* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Central Nervous System
Functional magnetic resonance imaging wikipedia , lookup
Blood–brain barrier wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Neuroscience and intelligence wikipedia , lookup
Development of the nervous system wikipedia , lookup
Intracranial pressure wikipedia , lookup
Neurolinguistics wikipedia , lookup
Dual consciousness wikipedia , lookup
Neurophilosophy wikipedia , lookup
Affective neuroscience wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Synaptic gating wikipedia , lookup
Selfish brain theory wikipedia , lookup
Limbic system wikipedia , lookup
Brain morphometry wikipedia , lookup
Lateralization of brain function wikipedia , lookup
Emotional lateralization wikipedia , lookup
Brain Rules wikipedia , lookup
Cortical cooling wikipedia , lookup
Neuropsychology wikipedia , lookup
Haemodynamic response wikipedia , lookup
Embodied language processing wikipedia , lookup
Environmental enrichment wikipedia , lookup
History of neuroimaging wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Eyeblink conditioning wikipedia , lookup
Cognitive neuroscience wikipedia , lookup
Neuroanatomy wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Neuroesthetics wikipedia , lookup
Time perception wikipedia , lookup
Neuroeconomics wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Circumventricular organs wikipedia , lookup
Evoked potential wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Neuroanatomy of memory wikipedia , lookup
Metastability in the brain wikipedia , lookup
Cognitive neuroscience of music wikipedia , lookup
Neuroplasticity wikipedia , lookup
Human brain wikipedia , lookup
Aging brain wikipedia , lookup
Inferior temporal gyrus wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Chapter 12 The Central Nervous System Regions and Organization • Adult brain regions 1.Cerebral hemispheres 2.Diencephalon 3.Brain stem (midbrain, pons, and medulla) 4.Cerebellum Regions and Organization of the CNS • Spinal cord – Central cavity surrounded by gray matter – External white matter composed of myelinated fiber tracts Regions and Organization of the CNS • Brain – Similar pattern – Additional areas of gray matter in brain – Cerebral hemispheres and cerebellum • Outer gray matter called cortex – Cortex disappears in brain stem • Scattered gray matter nuclei amid white matter Ventricles of the Brain • • • Filled with cerebrospinal fluid (CSF) Lined by ependymal cells Connected to one another and to central canal of spinal cord – Lateral ventricles third ventricle via interventricular foramen – Third ventricle fourth ventricle via cerebral aqueduct Ventricles of the Brain • Paired, C-shaped lateral ventricles in cerebral hemispheres – Separated anteriorly by septum pellucidum • Third ventricle in diencephalon © 2013 Pearson Education, Inc. • Fourth ventricle in hindbrain – Three openings: paired lateral apertures in side walls; median aperture in roof • Connect ventricles to subarachnoid space Cerebral Hemispheres • Surface markings – Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) – Longitudinal fissure • Separates two hemispheres – Transverse cerebral fissure • Separates cerebrum and cerebellum Cerebral Hemispheres • Five lobes – Frontal – Parietal – Temporal – Occipital – Insula Cerebral Hemispheres • Central sulcus – Separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe • Parieto-occipital sulcus – Separates occipital and parietal lobes • Lateral sulcus outlines temporal lobes Cerebral Hemispheres • Three basic regions – Cerebral cortex of gray matter superficially – White matter internally – Basal nuclei deep within white matter © 2013 Pearson Education, Inc. Cerebral Cortex • • • Thin (2–4 mm) superficial layer of gray matter 40% mass of brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding 4 General Considerations of Cerebral Cortex 1.Three types of functional areas – Motor areas—control voluntary movement – Sensory areas—conscious awareness of sensation – Association areas—integrate diverse information 2.Each hemisphere concerned with contralateral side of body 3. Lateralization of cortical function in hemispheres 4. Conscious behavior involves entire cortex in some way Motor Areas of Cerebral Cortex • • • • • In frontal lobe; control voluntary movement Primary (somatic) motor cortex in precentral gyrus Premotor cortex anterior to precentral gyrus Broca's area anterior to inferior premotor area Frontal eye field within and anterior to premotor cortex; superior to Broca's area Primary Motor Cortex • • • • Large pyramidal cells of precentral gyri Long axons pyramidal (corticospinal) tracts of spinal cord Allows conscious control of precise, skilled, skeletal muscle movements Motor homunculi - upside-down caricatures represent contralateral motor innervation of body regions Premotor Cortex • • • Helps plan movements; staging area for skilled motor activities Controls learned, repetitious, or patterned motor skills Coordinates simultaneous or sequential actions © 2013 Pearson Education, Inc. • Controls voluntary actions that depend on sensory feedback Broca's Area • • • Present in one hemisphere (usually the left) Motor speech area that directs muscles of speech production Active in planning speech and voluntary motor activities Frontal Eye Field • Controls voluntary eye movements Sensory Areas of Cerebral Cortex • • • • • • Conscious awareness of sensation Occur in parietal, insular, temporal, and occipital lobes Primary somatosensory cortex • Vestibular cortex Somatosensory association cortex • Olfactory cortex Visual areas • Gustatory cortex Auditory areas • Visceral sensory area Primary Somatosensory Cortex • In postcentral gyri of parietal lobe • Receives general sensory information from skin, and proprioceptors of skeletal muscle, joints, and tendons • Capable of spatial discrimination: identification of body region being stimulated • Somatosensory homunculus upside-down caricatures represent contralateral sensory input from body regions Somatosensory Association Cortex • • Posterior to primary somatosensory cortex • Determines size, texture, and relationship of parts of objects being felt Integrates sensory input from primary somatosensory cortex for understanding of object © 2013 Pearson Education, Inc. Visual Areas • Primary visual (striate) cortex – Extreme posterior tip of occipital lobe – Most buried in calcarine sulcus of occipital lobe – Receives visual information from retinas Visual Areas • Visual association area – Surrounds primary visual cortex – Uses past visual experiences to interpret visual stimuli (e.g., color, form, and movement) • E.g., ability to recognize faces – Complex processing involves entire posterior half of cerebral hemispheres Auditory Areas • Primary auditory cortex – Superior margin of temporal lobes – Interprets information from inner ear as pitch, loudness, and location • Auditory association area – Located posterior to primary auditory cortex – Stores memories of sounds and permits perception of sound stimulus Vestibular Cortex • • Posterior part of insula and adjacent parietal cortex Responsible for conscious awareness of balance (position of head in space) OIfactory Cortex • Primary olfactory (smell) cortex – Medial aspect of temporal lobes (in piriform lobes) – Part of primitive rhinencephalon, along with olfactory bulbs and tracts – Remainder of rhinencephalon in humans part of limbic system – Region of conscious awareness of odors Gustatory Cortex • In insula just deep to temporal lobe © 2013 Pearson Education, Inc. • Involved in perception of taste Visceral Sensory Area • • Posterior to gustatory cortex Conscious perception of visceral sensations, e.g., upset stomach or full bladder Multimodal Association Areas • • • Receive inputs from multiple sensory areas • • Sensations, thoughts, emotions become conscious – makes us who we are Send outputs to multiple areas, including premotor cortex Allows meaning to information received, store in memory, tying to previous experience, and deciding on actions Three broad parts: – Anterior association area (prefrontal cortex) – Posterior association area – Limbic association area Anterior Association Area (Prefrontal Cortex) • • • Most complicated cortical region • Development depends on feedback from social environment Involved with intellect, cognition, recall, and personality Contains working memory needed for abstract ideas, judgment, reasoning, persistence, and planning Posterior Association Area • • • Large region in temporal, parietal, and occipital lobes Plays role in recognizing patterns and faces and localizing us in space Involved in understanding written and spoken language (Wernicke's area) Limbic Association Area • • • Part of limbic system Involves cingulate gyrus, parahippocampal gyrus, and hippocampus Provides emotional impact that makes scene important and helps establish memories © 2013 Pearson Education, Inc. Lateralization of Cortical Function • • • Hemispheres almost identical Lateralization - division of labor between hemispheres Cerebral dominance - hemisphere dominant for language (left hemisphere 90% people) Lateralization of Cortical Function • Left hemisphere – Controls language, math, and logic • Right hemisphere – Visual-spatial skills, intuition, emotion, and artistic and musical skills • Hemispheres communicate almost instantaneously via fiber tracts and functional integration Cerebral White Matter • • Myelinated fibers and tracts Communication between cerebral areas, and between cortex and lower CNS – Association fibers— horizontal; connect different parts of same hemisphere – Commissural fibers— horizontal; connect gray matter of two hemispheres – Projection fibers— vertical; connect hemispheres with lower brain or spinal cord Diencephalon • Three paired structures – Thalamus – Hypothalamus – Epithalamus • Encloses third ventricle Thalamus • • • 80% of diencephalon Superolateral walls of third ventricle Bilateral nuclei connected by interthalamic adhesion (intermediate mass) – Contains several nuclei, named for location © 2013 Pearson Education, Inc. – Nuclei project and receive fibers from cerebral cortex Thalamic Function • • Gateway to cerebral cortex Sorts, edits, and relays ascending input – Impulses from hypothalamus for regulation of emotion and visceral function – Impulses from cerebellum and basal nuclei to help direct motor cortices – Impulses for memory or sensory integration • Mediates sensation, motor activities, cortical arousal, learning, and memory Hypothalamus • • Forms inferolateral walls of third ventricle Contains many nuclei – Example: mammillary bodies • Paired anterior nuclei • Olfactory relay stations • Infundibulum—stalk that connects to pituitary gland Hypothalamic Function • Controls autonomic nervous system (e.g., blood pressure, rate and force of heartbeat, digestive tract motility, pupil size) • Physical responses to emotions (limbic system) – Perception of pleasure, fear, and rage, and in biological rhythms and drives Hypothalamic Function • • • • Regulates body temperature – sweating/shivering Regulates hunger and satiety in response to nutrient blood levels or hormones Regulates water balance and thirst Regulates sleep-wake cycles – Suprachiasmatic nucleus (biological clock) • Controls endocrine system – Controls secretions of anterior pituitary gland – Produces posterior pituitary hormones © 2013 Pearson Education, Inc. Epithalamus • • Most dorsal portion of diencephalon; forms roof of third ventricle Pineal gland (body)—extends from posterior border and secretes melatonin – Melatonin—helps regulate sleep-wake cycle Brain Stem • Three regions – Midbrain – Pons – Medulla oblongata Brain Stem • • • • Similar structure to spinal cord but contains nuclei embedded in white matter Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Nuclei associated with 10 of the 12 pairs of cranial nerves Midbrain • • Between diencephalon and pons Cerebral peduncles ventrally – Contain pyramidal motor tracts • Cerebral aqueduct – Channel connecting third and fourth ventricles Midbrain Nuclei • Periaqueductal gray matter – Pain suppression; links amygdaloid body and ANS; controls cranial nerves III (oculomotor) and IV (trochlear) • Corpora quadrigemina— dorsal protrusions – Superior colliculi—visual reflex centers – Inferior colliculi—auditory relay centers • Substantia nigra—functionally linked to basal nuclei • Red nucleus—relay nuclei for some descending motor pathways; part of reticular formation © 2013 Pearson Education, Inc. Pons • Fourth ventricle seperates pons and cerebellum • Fibers of pons – Connect higher brain centers and spinal cord – Relay impulses between motor cortex and cerebellum • Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) • Some nuclei of reticular formation • Nuclei help maintain normal rhythm of breathing Medulla Oblongata (Medulla) • • • • • Joins spinal cord at foramen magnum Forms part of ventral wall of fourth ventricle Contains choroid plexus of fourth ventricle Pyramids—two ventral longitudinal ridges formed by pyramidal tracts Decussation of the pyramids—crossover of corticospinal tracts • Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum • Cranial nerves VIII, IX, X, and XII are associated with medulla • Vestibular nuclei (pons and medulla)—mediate responses that maintain equilibrium • Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information Medulla Oblongata: Functions • Autonomic reflex center – Functions overlap with hypothalamus • Hypothalamus relays instructions via medulla • Cardiovascular center – Cardiac center adjusts force and rate of heart contraction – Vasomotor center adjusts blood vessel diameter for blood pressure regulation • Respiratory centers – Generate respiratory rhythm – Control rate and depth of breathing (with pontine centers) • Additional centers regulate © 2013 Pearson Education, Inc. – Vomiting, Hiccuping, Swallowing, Coughing, and Sneezing Cerebellum • • • • • • • 11% of brain mass Dorsal to pons and medulla Input from cortex, brain stem and sensory receptors Allows smooth, coordinated movements Cerebellar hemispheres connected by vermis Folia—transversely oriented gyri Each hemisphere has three lobes – Anterior, posterior, and flocculonodular • Arbor vitae—treelike pattern of cerebellar white matter Cerebellar Processing of Motor Activity • Cerebellum receives impulses from cerebral cortex of intent to initiate voluntary muscle contraction • Signals from proprioceptors and visual and equilibrium pathways continuously "inform" cerebellum of body's position and momentum • Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction • "Blueprint" of coordinated movement sent to cerebral motor cortex and brain stem nuclei Cognitive Function of Cerebellum • • Role in thinking, language, and emotion May compare actual with expected output and adjust accordingly Functional Brain Systems • Networks of neurons that work together but span wide areas of brain – Limbic system – Reticular formation Limbic System • • Structures on medial aspects of cerebral hemispheres and diencephalon Includes parts of diencephalon and some cerebral structures that encircle © 2013 Pearson Education, Inc. brain stem • Emotional or affective brain – Amygdaloid body—recognizes angry or fearful facial expressions, assesses danger, and elicits fear response – Cingulate gyrus—role in expressing emotions via gestures, and resolves mental conflict • Puts emotional responses to odors – Example: skunks smell bad • Most output relayed via hypothalamus Limbic System: Emotion and Cognition • Limbic system interacts with prefrontal lobes – React emotionally to things we consciously understand to be happening – Consciously aware of emotional richness in our lives • Hippocampus and amygdaloid body—play a role in memory Reticular Formation • • Three broad columns run length of brain stem Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord can govern brain arousal Reticular Formation: RAS and Motor Function • Reticular activating system (RAS) – Sends impulses to cerebral cortex to keep it conscious and alert – Filters out repetitive, familiar, or weak stimuli (~99% of all stimuli!) – Inhibited by sleep centers, alcohol, drugs – Severe injury results in permanent unconsciousness (coma) Protection of the Brain • • • • Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood brain barrier © 2013 Pearson Education, Inc. Meninges • • • • Cover and protect CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in skull Meninges • Three layers – Dura mater – Arachnoid mater – Pia mater • Meningitis – Inflammation of meninges Dura Mater • • Strongest meninx • Dural septa limit excessive movement of brain Two layers of fibrous connective tissue (around brain) separate to form dural venous sinuses – Falx cerebri—in longitudinal fissure; attached to crista galli – Falx cerebelli—along vermis of cerebellum – Tentorium cerebelli—horizontal dural fold over cerebellum and in transverse fissure Arachnoid Mater • • • • Middle layer with weblike extensions Separated from dura mater by subdural space Subarachnoid space contains CSF and largest blood vessels of brain Arachnoid villi protrude into superior sagittal sinus and permit CSF reabsorption Pia Mater • Delicate vascularized connective tissue that clings tightly to brain © 2013 Pearson Education, Inc. Cerebrospinal Fluid (CSF) • Composition – Watery solution formed from blood plasma • Less protein and different ion concentrations than plasma – Constant volume • Functions – Gives buoyancy to CNS structures • Reduces weight by 97% – Protects CNS from blows and other trauma – Nourishes brain and carries chemical signals Choroid Plexuses • Hang from roof of each ventricle; produce CSF at constant rate; keep in motion – Clusters of capillaries enclosed by pia mater and layer of ependymal cells • Ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes • Normal volume ~ 150 ml; replaced every 8 hours Blood Brain Barrier • • • Helps maintain stable environment for brain Separates neurons from some bloodborne substances Composition – Continuous endothelium of capillary walls – Thick basal lamina around capillaries – Feet of astrocytes • Provide signal to endothelium for formation of tight junctions Blood Brain Barrier: Functions • Selective barrier – Allows nutrients to move by facilitated diffusion – Metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids, K+ denied – Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center and hypothalamus, where necessary to monitor chemical composition of blood © 2013 Pearson Education, Inc. Homeostatic Imbalances of the Brain • Traumatic brain injuries – Concussion—temporary alteration in function – Contusion—permanent damage – Subdural or subarachnoid hemorrhage—may force brain stem through foramen magnum, resulting in death – Cerebral edema—swelling of brain associated with traumatic head injury Homeostatic Imbalances of the Brain • Cerebrovascular accidents (CVAs or strokes) – Ischemia • Tissue deprived of blood supply; brain tissue dies, e.g., blockage of cerebral artery by blood clot – Hemiplegia (paralysis on one side), or sensory and speech deficits – Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia – Tissue plasminogen activator (TPA) is only approved treatment for stroke Homeostatic Imbalances of the Brain • Degenerative brain disorders – Alzheimer's disease (AD): a progressive degenerative disease of brain that results in dementia • Memory loss, short attention span, disorientation, eventual language loss, irritable, moody, confused, hallucinations • Plaques of beta-amyloid peptide form in brain – Toxic effects may involve prion proteins • Neurofibrillary tangles inside neurons kill them • Brain shrinks • Parkinson's disease – Degeneration of dopamine-releasing neurons of substantia nigra – Basal nuclei deprived of dopamine become overactive tremors at rest – Cause unknown • Mitochondrial abnormalities or protein degradation pathways? – Treatment with L-dopa; deep brain stimulation; gene therapy; research into stem cell transplants promising • Huntington's disease – Fatal hereditary disorder © 2013 Pearson Education, Inc. – Caused by accumulation of protein huntingtin • Leads to degeneration of basal nuclei and cerebral cortex • • • • Initial symptoms wild, jerky "flapping" movements Later marked mental deterioration Treated with drugs that block dopamine effects Stem cell implant research promising Spinal Cord: Gross Anatomy and Protection • Location – Begins at the foramen magnum – Ends at L1 or L2 vertebra • Functions – Provides two-way communication to and from brain – Contains spinal reflex centers Spinal Cord: Gross Anatomy and Protection • • Bone, meninges, and CSF Epidural space – Cushion of fat and network of veins in space between vertebrae and spinal dura mater • • CSF in subarachnoid space Dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 – Site of lumbar puncture or tap • • Terminates in conus medullaris Filum terminale extends to coccyx – Fibrous extension of conus covered with pia mater – Anchors spinal cord • Denticulate ligaments – Extensions of pia mater that secure cord to dura mater • Spinal nerves (Part of PNS) – 31 pairs • Cervical and lumbosacral enlargements – Nerves serving upper and lower limbs emerge here © 2013 Pearson Education, Inc. • Cauda equina – Collection of nerve roots at inferior end of vertebral canal Cross-sectional Anatomy • Two lengthwise grooves partially divide cord into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus • Gray commissure—connects masses of gray matter; encloses central canal Gray Matter •Dorsal horns - interneurons that receive somatic and visceral sensory input •Ventral horns - some interneurons; somatic motor neurons; axons exit cord via ventral roots •Lateral horns (only in thoracic and superior lumbar regions) - sympathetic neurons •Dorsal roots – sensory input to cord •Dorsal root (spinal) ganglia—cell bodies of sensory neurons White Matter • Myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain • Run in three directions – Ascending – up to higher centers (sensory inputs) – Descending – from brain to cord or lower cord levels (motor outputs) – Transverse – from one side to other (commissural fibers) Ascending Pathways • Three main pathways: – Two transmit somatosensory information to sensory cortex via thalamus •Dorsal column–medial lemniscal pathways •Spinothalamic pathways •Provide discriminatory touch and conscious proprioception – Spinocerebellar tracts terminate in the cerebellum Dorsal Column–Medial Lemniscal Pathways • Transmit input to somatosensory cortex for discriminative touch and vibrations © 2013 Pearson Education, Inc. • Composed of paired fasciculus cuneatus and fasciculus gracilis in spinal cord and medial lemniscus in brain (medulla to thalamus) Spinothalamic Pathways • • Lateral and ventral spinothalamic tracts Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract Spinocerebellar Tracts • • Ventral and dorsal tracts Convey information about muscle or tendon stretch to cerebellum – Used to coordinate muscle activity Descending Pathways and Tracts • • Deliver efferent impulses from brain to spinal cord Two groups – Direct pathways—pyramidal tracts – Indirect pathways—all others Descending Pathways and Tracts • Motor pathways involve two neurons: – Upper motor neurons •Pyramidal cells in primary motor cortex – Lower motor neurons •Ventral horn motor neurons •Innervate skeletal muscles The Direct (Pyramidal) Pathways • Impulses from pyramidal neurons in precentral gyri pass through pyramidal (corticospinal)l tracts • • • Descend without synapsing Axons synapse with interneurons or ventral horn motor neurons Direct pathway regulates fast and fine (skilled) movements © 2013 Pearson Education, Inc. Indirect (Multineuronal) System • • Complex and multisynaptic • These pathways regulate Includes brain stem motor nuclei, and all motor pathways except pyramidal pathways – Axial muscles maintaining balance and posture – Muscles controlling coarse limb movements – Head, neck, and eye movements that follow objects in visual field • • • Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli Poliomyelitis • • • • Destruction of ventral horn motor neurons by poliovirus • Destruction of ventral horn motor neurons and fibers of pyramidal tract Muscles atrophy Death may occur from paralysis of respiratory muscles or cardiac arrest Survivors often develop postpolio syndrome many years later from neuron loss Amyotrophic Lateral Sclerosis (ALS) (Lou Gehrig's Disease) – Symptoms—loss of ability to speak, swallow, and breathe – Death typically occurs within five years – Caused by environmental factors and genetic mutations involving RNA processing •Involves glutamate excitotoxicity • Drug riluzole interferes with glutamate signaling – only treatment Epilepsy •Victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking; 1% of population Assessing CNS Dysfunction • • Reflex tests Imaging techniques – CT, MRI, PET, radiotracer dyes for Alzheimer's, ultrasound, cerebral angiography © 2013 Pearson Education, Inc.