Nervous System II Divisions of the Nervous System Chapter 11 11-1

Membranous Coverings Meninges membranes surrounding CNS protect CNS three layers dura mater – outer, tough arachnoid mater – middle, 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

Knee-jerk Reflex helps maintain posture 11-10

Withdrawal Reflex protective 11-11

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 (red) Broca’s Area (purple) frontal lobes control voluntary muscles Broca’s Area (purple) 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 (yellow) Visual Area (blue) parietal lobe interprets sensations on skin Visual Area (blue) occipital lobe interprets vision Auditory Area (purple) 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 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 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) 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 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

Cranial Nerves 11-46

Cranial Nerves I and II Olfactory (I) sensory fibers transmit impulses associated with smell Optic (II) sensory fibers transmit impulses associated with vision 11-47

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 11-48

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 11-49

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 11-50

Cranial Nerves VIII and IX Glossopharyngeal (IX) mixed sensory from pharynx, tonsils, tongue, and carotid arteries motor to salivary glands and muscles of pharynx Vestibulocochlear (VIII) sensory sensory from equilibrium receptors of ear sensory from hearing receptors 11-51

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 11-52

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 11-53

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

Dermatome an area of skin that the sensory nerve fibers of a particular spinal nerve innervate 11-56

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

Sympathetic Division 11-64

Parasympathetic Division 11-66

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