Chapter 11 Nervous System II Meninges membranes surrounding CNS protect CNS three layers dura mater – outer, tough arachnoid mater - weblike pia mater – inner, delicate 11-2

Meninges of the Spinal Cord 11-3

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 11-4

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 11-5

Spinal Cord Structure extends foramen magnum to 2nd lumbar vertebra 11-6

Cross Section of Spinal Cord 11-7

Spinal Cord Functions center for spinal reflexes conduit for nerve impulses to and from the brain 11-8

Reflex Arcs Reflexes – automatic, subconscious responses to stimuli 11-9

Crossed-Extensor Reflex flexor muscles contract flexor muscles on opposite side inhibited extensor muscles on opposite side contract for balance 11-12

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 11-13

Brain Functions interprets sensations determines perception stores memory reasoning makes decisions coordinates muscular movements regulates visceral activities determines personality Major Parts cerebrum Two cerebral hemispheres diencephalon brain stem cerebellum two cerebellar hemispheres 11-16

Structure of Cerebrum corpus callosum connects hemispheres convolutions bumps or gyri sulci grooves longitudinal fissure separates hemispheres transverse fissure separates cerebrum from cerebellum 11-19

Lobes of Cerebrum Frontal Parietal Temporal Occipital Insula 11-20

Functions of Cerebrum interpretation initiating voluntary movements storing memory retrieving memory reasoning center for intelligence and personality 11-21

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 11-22

Motor Areas Primary Motor Areas Broca’s Area Frontal Eye Field 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 11-23

Motor Areas 11-24

Sensory Areas Cutaneous Sensory Area Visual Area Auditory Area parietal lobe interprets sensations on skin Visual Area occipital lobe interprets vision Auditory Area temporal lobe interprets hearing 11-25

Sensory Areas 11-26

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 11-27

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 11-28

Hemisphere Dominance In over 90% of population, left hemisphere is dominant Nondominant hemisphere controls nonverbal tasks motor tasks understanding and interpreting musical and visual patterns provides emotional and intuitive thought processes Dominant hemisphere controls speech writing reading verbal skills analytical skills computational skills 11-29

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 11-30

Basal Nuclei masses of gray matter deep within cerebral hemispheres caudate nucleus, putamen, globus pallidus produce dopamine control certain muscular activities 11-31

Diencephalon between cerebral hemispheres and brainstem surrounds third ventricle thalamus hypothalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland 11-32

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 Epithalamus region above thalamus involved in regulation of sleep/wake cycle and mood pineal gland secretes melatonin hormone Also contains one of choroid plexuses that produce CSF 11-33

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 11-34

Brain Stem Three Parts Midbrain Pons Medulla Oblongata 11-35

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 11-36

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 11-37

Medulla Oblongata enlarged continuation of spinal cord conduction pathway for ascending and descending impulses between brain and spinal cord contains autonomic reflex center for cardiac, vasomotor, and respiratory control centers contains various nonvital reflex control centers (coughing, sneezing, vomiting) 11-38

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 11-39

Types of Sleep Slow Wave Rapid Eye Movement (REM) person is tired decreasing activity of reticular system restful dreamless reduced blood pressure and respiratory rate ranges from light to heavy alternates with REM sleep Rapid Eye Movement (REM) some areas of brain active heart and respiratory rates irregular dreaming occurs 11-40

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 11-41

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 11-42

Structure of a Peripheral Nerve 11-43

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 afferent fibers carry sensory impulses to CNS from skin and skeletal muscles General somatic efferent fibers carry motor impulses from CNS to 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 11-44

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 11-45

Cranial Nerves 11-46

Cranial Nerves Designated by Roman numerals: I. Olfactory = sense of smell; sensory only. II. Optic = sense of vision; sensory only. III. Oculomotor = innervates eye muscles; motor only. IV. Trochlear = innervates eye muscles; motor only. V. Trigeminal = largest; sensory from face; motor to chewing muscles; mixed. VI. Abducens = innervates eye muscles; motor only. VII. Facial = innervates muscles of facial expression; sensory taste; mixed. VIII Vestibulocochlear = sense of hearing and equilibrium; sensory only. IX. Glossopharyngeal = moves tongue and pharynx muscles; mixed. X Vagus = innervates visceral smooth muscle; mixed. XI. Accessory = innervates neck muscles; motor only. XII. Hypoglossal = moves tongue; motor only. Memorize by using one of many mnemonic devices: One example is: Oh, Oh, Oh, To Touch And Feel Very Good Velvet AH!"

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) 11-54

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 11-56

Spinal Nerve Plexus Nerve plexus – complex networks formed by anterior branches of spinal nerves; fibers of various spinal nerves are sorted and recombined Cervical plexus: neck muscles and diaphragm (breathing) Brachial plexus: upper limb Lumbar plexus: anterior and medial thigh Sacral plexus: posterior lower limb, leg Each resulting branch of the plexus contains the fibers from several spinal nerves; Fibers from each spinal nerve are carried to the body periphery via several different routes or branches. Therefore, damage to one spinal segment cannot completely paralyze any limb muscle.

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 11-60

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 11-61

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 11-62

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 11-63

Sympathetic Division 11-64

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 11-65

Parasympathetic Division 11-66

Actions of Autonomic Neurotransmitters depend on receptor Cholinergic receptors bind to acetlycholine muscarinic excitatory nicotinic Adrenergic Receptors bind to norepinephrine alpha different responses on various effectors beta 11-68

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 11-70

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 11-71

Clinical Application Cerebral Injuries and Abnormalities Concussion brain jarred against cranium loss of consciousness temporary loss of memory mental cloudiness headache recovery usually complete Cerebral Palsy motor impairment at birth caused by blocked cerebral blood vessels during development seizues learning disabilities Cerebrovascular Accident stroke sudden interruption in blood flow brain tissues die 11-72