Nervous System II

Chapter

11

11-1

Divisions of the Nervous System

Membranous Coverings

Meninges• membranes surrounding CNS• protect CNS• three layers

• dura mater – outer, tough• arachnoid mater – middle, weblike• pia mater – inner, delicate

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Meninges of the Spinal Cord

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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

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Reflex Arcs

Reflexes – automatic, subconscious responses to stimuli

11-9

Knee-jerk Reflex

• helps maintain posture

11-10

Withdrawal Reflex• protective

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Crossed-Extensor Reflex

• flexor muscles contract• flexor muscles on opposite side inhibited• extensor muscles on opposite side contract for balance

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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

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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

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Structure of Cerebrum

• corpus callosum• connects hemispheres

• convolutions • bumps or gyri

• sulci• grooves

• longitudinal fissure• separates hemispheres

• transverse fissure• separates cerebrum from cerebellum

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Lobes of Cerebrum

• Frontal• Parietal• Temporal• Occipital• Insula

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Functions of Cerebrum

• interpretation• initiating voluntary movements• storing memory• retrieving memory• reasoning• center for intelligence and personality

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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

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Motor Areas

• Primary Motor Areas (red)• 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)

• parietal lobe• interprets sensations on skin

• Visual Area (blue)• occipital lobe• interprets vision

• Auditory Area (purple)• temporal lobe• interprets hearing

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Sensory Areas

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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

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Association Areas

Frontal Lobe Association Areas• concentrating• planning• problem solving• judging

Parietal Lobe Association Areas• understanding speech• using words to express thought

Temporal Lobe Association Areas• remember visual scenes• remember music• remember complex patterns

Occipital Lobe Association Areas• combine visual images with other sensory experiences

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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

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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

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Basal Nuclei

• masses of gray matter• deep within cerebral hemispheres• caudate nucleus, putamen, globus pallidus• produce dopamine• control certain muscular activities

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Diencephalon

• between cerebral hemispheres and brainstem• surrounds third ventricle

• thalamus• hypothalamus• optic tracts• optic chiasm• infundibulum• posterior pituitary• mammillary bodies• pineal gland

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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

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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

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Brain Stem

Three Parts1. Midbrain2. Pons3. Medulla Oblongata

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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

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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

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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)

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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

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Cranial Nerves

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Cranial Nerves I and II

Olfactory (I)• sensory• fibers transmit impulses associated with smell

Optic (II)• sensory• fibers transmit impulses associated with vision

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Cranial Nerves III and IV

Trochlear (IV)• primarily motor• motor impulses to muscles that move the eyes

Oculomotor (III)• primarily motor• motor impulses to muscles that

• raise eyelids• move the eyes• focus lens•adjust light entering eye

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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

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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

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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

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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)

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Dermatome

• an area of skin that the sensory nerve fibers of a particular spinal nerve innervate

11-56

Autonomic Nervous System

11-60

• 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

Sympathetic Division

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Parasympathetic Division

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Control of Autonomic Activity

11-70

• 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

11-71

• 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

11-72

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