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Exam 3 Notes

by: Katy Cook

Exam 3 Notes BIOL 301

Katy Cook
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Detailed notes from all the readings for Exam 3: Chapters 13, 14, 16, & 17
Anatomy & Physiology
Dr. Rupa De
Study Guide
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This 36 page Study Guide was uploaded by Katy Cook on Sunday November 8, 2015. The Study Guide belongs to BIOL 301 at Purdue University taught by Dr. Rupa De in Fall 2015. Since its upload, it has received 38 views. For similar materials see Anatomy & Physiology in Biology at Purdue University.


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Date Created: 11/08/15
Chapter 13- Spinal Cord and Spinal Nerves  Spinal Cord- the part of the CNS that extends from the brain  Spinal cord reflex- a quick, automatic response to certain kinds of stimuli  Gray matter is a site for integration of EPSPs and IPSPs  White matter contains major sensory and motor tracts along which sensory input travels to the brain and motor output travels from the brain to skeletal muscles and effectors  Spinal Cord Anatomy  Nervous tissue does not respond well to injury or damage  First layer of protection is the skull and vertebral column  Second protective layer is the meninges- three membranes that lie between the bony encasement and the nervous tissue in the brain and spinal cord  Space between two of the meningeal membranes contains cerebrospinal fluid- a buoyant liquid that suspends the central nervous tissue in a weightless environment while surrounding it with a shock-absorbing, hydraulic cushion  Vertebral Column  Spinal cord located within the vertebral canal of the vertebral column  The vertebral foramina of all the vertebrae, stacked one on top of the other, form the vertebral canal  Meninges  Three protective, connective tissue coverings that encircle the spinal cord and brain  From superficial to deep: 1. Dura mater - Thick strong layer - Composed of dense irregular connective tissue - Forms a sac from the level of the foramen magnum in the occipital bone - Continuous with the epineurium, the outer covering of spinal and cranial nerves 2. Arachnoid mater - Middle membrane, thin, avascular - Comprised of cells and thin, loosely arranged collagen and elastic fibers - Spider web arrangement - Continuous through the foramen magnum with the arachnoid mater of the brain - Between the dura mater and arachnoid mater is a thin subdural space, which contains interstitial fluid 3. Pia mater - Thin transparent connective tissue - Adheres to the surface of the spinal cord and brain - Thin squamous to cuboidal cells with interlacing bundles of collagen fibers and elastic fibers - Many blood vessels that supply oxygen and nutrients to the spinal cord - Denticulate ligaments are thickenings of pia mater, project laterally and fuse with arachnoid mater and inner surface of dura mater, protect spinal cord against sudden displacement - Subarachnoid space between arachnoid mater and pia mater, contains shock-absorbing cerebrospinal fluid  The spinal meninges surround the spinal cord and are continuous with the cranial meninges (encircle brain)  All three spinal meninges cover spinal nerves up to the point where they exit the spinal column through the intervertebral foramina  Epidural space- space between dura mater and wall of vertebral canal, fat and connective tissue  External Anatomy of the spinal cord  Spinal cord is roughly oval in shape, flattened slightly anteriorly and posteriorly  Extends from the medulla oblongata to the superior border of the second lumbar vertebra  During childhood, both spinal cord and vertebral column grow longer as part of overall body growth (stops around ages 4-5)  Does not extend entire length of adult vertebral column  Cervical nerves: 8 pairs  Thoracic nerves: 12 pairs  Lumbar nerves: 5 pairs  Sacral nerves: 5 pairs  Coccygeal nerves: 1 pair  Cervical plexus: C1-C5  Brachial Plexus: C5-T1  Lumbar plexus: L1-L4  Sacral plexus: L4-S4  Cervical enlargement- extends from C4-T1, nerves to and from the upper limbs arise  Lumbar enlargement: T9-T12, nerves to and from the lower limbs  Conus medullaris- inferior to lumbar enlargement, spinal cord terminates as a tapering, conical structure, ends between L1-L2  Filum terminale- arising from conus medullaris, extension of pia mater, fuses with arachnoid mater and dura mater, anchors spinal cord to coccyx  Spinal nerves- paths of communication between spinal cord and specific regions of the body  Each pair of spinal nerves arise from spinal segment  Two bundles of axons called roots connect each spinal nerve to segment of the cord by even smaller bundles of axons called rootlets  The posterior (dorsal) root contain only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the CNS  Each posterior root has a swelling, the posterior (dorsal) root ganglion- contains the cell bodies of sensory neurons  Anterior (ventral) root contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands)  Nerves that arise from the lumbar, sacral, and coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exit the cord - The roots of these spinal nerves angle inferiorly alongside the filum terminale in the vertebral canal- called cauda equina  Internal anatomy of the spinal cord  White matter- bundles of myelinated axons of neurons  Anterior median fissure- wide groove on the anterior (ventral) side  Posterior median sulcus- narrow furrow on posterior side  Gray matter shaped like a butterfly; consists of dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia  Gray commissure- forms the crossbar of the H  Central canal- extends entire spinal cord, filled with cerebrospinal fluid  Continuous with the fourth ventricle in the medulla oblongata of the brain  Anterior white commissure- connects white matter of the right and left sides of the spinal cord  Nuclei- clusters of neuronal cell bodies in gray matter  Sensory nuclei receive input from receptors via sensory neurons  Motor nuclei provide output to effector tissues via motor neurons  Gray matter divided into regions called horns  Posterior gray horns- contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons  Anterior gray horns- contain somatic motor nuclei (clusters of cell bodies of somatic motor neurons that provide impulses for skeletal muscle contraction)  Lateral gray horns- present only in thoracic and upper lumbar segments of the spinal cord, contain autonomic motor nuclei that regulate activity of cardiac muscle, smooth muscle, and glands  White matter divided into three broad areas called columns: 1. Anterior (ventral) white columns 2. Posterior (dorsal) white columns 3. Lateral white columns  Each column contains distinct bundles of axons having a common origin or destination and carrying similar information  Tracts- Bundles of axons that extend up or down the spinal cord  Sensory tracts- consist of axons that conduct nerve impulses to brain  Motor tracts- axons that carry nerve impulses from brain  Sensory input and motor output processing: 1. Sensory receptors detect a sensory stimulus 2. Sensory neurons convey this sensory input in the form of nerve impulses along their axons (from sensory receptors in to the spinal nerve, then into the posterior root) 3. Axons of sensory neurons may extend into white matter and ascend to the brain as part of a sensory tract 4. Axons of sensory neurons may enter the posterior gray horn and synapse with interneurons whose axons extend into the white matter and ascend to the brain as part of a sensory tract 5. Axons of sensory neurons may enter posterior gray horn and synapse with interneurons that synapse with somatic motor neurons that are involved in spinal reflex pathways 6. Motor output from the spinal cord to skeletal muscles involves somatic motor neurons of the anterior gray horn. Axons from higher brain centers form motor tracts that descend into the white matter of spinal cord and synapse with somatic motor neurons either directly or indirectly by first synapsing with interneurons 7. When activated, somatic motor neurons convey motor output in the form of nerve impulses along their axons, which pass through anterior gray horn and anterior root to enter spinal nerve. From the spinal nerve, axons of somatic motor neurons extend to skeletal muscles of the body 8. Motor output from spinal cord to cardiac muscle, smooth muscle, and glands involves autonomic motor neurons of the lateral gray horn. Autonomic motor neurons convey motor output in form of nerve impulses along their axons, which pass through the lateral gray horn, anterior gray horn, and anterior root to enter the spinal nerve 9. From the spinal nerve, axons of autonomic motor neurons from spinal cord synapse with another group of autonomic motor neurons in the PNS. The axons of this second group in turn synapse with cardiac muscle, smooth muscle, and glands  The amount of white matter decreases from cervical to sacral segments of the spinal cord - As the spinal cord ascends from sacral to cervical segments, more ascending axons are added to spinal cord white matter to form more sensory tracts - As the spinal cord descends from cervical to sacral segments, the motor tracts decrease in thickness as more descending axons leave the motor tracts to synapse with neurons in the gray matter of the spinal cord  Connective tissue coverings of spinal nerves  Individual axons within a nerve are wrapped in endoneurium, the innermost layer  Groups of axons with their endoneurium are held together in bundles called fascicles  Each fascicle is wrapped in perineurium, the middle layer, thick connective tissue  Outermost layer of entire nerve is epineurium (fibroblasts and thick collagen fibers)  Dermatomes  Each spinal nerve contains sensory neurons that serve a specific, predictable segment of the body  Trigeminal (V) nerve, serves most of the skin of the face and scalp  The area of skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal (V) nerve is called a dermatome  The nerve supply in adjacent dermatomes overlaps somewhat  Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord  Spinal Cord Physiology  Spinal cord has two principal functions in maintaining homeostasis: nerve impulse propagation and integration of information  White matter tracts are highways for nerve impulse propagation  Gray matter of the spinal cord receives and integrates incoming and outgoing information  Often the name of a tract indicates its position in the white matter and where it begins and ends  Sensory and motor tracts  Example: anterior corticospinal tract: located in the anterior white column; beings in the cerebral cortex, ends in the spinal cord, motor, descending tract  Nerve impulses from sensory receptors propagate up the spinal cord to the brain along two main routes on each side: the spinothalamic tract (nerve impulses for sensing pain, warmth, coolness, itching, tickling, deep pressure, and crude touch) and the posterior column (gracile fasciculus and the cuneate fasciculus to convey nerve impulses for discriminative touch, light pressure, vibration, and conscious proprioception)  Sensory systems keep the CNS informed of change sin the external and internal environments  Responses to integrative decisions are brought about by motor activities  Cerebral cortex plays major role I controlling precise voluntary muscular movements  Other brain regions provide integration for regulation of automatic movements  Direct motor pathways- include the lateral corticospinal, anterior corticospinal, and corticobulbar tracts - Convey nerve impulses that originate in the cerebral cortex and are destined to cause voluntary movements of skeletal muscles  Indirect motor pathways- include the rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal, and medial reticulospinal tracts - Convey nerve impulses from the brain stem to cause automatic movements & help coordinate body movements with visual stimuli - Maintain skeletal muscle tone, sustain contraction of postural muscles, maintain equilibrium by regulating muscle tone in response to movements of the head  Reflexes and reflex arcs  Reflex- a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus  Some reflexes are inborn (pulling hand from hot surface), other learned  Spinal reflex- when integration takes place in the spinal cord gray matter  Cranial reflex- integration occurs in brain stem  Somatic reflexes- involve contraction of skeletal muscles  Autonomic (visceral) reflexes- not consciously perceived, involve responses of smooth muscle, cardiac muscle, and glands  Reflex arc- the pathway followed by nerve impulses that produce a reflex  Reflex arc includes five functional components 1. Sensory receptor: distal end of a sensory neuron (dendrite) or an associated sensory structure. Responds to specific stimulus by producing a graded potential called a generator (or receptor) potential 2. Sensory neuron- nerve impulses propagate from sensory receptor along axon of sensory neuron to axon terminals in gray matter of the spinal cord or brain stem. Relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred 3. Integrating center- one or more regions of gray matter with in the CNS act as integrating center. In simplest reflex, the integrating center is a single synapse between a sensory neuron and motor neuron. A reflex pathway having only one synapse in the CNS is termed a monosynaptic reflex arc. Polysynaptic reflex arc involves more than two types of neurons and more than one CNS synapse 4. Motor neuron- impulses triggered by the integrating center propagate out of the CNS along a motor neuron to the part of the body that will respond 5. Effector- part of the body that responds to the motor nerve impulse, its action is called a reflex. Somatic reflex if the effector is skeletal muscle, autonomic reflex if effector is smooth muscle, cardiac muscle, or gland  Stretch reflex  Causes contraction of a skeletal muscle in response to stretching of the muscle  Occurs via a monosynaptic reflex arc  Can be elicited by tapping on tendons attached to muscles a the elbow, wrist, knee, and ankle joints (ex: patellar reflex) 1. Slight stretching a muscle stimulates sensory receptors in the muscle called muscle spindles (monitor changes in length of muscle) 2. In response to being stretched, the muscle spindle generates one or more nerve impulses that propagate along a somatic sensory neuron through the posterior root of the spinal nerve into the spinal cord 3. In the spinal cord (integrating center), the sensory neuron makes an excitatory synapse with a motor neuron in the gray horn 4. If excitation is strong enough, one or more nerve impulses arises in the motor neuron and propagates along its axon, which extends from the spinal cord into the anterior root and through peripheral nerves to the stimulated muscle. The axon terminals of the motor neuron form NMJs with skeletal muscle fibers of the stretched muscle 5. Ach released by nerve impulses at the NMJs triggers one or more muscle action potentials and the muscle contracts  Ipsilateral reflex- sensory nerve impulses enter the spinal cord on the same side from which motor nerve impulses leave it (all monosynaptic reflexes)  Brain can adjust how vigorously a muscle spindle responds to stretching, sets an overall level of muscle tone (small degree of contraction present while muscle at rest)  Stretch reflex helps aver injury by preventing overstretching of muscle  A polysynaptic reflex arc to the antagonistic muscle operates at the same time - Involves three neurons and two synapses - Collateral branch from the muscle spindle sensory neuron also synapses with an inhibitory interneuron in the integrating center - The interneuron synapses and inhibits a motor neuron that normally excites that antagonistic muscle - When stretched muscle contracts during a stretch reflex, antagonistic muscles that oppose the contraction relax  Reciprocal innervation- components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonist (prevents conflict between opposing muscles, coordinates body movements)  Nerve impulses also pass to the brain to allow conscious awareness that the reflex has occurred  Stretch reflex can also help maintain posture  Tendon reflex  Operates as a feedback mechanism to control muscle tension by causing muscle relaxation (prevents torn tendons)  Less sensitive than stretch reflex  Ipsilateral  Polysynaptic  Sensory receptors are called tendon organs which lie within a tendon near its junction with a muscle 1. As the tension applied to a tendon increases, the tendon organ (sensory receptor) is stimulated (depolarized to threshold) 2. Nerve impulses arise and propagate into the spinal cord along a sensory neuron 3. Within the spinal cord (integrating center), the sensory neuron activates in inhibitory interneuron that synapses with a motor neuron 4. The inhibitory NT inhibits (hyperpolarizes) the motor neuron, which then generates fewer nerve impulses 5. The muscle relaxes and relieves tension  As tension on the tendon organ increases, the frequency of inhibitory impulses increases  Sensory neuron from tendon also synapses with excitatory interneuron controlling antagonistic muscles  Flexor and crossed extensor reflexes  Polysynaptic  Ex: stepping on a tack  Flexor (withdrawal reflex): 1. Stepping on tack stimulates dendrites (sensory receptor) of pain-sensitive neuron 2. Sensory neuron generates nerve impulses into spinal cord 3. Within the spinal cord (integrating center), the sensory neuron activates interneurons that extend to several spinal cord segments 4. Interneurons activate motor neurons in several spinal cord segments, generating nerve impulses which propagate toward the axon terminals 5. Ach released by motor neurons causes the flexor muscle in thigh (effectors) to contract, producing withdrawal of the leg  Ipsilateral (incoming and outgoing impulses on same side of spinal cord)  Intersegmental reflex arc- a single sensory neuron can activate several motor neurons, stimulating more than one effector  Crossed extensor reflex 1. Stepping on a tack stimulates the sensory receptor of a pain- sensitive neuron in the right foot 2. This sensory neuron generates nerve impulses into the spinal cord 3. Within the spinal cord the sensory neuron activates several interneurons that synapse with motor neurons on the left side of the spinal cord in several segments. Incoming pain signals cross to the opposite side through interneurons at that level, and at several levels above and below the point of entry into the spinal cord 4. The interneurons excite motor neurons in several segments that innervate extensor muscles. The motor neurons generate more nerve impulses, which propagate toward the axon terminals 5. Ach released by motor neurons cause extensor muscles of the thigh (effectors) of the unstimulated left limb to contract, producing extension of the left leg  Involves a contralateral reflex arc- sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side  Synchronizes the extension of the contralateral limb with the withdrawal of the stimulated limb  Disorders  Complete transection- cord is severed from one side to the other, cutting all sensory and motor tracts - Results in loss of all sensations and voluntary movement below the level of transection - C1-C3: no function maintained from neck down; ventilator needed for breathing - C4-C5: diaphragm, which allows breathing - C6-C7: some arm and chest muscles which allows feeding, some dressing, manual wheelchair required - T1-T3: intact arm function - L1-L2: most leg muscles, which allows walking with short leg braces  Shingles: acute infection of the peripheral nervous system caused by herpes zoster - Reactivated virus overcomes a weakened immune system, eaves the ganglion, and travels down sensory neurons of the skin by fast axonal transport - Pain, discoloration of the skin, line of skin blisters (marks distribution (dermatome) of the particular nerve belonging to infected posterior root ganglion)  Polio- caused by poliovirus, fever, severe headache, stiff neck and back, deep muscle pain and weakness, loss of certain somatic reflexes - Virus produces paralysis by destroying cell bodies of motor neurons, specifically in anterior horns of the spinal cord and nuclei of cranial nerves - Can cause death from respiratory or heart failure  Meningitis- inflammation of the meninges due to an infection, usually caused by a bacterium or virus - Fever, headache, stiff neck, vomiting, confusion, drowsiness - Bacterial strain much more serious and treated with antibiotics - Bacterial meningitis may be fatal if not treated promptly Chapter 14- The brain and cranial nerves Specific types of sensory, motor, and integrative signals are processed in certain regions of the cerebral cortex Sensory areas receive sensory information and are involved in perception (conscious awareness of a sensation) Motor areas control the execution of voluntary movements Association areas deal with more complex integrative functions such as memory, emotions, reasoning, will, judgment, personality, intelligence Sensory areas Sensory impulses arrive mainly in the posterior half of both cerebral hemispheres, behind the central sulci Sensory association areas often are adjacent to the primary areas Sensory association areas integrate sensory experiences to generate meaningful patterns of recognition and awareness Primary somatosensory area- located directly posterior to the central sulcus of each cerebral hemisphere in the postcentral gyrus of each parietal lobe - Along the lateral surface of the parietal lobe to the longitudinal fissure - Receives nerve impulses for touch, pressure, vibration, itch, tickle, temperature, pain, proprioception - A “map” of the entire body is present in the primary somatosensory area - Size of the area receiving impulses depends on the number of receptors present there rather than the size of the body part - Sensory homunculus- distorted somatic sensory map of the body  Primary visual area- posterior tip of the occipital lobe, receives visual information, involved in visual perception  Primary auditory area- located in the superior part of the temporal lobe, receives information for sound and involved in auditory perception  Primary gustatory area- located at the base of the postcentral gyrus, receives impulses for taste and involved in gustatory perception and taste discrimination  Primary olfactory area- located in the temporal lobe on the medial aspect, receives impulses for smell and involved in olfactory perception  Motor areas  Primary motor area- located in the precentral gyrus of the frontal lobe - A “map” of the entire body is present in the primary motor area - Each region controls voluntary contractions of specific muscles or groups of muscles - More area devoted to those muscles involved in skilled, complex, or delicate movement - Motor homunculus- distorted muscle map of the body - Movements to opposite side of body  Broca’s speech area- located in the frontal lobe close to the lateral cerebral sulcus, speaking and understanding language - The planning and production of speech occur in the left frontal lobe of most people - Nerve impulses pass to the premotor regions that control muscles of the larynx, pharynx, and mouth - Breathing muscles regulate proper flow of air past the vocal cords  Association areas  Large areas of the occipital, parietal, and temporal lobes and of the frontal lobes anterior to the motor areas  Connected with one another by association tracts  Somatosensory association area- posterior to and receives input from primary somatosensory area, permits you to determine exact shape and texture of an object by feeling it, to determine the orientation of one objects with respect to another as they are felt, and to sense the relationship of body parts with respect to one another - Storage of memories of past somatic sensory experiences  Visual association area- located in the occipital lobe, receives sensory impulses from primary visual area, relates present and past visual experiences, essential for recognizing and evaluating what is seen  Facial recognition area- in the inferior temporal lobe, receives nerve impulses from the visual association area, stores information about faces, allows you to recognize people  Auditory association area- located inferior and posterior to the primary auditory area in the temporal cortex, allows you to recognize a particular sound as speech, music, or noise  Orbitofrontal cortex- lateral part of frontal lobe, receives sensory impulses from primary olfactory area, identify odors and discriminate among different odors  Wernicke’s area- broad region in the left temporal and parietal lobes, interprets meaning of speech by recognizing spoken words, active as you translate words into thoughts - The regions in the right hemisphere that correspond to Broca’s and Wernicke’s areas in the left hemisphere contribute to verbal communication by adding emotional content to spoken words  Common integrative area- bordered by somatosensory, visual, and auditory association areas, receives impulses from these areas and from the primary gustatory area, olfactory area, thalamus, and brain stem - Integrates sensory interpretations from association areas and impulses from other areas, allowing formation of thoughts - Transmits signals to other parts of brain for appropriate response to signals it has interpreted  Prefrontal cortex- anterior portion of the frontal lobe, numerous connections with other areas of the cerebral cortex, thalamus, hypothalamus, limbic system, and cerebellum - Makeup of a person’s personality, intellect, learning abilities, recall of information, initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, development of abstract ideas  Premotor area- motor association area anterior to the primary motor area, communicate with the primary motor cortex, sensory association areas, basal nuclei, and thalamus - Deals with learned motor activities of complex and sequential nature - Memory bank for movements  Frontal eye field area- frontal cortex, sometimes included in premotor area, controls voluntary scanning movements of the eyes  Hemispheric lateralization  Each hemisphere specializes in performing certain unique functions  Lateralization is less pronounced in females than in males  Right hemisphere functions: controls left side of body, musical and artistic awareness, space and pattern perception, recognition of faces and emotion of facial expression, emotional content of language,  Left hemisphere functions: controls right side of body, reasoning, numerical and scientific skill, ability to use and understand sign language, spoken and written language  Brain waves  Electrical signals of nerve impulses  Brain waves generated by neurons close to the brain surface (cerebral cortex) can be detected by sensors called electrodes  Electroencephalogram EEG- record of brain waves  Diagnose variety of brain disorders, study abnormal brain functions, sleep  Patterns of activation of brain neurons produce four types of brain waves 1. Alpha waves- rhythmic waves of 8-13 Hz, present when individual is awake and resting with eyes closed 2. Beta waves- 14-30 Hz, appear when nervous system is active, during periods of sensory input and mental activity 3. Theta waves- 4-7 Hz, occur in children and adults experiencing emotional stress and disorders of the brain 4. Delta waves- 1-5 Hz, occur during sleep in adults, and awake infants, indicate brain damage in an awake adult  Cranial Nerves  12 pairs  Pass through various foramina in the bones of the cranium and arise from the brain inside the cranial cavity  Part of the PNS  Numbers indicate order from anterior to posterior  Special sensory nerves- (I, II, VIII) unique to the head and associated with special senses of smelling, seeing, and hearing, most cell bodies located in ganglia outside the brain  Motor nerves- (III, IV, VI, XI, and XII) contain only axons of motor neurons as they leave the brain stem, cell bodies lie in nuclei within the brain, two types: 1. Branchial motor axons- innervate skeletal muscles that develop from the pharyngeal arches 2. Somatic motor axons- innervate skeletal muscles that develop from head somites (eye muscles and tongue muscles) 3. Autonomic motor axons- part of parasympathetic division  Mixed nerves (V, VII, IX, and X)- contain both sensory neurons entering the brain stem and motor neurons leaving the brain stem  Olfactory (I) Nerve  Entirely sensory; contains axons that conduct nerve impulses for olfaction, the sense of smell  Olfactory receptors are bipolar neurons, each has a single odor- sensitive, knob-shaped dendrite projecting from one side and an unmyelinated axon extending from the other side  Olfactory nerves end in the brain in paired masses of gray matter called olfactory bulbs  Axons of these neurons make up the olfactory tracts  Optic (II) Nerve  Entirely sensory, contains axons that conduct nerve impulses for vision  Axons of all ganglion cells in the retina of each eye join to form an optic nerve  Two optic nerves merge to form the optic chiasm  Oculomotor (III), Trochlear (IV), and Abducens (VI) nerves  Control muscles that move the eyeballs  All motor nerves that contain only motor axons as they exit the brain stem  Convey nerve impulses from the extrinsic eyeball muscles for proprioception  Oculomotor nerve- control movements of the eyeball and upper eyelid, adjust lens for near vision, constriction of pupil  Trochlear nerve- movement of eyeball  Abducens nerve- nerve impulses cause abduction (lateral rotation) of eyeball  Trigeminal (V) Nerve  Mixed cranial nerve and largest of cranial nerve  Three branches: - Ophthalmic nerve - Maxillary nerve - Mandibular nerve  Sensory- touch, pain, and thermal sensations from scalp, face, and oral cavity (including teeth and anterior two-thirds of tongue)  Motor (branchial)- chewing and controls middle ear muscle  Facial (VII) Nerve  Mixed cranial nerve  Sensory- taste from anterior two-thirds of tongue, touch, pain, and thermal sensations from skin in external ear canal  Motor (branchial)- control of muscles of facial expression and middle ear muscle  Motor (autonomic)- secretion of tears and saliva  Vestibulocochlear (VIII)  Special sensory- hearing and equilibrium  Glossopharyngeal (IX)  Mixed  Sensory- taste from posterior one-third of tongue, proprioception in some swallowing muscles, monitors blood pressure and oxygen and carbon dioxide levels in blood, touch, pain and thermal sensations from skin of external ear and upper pharynx  Motor (Branchial)- assists in swallowing  Motor (autonomic)- secretion of saliva  Vagus (X)  Mixed  Sensory- taste from epiglottis, proprioception from throat and voice box muscles, monitors blood pressure and oxygen and carbon dioxide levels in blood, touch, pain, and thermal sensations from skin of external ear, sensations from thoracic and abdominal organs  Motor (branchial)- swallowing, vocalization, coughing  Motor (autonomic)- motility and secretion of gastrointestinal organs, constriction of respiratory passageways, decreases heart rate  Accessory (XI)  Motor  Brachial- movement of head and pectoral girdle  Hypoglossal (XII)  Motor Somatic- Speech, manipulation of food, and swallowing  Disorders  Cerebrovascular accident (CVA)- stroke, third leading cause of death, abrupt onset of persisting neurological symptoms - Paralysis, loss of sensation - Arise from destruction of brain tissue - Common causes are intracerebral hemorrhage (bleeding in brain), blood clots, and atherosclerosis of the cerebral arteries (cholesterol-containing plaques that block blood flow) - Risk factors: high blood pressure, high cholesterol, heart disease, narrowed carotid arteries, diabetes, smoking, obesity, excessive alcohol intake - “Cold therapy”- limit amount of damage, states of hypothermia trigger survival response in which body requires less oxygen  Alzheimer’s Disease (AD)- disabling senile dementia, loss of reasoning and ability to care for oneself - Fourth leading cause of death among the elderly - Due to combination of genetic factors, environmental or lifestyle factors, and aging process - Risk factor includes history of head injury - Have trouble remembering recent events, become more confused and forgetful 1. Loss of neurons that liberate acetylcholine- axons of these neurons project widely throughout the cerebral cortex and limbic system, their destruction is a hallmark of Alzheimer’s 2. Beta-amyloid plaques- clusters of abnormal proteins deposited outside neurons 3. Neurofibrillary tangles- abnormal bundles of filaments inside neurons in affected brain regions  Dementia- permanent or progressive general loss of intellectual abilities, including impairment of memory, judgment, and abstract thinking and changes in personality  Encephalitis- acute inflammation of the brain caused by either a direct attack by any of several viruses or an allergic reaction to any of the many viruses that are normally harmless to the CNS  Brain tumors- abnormal growth of tissue in the brain that may be malignant or benign - Compress adjacent tissues and cause buildup of pressure in skull - Most common are secondary tumors that metastasize from other cancers in the body - Most brain tumors are gliomas, which develop in neuroglia - Symptoms range, but include headache, poor balance and coordination, dizziness, double vision, slurred speech, nausea, fever, abnormal pulse and breathing rates, etc. - Treatments include: surgery, radiation therapy, or chemotherapy (unfortunately chemotherapeutic agents don’t cross the BB barrier) Chapter 16- Sensory, Motor, and Integrative systems  Sensation- conscious or subconscious awareness of changes in the external or internal environment  Nature of sensation and type of reaction vary according to the ultimate destination of nerve impulses that convey sensory info to the CNS  Perception- conscious interpretation of sensations and is primarily a function of the cerebral cortex  Sensory modalities  Each unique type of sensation- touch, pain, vision, hearing is called a sensory modality  A given sensory neuron carries information for only one sensory modality  General senses- refer to somatic and visceral senses - Somatic senses- include tactile sensations (touch, pressure, vibration, itch, tickle), thermal sensations, pain, and proprioceptive sensations - Proprioceptive sensations allow perception of both the static positions of limbs and body parts and movements of the limbs and head - Visceral senses provide info about conditions within internal organs- pressure, stretch, chemicals, nausea, hunger, temperature  Special senses- include modalities of smell, taste, vision, hearing, and equilibrium or balance  Process of sensation  Beings in a sensory receptor (specialized cell or dendrites of sensory neuron)  A given sensory receptor responds vigorously to one particular kind of stimulus and weakly or not at all to other stimulus (selectivity) 1. Stimulation of the sensory receptor- an appropriate stimulus must occur within the sensory receptor’s receptive field (body region where stimulation activates the receptor and produces a response) 2. Transduction of the stimulus- a sensory receptor transduces (converts) energy in a stimulus into a graded potential 3. Generation of nerve impulses- when graded potential in a sensory neuron reaches threshold, it triggers one or more nerve impulses which propagate toward the CNS. Sensory neurons that conduct impulses from the PNS into the CNS are called first-order neurons 4. Integration of sensory input- a particular region of the CNS receives and integrates the sensory nerve impulses, conscious sensations or perceptions are integrated in the cerebral cortex  Sensory receptors  Grouped into microscopic structure, location of the receptors and the origin of stimuli that activate them, and type of stimulus detected  Microscopic structure: - May be one of the following: free nerve endings of first- order sensory neurons, encapsulated nerve endings of first-order sensory neurons, or separate cells that synapse with first-order sensory neurons - Free nerve endings- bare dendrites, lack any structural specializations that can be seen under a light microscope, receptors for pain, temperature, tickle, itch, and some touch sensations - Encapsulated nerve endings- dendrites enclosed in a connective tissue capsule, receptors for other somatic and visceral sensations, different types of capsules enhance the sensitivity or specificity of the receptor - Separate cells that synapse with sensory neurons- special senses, hair cells for hearing and equilibrium, gustatory receptor cells in taste buds, photoreceptors in the retina of the eye for vision  Sensory receptors produce two different kinds of graded potentials: generator potentials and receptor potentials  Dendrites of free nerve endings, encapsulated nerve endings, and the receptive part of olfactory receptors produce a generator potential- triggers one or more nerve impulses in axon of a first- order sensory neuron, nerve impulse propagates into the CNS  Generator potentials generate action potentials  Sensory receptors that are separate cells produce graded potentials termed receptor potentials  Receptor potentials trigger release of NT through exocytosis of synaptic vesicles, NT molecules diffuse across the synaptic cleft and produce a postsynaptic potential in the first-order neurons  the PSP may trigger one or more nerve impulses, which propagate into the CNS  Receptor potentials vary with intensity of stimulus- large or small  Generator potentials vary with intensity of stimulus- high or low frequency  Location of receptors and origin of activating stimuli:  Exteroceptors- located at or near external surface of body; sensitive to stimuli originating outside the body and provide info about external environment (hearing, vision, smell, taste, touch, pressure, vibration, temperature, pain)  Interoceptors- located in blood vessels, visceral organs, muscles, and the nervous system and monitor internal environment, usually not consciously perceived, activation of interoceptors by strong stimuli may be felt as pain or pressure  Proprioceptors- located in muscles, tendons, joints, and inner ear, provide info about body position, muscle length and tension and position and movement of joints  Types of stimuli detected:  Most stimuli are in the form of mechanical energy, such as sound waves or pressure changes; electromagnetic energy, such as light or heat; or chemical energy, such as in molecule of glucose  Mechanoreceptors- sensitive to mechanical stimuli such as deformation, stretching, or bending of cells, provide sensations of touch, pressure, vibration, proprioception, hearing and equilibrium, also monitor stretching of blood vessels and internal organs  Thermoreceptors- detect changes in temperature  Nociceptors- respond to painful stimuli resulting from physical or chemical damage to tissue  Photoreceptors- detect light that strikes the retina of the eye  Chemoreceptors- detect chemicals in the mouth (taste), nose (smell), and body fluids  Osmoreceptors- detect the osmotic pressure of body fluids  Adaptation in sensory receptors  Adaptation- generator potential or receptor potential decreases in amplitude during a maintained, constant stimulus  Causes the frequency of nerve impulses in the first-order neuron to decrease  Perception of a sensation may fade or disappear even though stimulus persists  Rapidly adapting receptors- adapt quickly, specialized for signaling changes in a stimulus (pressure, touch, smell)  Slowly adapting receptors- adapt slowly and continue to trigger nerve impulses as long as the stimulus persists (pain, body position, chemical composition of the blood)  Pain sensations  Protective function by signaling the presence of noxious, tissue- damaging conditions  Nociceptors- receptors for pain, free nerve endings found in every tissue except the brain  Intense thermal, mechanical, or chemical stimuli can activate nociceptors  Tissue irritation or injury releases chemicals such as prostaglandins, kinins, potassium ions that simulate nociceptors  Pain can persist after pain stimulus is removed due to lingering chemicals  Fast pain: occurs rapidly, 0.1 second after stimulus is applied - Nerve impulses propagate along medium-diameter, myelinated, type A fibers - Also known as acute, sharp, or pricking pain - Ex: needle puncture, knife cut - Not felt in deeper tissues of body  Slow pain: begins a second or more after stimulus, gradually increases intensity over several seconds or minutes - Conduct along small-diameter, unmyelinated type C fibers - Also known as chronic pain, burning, aching, throbbing - Can occur in skin and deeper tissue or internal organs - Ex: toothache  Superficial somatic pain- stimulation of receptors in skin  Deep somatic pain- stimulation of receptors in skeletal muscles, joints, tendons, fascia  Visceral pain- stimulation of nociceptors in visceral organs  Fast pain is precisely localized to stimulated area  Somatic slow pain also is well localized by more diffuse  Referred pain- pain is felt in or just deep to the skin that overlies the stimulated organ or in a surface area far from the stimulated organ  Analgesia- pain relief - Analgesic drugs such as aspirin and ibuprofen block formation of prostaglandins that stimulate nociceptors - Local anesthetics like Novocain provide short-term pain relief by blocking conduction of nerve impulses along axons of first order pain neurons - Morphine and other opiate drugs alter quality of pain perception in brain  Somatic sensory pathways  Relay information from the somatic sensory receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum  First-order neurons- conduct impulses from somatic receptors into the brain stem or spinal cord - From face, mouth, teeth, eyes  impulses propagate along cranial nerves - From neck, trunk, limbs, posterior aspect of head  impulses propagate along spinal nerves into spinal cord  Second order neurons- conduct impulses from the brain stem and spinal cord to the thalamus - Axons decussate (cross over to opposite side) before ascending to the ventral posterior nucleus of the thalamus - All info from one side of the body reaches the thalamus on the opposite side  Third-order neurons- conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side  Relay stations- regions within the CNS where neurons synapse with other neurons that are part of a particular sensory or motor pathway - Signals are being relayed from one region of the CNS to another  Somatic sensory impulses ascend to the cerebral cortex via three general pathways 1. The posterior column-medial lemniscus pathway 2. The anteriolateral (spinothalamic) pathway 3. The trigeminothalamic pathway  Somatic sensory impulses reach the cerebellum via the spinocerebellar tracts  Posterior column-Medial lemniscus pathway to the cortex  Nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head  Name comes from names of two white-matter tracts that convey the impulses: posterior column of the spinal cord and medial lemniscus of the brain stem  First-order neurons extend from sensory receptors in limbs, trunk, neck, and posterior head into the spinal cord and ascend to the medulla oblongata on the same side of the body  The cell bodies of the first-order neurons are in the posterior (dorsal) root ganglia of spinal nerves  Their axons form the posterior columns (which consist of the gracile fasciculus and the cuneate fasciculus)  The axons synapse with the dendrites of second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the medulla  Nerve impulses for touch, pressure, vibration and conscious proprioception from the upper limbs, upper trunk, neck, and posterior head propagate along axons in the cuneate fasciculus and arrive at the cuneate nucleus  Nerve impulses for touch, pressure, and vibration from the lower limbs and lower trunk propagate along axons in the gracile fasciculus and arrive at the gracile nucleus  The axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus (extends from medulla to ventral posterior nucleus of the thalamus)  In the thalamus, the axon terminals of second-order neurons synapse wit third-order neurons which project axons to the primary somatosensory area of the cerebral cortex  Anteriolateral pathway to the cortex  Nerve impulses for pain, temperature, itch, and tickle from the limbs, trunk, neck, and posterior head  Composed of three neuron sets  First-order neurons connect a receptor of the limbs, trunk, neck, or posterior head with the spinal cord  Cell bodies of the first-order neurons are in the posterior root ganglion  Axon terminals of the first-order neurons synapse with second- order neurons whose cell bodies are in t he posterior gray horn of the spinal cord  Axons of second-order neurons cross to the opposite side of spinal cord and pass upward to the brain stem as the spinothalamic tract  Axons of the second-order neurons send in the ventral posterior nucleus of the thalamus where the synapse with third-order neurons  Axons of third-order neurons project to primary somatosensory area on the same side of the cerebral cortex as the thalamus  Trigeminothalamic pathway to the cortex  Nerve impulses for most somatic sensations (tactile, thermal, and pain) from face, nasal cavity, oral cavity, and teeth  First-order neurons extend from somatic sensory receptors in the face, nasal cavity, oral cavity, and teeth into the pons through the trigeminal (V) nerves  The cell bodies of the first-order neurons are in the trigeminal ganglion  The axons of some first-order neurons synapse with second-order neurons in the pons  Axons of other first-order neurons descend into the medulla to synapse with second-order neurons  The axons of the second-order neurons cross to the opposite side of the pons and medulla and ascend as the trigeminothalamic tract to the ventral posterior nucleus of the thalamus  In the thalamus the axon terminals of the second-order neurons synapse with third-order neurons that project axons to primary somatosensory area on same side of the cerebral cortex as the thalamus  Mapping the primary somatosensory area  Specific areas of the cerebral cortex receive somatic sensory input from particular parts of the body  Other areas of the cerebral cortex provide output for movement of particular parts of the body  The somatic sensory map and somatic motor map relate body parts to these cortical areas  Precise localization of somatic sensations occurs when nerve impulses arrive at the primary somatosensory area  Relatives sizes of these regions are proportional to the number of specialized sensory receptors within the corresponding part of the body  Sensory homunculus- the distorted somatic sensory map of the body  Somatic sensory pathways to the cerebellum  Posterior spinocerebellar tract and the anterior spinocerebellar tract are the major routes proprioceptive impulses take to reach the cerebellum - Not consciously perceived, critical for posture, balance, coordination  Somatic motor pathways  All excitatory and inhibitory signals that control movement converge on the motor neurons that extend out of the brain stem and spinal cord to innervate skeletal muscles in the body  Lower motor neurons (LMNs) have cell bodies in the brain stem and spinal cord  From the brain stem, axons of LMNs extend through cranial nerves to innervate skeletal muscles of the face and head  From the spinal cord, axons of LMNs extend through spinal nerves to innervate skeletal muscles of the limbs and trunk  Only LMNs provide output from the CNS to skeletal muscle fibers (also called the final common pathway)  Four distinct but highly interactive neural circuits (somatic motor pathways) 1. Local circuit neurons- input arrives at lower motor neurons from nearby interneurons called local circuit neurons - Neurons are located close to lower motor neuron cell bodies in brain stem and spinal cord - Receive input form somatic sensory receptors such as nociceptors and muscle spindles as well as from higher centers in the brain - Help coordinate rhythmic activity in specific muscle groups (ex: alternating flexion and extension while walking) 2. Upper motor neurons- most upper motor neurons synapse with local circuit neurons, which in turn synapse with LMNs - UMNs from the cerebral cortex are essential for the execution of voluntary movements of the body - Other UMNs originate in motor centers of the brain stem - UMNs from brain stem regulate muscle tone, control postural muslces, maintain balance and orientation of the head and body - Both basal nuclei and cerebellum exert influence on UMNs 3. Basal nuclei neurons- assist movement by providing input to UMNs - Neural circuits interconnect the basal nuclei with motor areas of the cerebral cortex (via the thalamus) and brain stem - Circuits help initiate and terminate movements, suppress unwanted movements, and establish normal level of muscle tone 4. Cerebellar neurons- aid movement by controlling activity of UMNs - Neural circuits interconnect the cerebellum with motor areas of the cerebral cortex (via the thalamus) and brain stem - Prime function of the cerebellum is to monitor differences between intended movements and movements actually performed - Issues commands to UMNs to reduce errors in movement - Coordinates body movements, helps maintain posture and balance  Organization of upper motor neuron pathways  Axons of upper motor neurons extend from the brain to lower motor neurons via two somatic motor pathways: direct and indirect  Direct motor pathways- provide input to LMNs via axons that extend directly from the cerebral cortex  Indirect motor pathways- provide input to LMNs from motor centers in the basal nuclei, cerebellum, and cerebral cortex  Both pathways govern generation of nerve impulses in the LMNs  Control of body movements occurs via neural circuits in several regions of the brain  Primary motor area- located in the precentral gyrus of the frontal lobe of the cerebral cortex, major control region for execution of voluntary movements  Premotor area- also contributes axons to descending motor pathways  Motor homunculus- distorted muscle map of the body  Direct motor pathways  Nerve impulses for voluntary movements propagate from the cerebral cortex to LMNs  Also known as pyramidal pathways, consist of axons that descend from pyramidal cells (UMNs with pyramid-shaped cell bodies)  Corticospinal pathways- conduct impulses for the control of muscles of the limbs and trunk  Axons of UMNs in the cerebral cortex form the corticospinal tracts, which descend through the internal capsule of the cerebrum and the cerebral peduncle of the midbrain  In the medulla oblongata, the axon bundles of the corticospinal tracts form the ventral bulges known as the pyramids  90% of the corticospinal axons decussate to the contralateral (opposite) side in the medulla and then descend into the spinal cord to synapse with a local circuit neuron or LMN  10% that remain on the ipsilateral (same) side eventually decussate at the spinal cord levels where they synapse with a local circuit neuron or LMN 1. Lateral corticospinal tract- corticospinal axons that decussate in the medulla form the lateral corticospinal tract in the lateral white column of the spinal cord - Axons synapse in the anterior gray horn of the spinal cord - Axons of LMNs exit the cord in the anterior roots of spinal nerves and terminate in skeletal muscles that control movements of the distal parts of the limbs - Distal muslces are responsible for precise, agile, and highly skilled movements of the hands and feet (ex: button shirt) 2. Anterior corticospinal tract- corticospinal axons that do not decussate in the medulla form the anterior corticospinal tract in the anterior white column of the spinal cord - At each spinal level, some of these axons decussate via the anterior white commissure - They then synapse with local circuit neurons or LMNs in the anterior gray horn - Axons of these LMNs exit the cord in the anterior roots of spinal nerves - Terminate in skeletal muscles that control movements to he trunk and proximal parts of the limbs  Corticobulbar pathway- conducts impulses for the control of skeletal muscles in the head - Axons of UMNs from the cerebral cortex form the corticobulbar tract - Descends along with the corticospinal tracts through the internal capsule of the cerebrum and cerebral peduncle of the midbrain - Some of the axons of the corticubulbar tract decussate, others do not - Axons terminate in the motor nuclei of nine pairs of cranial nerves in the brain stem - The LMNs of the cranial nerves convey impulses that control precise, voluntary movements of the eyes, tongue, and neck, plus chewing, facial expression, speech, and swallowing  ALS- amyotrophic lateral sclerosis - A progressive, degenerative disease that attacks motor areas of the cerebral cortex, axons of upper motor neurons in the lateral white columns, and LMN cell bodies - Progressive muscle weakness and atrophy - Noninherited cases appear to be due to buildup in the synaptic cleft of the NT glutamate released by motor neurons - Drug riluzole reduces damage to motor neurons by decreasing release of glutamate  Indirect motor pathways  Extrapyramidal pathways include all somatic motor tracts other than the corticospinal and corticubulbar tracts  Axons of UMNs descend from various nuclei of the brain stem into five major tracts of the spinal cord and terminate on local circuit neurons or LMNs  Five tracts: rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal, medial reticulospinal  Roles of basal nuclei  Influence movement through effects on UMNs  Role in the initiation and termination of movements- caudate nucleus and putamen receive input from sensory, association, and motor areas of the cerebral cortex and from the substantia nigra - Output from the basal nuclei comes from the globus pallidus and substantia nigra, which send feedback signals to the upper motor cortex by way of the thalamus - The circuit (from cortex to basal nuclei to thalamus to cortex) appears to function in initiation and terminating movements  Basal nuclei suppress unwanted movements by their inhibitory effects on the thalamus and superior colliculus  Basal nuclei influences muscle tone- globus pallidus sends impulses into the reticular formation that reduce muscle tone, damage of some basal nuclei connections causes general increase in muscle tone  Basal nuclei influence many aspects of cortical function (sensory, limbic, cognitive, linguistic function)  Disorders of the basal nuclei  Parkinson’s disease- uncontrollable shaking and muscle rigidity - Dopamine-releasing neurons that extend from the substantia nigra to the putamen and caudate nucleus degenerate  Huntington disease (HD)- inherited disorder in which the caudate nucleus and putamen degenerate - Loss of neurons that normally release GABA or acetylcholine - Results in chorea- rapid, jerky movements occur involuntarily and without purpose - Progressive mental deterioration  Modulation of movement by the cerebellum  Cerebellum active in learning and performing rapid, coordinated, highly skilled movements like hitting golf ball, speaking, swimming  Cerebellar function involves four activities 1. Monitoring intentions for movement- receives impulses from the motor cortex and basal nuclei via the pontine nuclei in the pons regarding what movements are planned 2. Monitoring actual movement- receives input from proprioceptors in joints and muscles that reveal what is actually happening, impulses travel in the anterior and posterior spinocerebellar tracts 3. Comparing command signals with sensory information- compares intentions for movement with the actual movement performed 4. Sending out corrective feedback- if there is discrepancy, cerebellum sends feedback to UMNs, information travels via the thalamus to UMNs in the cerebral cortex but goes directly to UMNs in brain stem motor centers - As movements occur, the cerebellum continuously provides error corrections to upper motor neurons, which decreases errors and smoothes the motion  Integrative functions of the cerebrum  The processing of sensory information by analyzing and storing it and making decisions for various responses  Integrative functions include cerebral activities such as sleep and wakefulness, learning and memory, and emotional responses  Wakefulness and sleep  Circadian rhythm- sleep and awaken in 24-hour cycle, established by the suprachiasmatic nucleus of the hypothalamus  Reticular activating system (RAS)- When active, many nerve impulses are transmitted to widespread areas of the cerebral cortex  increase in cortical activity  Arousal- awakening from sleep, involves increased activity in the RAS - RAS must be stimulated: painful stimuli detected by nociceptors, touch and pressure on the skin, movement of the limbs, bright light, alarm clock  Consciousness- state of wakefulness  No input to RAS from olfactory receptors  Sleep- state of altered consciousness or partial unconsciousness from which an individual can be aroused  Normal sleep consists of two components: non-rapid eye movement (NREM) and rapid eye movement (REM) sleep  NREM sleep: 1. Stage 1- transition between wakefulness and sleep, 1-7 minutes, person relaxed with eyes closed 2. Stage 2- light sleep, first stage of true sleep, fragments of dreams, eyes may slowly roll from side to side 3. Stage 3- moderately deep sleep, body temp and blood pressure decrease, difficult to awaken the person, about 20 minutes after falling asleep 4. Stage 4- deepest sleep, brain metabolism decreases significantly, body temp drops, muscle tone decreased only slightly, sleepwalking  During typical 7-8 hour sleep period, there are 3-5 episodes of REM sleep  REM and NREM alternate throughout the night  REM periods occur approximately every 90 minutes and gradually lengthen until final one lasts about 50 minutes  REM thought to be important for maturation of the brain (50% in infants vs 25% of period in adults)  Neuronal activity is high during REM sleep  Neuro


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