Chapter 11Nervous System II

Meninges•

• protect CNS• three layers

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Meninges of the Spinal Cord

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Cerebrospinal Fluid

• 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

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Spinal Cord Structure

• extends foramen magnum to 2nd lumbar vertebra

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Cross Section of Spinal Cord

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Spinal Cord Functions

• center for spinal reflexes

• conduit for nerve impulses to and from the brain

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Reflex Arcs

Reflexes –

11-9Reflex Ark.mov

Knee-jerk Reflex

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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 • Descending

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Brain

Functions• • determines perception• stores memory• • makes decisions• • regulates visceral activities• determines personality

Major Parts• cerebrum

• two cerebellar hemispheres• diencephalon• brain stem• cerebellum

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Brain Development

Three Major Vesicles1. Forebrain2. Midbrain3. Hindbrain

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Structure of Cerebrum

• corpus callosum•

• convolutions • bumps or gyri

• sulci•

• 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 –

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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 11-23

Motor Areas

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Sensory Areas

• Cutaneous Sensory Area

• parietal lobe• interprets sensations on skin

• Visual Area• occipital lobe• interprets vision

• Auditory Area• temporal lobe• interprets hearing

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Sensory Areas

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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

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• 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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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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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

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Peripheral Nervous System

• Cranial nerves • Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

• Spinal nerves • Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

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Nerve Fiber Classification

• Sensory Nerves – • Motor Nerves – • Mixed Nerves – contain both sensory nerve fibers and motor nerve fibers; most nerves

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Cranial Nerves

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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

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Autonomic Nervous System

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• 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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Life-Span Changes

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• 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

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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