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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 12 The Central Nervous System: Part A Copyright © 2010 Pearson Education, Inc. Central Nervous System (CNS) • CNS consists of the brain and spinal cord • Cephalization • Evolutionary development of the rostral (anterior) portion of the CNS • Increased number of neurons in the head • Highest level is reached in the human brain Copyright © 2010 Pearson Education, Inc. Functions of the Nervous System 1. Sensory input • Information gathered by sensory receptors about internal and external changes 2. Integration • Interpretation of sensory input 3. Motor output • Activation of effector organs (muscles and glands) produces a response Copyright © 2010 Pearson Education, Inc. Sensory input Integration Motor output Copyright © 2010 Pearson Education, Inc. Figure 11.1 Divisions of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Integration and command center • Peripheral nervous system (PNS) • Paired spinal and cranial nerves carry messages to and from the CNS Copyright © 2010 Pearson Education, Inc. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Nucleus Nissl bodies Axon hillock (b) Copyright © 2010 Pearson Education, Inc. Impulse direction Node of Ranvier Schwann cell Neurilemma (one interTerminal node) branches Axon terminals (secretory region) Figure 11.4b Peripheral Nervous System (PNS) • Two functional divisions 1. Sensory (afferent) division • Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints • Visceral afferent fibers—convey impulses from visceral organs Copyright © 2010 Pearson Education, Inc. 2. Motor (efferent) division • Transmits impulses from the CNS to effector organs Copyright © 2010 Pearson Education, Inc. Motor Division of PNS 1. Somatic (voluntary) nervous system • Conscious control of skeletal muscles Copyright © 2010 Pearson Education, Inc. Peripheral nervous system (PNS) Central nervous system (CNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body Brain and spinal cord Integrative and control centers Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS Somatic sensory fiber Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Somatic nervous system Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles Skin Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Mobilizes body systems during activity Sympathetic motor fiber of ANS Structure Function Sensory (afferent) division of PNS Motor (efferent) division of PNS Copyright © 2010 Pearson Education, Inc. Parasympathetic motor fiber of ANS Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Parasympathetic division Conserves energy Promotes housekeeping functions during rest Heart Bladder Figure 11.2 Embryonic Development Don’t copy • Neural plate forms from ectoderm • Neural plate invaginates to form a neural groove and neural folds Copyright © 2010 Pearson Education, Inc. Surface ectoderm Head Neural plate Tail 1 The neural plate forms from surface ectoderm. Copyright © 2010 Pearson Education, Inc. Figure 12.1, step 1 Neural folds Neural groove 2 The neural plate invaginates, forming the neural groove, flanked by neural folds. Copyright © 2010 Pearson Education, Inc. Figure 12.1, step 2 Embryonic Development don’t copy • Neural groove fuses dorsally to form the neural tube • Neural tube gives rise to the brain and spinal cord Copyright © 2010 Pearson Education, Inc. Neural crest 3 Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. Copyright © 2010 Pearson Education, Inc. Figure 12.1, step 3 Head Surface ectoderm Tail Neural tube 4 The neural groove becomes the neural tube, which will form CNS structures. Copyright © 2010 Pearson Education, Inc. Figure 12.1, step 4 Anterior (rostral) Metencephalon Mesencephalon Diencephalon Telencephalon Myelencephalon (a) Week 5 Copyright © 2010 Pearson Education, Inc. Posterior (caudal) Midbrain Cervical Flexures Spinal cord Figure 12.3a Cerebral hemisphere Outline of diencephalon Midbrain Cerebellum Pons Medulla oblongata (b) Week 13 Copyright © 2010 Pearson Education, Inc. Spinal cord Figure 12.3b (c) Week 26 Copyright © 2010 Pearson Education, Inc. Cerebral hemisphere Cerebellum Pons Medulla oblongata Spinal cord Figure 12.3c Copyright © 2010 Pearson Education, Inc. *Regions and Organization of the CNS • Adult brain regions 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem (midbrain, pons, and medulla) 4. Cerebellum Copyright © 2010 Pearson Education, Inc. Cerebral hemisphere Diencephalon (d) Birth Copyright © 2010 Pearson Education, Inc. Cerebellum Brain stem • Midbrain • Pons • Medulla oblongata Figure 12.3d Regions and Organization of the CNS • Spinal cord • Central cavity surrounded by a gray matter core • External white matter composed of myelinated fiber tracts Copyright © 2010 Pearson Education, Inc. Regions and Organization of the CNS • Brain • Similar pattern with additional areas of gray matter • Nuclei in cerebellum and cerebrum • Cortex of cerebellum and cerebrum Copyright © 2010 Pearson Education, Inc. Cortex of gray matter Inner gray matter Central cavity Migratory pattern of neurons Cerebrum Cerebellum Region of cerebellum Outer white matter Gray matter Central cavity Inner gray matter Outer white matter Brain stem Gray matter Central cavity Outer white matter Spinal cord Copyright © 2010 Pearson Education, Inc. Inner gray matter Figure 12.4 Ventricles of the Brain • Connected to one another and to the central canal of the spinal cord • Lined by ependymal cells Copyright © 2010 Pearson Education, Inc. Ventricles of the Brain • Contain cerebrospinal fluid • Two C-shaped lateral ventricles in the cerebral hemispheres • Third ventricle in the diencephalon • Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tube Copyright © 2010 Pearson Education, Inc. Lateral ventricle Septum pellucidum Anterior horn Inferior horn Lateral aperture Interventricular foramen Third ventricle Inferior horn Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view (b) Left lateral Copyright © 2010 Pearson Education, Inc. Posterior horn Median aperture Lateral aperture view Figure 12.5 *Cerebral Hemispheres • Surface markings • Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) • Five lobes • Frontal • Parietal • Temporal • Occipital • Insula Copyright © 2010 Pearson Education, Inc. *Cerebral Hemispheres • Surface markings • Central sulcus • Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe • Longitudinal fissure • Separates the two hemispheres • Transverse cerebral fissure • Separates the cerebrum and the cerebellum PLAY Animation: Rotatable brain Copyright © 2010 Pearson Education, Inc. Precentral gyrus Frontal lobe Central sulcus Postcentral gyrus Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Spinal cord Fissure (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter (a) Copyright © 2010 Pearson Education, Inc. Figure 12.6a Frontal lobe Central sulcus Gyri of insula Temporal lobe (pulled down) (b) Copyright © 2010 Pearson Education, Inc. Figure 12.6b Anterior Longitudinal fissure Frontal lobe Cerebral veins and arteries covered by arachnoid mater Parietal lobe Right cerebral hemisphere Occipital lobe Left cerebral hemisphere (c) Copyright © 2010 Pearson Education, Inc. Posterior Figure 12.6c Left cerebral hemisphere Brain stem Transverse cerebral fissure Cerebellum (d) Copyright © 2010 Pearson Education, Inc. Figure 12.6d *Cerebral Cortex • Thin (2–4 mm) superficial layer of gray matter • 40% of the mass of the brain • Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding • Each hemisphere connects to contralateral side of the body • There is lateralization of cortical function in the hemispheres 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 • Conscious behavior involves the entire cortex Copyright © 2010 Pearson Education, Inc. Cerebral hemisphere Septum pellucidum Interthalamic adhesion (intermediate mass of thalamus) Interventricular foramen Anterior commissure Hypothalamus Optic chiasma Pituitary gland Mammillary body Pons Medulla oblongata Corpus callosum Fornix Choroid plexus Thalamus (encloses third ventricle) Posterior commissure Pineal gland (part of epithalamus) Corpora quadrigemina MidCerebral brain aqueduct Arbor vitae (of cerebellum) Fourth ventricle Choroid plexus Cerebellum Spinal cord Copyright © 2010 Pearson Education, Inc. Figure 12.12 *Motor Areas • Primary (somatic) motor cortex • Premotor cortex • Broca’s area • Frontal eye field Copyright © 2010 Pearson Education, Inc. Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Copyright © 2010 Pearson Education, Inc. Figure 12.8a *Primary Motor Cortex • Allows conscious control of precise, skilled, voluntary movements • Motor homunculi: upside-down caricatures representing the motor innervation of body regions Copyright © 2010 Pearson Education, Inc. Posterior Motor Motor map in precentral gyrus Anterior Toes Jaw Tongue Swallowing Copyright © 2010 Pearson Education, Inc. Primary motor cortex (precentral gyrus) Figure 12.9 *Premotor Cortex • Anterior to the precentral gyrus • Controls learned, repetitious, or patterned motor skills • Coordinates simultaneous or sequential actions • Involved in the planning of movements that depend on sensory feedback Copyright © 2010 Pearson Education, Inc. Broca’s Area • 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 Copyright © 2010 Pearson Education, Inc. Frontal Eye Field • Anterior to the premotor cortex and superior to Broca’s area • Controls voluntary eye movements Copyright © 2010 Pearson Education, Inc. Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Copyright © 2010 Pearson Education, Inc. Figure 12.8a Primary Somatosensory Cortex • In the postcentral gyri • Receives sensory information from the skin, skeletal muscles, and joints • Capable of spatial discrimination: identification of body region being stimulated Copyright © 2010 Pearson Education, Inc. Posterior Sensory Anterior Sensory map in postcentral gyrus Genitals Primary somatosensory cortex (postcentral gyrus) Copyright © 2010 Pearson Education, Inc. Intraabdominal Figure 12.9 Motor areas Central sulcus Primary motor cortex Premotor cortex Frontal eye field Broca’s area (outlined by dashes) Prefrontal cortex Working memory for spatial tasks Executive area for task management Working memory for object-recall tasks Solving complex, multitask problems (a) Lateral view, left cerebral hemisphere Sensory areas and related association areas Primary somatosensory cortex Somatic Somatosensory sensation association cortex Gustatory cortex (in insula) Taste Wernicke’s area (outlined by dashes) Primary visual cortex Visual association area Auditory association area Primary auditory cortex Vision Hearing Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Copyright © 2010 Pearson Education, Inc. Figure 12.8a Premotor cortex Corpus callosum Cingulate gyrus Primary motor cortex Frontal eye field Prefrontal cortex Processes emotions related to personal and social interactions Orbitofrontal cortex Olfactory bulb Olfactory tract Fornix Temporal lobe (b) Parasagittal view, right hemisphere Uncus Primary olfactory cortex Central sulcus Primary somatosensory cortex Parietal lobe Somatosensory association cortex Parieto-occipital sulcus Occipital lobe Visual association area Primary visual cortex Calcarine sulcus Parahippocampal gyrus Motor association cortex Primary sensory cortex Primary motor cortex Sensory association cortex Multimodal association cortex Copyright © 2010 Pearson Education, Inc. Figure 12.8b Copyright © 2010 Pearson Education, Inc. Copyright © 2010 Pearson Education, Inc. Anterior Association Area (Prefrontal Cortex) • Most complicated cortical region • Involved with intellect, cognition, recall, and personality • Contains working memory needed for judgment, reasoning, persistence, and conscience • Development depends on feedback from social environment Copyright © 2010 Pearson Education, Inc. Hypothalamic Function • Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility) • Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives Copyright © 2010 Pearson Education, Inc. Hypothalamic Function • Regulates body temperature, food intake, water balance, and thirst • Regulates sleep and the sleep cycle • Controls release of hormones by the anterior pituitary • Produces posterior pituitary hormones Copyright © 2010 Pearson Education, Inc. Brain Stem • Three regions • Midbrain • Pons • Medulla oblongata Copyright © 2010 Pearson Education, Inc. Medulla Oblongata • Autonomic reflex centers • Cardiovascular center • Cardiac center adjusts force and rate of heart contraction • Vasomotor center adjusts blood vessel diameter for blood pressure regulation Copyright © 2010 Pearson Education, Inc. Medulla Oblongata • Respiratory centers • Generate respiratory rhythm • Control rate and depth of breathing, with pontine centers Copyright © 2010 Pearson Education, Inc. Medulla Oblongata • Additional centers regulate • Vomiting • Hiccuping • Swallowing • Coughing • Sneezing Copyright © 2010 Pearson Education, Inc. The Cerebellum • 11% of brain mass • Dorsal to the pons and medulla • Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction Copyright © 2010 Pearson Education, Inc. Anterior lobe Cerebellar cortex Arbor vitae Cerebellar peduncles • Superior • Middle • Inferior Medulla oblongata (b) Copyright © 2010 Pearson Education, Inc. Flocculonodular lobe Posterior lobe Choroid plexus of fourth ventricle Figure 12.17b 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. Outside stimuli General and special sensory receptors Afferent inputs Temporary storage (buffer) in cerebral cortex Automatic memory Data permanently lost Data selected for transfer Short-term memory (STM) Forget Forget Data transfer influenced by: Retrieval Excitement Rehearsal Association of old and new data Long-term memory (LTM) Copyright © 2010 Pearson Education, Inc. Data unretrievable Figure 12.22 Transfer from STM to LTM • Factors that affect transfer from STM to LTM • Emotional state—best if alert, motivated, surprised, and aroused • 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. Thalamus Basal forebrain Touch Prefrontal cortex Hearing Vision Taste Smell Hippocampus Sensory input (a) Declarative memory circuits Association cortex Thalamus Medial temporal lobe (hippocampus, etc.) Prefrontal cortex ACh ACh Basal forebrain Copyright © 2010 Pearson Education, Inc. Figure 12.23a 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. Sensory and motor inputs Association cortex Basal nuclei Thalamus Dopamine Premotor cortex Premotor cortex Substantia nigra Thalamus Basal nuclei Substantia nigra (b) Procedural (skills) memory circuits Copyright © 2010 Pearson Education, Inc. Figure 12.23b Molecular Basis of Memory • During learning: • Altered mRNA is synthesized and moved to axons and dendrites • Extracellular proteins are deposited at synapses involved in LTM • More neurotransmitter is released by presynaptic neurons Copyright © 2010 Pearson Education, Inc. Protection of the Brain • Bone (skull) • Membranes (meninges) • Watery cushion (cerebrospinal fluid) • Blood-brain barrier Copyright © 2010 Pearson Education, Inc. Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus Subdural space Subarachnoid space Copyright © 2010 Pearson Education, Inc. Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Cerebrospinal Fluid (CSF) • Composition • Watery solution • Less protein and different ion concentrations than plasma • Constant volume Copyright © 2010 Pearson Education, Inc. Cerebrospinal Fluid (CSF) • Functions • Gives buoyancy to the CNS organs • Protects the CNS from blows and other trauma • Nourishes the brain and carries chemical signals Copyright © 2010 Pearson Education, Inc. Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation Copyright © 2010 Pearson Education, Inc. 2 choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances • Antibodies are too large to cross the blood– brain barrier, and only certain antibiotics are able to pass • Exceptions are the bacteria that causes Lyme’s disease and syphilis Copyright © 2010 Pearson Education, Inc. Blood-Brain Barrier • There are also some biochemical poisons that are made up of large molecules that are too big to pass through the blood–brain barrier. • Composition • Continuous endothelium of capillary walls • Basal lamina • formation of tight junctions Copyright © 2010 Pearson Education, Inc. Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia. Copyright © 2010 Pearson Education, Inc. Figure 11.3a Blood-Brain Barrier: Functions • Selective barrier • Allows nutrients to move by facilitated diffusion • Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood Copyright © 2010 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 the foramen magnum, resulting in death • Cerebral edema—swelling of the brain associated with traumatic head injury Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances of the Brain • Cerebrovascular accidents (CVAs)(strokes) • Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot • Typically leads to hemiplegia, or sensory and speed deficits • Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia • Tissue plasminogen activator (TPA) is the only approved treatment for stroke Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances of the Brain • Degenerative brain disorders • Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia • Parkinson’s disease: degeneration of the dopaminereleasing neurons of the substantia nigra • Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex Copyright © 2010 Pearson Education, Inc. • The cranial nerves are: • I - Olfactory nerve • II - Optic nerve • III - Oculomotor nerve • IV - Trochlear nerve • V - Trigeminal nerve/dentist nerve • VI - Abducens nerve • VII - Facial nerve • VIII - Vestibulocochlear nerve/Auditory nerve • IX - Glossopharyngeal nerve • X - Vagus nerve • XI - Accessory nerve/Spinal accessory nerve • XII - Hypoglossal nerve Copyright © 2010 Pearson Education, Inc. • Odor Of Orangutan Terrified Tarzan After Forty Voracious Gorillas Viciously Attacked Him • Old Opie Occasionally Tries Trigonometry And Feels Very Gloomy, Vague And Hypoactive Copyright © 2010 Pearson Education, Inc. Sleep • State of partial unconsciousness from which a person can be aroused by stimulation • Two major types of sleep (defined by EEG patterns) • Nonrapid eye movement (NREM) • Rapid eye movement (REM) Copyright © 2010 Pearson Education, Inc. Sleep • First two stages of NREM occur during the first 30–45 minutes of sleep • Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly Copyright © 2010 Pearson Education, Inc. Awake REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs. NREM stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy. NREM stage 2: Irregular EEG with sleep spindles (short high- amplitude bursts); arousal is more difficult. NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline. (a) Typical EEG patterns Copyright © 2010 Pearson Education, Inc. NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur. Figure 12.21a Sleep Patterns • Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm • A typical sleep pattern alternates between REM and NREM sleep Copyright © 2010 Pearson Education, Inc. Awake REM Stage 1 Stage 2 Non REM Stage 3 Stage 4 Time (hrs) (b) Typical progression of an adult through one night’s sleep stages Copyright © 2010 Pearson Education, Inc. Figure 12.21b Importance of Sleep • Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage • People deprived of REM sleep become moody and depressed • REM sleep may be a reverse learning process where superfluous information is purged from the brain • Daily sleep requirements decline with age • Stage 4 sleep declines steadily and may disappear after age 60 Copyright © 2010 Pearson Education, Inc. Sleep Disorders • Narcolepsy • Lapsing abruptly into sleep from the awake state • Insomnia • Chronic inability to obtain the amount or quality of sleep needed • Sleep apnea • Temporary cessation of breathing during sleep Copyright © 2010 Pearson Education, Inc.