Chapter 11 Nervous System II

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Chapter 11Nervous System II

• Meninges
• membranes surrounding CNS
• protect CNS
• three layers
• dura mater outer, tough
• arachnoid mater - 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

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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

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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 automatic, subconscious responses to
stimuli
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Knee-jerk Reflex

• helps maintain posture

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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 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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Ascending Tracts

• fasciculus cuneatus
• lateral spinothalamic

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Corticospinal Tract
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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 cerebellar hemispheres
• diencephalon
• brain stem
• cerebellum

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Brain Development

• Three Major Vesicles
• Forebrain
• Midbrain
• Hindbrain

• Forebrain (prosencephalon)
• anterior portion (telencephalon)
• cerebrum
• basal ganglia
• posterior portion (diencephalon)
• thalamus
• hypothalamus
• posterior pituitary
• pineal gland

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Brain Development

• Midbrain (mesencephalon)
• midbrain

• Hindbrain (rhombencephalon)
• anterior portion (metencephalon)
• cerebellum
• pons
• posterior portion (myelencephalon)
• medulla oblongata

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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
• frontal lobes
• control voluntary muscles

• Brocas Area
• anterior to primary motor cortex
• usually in one hemisphere
• controls muscles needed for speech

• Frontal Eye Field
• above Brocas area
• controls voluntary movements of eyes and eyelids

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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

• 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

• 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

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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

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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 Parts
• Midbrain
• Pons
• 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

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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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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

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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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Structure of a Peripheral Nerve
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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

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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

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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

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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

• 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

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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

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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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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

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Dermatome

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

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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

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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

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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

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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

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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

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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

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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

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Sympathetic Division
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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

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Parasympathetic Division
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Autonomic Neurotransmitters

• Cholinergic Fibers
• release acetylcholine
• preganglionic sympathetic fibers
• preganglionic parasympathetic fibers
• postganglionic parasympathetic fibers

• Adrenergic Fibers
• release norepinephrine
• postganglionic sympathetic fibers

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Actions of AutonomicNeurotransmitters

• 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

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Insert figure 11.39
Actions of AutonomicNeurotransmitters
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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

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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

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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

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