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Chapter 11 Nervous System II Meninges • membranes surrounding CNS • protect CNS • three layers • dura mater – outer, tough • arachnoid mater weblike • pia mater – inner, delicate Meninges of the Spinal Cord Ventricles • interconnected cavities • within cerebral hemispheres and brain stem • continuous with central canal of spinal cord • filled with cerebrospinal fluid (csf) • lateral ventricles • third ventricle • fourth ventricle • cerebral aqueduct Cerebrospinal Fluid • secreted by choroid plexus • circulates in ventricles, central canal of spinal cord, and subarachnoid space • completely surrounds brain and spinal cord • clear liquid • nutritive and protective • helps maintain stable ion concentrations in CNS Spinal Cord Structure • extends foramen magnum to 2nd lumbar vertebra Cross Section of Spinal Cord Spinal Cord Functions • center for spinal reflexes • conduit for nerve impulses to and from the brain Reflex Arcs Reflexes – automatic, subconscious responses to stimuli Knee-jerk Reflex • helps maintain posture Withdrawal Reflex • protective Crossed-Extensor Reflex • flexor muscles contract • flexor muscles on opposite side inhibited • extensor muscles on opposite side contract for balance Tracts of the Spinal Cord • Ascending tracts conduct sensory impulses to the brain • Descending tracts conduct motor impulses from the brain to motor neurons reaching muscles and glands Ascending Tracts • fasciculus cuneatus • lateral spinothalamic Corticospinal Tract Brain Functions Major Parts • interprets sensations • cerebrum • two cerebellar hemispheres • determines perception • diencephalon • stores memory • brain stem • reasoning • cerebellum • makes decisions • coordinates muscular movements • regulates visceral activities • determines personality Brain Development Three Major Vesicles 1. Forebrain 2. Midbrain 3. Hindbrain Forebrain (prosencephalon) • anterior portion (telencephalon) • cerebrum • basal ganglia • posterior portion (diencephalon) • thalamus • hypothalamus • posterior pituitary • pineal gland Brain Development Midbrain (mesencephalon) • midbrain Hindbrain (rhombencephalon) • anterior portion (metencephalon) • cerebellum • pons • posterior portion (myelencephalon) • medulla oblongata Structure of Cerebrum • corpus callosum • connects hemispheres • convolutions • bumps or gyri • sulci • grooves • longitudinal fissure • separates hemispheres • transverse fissure • separates cerebrum from cerebellum Lobes of Cerebrum • Frontal • Parietal • Temporal • Occipital • Insula Functions of Cerebrum • interpretation • initiating voluntary movements • storing memory • retrieving memory • reasoning • center for intelligence and personality Functional Regions of Cerebral Cortex Cerebral Cortex – thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system Motor Areas • Primary Motor Areas • frontal lobes • control voluntary muscles • Broca’s Area • anterior to primary motor cortex • usually in one hemisphere • controls muscles needed for speech • Frontal Eye Field • above Broca’s area • controls voluntary movements of eyes and eyelids Motor Areas Sensory Areas • Cutaneous Sensory Area • parietal lobe • interprets sensations on skin • Visual Area • occipital lobe • interprets vision • Auditory Area • temporal lobe • interprets hearing Sensory Areas Association Areas • regions of cortex that are not primary motor or primary sensory areas • widespread throughout the cerebral cortex • analyze and interpret sensory experiences • provide memory, reasoning, verbalization, judgment, emotions Association Areas Frontal Lobe Association Areas • concentrating • planning • problem solving • judging Temporal Lobe Association Areas • remember visual scenes • remember music • remember complex patterns Parietal Lobe Association Areas • understanding speech • using words to express thought Occipital Lobe Association Areas • combine visual images with other sensory experiences Hemisphere Dominance • In over 90% of population, left hemisphere is dominant • Dominant hemisphere controls • speech • writing • reading • verbal skills • analytical skills • computational skills • Nondominant hemisphere controls • nonverbal tasks • motor tasks • understanding and interpreting musical and visual patterns • provides emotional and intuitive thought processes Memory Short Term • working memory • closed circuit • circuit is stimulated over and over • when impulse flow stops, memory disappears Long Term • changes structure and function of neurons • enhanced synaptic transmission Basal Nuclei • masses of gray matter • deep within cerebral hemispheres • caudate nucleus, putamen, globus pallidus • produce dopamine • control certain muscular activities Diencephalon • between cerebral hemispheres and brainstem • surrounds third ventricle • thalamus • hypothalamus • optic tracts • optic chiasm • infundibulum • posterior pituitary • mammillary bodies • pineal gland Diencephalon Thalamus • gateway for sensory impulses heading to cerebral cortex • receives all sensory impulses (except smell) • channels impulses to appropriate part of cerebral cortex for interpretation Hypothalamus • maintains homeostasis by regulating visceral activities • links nervous and endocrine systems Limbic System Consists of • portions of frontal lobe • portions of temporal lobe • hypothalamus • thalamus • basal nuclei • other deep nuclei Functions • controls emotions • produces feelings • interpret sensory impulses Brain Stem Three Parts 1. Midbrain 2. Pons 3. Medulla Oblongata Midbrain • between diencephalon and pons • contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain • cerebral aqueduct • cerebral peduncles – bundles of nerve fibers • corpora quadrigemina – centers for visual and auditory reflexes Pons • rounded bulge on underside of brainstem • between medulla oblongata and midbrain • helps regulate rate and depth of breathing • relays nerve impulses to and from medulla oblongata and cerebellum Medulla Oblongata • enlarged continuation of spinal cord • conducts ascending and descending impulses between brain and spinal cord • contains cardiac, vasomotor, and respiratory control centers • contains various nonvital reflex control centers (coughing, sneezing, vomiting) Reticular Formation • complex network of nerve fibers scattered throughout the brain stem • extends into the diencephalon • connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum • filters incoming sensory information • arouses cerebral cortex into state of wakefulness Types of Sleep Slow Wave Rapid Eye Movement (REM) • person is tired • some areas of brain active • decreasing activity of • heart and respiratory rates reticular system irregular • restful • dreaming occurs • dreamless • reduced blood pressure and respiratory rate • ranges from light to heavy • alternates with REM sleep Cerebellum • inferior to occipital lobes • posterior to pons and medulla oblongata • two hemispheres • vermis connects hemispheres • cerebellar cortex – gray matter • arbor vitae – white matter • cerebellar peduncles – nerve fiber tracts • dentate nucleus – largest nucleus in cerebellum • integrates sensory information concerning position of body parts • coordinates skeletal muscle activity • maintains posture Peripheral Nervous System • Cranial nerves arising from the brain • Somatic fibers connecting to the skin and skeletal muscles • Autonomic fibers connecting to viscera • Spinal nerves arising from the spinal cord • Somatic fibers connecting to the skin and skeletal muscles • Autonomic fibers connecting to viscera Structure of a Peripheral Nerve Nerve Fiber Classification • Sensory Nerves – conduct impulses into CNS • Motor Nerves – conduct impulses to muscles or glands • Mixed Nerves – contain both sensory nerve fibers and motor nerve fibers; most nerves General somatic efferent fibers • carry motor impulses from CNS to skeletal muscles General somatic afferent fibers • carry sensory impulses to CNS from skin and skeletal muscles General visceral efferent fibers • carry motor impulses away from CNS to smooth muscles and glands General visceral afferent fibers • carry sensory impulses to CNS from blood vessels and internal organs Nerve Fiber Classification Special somatic efferent fibers • carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions Special visceral afferent fibers • carry sensory impulses to brain from olfactory and taste receptors Special somatic afferent fibers • carry sensory impulses to brain from receptors of sight, hearing, and equilibrium Cranial Nerves Cranial Nerves I and II Olfactory (I) • sensory • fibers transmit impulses associated with smell Optic (II) • sensory • fibers transmit impulses associated with vision Cranial Nerves III and IV Oculomotor (III) • primarily motor • motor impulses to muscles that • raise eyelids • move the eyes • focus lens •adjust light entering eye Trochlear (IV) • primarily motor • motor impulses to muscles that move the eyes Cranial Nerve V Trigeminal (V) • mixed • opthalmic division • sensory from surface of eyes, tear glands, scalp, forehead, and upper eyelids • maxillary division • sensory from upper teeth, upper gum, upper lip, palate, and skin of face • mandibular division • sensory from scalp, skin of jaw, lower teeth, lower gum, and lower lip • motor to muscles of mastication and muscles in floor of mouth Cranial Nerves VI and VII Abducens (VI) • primarily motor • motor impulses to muscles that move the eyes Facial (VII) • mixed • sensory from taste receptors • motor to muscles of facial expression, tear glands, and salivary glands Cranial Nerves VIII and IX Vestibulocochlear (VIII) • sensory • sensory from equilibrium receptors of ear • sensory from hearing receptors Glossopharyngeal (IX) • mixed • sensory from pharynx, tonsils, tongue, and carotid arteries • motor to salivary glands and muscles of pharynx Cranial Nerve X Vagus (X) • mixed • somatic motor to muscles of speech and swallowing • autonomic motor to viscera of thorax and abdomen • sensory from pharynx, larynx, esophagus, and viscera of thorax and abdomen Cranial Nerves XI and XII Accessory (XI) • primarily motor • motor to muscles of soft palate, pharynx, larynx, neck, and back Hypoglossal (XII) • primarily motor • motor to muscles of the tongue Spinal Nerves • mixed nerves • 31 pairs • 8 cervical (C1 to C8) • 12 thoracic (T1 to T12) • 5 lumbar (L1 to L5) • 5 sacral (S1 to S5) • 1 coccygeal (Co) Spinal Nerves Dorsal root • axons of sensory neurons in the dorsal root ganglion Dorsal root ganglion • cell bodies of sensory neurons Ventral root • axons of motor neurons whose cell bodies are in spinal cord Spinal nerve • union of ventral root and dorsal root Dermatome • an area of skin that the sensory nerve fibers of a particular spinal nerve innervate Cervical Plexus Nerve plexus – complex networks formed by anterior branches of spinal nerves; fibers of various spinal nerves are sorted and recombined Cervical Plexus • C1-C4 • lies deep in the neck • supply muscles and skin of the neck • contribute to phrenic nerve Brachial Plexus • C5-T1 • lies deep within shoulders • musculocutaneous nerves • supply muscles of anterior arms and skin of forearms • ulnar nerves • supply muscles of forearms and hands • supply skin of hands • radial nerves • supply posterior muscles of arms and skin of forearms and hands • axillary nerves • supply muscles and skin of superior, lateral, and posterior arms Lumbosacral Plexus • T12 – S5 • extend from lumbar region into pelvic cavity • obturator nerves • supply adductors of thighs • femoral nerves • supply muscles and skin of thighs and legs • sciatic nerves • supply muscles and skin of thighs, legs, and feet Autonomic Nervous System • functions without conscious effort • controls visceral activities • regulates smooth muscle, cardiac muscle, and glands • efferent fibers typically lead to ganglia outside CNS Two Divisions • sympathetic – prepares body for fight or flight situations • parasympathetic – prepares body for resting and digesting activities Autonomic Nerve Fibers • all are motor (efferent) • preganglionic fibers • axons of preganglionic neurons • neuron cell bodies in CNS • postganglionic fibers • axons of postganglionic neurons • neuron cell bodies in ganglia Sympathetic Division • thoracolumbar divison – location of preganglionic neurons • preganglionic fibers leave spinal nerves through white rami and enter paravertebral ganglia • paraverterbral ganglia and fibers that connect them make up the sympathetic trunk Sympathetic Division • postganglionic fibers extend from sympathetic ganglia to visceral organs • postganglionic fibers usually pass through gray rami and return to a spinal nerve before proceeding to an effector • preganglionic fibers to adrenal medulla do not synapse with postganglionic neurons Sympathetic Division Parasympathetic Division • craniosacral division – location of preganglionic neurons • preganglionic fibers of the head in III, VII, and IX • ganglia are near or within various organs • preganglionic fibers of thorax and abdomen in X • short postganlionic fibers Parasympathetic Division Autonomic Neurotransmitters Cholinergic Fibers • release acetylcholine • preganglionic sympathetic fibers • preganglionic parasympathetic fibers • postganglionic parasympathetic fibers Adrenergic Fibers • release norepinephrine • postganglionic sympathetic fibers Actions of Autonomic Neurotransmitters • depend on receptor Cholinergic receptors • bind to acetlycholine • muscarinic • excitatory • nicotinic • excitatory Adrenergic Receptors • bind to norepinephrine • alpha • different responses on various effectors • beta • different responses on various effectors Actions of Autonomic Insert figure 11.39 Neurotransmitters Control of Autonomic Activity • Controlled largely by CNS • Medulla oblongata regulates cardiac, vasomotor and respiratory activities • Hypothalamus regulates visceral functions • Limbic system and cerebral cortex control emotional responses Life-Span Changes • Brain cells begin to die before birth • Over average lifetime, brain shrinks 10% • Most cell death occurs in temporal lobes • By age 90, frontal lobe has lost half its neurons • Number of dendritic branches decreases • Decreased levels of neurotransmitters • Fading memory • Slowed responses and reflexes • Changes increase risk of falling • Sleep problems common Clinical Application Cerebral Injuries and Abnormalities Concussion • brain jarred against cranium • loss of consciousness • temporary loss of memory • mental cloudiness • headache • recovery usually complete Cerebrovascular Accident • stroke • sudden interruption in blood flow • brain tissues die Cerebral Palsy • motor impairment at birth • caused by blocked cerebral blood vessels during development • seizues • learning disabilities TABLES FOR CHAPTER 11