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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 12 The Central Nervous System Copyright © 2010 Pearson Education, Inc. The Nervous System Central Nervous System (CNS) Brain Peripheral Nervous System (PNS) Spinal Cord Motor Neurons Somatic Nervous System Sympathetic Copyright © 2010 Pearson Education, Inc. Sensory Neurons Autonomic Nervous System Parasympathetic CNS protection Copyright © 2010 Pearson Education, Inc. CSF – cerebrospinal fluid • Liquid cushion for brain and spinal cord • Nourishes brain • Removes waste • Conducts chemical signals between parts of CNS • Produced in Choroid Plexuses: group of capillaries surrounded by ependymal cells AP revealed – CSF flow Copyright © 2010 Pearson Education, Inc. Choroid Plexuses http://cal.man.ac.uk/student_projects/2002/MNQJ9PP2/Webpages/structure&functionchoroid.htm • Clusters of capillaries that form tissue fluid filters, which hang from the roof of each ventricle • Have ion pumps that allow them to alter ion concentrations of the CSF Copyright © 2010 Pearson Education, Inc. CSF production • CSF is formed by the choroid plexus present within the four cerebral ventricles and a small amount by the ependymal cells • the choroid plexus of the lateral ventricles producing the most. • The rate of formation is approximately 0.35 ml/min or 500 ml/day; a rate which replaces the total volume of CSF approximately 2-3 times over in 24 hours. Copyright © 2010 Pearson Education, Inc. Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances • Composition • Continuous endothelium of capillary walls • Basal lamina • Feet of astrocytes • Provide signal to endothelium for the formation of tight junctions Copyright © 2010 Pearson Education, Inc. Blood-Brain Barrier: Functions • Selective barrier that allows nutrients to pass freely • Is ineffective against substances that can diffuse through plasma membranes (ex. Ethanol, caffeine) • Absent in some areas: • Ex. - hormones generally do not penetrate the brain from the blood, so in order to control the rate of hormone secretion effectively, there are specialized sites where neurons can "sample" the composition of the circulating blood. At these sites, the blood-brain barrier is 'leaky‘ (pituitary gland) • Capillaries of the choroid plexus • The BBB can break down under certain conditions: • hypertension, radiation, infection and brain trauma Copyright © 2010 Pearson Education, Inc. The Brain • 4 Parts • Cerebrum • Diencephalon • Brain Stem • Cerebellum pg 348 Copyright © 2010 Pearson Education, Inc. Cerebral Cortex • The cortex – superficial gray matter; accounts for 40% of the mass of the brain • It enables sensation, communication, memory, understanding, and voluntary movements • Each hemisphere acts contralaterally (controls the opposite side of the body) • Hemispheres are not equal in function • No functional area acts alone; conscious behavior involves the entire cortex Copyright © 2010 Pearson Education, Inc. Functional Areas of the Cerebral Cortex • The three types of functional areas are: • Motor areas – control voluntary movement • Sensory areas – conscious awareness of sensation • Association areas – integrate diverse information Copyright © 2010 Pearson Education, Inc. Cerebral Cortex: Motor Areas; Frontal Lobe Cortical Regions • Controls voluntary movement and found in the posterior part of the frontal lobe • Primary Motor cortex • Conscious motor control • Motor homonculus • Premotor Cortex • Learned motor skills Copyright © 2010 Pearson Education, Inc. Cerebral Cortex: Motor Areas; Frontal Lobe Cortical Regions • Broca’s area • Motor for speech • Frontal Eye Field • Prefrontal Cortex • Personality • Intelligence • Language comprehension Copyright © 2010 Pearson Education, Inc. Primary Motor Cortex • Located in the precentral gyrus in the frontal lobe in each hemisphere • Pyramidal cells that have long axon project to the spinal cord and form a voluntary motor tracts called pyramidal tracts/corticospinal tracts • A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar neuron found in the cerebral cortex. • These cells have a triangularly shaped soma • Pyramidal neurons compose approximately 80% of the neurons of the cortex • Release glutamate as their neurotransmitters, making them the major excitatory component of the cortex • Allows conscious movements Copyright © 2010 Pearson Education, Inc. control of precise, skilled, voluntary Primary Motor Cortex Homunculus Posterior • Somatotopy mapping • Body is represented upside down • Although simplified in the figure, one should remember that: Motor Motor map in precentral gyrus Anterior • A given muscle is controlled by multiple spots on the cortex Toes • Individual cortical neurons send impulses to more than one muscle • Neurons that control related movements will overlap • Neurons that control unrelated movements do not cooparate Copyright © 2010 Pearson Education, Inc. Jaw Tongue Swallowing Primary motor cortex (precentral gyrus) Figure 12.9.1 Premotor Cortex • Located anterior to the precentral gyrus in the frontal lobe • Controls learned, repetitious, or patterned motor skills (playing a musical instrument) • Coordinates the movements of muscle groups either for simultaneous or sequential actions • mainly by sending activating impulses to the primary motor cortex • also by controlling directly by supplying 15% of the pyramidal tract fibers • Involved in the planning of movements by receiving sensory information and process them (moving arm through maze to take hidden object) Copyright © 2010 Pearson Education, Inc. • Broca’s Area • Located anterior to the inferior region of the premotor area • Present in one hemisphere (usually the left) • A motor speech area that directs muscles of the tongue • Is active as one prepares to speak • Frontal eye field • Located anterior to the premotor cortex and superior to Broca’s area • Controls voluntary eye movement Copyright © 2010 Pearson Education, Inc. Prefrontal Cortex • Located in the anterior portion of the frontal lobe • Involved with intellect, cognition (complex learning activities), recall and personality • Necessary for judgment, reasoning, persistence, and conscience • Closely linked to the limbic system (emotional part of the brain) Copyright © 2010 Pearson Education, Inc. Sensory Areas • Areas that are associated with conscious awareness of sensation • Found in the parietal, temporal, occipital and insular lobes • Primary somatosensory cortex • Somatosensory association cortex • Visual and auditory areas • Olfactory, gustatory, and vestibular cortices Copyright © 2010 Pearson Education, Inc. Primary Somatosensory Cortex Posterior • Located in the postcentral gyrus, this area: Sensory Anterior • Receives information from the skin and from proprioceptors (position) in the skeletal muscles, joints and tendons • Identify the area of the body from which the signal was sent - spatial discrimination Copyright © 2010 Pearson Education, Inc. Sensory map in postcentral gyrus Genitals Primary somatosensory cortex (postcentral gyrus) Intraabdominal Somatosensory Association Cortex • Located posterior to the primary somatosensory cortex and has connection with it • Integrates sensory information like temperature and pressure coming from the primary somatosensory cortex. • Forms understanding of the stimulus like size, texture, and relationship of parts • Ex.: putting the hand in the pocket and feeling something. The center integrate previous information to identify objects without seeing them Copyright © 2010 Pearson Education, Inc. Visual Areas • Primary visual (striate) cortex • Seen on the extreme posterior tip of the occipital lobe • Most of it is buried in the calcarine sulcus (medial aspect of the occipital lobe) • Receives visual information from the retinas • Visual association area • Surrounds the primary visual cortex and covers much of the occipital lobe. • Interprets visual stimuli (e.g., color, form, and movement) by processing previous experiences Copyright © 2010 Pearson Education, Inc. Auditory Areas • Primary auditory cortex • Located at the superior margin of the temporal lobe • Receives information from mechanoreceptors in the inner ear related to pitch, rhythm, and loudness • Auditory association area • Located posterior to the primary auditory cortex • Stores memories of sounds and permits perception of sounds (is it scream, speech, singing etc.) • Wernicke’s area - on the left posterior section of the superior temporal lobe, encircling the auditory cortex. Function in language comprehension Copyright © 2010 Pearson Education, Inc. multimodal association areas • Most of the cortex receives inputs from multiple senses and sends outputs to multiple areas • Theses areas are called – multimodal association areas • In general the route is : • Information accepted by sensory receptors • Signal is transported to the appropriate primary sensory cortex • To sensory association cortex • To multimodal association cortex • Multimodal association allows to give a meaning to received information, stores memory, connect signal to previous experience, decide what action to take Copyright © 2010 Pearson Education, Inc. Language Areas as example of multimodal association • Located in a large area surrounding the left (or languagedominant) lateral sulcus • Major parts and functions: • Wernicke’s area –sounding out unfamiliar words (sensory) • Broca’s area – speech preparation and production (motor) • Lateral prefrontal cortex – language comprehension and word analysis • Lateral and ventral temporal lobe – coordinate auditory and visual aspects of language Copyright © 2010 Pearson Education, Inc. Copyright © 2010 Pearson Education, Inc. http://www.colorado.edu/kines/Class/IPHY3730/image/figure5-21.jpg Lateralization of Cortical Function • Lateralization – each hemisphere has abilities not shared with its partner • Cerebral dominance – designates the hemisphere dominant for language. For most people: • Left hemisphere – controls language, math, and logic • Right hemisphere – controls visual skills, emotion, and artistic skills • For 10% of people the roles of the hemispheres are reversed or the hemispheres share functions equally • The hemispheres have communication with one another Copyright © 2010 Pearson Education, Inc. Cerebral White Matter • Consists of deep myelinated fibers bundled into tracts • The tracts are classified according to the direction in which they run: • Commissures – • connect corresponding gray areas of the hemispheres allowing them to work as one unit two • The largest is the corpus callosum • Anterior and posterior commisures • Association fibers – connect different parts of the same hemisphere • Projection fibers – enter the hemispheres from lower brain or cord centers Copyright © 2010 Pearson Education, Inc. Basal Nuclei • Masses of gray matter found deep within the cortical white matter • its major components include the caudate, Putamen, globus pallidus • The putamen and the globus pallidus form the lentiform nucleus • The lentiform and the caudata are called the corpus striatum Copyright © 2010 Pearson Education, Inc. lentiform Copyright © 2010 Pearson Education, Inc. Basal Ganglia Function • Organization • Input from cortex • Project motor to cortex • Function • coordinating the initiation of movements • Monitor movement • Inhibit unnecessary movement Copyright © 2010 Pearson Education, Inc. The picture represents the Somatotopy mapping/ homunculi of the cerebral cortex Copyright © 2010 Pearson Education, Inc. What white matter structure connects the two cerebral hemispheres? A. longitudinal fissure B. lateral ventricles C. corpus callosum D. diencephalons Copyright © 2010 Pearson Education, Inc. Damage to the white matter of the brain would prevent transmission of information between nuclei. Copyright © 2010 Pearson Education, Inc. Diencephalon • Consists of three paired structures – • thalamus • Hypothalamus • epithalamus • Encloses the third ventricle Copyright © 2010 Pearson Education, Inc. Thalamic Function • The thalamus is the “gateway to the cerebral cortex” • Major relay station for most sensory impulses that arrive to the primary sensory areas in the cerebral cortex: • taste, smell, hearing, equilibrium, vision, touch, pain, pressure, temperature • Contributes to motor functions by transmitting information from the cerebellum and basal ganglia to the cerebral primary motor area • Connects areas of the cerebrum • Impulses of similar function are sorted out, edited, and relayed as a group Copyright © 2010 Pearson Education, Inc. Hypothalamus • Located below the thalamus and forms the inferolateral walls of the third ventricle • Infundibulum – stalk of the hypothalamus; connects to the pituitary gland • Mammillary bodies • Small, paired nuclei bulging anteriorly from the hypothalamus • Relay station for olfactory pathways Copyright © 2010 Pearson Education, Inc. Hypothalamic Function • Function as the main visceral control in the body • Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, eye pupil size etc. • Perception of pleasure, fear, and rage • Maintains normal body temperature (contains body’s “thermostat”) by initiating cooling or heat-generating processes • Regulates food intake (hunger) • Regulation of water intake contain thirst center and thirst – produce ADH, • Regulates sleep and the sleep cycle Copyright © 2010 Pearson Education, Inc. Endocrine Functions of the Hypothalamus • Releasing hormones control secretion of hormones by the anterior pituitary • The supraoptic and paraventricular nuclei produce ADH and oxytocin Copyright © 2010 Pearson Education, Inc. Epithalamus • Most dorsal portion of the diencephalon; forms roof of the third ventricle • Pineal gland – extends from the posterior border and secretes melatonin • Melatonin – a hormone involved with sleep regulation, sleep-wake cycles, and mood • Choroid plexus – a structure that secretes cerebral spinal fluid (CSF) Copyright © 2010 Pearson Education, Inc. Brain Stem • Consists of three regions – • midbrain, • Pons • medulla oblongata • Similar to spinal cord – deep gray matter surrounded by white tracts but contains embedded nuclei in the white matter • Controls automatic behaviors necessary for (breathing, digestion, heart rate, blood pressure) survival • Provides the pathway for tracts between higher and lower brain centers • Associated with 10 of the 12 pairs of cranial nerves Copyright © 2010 Pearson Education, Inc. Midbrain • Located between the diencephalon and the pons • Midbrain structures include: • Cerebral peduncles of the midbrain – two structures that contain descending pyramidal motor tracts (what areas do the pyramidal tracts connect?) • Cerebral aqueduct – hollow tube that connects the third and fourth ventricles • Various nuclei (what are nuclei) Copyright © 2010 Pearson Education, Inc. Midbrain Nuclei • Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) • Corpora quadrigemina • 2 Superior colliculi – visual reflex centers; coordinate head and eye movement when we follow a moving object (does not have to be a conscious decision) • 2 Inferior colliculi – auditory relay centers between hearing receptors to sensory cortex. • Reflexive responses to sound – turn head toward sound Copyright © 2010 Pearson Education, Inc. Midbrain Nuclei • Substantia nigra – functionally linked to basal nuclei, contains melanin pigment (precursor of dopamine NT) • Red nucleus – largest nucleus (rich blood supply) of the reticular formation; relay nuclei for some descending motor pathways Copyright © 2010 Pearson Education, Inc. Pons • between the midbrain and the medulla oblongata • Forms part of the anterior wall of the fourth ventricle • Fibers of the pons: • Connect higher brain centers and the spinal cord • Relay impulses between the motor cortex and the cerebellum • Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) • Contains nuclei of the reticular formation Copyright © 2010 Pearson Education, Inc. Medulla Oblongata • Most inferior part of the brain stem • Along with the pons, forms the ventral wall of the fourth ventricle • Contains the choroid plexus of the fourth ventricle • Pyramids – two longitudinal ridges formed by corticospinal tracts descending from the motor cortex • Before entering the spinal cord the corticospinal tracts crossover. • The point in which the crossover occur is called decussation of the pyramids • Results in the controlling of each cerebral hemisphere in the movements of the opposite side Copyright © 2010 Pearson Education, Inc. Medulla Nuclei • Inferior olivary nuclei – gray matter that relays sensory information regarding the stretch of muscle and joints • Cranial nerves IX (glosopharyngeal, X (vagus), XI (accessory; neck muscle), and XII (hypoglossal; tongue) are associated with the medulla • Vestibular nuclear complex – synapses that mediate and maintain equilibrium • Ascending sensory tract nuclei, including nucleus cuneatus and nucleus gracilis • Serve as relay station for general somatic sensation Copyright © 2010 Pearson Education, Inc. Medulla Nuclei • The medulla has an important role in the autonomic reflex center that maintain homeostasis: • Cardiovascular control center – adjusts force and rate of heart contraction • Respiratory centers – control rate and depth of breathing • Additional centers – regulate vomiting, hiccuping, swallowing, coughing, and sneezing • There is an overlap between medulla and hypothalamus that uses medullary centers to carry out instructions Copyright © 2010 Pearson Education, Inc. The Cerebellum • Located dorsal to the pons and medulla; the activity is subconscious • Two bilaterally symmetrical hemispheres connected medially by the vermis • Folia – transversely oriented gyri • Each hemisphere has three lobes – anterior, posterior, and flocculonodular (deep to the vermis and posterior lobe; can not be seen from the outside) • Neural arrangement – gray matter cortex, internal white matter, scattered nuclei • Arbor vitae – distinctive treelike pattern of the cerebellar white matter Copyright © 2010 Pearson Education, Inc. Cerebellar Function • Adjust ongoing movements on the basis of comparison between arriving sensation to one previously experienced • Posture: • Balance • Equilibrium • Fine Tune Movements • Timing • Rate • Range • Force Copyright © 2010 Pearson Education, Inc. Cerebellar Processing • Cerebellum receives impulses of the intent to initiate voluntary muscle contraction • Proprioceptors and visual signals “inform” the cerebellum of the body’s condition • Cerebellar cortex calculates the best way to perform a movement • A “blueprint” of coordinated movement is sent to the cerebral motor cortex Copyright © 2010 Pearson Education, Inc. Initiation of Skilled Movement Frontal Association and Primary Motor Cortex Frontal cortex can plan and initiate movement but cannot calculate the complex, timed sequence of muscle contraction Send information about intended movements to the cerebellum Basal Ganglia Somatosensory System Information on current position Lateral Zone of Cerebellum When cerebellum receives information about initiated movement it computes the contribution that various muscles will have to make Sends results Dentate Nucleus In cerebellum Via basal ganglia Allows the cerebellum to modify the ongoing movement that was initiated by the frontal cortex Thalamus The cerebellum can also control a skilled movement by timing the movement and by turning on the antagonist muscle. This happens when the movement is rapid and cannot relay on feedback. Copyright © 2010 Pearson Education, Inc. Cerebellum White tracts • Three paired fiber tracts that connect the cerebellum to the brain stem • All fibers in the cerebellum are ipsilateral (from and to same side of the body) • The superior cerebellar cerebellum to the midbrain peduncle connects the • These are the axons that send feedback to the motor cortex in the frontal lobe via the red nucleus in the midbrain and thalamus. • afferent fibers traveling in this peduncle bring proprioceptive information to the cerebellum from the lower body. Copyright © 2010 Pearson Education, Inc. Cerebellum White tracts • The middle cerebellar peduncle is the largest of the peduncles and carry one-way communication from the pons to the cerebellum. • Via this connection, the cerebellum receives “a copy” of the information for voluntary muscle movement that the pyramidal tract is carrying down from the motor cortex to lower motor neurons. • The inferior cerebellar peduncle connects the cerebellum with the medulla • Bring sensory information from the muscle proprioceptors around the body and the vestibular nuclei in the brain stem (equilibrium) Copyright © 2010 Pearson Education, Inc. Memory • Memory is the storage and retrieval of information • The three principles of memory are: • Storage – occurs in stages and is continually changing • Processing – accomplished by the hippocampus and surrounding structures • Memory traces – chemical or structural changes that encode memory Copyright © 2010 Pearson Education, Inc. Memory • Storage and retrieval of information • Two stages of storage • Short-term memory (STM, or working memory)— temporary holding of information; limited to seven or eight pieces of information • Long-term memory (LTM) has limitless capacity Copyright © 2010 Pearson Education, Inc. Transfer from STM to LTM • Factors that affect transfer from STM to LTM • Emotional state —best surprised, and aroused if alert, motivated, • Rehearsal —repetition and practice • Association —tying new information with old memories • Automatic memory — subconscious information stored in LTM Copyright © 2010 Pearson Education, Inc. Categories of Memory 1. Declarative memory (factual knowledge) • Explicit information • Related to our conscious thoughts and our language ability • Stored in LTM with context in which it was learned Copyright © 2010 Pearson Education, Inc. Categories of Memory 2. Nondeclarative memory • Less conscious or unconscious • Acquired through experience and repetition • Best remembered by doing; hard to unlearn • Includes procedural (skills) memory, motor memory, and emotional memory Copyright © 2010 Pearson Education, Inc. Brain Structures Involved in Nondeclarative Memory • Procedural memory • Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex • Dopamine from substantia nigra is necessary • Motor memory—cerebellum • Emotional memory—amygdala Copyright © 2010 Pearson Education, Inc. Spinal Cord • CNS tissue is enclosed within the vertebral column from the foramen magnum to L1 • Provides two-way communication to and from the brain • Protected by bone, meninges, and CSF • Conus medullaris – terminal portion of the spinal cord • Filum terminale – fibrous extension of the pia mater; anchors the spinal cord to the coccyx • Denticulate ligaments – delicate shelves of pia mater; attach the spinal cord to the vertebrae • Spinal nerves – 31 pairs attach to the cord by paired roots (8 cervical, 12thoracic, 5 lumbar, 5 sacral 1 coccygeal) • Cervical and lumbar enlargements – sites where nerves serving the upper and lower limbs emerge Copyright © 2010 Pearson Education, Inc. Figure 12.29a Spinal Cord • Because the cord does not reach the end of the vertebral column, the lumbar and sacral spinal nerve roots angle sharply downward and travel inferiorly before reaching their intervertebral foramina • This collection of nerve roots at the inferior end of the vertebral canal is called the cauda equina Copyright © 2010 Pearson Education, Inc. White Matter in the Spinal Cord • Composed of both myelinated and unmyelinated fibers that run in three directions • Ascending – to higher centers; sensory • Descending – to lower levels from brain or higher places in the cord; motor • Transversely – from one side of the cord to the other • Divided into three funiculi (columns) – posterior, lateral, and anterior • Each funiculus contains several fiber tracks with similar destination and function • Fiber tract names reveal their origin and destination • Fiber tracts are composed of axons with similar functions Copyright © 2010 Pearson Education, Inc.