPINAL CORD responsible for both relaying and processing information; less anatomically complex than brain but still vitally important to normal nervous system function; two primary roles: Serves as a relay station and as an intermediate point between body and brain; only means by which brain can interact with body below head and neck Processing station for some less complex activities such as spinal reflexes; do not require higher level processing © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 22 8/19/2015 PROTECTION OF THE SPINAL CORD Brain’s meninges pass through foramen magnum to provide a continuous protective covering of spinal cord and distal nerves at base (Figure 12.22) • Three spinal meninges include dura mater, arachnoid, and pia mater; structurally similar to brain meninges except that spinal cord dura has only one layer and pia mater has some structural enhancements (Figure 12.22a) PROTECTION OF THE SPINAL CORD • Three spinal meninges include dura mater, arachnoid, and pia mater; structurally similar to brain meninges except that spinal cord dura has only one layer and pia mater has some structural enhancements (Figure 12.22a) (continued): Spinal dura mater does not have periosteal layer found in dura mater of brain; consists of only a meningeal layer Spinal pia mater has added function of anchoring spinal cord to surrounding vertebral cavity; thin pia extensions called denticulate ligaments pass through arachnoid and adhere to dura mater © 2016 Pearson Education, Inc. PROTECTION OF THE SPINAL CORD • Actual or potential spaces between spinal cord © 2016 Pearson Education, Inc. PROTECTION OF THE SPINAL CORD • Actual or potential spaces between spinal cord meninges are same as those found between cranial meninges with following features (Figure 12.22b): meninges are same as those found between cranial meninges with following features (Figure 12.22b): Epidural space – actual space due to absence of a Subdural space – only a potential space much like periosteal dura; found between meningeal dura and walls of vertebral foramina; space is filled with veins and adipose tissue; cushions and protects spinal cord epidural space surrounding brain; dura and arachnoid are normally adhered to one another Subarachnoid space – found between arachnoid and pia mater; filled with CSF; base of spinal cord contains a large volume of CSF; useful site for withdrawing samples for clinical laboratory testing © 2016 Pearson Education, Inc. PROTECTION OF THE SPINAL CORD Figure 12.22a Structure of the spinal meninges. © 2016 Pearson Education, Inc. PROTECTION OF THE SPINAL CORD Figure 12.22b Structure of the spinal meninges. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 23 8/19/2015 EPIDURAL ANESTHESIA AND LUMBAR PUNCTURES • Epidural (spinal) anesthesia – local anesthetic medication is injected into epidural space through an inserted needle • Causes “numbing” (inability to transmit motor or sensory impulses) of nerves extending off spinal cord below level of injection • Commonly given during childbirth and other surgical procedures EPIDURAL ANESTHESIA AND LUMBAR PUNCTURES • Lumbar puncture (spinal tap) – needle inserted into subarachnoid space between fourth and fifth lumbar vertebrae; avoids possibility of injuring spinal cord • CSF is withdrawn for analysis; used to assess conditions like meningitis, encephalitis and multiple sclerosis © 2016 Pearson Education, Inc. EXTERNAL SPINAL CORD ANATOMY © 2016 Pearson Education, Inc. EXTERNAL SPINAL CORD ANATOMY Spinal cord extends proximally from foramen magnum to region between first and second lumbar vertebrae; following structural features can be seen on spinal cord (Figure 12.23): • Filum terminale – found between first and second • Narrow posterior median sulcus can be seen on entire length of posterior side of cord • Spinal cord has two enlarged regions (cervical and • Wider anterior median sulcus can be seen on entire length of anterior side of cord • Conus medullaris is cone-shaped distal end of cord lumbar vertebrae; composed of spinal pia mater; thin layer of pia continues through vertebral cavity to form an anchor that is attached to first coccygeal vertebra lumbar enlargements); nerve roots fuse together to form spinal nerves (serve upper and lower extremities respectively) in these enlargements (Figure 12.23a) © 2016 Pearson Education, Inc. EXTERNAL SPINAL CORD ANATOMY © 2016 Pearson Education, Inc. EXTERNAL SPINAL CORD ANATOMY • Spinal nerves are components of PNS; carry sensory and motor impulses to and from spinal cord Projections visible on each side of spinal cord between vertebrae are called posterior and anterior nerve roots Roots of spinal nerves extend inferiorly from conus medullaris and fill remainder of vertebral cavity; this bundle of spinal nerve roots is called cauda equina due to its horsetail-like appearance Figure 12.23 External structure of the spinal cord. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 24 8/19/2015 INTERNAL SPINAL CORD ANATOMY INTERNAL SPINAL CORD ANATOMY Butterfly-shaped spinal gray matter is surrounded by tracts of white matter; following features are seen on cross section of spinal cord (Figures 12.24, 12.25): • Anterior to posterior orientation of spinal cord can be • • Anterior wings are broader while thinner posterior Central canal – filled with CSF; seen in center of spinal cord; surrounded by two thin strips of gray matter (gray commissure); connects each “butterfly” wing determined by using shape and size of gray matter wings wings extend almost to outer surface of spinal cord © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY • Spinal gray matter makes up three distinct regions found within spinal cord; houses neurons with specific functions and includes (Figure 12.24): Anterior horn (ventral horn) makes up anterior wing of gray matter and gives rise to anterior motor nerve roots; neuron cell bodies found in this region are involved in somatic motor functions (skeletal muscle contraction) © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY • Spinal gray matter (continued): Posterior horn (or dorsal horn) makes up posterior wing of gray matter and gives rise to posterior sensory nerve roots; neuron cell bodies found in this region are involved in processing incoming somatic and visceral sensory information Lateral horn, found only in spinal cord between first thoracic vertebra and lumbar region; contains cell bodies of neurons involved in control of viscera via autonomic nervous system © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY • Spinal White Matter: Ascending and Descending Tracts Contains axons of neurons that travel to and from brain; allows spinal cord to fulfill one of its primary functions as a relay station Organized into general regions called funiculi; three (posterior funiculus, lateral funiculus, and anterior funiculus) lie on each side of spinal cord (Figure 12.25) Figure 12.24 Overview of internal spinal cord structure and function. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 25 8/19/2015 INTERNAL SPINAL CORD ANATOMY • Spinal White Matter (continued): • Spinal White Matter (continued): Funiculi features o INTERNAL SPINAL CORD ANATOMY Ascending tracts carry various kinds of sensory White matter in each funiculus is organized into tracts or columns; bilaterally symmetrical (left and right side of spinal cord have identical tracts serving their respective side of body) o Ascending and descending tracts bring information to and from a specific part of brain o Sensory pathways travel in posterior and lateral funiculi while motor pathways travel in anterior and lateral funiculi information (Figure 12.25a): o Posterior columns – found in posterior funiculus; made up of two tracts, medial fasciculus gracilis and lateral fasciculus cuneatus; carry somatosensory information, such as proprioception and touch; nucleus gracilis transmits stimuli from lower limbs and lower trunk while nucleus cuneatus transmits stimuli from upper limbs and upper trunk © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY • Spinal White Matter (continued): Ascending tracts (continued): o o Spinocerebellar tracts – found in lateral funiculi; carry information about joint position and muscle stretch from entire body to cerebellum Anterolateral system includes spinothalamic tracts that travel in anterior and lateral funiculi; transmit pain and temperature stimuli from entire body to brain Figure 12.25a Ascending and descending tracts of the spinal cord. © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY © 2016 Pearson Education, Inc. INTERNAL SPINAL CORD ANATOMY • Spinal White Matter (continued): Descending tracts transmit motor information from specific regions in brain down spinal cord to specific regions in body (Figure 12.25b) o Corticospinal tracts – largest of descending tracts; help control skeletal muscles below head and neck o Originate from motor areas of cerebral cortex; descend as part of internal capsule then decussate within brainstem Travel through lateral funiculi of spinal cord; fibers deliver motor information to appropriate locations in anterior horn o Figure 12.25b Ascending and descending tracts of the spinal cord. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 26 8/19/2015 SENSORY STIMULI • Sensory stimuli – those effects that cause senses to respond; multiple sensory stimuli from different regions of brain can be pulled together into a single mental picture MODULE 12.5 SENSATION PART I: ROLE OF THE CNS IN SENSATION Each of these disparate stimuli reaches brain in following two-part process: o Stimulus is detected by neurons in PNS and sent as sensory input to CNS o In CNS, sensory input is sent to cerebral cortex for interpretation © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. SENSORY STIMULI GENERAL SOMATIC SENSES • Sensory stimuli (continued): When CNS has received all different sensory inputs, it integrates them into a single perception (a conscious awareness of sensation) Sensations can be grouped into two basic types: o o Special senses – detected by special sense organs and include vision, hearing, equilibrium, smell, and taste General senses – detected by sensory neurons in skin, muscles, or walls of organs; can be further subdivided into general somatic senses that involve skin, muscles, and joints and general visceral senses that involve internal organs General somatic senses pertain to touch, stretch, joint position, pain, and temperature (Figures 12.26–12.28) • Two types of touch stimuli are delivered to appropriate part of cerebral cortex by different pathways: Tactile senses – (fine or discrimination touch) include vibration, two-point discrimination, and light touch Nondiscriminative touch (crude touch) lacks fine spatial resolution of tactile senses © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Most of general somatic senses are considered mechanical senses; neurons that detect them are responsive to mechanical deformation • Two major ascending tracts in spinal cord carry somatic sensory information to brain: posterior columns/medial lemniscal system and anterolateral system © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Basic pathway consists of following: First-order neuron detects initial stimulus in PNS; axon of this neuron then synapses on a second-order neuron Second-order neuron – interneuron located in posterior horn of spinal cord or in brainstem; relays stimulus to a third-order neuron Third-order neuron – an interneuron found in thalamus; delivers impulse to cerebral cortex © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 27 8/19/2015 GENERAL SOMATIC SENSES GENERAL SOMATIC SENSES • Posterior columns/medial lemniscal system includes axons of neurons that transmit tactile information about discriminative touch and axons that convey information regarding proprioception (Figure 12.26) Ascend through posterior columns; medial fasciculus gracilis (carries impulses from lower limbs) and fasciculus cuneatus (carries impulses from upper limbs, trunk, and neck) © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Posterior columns/medial lemniscal system (continued): Fasciculus gracilis and cuneatus axons synapse with second-order neurons when they enter medulla, nucleus gracilis, and nucleus cuneatus, respectively Axons of second-order neurons decussate and form tracts called medial lemniscus Fibers of medial lemniscus ascend through pons and midbrain until they reach third-order neurons in thalamus; axons of these third-order neurons proceed to cerebral cortex © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES Figure 12.26 Ascending (sensory) pathways: the posterior column/medial lemniscal systems in the right and left sides of the body. © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Anterolateral system fibers transmit pain, temperature, and nondiscriminative touch stimuli in anterolateral spinal cord (Figure 12.27) First-order neurons synapse on second-order neurons in posterior horn; then decussate Spinothalamic tract – largest member of anterolateral system; transmits signals through spinal cord to sensory relay nuclei of thalamus; third-order neurons in thalamus then transmit impulses to cerebral cortex Figure 12.27 Ascending (sensory) pathways: the right and left spinothalamic tracts (part of the anterolateral system). © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 28 8/19/2015 GENERAL SOMATIC SENSES • Role of Cerebral Cortex in Sensation, S1 and Somatotopy: GENERAL SOMATIC SENSES • Role of Cerebral Cortex (continued): Mapping of primary somatosensory cortex (S1) Thalamus relays most incoming information to primary somatosensory cortex (S1) in postcentral gyrus illustrates that different parts of body are unequally represented (Figure 12.28a) Each part of body is represented by a specific region of More S1 space is dedicated to hands and face; represents S1, a type of organization called somatotopy (Figure 12.28) importance of manual dexterity, facial expression, and speech to human existence Unequal representation of body parts in S1 is exemplified by sensory homunculus (Figure 12.28b) © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Touch Stimuli: Thalamic nuclei relay touch information from spinothalamic tracts and posterior columns primarily to S1 for conscious perception Once sensory information reaches S1, it is processed, perceived, and passed along to cortical association areas Figure 12.28 Representations of the primary somatosensory cortex. © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Touch Stimuli (continued): Somatosensory association cortex (S2) plays a major role in processing sensory input and sending it to limbic system Limbic system is involved in tactile learning and memory S1 also sends sensory input to parietal and temporal association areas which integrate and relay information to motor areas of frontal lobe © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Pain Stimuli: perception of pain stimuli is called nociception Thalamus relays pain stimuli to several brain regions including S1 and S2 where sensory discrimination (localization, intensity, and quality) is perceived and analyzed Also sent to basal nuclei, regions of limbic system, hypothalamus, and prefrontal cortex, where emotional and behavioral aspects of pain are processed © 2016 Pearson Education, Inc. 29 8/19/2015 GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Pain Stimuli (continued): GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Pain Stimuli (continued): Cerebral cortex appears to have a significant influence on perception and modulation of pain; evident by a phenomenon called placebo effect where a dummy treatment with no active pain-killing ingredients produces pain relief A descending pathway originating mostly in S1, amygdala, and a region of midbrain called periaqueductal gray matter provides an explanation for placebo effect Neurons in the periaqueductal gray matter release neurotransmitters called endorphins © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. GENERAL SOMATIC SENSES • Role of the Cerebral Cortex in Sensation – Processing of Pain Stimuli (continued): Endorphins decrease sensitivity to pain stimuli of posterior horn neurons o o o Pain input is still present and its intensity is unaffected CNS neurons perceive pain as being less intense (or absent) Example of Cell-Cell Communication Core Principle PHANTOM LIMB PAIN • Phantom limb – occurs after amputation of limb, digit, or even breast; patients perceive body part is still present and functional in absence of sensory input; small percentage develop phantom pain (burning, tingling, or severe pain) in missing part • Difficult to treat due to complex way CNS processes pain; supports idea that S1 has “map” of body that exists independently of PNS • Over time, map generally rearranges itself so body is represented accurately; phantom sensations decrease © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. INTRODUCTION TO SPECIAL SENSES INTRODUCTION TO SPECIAL SENSES • Special senses include vision, hearing (audition), taste • Special senses include vision, hearing (audition), taste (gustation), smell (olfaction), and balance (vestibular sensation) (gustation), smell (olfaction), and balance (vestibular sensation) (continued): Each involves neurons that detect a stimulus and send it to CNS for processing and integration Pathways for processing each type of special sensory stimuli: Thalamus – gateway for entry of special sensory stimuli into cerebral cortex; interprets majority of this information; olfaction is exception © 2016 Pearson Education, Inc. o Visual • Most stimuli are sent directly to thalamus; then relayed to primary visual cortex (processes stimuli and perceives an object’s depth, color, and detects rapid changes in stimuli) • Information is shared with association areas in temporal and parietal lobes; crucial for object recognition and spatial awareness, respectively © 2016 Pearson Education, Inc. 30 8/19/2015 INTRODUCTION TO SPECIAL SENSES INTRODUCTION TO SPECIAL SENSES • Special senses include vision, hearing (audition), taste • Special senses include vision, hearing (audition), taste (gustation), smell (olfaction), and balance (vestibular sensation) (continued): (gustation), smell (olfaction), and balance (vestibular sensation) (continued): Pathways for processing each type of special sensory stimuli (continued): o Pathways for processing each type of special sensory stimuli (continued): Auditory o Gustatory • Stimuli first go to nuclei in brainstem where limited processing occurs • Stimuli are sent to nuclei in medulla before being relayed to thalamus • Majority of stimuli are routed to thalamus and then primary auditory cortex (superior temporal lobe), for sound processing • Then sent to gustatory cortices (insula and parietal lobes) for processing • Information is relayed to other association areas such as Wernicke’s area for language comprehension • Information is sent to hypothalamus and limbic system likely for processing of taste preferences and food-seeking behaviors © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. INTRODUCTION TO SPECIAL SENSES INTRODUCTION TO SPECIAL SENSES • Special senses include vision, hearing (audition), taste • Special senses include vision, hearing (audition), taste (gustation), smell (olfaction), and balance (vestibular sensation) (continued): (gustation), smell (olfaction), and balance (vestibular sensation) (continued): Pathways for processing each type of special sensory stimuli (continued): o Pathways for processing each type of special sensory stimuli (continued): Olfactory o • Stimuli enter limbic system of cerebral cortex for initial processing, bypassing thalamus • Then sent to several regions of brain including thalamus, prefrontal cortex, hypothalamus, and other limbic system components • Allows smell stimuli to influence behaviors such as emotion, cognition, and those related to feeding Balance • Processing vestibular stimuli involves several brainstem nuclei, cerebellum, descending pathways through spinal cord, and pathways through thalamus to cerebral cortex © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. VOLUNTARY MOVEMENT • Planning and coordination of voluntary movement are MODULE 12.6 MOVEMENT PART I: ROLE OF THE CNS IN VOLUNTARY MOVEMENT © 2016 Pearson Education, Inc. carried out within CNS; involve motor areas of cerebral cortex, basal nuclei, cerebellum, and spinal cord • Three types of neurons are directly involved in eliciting a muscle contraction (next slide) © 2016 Pearson Education, Inc. 31 8/19/2015 VOLUNTARY MOVEMENT 1. Upper motor neurons with cell bodies in motor area of cerebral cortex (most) or brainstem (some) – axons descend through cerebral white matter to brainstem and spinal cord; synapse with local interneurons 2. Local interneurons – pass messages from upper motor neurons to neighboring lower motor neurons 3. Cell bodies of lower motor neurons reside in anterior horn of spinal gray matter; axons (components of PNS) exit CNS to innervate skeletal muscles MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Axons from cortical motor areas unite to form several white matter tracts; largest of these tracts are (Figure 12.29): Corticospinal tract – controls muscles below head and neck utilizing lower motor neurons of spinal nerves Corticonuclear tract – formerly known as corticobulbar tracts; controls muscles of head and neck utilizing lower motor neurons of cranial nerves © 2016 Pearson Education, Inc. MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Corticospinal tract pathway (Figure 12.29): Axons that form corticospinal tracts originate from upper motor neuron cell bodies in primary motor and premotor cortices © 2016 Pearson Education, Inc. MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Corticospinal tract pathway (continued): Most of these fibers decussate at level of medullary pyramids; neurons on right side of brain send fibers to left side of body and vice versa Axons unite and descend through corona radiata and Fibers that decussate travel in lateral funiculi; are then internal capsule on way to brainstem (midbrain and pons) known as right and left lateral corticospinal tracts © 2016 Pearson Education, Inc. MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD © 2016 Pearson Education, Inc. MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Corticospinal tract pathway (continued): Fibers of lateral corticospinal tracts synapse on local interneurons in anterior horn of spinal gray matter; over half terminate in cervical spinal cord to control motor functions of upper limbs 10–15% of motor fibers from cerebrum do not decussate; travel through anterior funiculi of spinal white matter; become right and left anterior corticospinal tracts Figure 12.29 Descending (motor) pathways: the right and left lateral corticospinal tracts. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 32 8/19/2015 MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Corticonuclear tracts originate from cell bodies of upper motor neurons; travel with corticospinal tracts through corona radiata and internal capsule to brainstem MOTOR PATHWAYS FROM BRAIN THROUGH SPINAL CORD • Corticonuclear tracts (continued): Cranial nerve nuclei give rise to lower motor neurons that innervate muscles of head and neck Fibers do not decussate but most cranial nerve nuclei Do not enter spinal cord; instead synapse on interneurons that communicate with cranial nerve nuclei at various levels of brainstem communicate with upper motor neurons from both cerebral hemispheres; damage to upper motor neurons on one side of cerebrum does not lead to noticeable deficits from many cranial nerves © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT Even simple movements require simultaneous firing of countless neurons as part of a selected group of actions called a motor program • • Execution of any motor program requires firing of neurons in motor association areas, firing of upper motor neurons, and input from basal nuclei, cerebellum, spinal cord, and multimodal association areas (prefrontal cortex and various sensory areas) © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Cerebral Cortex – majority of upper motor neurons that control complex movements reside in primary motor cortex and premotor and motor association areas Plan and initiate voluntary movement by selecting an appropriate motor program and coordinating sequence of skilled movements Firing of lower motor neurons in PNS is necessary to complete task © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Cerebral Cortex (continued): © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Cerebral Cortex (continued): Upper motor neurons are also located in certain nuclei of brainstem; work to maintain posture, balance, and body position especially during locomotion; also produce motor responses to sensory stimuli Map of upper motor neurons in primary motor cortex and motor homunculus resemble sensory map and homunculus (Figure 12.30) © 2016 Pearson Education, Inc. Primary motor cortex is organized somatotopically; certain body regions have disproportionately more cortical area devoted to them (especially lips, tongue, and hands); signifies importance of vocalization and manual dexterity to human survival Upper motor neurons do not act alone when delivering commands to lower motor neurons; smooth, fluid motion requires input from basal nuclei and cerebellum © 2016 Pearson Education, Inc. 33 8/19/2015 ROLE OF BRAIN IN VOLUNTARY MOVEMENT ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Basal Nuclei – three collections of cell bodies make up basal nuclei: caudate nucleus, globus pallidus, and putamen; complicated interconnections form a circuit between basal nuclei and other structures of brain (Figure 12.31): Substantia nigra of midbrain works closely with basal nuclei; often grouped together because of shared functions Basal nuclei modify activity of upper motor neurons to produce voluntary movements and inhibit involuntary ones Figure 12.30 Representations of the primary motor cortex. © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Basal Nuclei (continued): A critical function of basal nuclei is to inhibit inappropriate movements (Figure 12.31a): o In absence of voluntary movement neurons in globus pallidus fire continuously to inhibit motor nuclei of thalamus o Inhibits upper motor neurons of cortical motor areas from firing Figure 12.31a Role of the basal nuclei in voluntary movement. © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Basal Nuclei (continued): function of basal nuclei (Figure 12.31b) o o ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Basal Nuclei (continued): Initiation of voluntary movement is another critical o © 2016 Pearson Education, Inc. If voluntary movement has been initiated, neurons of caudate nucleus and putamen receive input from cerebral cortex, with which they form excitatory synapses These neurons inhibit globus pallidus neurons from firing; enhanced by substantia nigra (increases output of caudate nucleus and putamen) Overall effect – inhibitor (globus pallidus) is inhibited; allows motor nuclei of thalamus to fire and stimulate upper motor neurons of cerebral cortex; enables motion © 2016 Pearson Education, Inc. Neurons of substantia nigra are dopaminergic (secrete dopamine); project to caudate nucleus and putamen where dopamine enhances inhibitory output to globus pallidus Input of substantia nigra is vital for initiating movement © 2016 Pearson Education, Inc. 34 8/19/2015 ROLE OF BRAIN IN VOLUNTARY MOVEMENT ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of Basal Nuclei (continued): Damage to any component of basal nuclei system results in a movement disorder; two main forms: o Inability to initiate voluntary movement, making simple activities such as walking or talking difficult o Inability to inhibit inappropriate, involuntary movements; some of which are mild (throat clearing or blinking); others may be severe enough to cause disability Figure 12.31b Role of the basal nuclei in voluntary movement. © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of the Cerebellum – cerebellum monitors ongoing movements and integrates information about contraction and relaxation of muscles, positions of joints, and direction, force, and type of movement that is going to occur (Figure 12.32) Once information is integrated, cerebellum determines motor error – difference between intended movement and actual movement that is taking place Figure 12.31 Role of the basal nuclei in voluntary movement. © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of the Cerebellum (continued): © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Role of the Cerebellum (continued): Cerebellum then influences other regions of brain to reduce this error; can occur over both short and long term by a process called motor learning Corrections for motor error are added over time to motor program; more repetition of specific action more corrections for motor error added to program more fluid and error-free motion becomes © 2016 Pearson Education, Inc. Cerebellum receives input from three sources simultaneously: o motor areas of cerebral cortex via upper motor neurons o vestibular nuclei of pons ascending sensory tracts from spinal cord o © 2016 Pearson Education, Inc. 35 8/19/2015 ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Motor areas provide information on intended movement, and vestibular nuclei and ascending tracts supply data on actual movement performed • Cerebellar neurons process and integrate input from these sources; send output to correct motor error, primarily to upper motor neurons via premotor cortex and primary motor cortex ROLE OF BRAIN IN VOLUNTARY MOVEMENT • Like basal nuclei, cerebellum affects movement by modifying activity of upper motor neurons; cerebellum does not have direct connections with lower motor neurons • Damage to cerebellum makes fluid, well-coordinated movements nearly impossible; movements become jerky and inaccurate; called cerebellar ataxia © 2016 Pearson Education, Inc. ROLE OF BRAIN IN VOLUNTARY MOVEMENT © 2016 Pearson Education, Inc. PARKINSON’S DISEASE • One of most common movement disorders; termed hypokinetic, meaning that movement is difficult to initiate and once started, difficult to terminate Symptoms – minimal facial expression, shuffling gait with no arm swing, resting tremor (uncontrollable shaking movements), difficulty swallowing, and rigid movements of arms and legs Figure 12.32 Role of the cerebellum in voluntary movement. © 2016 Pearson Education, Inc. PARKINSON’S DISEASE © 2016 Pearson Education, Inc. THE BIG PICTURE OF CNS CONTROL OF VOLUNTARY MOVEMENT • One of most common movement disorders (continued): Cause – degeneration of dopamine-secreting neurons of substantia nigra; progresses slowly over 10–20 years; underlying mechanism unknown, but genetics suspected in ~10% of cases Treatment – medications that increase level of dopamine in brain; compensate for decreased level Figure 12.33 The Big Picture of CNS Control of Voluntary Movement. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 36 8/19/2015 ROLE OF CNS IN MAINTENANCE OF HOMEOSTASIS MODULE 12.7 HOMEOSTASIS PART I: ROLE OF THE CNS IN MAINTENANCE OF HOMEOSTASIS Homeostasis is defined as maintenance of a relatively stable internal environment in face of ever-changing conditions • Homeostatic functions include maintaining fluid, electrolyte, and acid-base balance; blood pressure; blood glucose and oxygen concentrations; biological rhythms; and body temperature © 2016 Pearson Education, Inc. ROLE OF CNS IN MAINTENANCE OF HOMEOSTASIS • Nervous system and endocrine system are main systems dedicated to maintaining homeostasis; work together but each has its own mechanisms for performing vital homeostatic regulation Endocrine system secretes hormones into blood; regulates functions of other cells Nervous system sends action potentials; excite or inhibit target cells Actions of endocrine system are typically slow (take several hours or even days to have an effect) whereas actions of nervous system are generally immediate © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. ROLE OF CNS IN MAINTENANCE OF HOMEOSTASIS • Two structures of CNS are concerned directly with maintenance of homeostasis: Reticular formation – controls functions of many internal organs as well as aspects of behavior Hypothalamus – closely associated (anatomically and functionally) with pituitary gland; reflects close relationship between these vital systems Reticular formation and hypothalamus have many interconnections; enable them to coordinate many homeostatic functions © 2016 Pearson Education, Inc. HOMEOSTASIS OF VITAL FUNCTIONS HOMEOSTASIS OF VITAL FUNCTIONS • Maintenance of vital functions (heart pumping, blood • Although ANS is a component of PNS it is controlled pressure, and digestion) is largely controlled by autonomic nervous system (ANS); regulates function of body’s viscera • Although ANS is a component of PNS it is controlled by components of CNS, mainly hypothalamus by components of CNS, mainly hypothalamus (continued): Hypothalamus receives sensory input from viscera, components of the limbic system, and the cerebral cortex Allows hypothalamus to respond to both normal physiological changes and emotional changes and to adjust ANS output to maintain homeostasis © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 37 8/19/2015 HOMEOSTASIS OF VITAL FUNCTIONS • Hypothalamus maintains homeostasis largely by relaying instructions to nuclei in reticular formation of medulla; include following centers: Neurons of vasopressor center – located in anterolateral medulla; when stimulated by hypothalamus, center increases rate and force of cardiac contractions and causes blood vessels to narrow; increases blood pressure HOMEOSTASIS OF VITAL FUNCTIONS • Hypothalamus maintains homeostasis largely by relaying instructions to nuclei in reticular formation of medulla; include following centers (continued): Vasodepressor center – located inferior and medial to vasopressor center; decreases rate and force of heart contractions and opens blood vessels; all three effects decrease blood pressure Other centers: many nuclei in reticular formation participate in regulation of digestive processes and control of urination © 2016 Pearson Education, Inc. HOMEOSTASIS OF VITAL FUNCTIONS • Respiration is one of few vital functions not under ANS control © 2016 Pearson Education, Inc. BODY TEMPERATURE HOMEOSTASIS • Hypothalamus regulates body temperature Acts as body’s thermostat; creates a set point for normal Rate and depth of breathing are regulated by group of neurons in anterior medullary reticular formation Several factors influence neuron firing rates: input from cerebral cortex, limbic system, hypothalamus, certain sensory receptors, and nuclei in pons body temperature, about 37 C or 98.6 F Input is received from temperature-sensitive neurons located in several places (skin and areas deeper in body) and from neurons in hypothalamus itself © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. BODY TEMPERATURE HOMEOSTASIS FEVER • Hypothalamus regulates body temperature (continued): • Elevation of body temperature can accompany variety When body temperature increases above set point, a negative feedback loop is initiated whereby certain hypothalamic nuclei induce changes that cool body When body temperature decreases below set point, a different feedback loop is initiated that conserves heat Both are examples of Feedback Loops Core Principle Fever ensues when body temperature set point is temporarily set higher than normal © 2016 Pearson Education, Inc. of infectious and noninfectious conditions • Caused by pyrogens (chemicals) secreted by cells of immune system and by certain bacteria; cross bloodbrain barrier and interact with nuclei of hypothalamus (control temperature) • Pyrogens increase hypothalamic set point to higher temperature; feedback loop triggers shivering and muscle aches due to increased muscle tone; constricts blood vessels serving skin © 2016 Pearson Education, Inc. 38 8/19/2015 FEVER REGULATION OF FEEDING • Treatment is not always necessary; often more important to address underlying cause • Hypothalamus also regulates feeding Stimulation of certain hypothalamic nuclei induces • Antipyretics – used to treat fever; include acetaminophen and aspirin; work by blocking formation of pyrogens; permits hypothalamus to return to normal set point hunger and feeding behaviors; indirectly preserves homeostasis of glucose Thought to be related to secretion of neurotransmitters called orexins © 2016 Pearson Education, Inc. REGULATION OF FEEDING • Hypothalamus also regulates feeding (continued): Orexins are secreted by hypothalamic neurons during periods of fasting; appear to induce eating; also play an important role regulating sleep/wake cycle Stimulation of different hypothalamic nuclei seems to inhibit feeding; mechanisms controlling food intake are complex and involve hormones, several hypothalamic nuclei, and other regions of brain © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS • Sleep, defined as a reversible and normal suspension of consciousness; one of most fundamental homeostatic processes carried out by humans and most other animals Information is known pertaining to how we sleep, how sleep is regulated, and brain activity during sleep, but why most animals sleep is as yet unknown Physiologically, sleep appears to serve an energy restoration function; allows brain to replenish its glycogen supply © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS • Sleep (continued): © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS • Sleep (continued): Sleep is required for survival; deprivation can cause imbalances in temperature homeostasis, weight loss, a decrease in cognitive abilities, hallucinations, and even death Most adults only require 7–8 hours of sleep while Circadian Rhythms and Biological “Clock”: Human sleep follows a circadian rhythm o We spend a period of cycle awake and remainder asleep o Rhythm is controlled by hypothalamus; causes changes in level of wakefulness in response to day and night cycles infants require about 17 hours per night © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 39 8/19/2015 SLEEP AND WAKEFULNESS • Sleep occurs in following sequence of events (Figure 12.34): SLEEP AND WAKEFULNESS • Sleep (continued): Decreased activity of reticular formation “disconnects” Nerves from eye signal suprachiasmatic nucleus (SCN) of hypothalamus that light level is decreasing SCN stimulates ventrolateral preoptic nucleus (hypothalamus); stimulates pineal gland to secrete melatonin thalamus from cerebral cortex; decreases level of consciousness Arousal from sleep is mediated by a different group of hypothalamic neurons; secrete neurotransmitter orexin; example of Cell-Cell Communication Core Principle Ventrolateral preoptic nucleus decreases activity of reticular formation © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS • Brain Waves and Stages of Sleep – stages of sleep can be monitored using electroencephalogram (EEG); measure electrical activity of brain using electrodes attached to skin (Figure 12.35) Tracings of electrical activity (brain waves) show characteristic patterns during wakefulness and different stages of sleep Waves differ in height (amplitude) and speed at which they are generated (frequency) Figure 12.34 The process of falling asleep. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. SLEEP AND WAKEFULNESS SLEEP AND WAKEFULNESS • Brain Waves and Stages of Sleep (continued): • Brain Waves and Stages of Sleep (continued): Beta waves – low amplitude and high frequency; occur when we are awake and engaged in mental activity Stages I–III sleep are characterized by drowsiness progressing to moderately deep sleep; betas waves slow to theta waves with progressively decreasing frequency (and increasing amplitude) © 2016 Pearson Education, Inc. State IV sleep is deepest stage with characteristic low- frequency, high-amplitude delta waves; stages I–IV collectively is known as non-REM sleep or non-rapid eye movement sleep REM sleep (rapid eye movement) lasts for 10–15 minutes and occurs after stage IV sleep; known for back and forth eye movements; stage where most dreaming occurs; REM waves resemble beta waves of wakefulness © 2016 Pearson Education, Inc. 40 8/19/2015 STATES OF ALTERED CONSCIOUSNESS MIMICKING SLEEP SLEEP AND WAKEFULNESS • Altered consciousness can indicate serious problems with brain function; examples include: Stupor – diminished level of cortical activity; arousable with strong/painful stimuli; caused by infections, mental illnesses, and brain conditions (such as brain tumors) Coma – unarousable unconsciousness; no purposeful responses to any stimuli (even pain); underlying defect is damage to reticular activating system or related component; prohibits normal arousal of cerebral cortex Figure 12.35 Stages of wakefulness and sleep as shown by EEG patterns. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. STATES OF ALTERED CONSCIOUSNESS MIMICKING SLEEP STATES OF ALTERED CONSCIOUSNESS MIMICKING SLEEP • Altered consciousness can indicate serious problems • Altered consciousness can indicate serious problems with brain function; examples include (continued): with brain function; examples include (continued): Persistent vegetative state – some patients move from Coma (continued): o o o EEG demonstrates slow, fixed pattern with no observable sleep/wake cycles Brainstem reflexes remain intact; certain patients exhibit involuntary movements coma state to condition where they are awake but unaware because of damage to cerebral cortex; also lack voluntary movement o Sleep/wake cycles do occur; brainstem reflexes remain intact, leading to involuntary movements (head turning and grunt-like vocalizations) o Can be misinterpreted as meaningful but not mediated by cortex, thus do not imply conscious awareness May result from head trauma, certain drugs, disturbances in acid-base homeostasis and various neurological conditions © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. STATES OF ALTERED CONSCIOUSNESS MIMICKING SLEEP • People in altered states of consciousness may occasionally regain consciousness, depending on cause of state • Brain death – most extreme state of altered consciousness; EEG shows no activity; brainstem reflexes are absent; cerebral blood flow and metabolism are reduced to zero; consciousness will not be regained © 2016 Pearson Education, Inc. MODULE 12.8 HIGHER MENTAL FUNCTIONS © 2016 Pearson Education, Inc. 41 8/19/2015 COGNITION AND LANGUAGE COGNITION AND LANGUAGE • Cognition – collective term for diverse group of tasks; • Localization of Cognitive Function – following areas performed by association areas of cerebral cortex Cognitive functions – include processing and responding to complex external stimuli, recognizing related stimuli, processing internal stimuli, and planning appropriate responses to stimuli Cognitive processes – responsible for social and moral behavior, intelligence, thoughts, problem-solving skills, language, and personality and their functions are involved in cognition: Parietal association cortex – responsible for spatial awareness and attention; allows us to focus on distinct aspects of a specific object and recognize position of object in space Temporal association cortex – primarily responsible for recognizing stimuli, especially complex stimuli such as faces © 2016 Pearson Education, Inc. COGNITION AND LANGUAGE • Localization of Cognitive Function (continued): Prefrontal cortex – largest and most complex of association cortices o Responsible for majority of cognitive functions that make up a person’s “character” or “personality” o Gathers information from other association cortices and from other sensory and motor cortices and integrates information to create an awareness of “self” o Allows for planning and execution of behaviors appropriate for given circumstances © 2016 Pearson Education, Inc. COGNITION AND LANGUAGE • Cerebral lateralization – phenomenon in which many cognitive functions are unequally represented in right and left hemispheres Represents a division of labor between hemispheres to maximize a limited amount of brain space Following functions appear to be lateralized although this is not an absolute (next slide) © 2016 Pearson Education, Inc. COGNITION AND LANGUAGE • Cerebral lateralization (continued): this is not an absolute (continued): o o DEMENTIA • Patients with dementia exhibit a progressive loss of Following functions appear to be lateralized although o © 2016 Pearson Education, Inc. Emotional functions – left frontal cortex is mostly responsible for “positive” emotions while right cortex for “negative” emotions Attention is lateralized to right parietal cortex while facial recognition is lateralized in right temporal cortex Language-related recognition and ability to identify an object with its proper name are lateralized in left temporal cortex © 2016 Pearson Education, Inc. recent memory, degeneration of cognitive functions, and changes in personality • No proven method for prevention or cure of dementia exists; some drugs may slow progression of Alzheimer’s disease in certain patients but do not reverse changes that already exist; ineffective in other forms of dementia © 2016 Pearson Education, Inc. 42 8/19/2015 DEMENTIA DEMENTIA • Common (most to least) forms of dementia include: • Common (most to least) forms of dementia include (continued): Alzheimer’s disease (AD) o o Vascular dementia Neurofibrillary tangles (aggregates of proteins in neurons), senile plaques (extracellular deposits of specific protein around neurons), and degeneration of cortical neurons and synaptic connections occur throughout brain; especially numerous in cortical association areas and hippocampus Earliest signs are recent memory loss and forgetfulness; progresses to impairment of attention, language skills, critical thinking and visual-spatial abilities, and changes in personality; eventually motor skills, sensory perception, and long-term memory are affected o o o Group of diseases; share common feature of disruption in blood flow to parts of brain, particularly cerebral cortex Signs and symptoms are highly variable because of range of brain regions affected Significant overlap with AD; patients often have both forms; known as mixed dementia © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. DEMENTIA DEMENTIA • Common (most to least) forms of dementia include • Common (most to least) forms of dementia include (continued): (continued): Pick’s disease Lewy body dementia o o Cytoplasmic inclusions (Lewy bodies) in neurons of certain brain parts Fluctuation in cognitive functions, impaired memory formation, hallucinations, delusions, sleep disorders, and motor features of Parkinson’s disease o o o o Cerebral cortex of frontal and temporal lobes progressively degenerates Results in severe atrophy due to loss of neurons with excess neuroglia Unusual, in that younger population affected (age 55–65) Patients deteriorate rapidly; dramatic personality changes and behavioral problems common because of prefrontal cortex involvement © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. COGNITION AND LANGUAGE • Language, arguably one of most important cognitive functions of brain; refers to ability to comprehend and produce words through speaking, writing, and/or signing, and to assign and recognize symbolic meaning of a word correctly COGNITION AND LANGUAGE • Multiple brain regions are required for communication but two multimodal association areas are critical (Figure 12.36): Broca’s area – in frontal lobe; responsible for production of language, including planning and ordering of words with proper grammar and syntax Wernicke’s area – in temporal lobe; responsible for understanding language and linking a word with its correct symbolic meaning Aphasia – language deficit; occurs when either of these two critical areas is damaged © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 43 8/19/2015 COGNITION AND LANGUAGE APHASIAS • Aphasia (language deficits) Broca’s – inability to correctly plan and order grammar and syntax; words and phrases repeated; grammar, syntax, and structure of individual words are disordered; frustrating for patients because language comprehension is intact Wernicke’s – inability to understand language; speak Figure 12.36 Functional neuroimaging (functional magnetic resonance imaging, fMRI) of the brain during speech. fluently with adequate grammar and syntax but words and meanings are not correctly linked; cannot realize that what they are saying makes no sense; language comprehension is not intact © 2016 Pearson Education, Inc. LEARNING AND MEMORY • Two basic types of memory: declarative (fact) memory – defined as memory of things that are readily available to consciousness; could in principle be expressed aloud (hence term “declarative”), and nondeclarative memory (procedural or skills memory); includes skills and associations that are largely unconscious Declarative examples – phone number, a quote, or pathway of corticospinal tracts Nondeclarative examples – how to enter phone number on a phone, how to move your mouth to speak, and how to read this chapter © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. LEARNING AND MEMORY • Declarative and nondeclarative memory can be classified by length of time in which they are stored: Immediate memory – stored only for a few seconds; is critical for carrying out normal conversation, reading, and daily tasks Short-term (working) memory – stored for several minutes; allows you to remember and manipulate information with a general behavioral goal in mind Long-term memory – a more permanent form of storage for days, weeks, or even a lifetime © 2016 Pearson Education, Inc. LEARNING AND MEMORY LEARNING AND MEMORY • Process of converting immediate or working memory • Long-term potentiation (LTP) – mechanism by which into long-term memory involves a process called consolidation (Figure 12.37) • Formation and storage of declarative memory appears to require hippocampus (component of limbic system); immediate and short-term memories are likely stored in this region hippocampal neurons encode long-term declarative memories, seems to involve an increase in synaptic activity between associated neurons; example of CellCell Communication Core Principle Although hippocampus is required to form new declarative memories, long-term memories are not stored in this region; stored in cerebral cortex that correlates with their functions Retrieval of memories seems to be mediated by pathways involving hippocampus and prefrontal cortex © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 44 8/19/2015 LEARNING AND MEMORY LEARNING AND MEMORY • Formation and storage of nondeclarative memory doesn’t rely on hippocampus; memories seem to be stored in cerebral cortex, cerebellum, and basal nuclei Figure 12.37 Pathways for consolidation of memories. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. LEARNING AND MEMORY • Emotion – complex combination of three separate phenomena: LEARNING AND MEMORY • Emotion (continued): “Feelings” – highly subjective; most complex; Visceral motor responses – blushing or heart racing; mediated by hypothalamus Somatic motor responses – smiling, laughing, frowning, and crying; mediated by hypothalamus and limbic cortex through reticular formation © 2016 Pearson Education, Inc. integrated with sensory and/or cognitive stimuli o Feeling sad when remembering a lost pet or feeling tense when watching a suspenseful movie o Amygdala receives input from brainstem, thalamus, cerebral cortex, and basal nuclei, analyzes emotional significance of stimuli; creates associations between different stimuli; projects to prefrontal cortex © 2016 Pearson Education, Inc. 45