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Chapter 11
Nervous System II
Meninges
• membranes
surrounding CNS
• protect CNS
• three layers
• dura mater – outer,
tough
• arachnoid mater weblike
• pia mater – inner,
delicate
Meninges of the Spinal Cord
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
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
Spinal Cord Structure
• extends foramen magnum to 2nd lumbar vertebra
Cross Section of Spinal Cord
Spinal Cord Functions
• center for spinal reflexes
• conduit for nerve impulses to and
from the brain
Reflex Arcs
Reflexes – automatic, subconscious responses to stimuli
Knee-jerk Reflex
• helps maintain posture
Withdrawal Reflex
• protective
Crossed-Extensor Reflex
• flexor muscles contract
• flexor muscles on opposite side inhibited
• extensor muscles on opposite side contract for balance
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
Ascending Tracts
• fasciculus cuneatus
• lateral spinothalamic
Corticospinal Tract
Brain
Functions
Major Parts
• interprets sensations
• cerebrum
• two cerebellar hemispheres
• determines perception
• diencephalon
• stores memory
• brain stem
• reasoning
• cerebellum
• makes decisions
• coordinates muscular
movements
• regulates visceral activities
• determines personality
Brain Development
Three Major Vesicles
1. Forebrain
2. Midbrain
3. Hindbrain
Forebrain (prosencephalon)
• anterior portion (telencephalon)
• cerebrum
• basal ganglia
• posterior portion (diencephalon)
• thalamus
• hypothalamus
• posterior pituitary
• pineal gland
Brain Development
Midbrain (mesencephalon)
• midbrain
Hindbrain (rhombencephalon)
• anterior portion (metencephalon)
• cerebellum
• pons
• posterior portion (myelencephalon)
• medulla oblongata
Structure of Cerebrum
• corpus callosum
• connects hemispheres
• convolutions
• bumps or gyri
• sulci
• grooves
• longitudinal fissure
• separates hemispheres
• transverse fissure
• separates cerebrum from
cerebellum
Lobes of Cerebrum
• Frontal
• Parietal
• Temporal
• Occipital
• Insula
Functions of Cerebrum
• interpretation
• initiating voluntary movements
• storing memory
• retrieving memory
• reasoning
• center for intelligence and personality
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
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
Motor Areas
Sensory Areas
• Cutaneous Sensory
Area
• parietal lobe
• interprets sensations
on skin
• Visual Area
• occipital lobe
• interprets vision
• Auditory Area
• temporal lobe
• interprets hearing
Sensory Areas
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
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
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
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
Basal Nuclei
• masses of gray matter
• deep within cerebral
hemispheres
• caudate nucleus, putamen,
globus pallidus
• produce dopamine
• control certain muscular
activities
Diencephalon
• between cerebral hemispheres and brainstem
• surrounds third ventricle
• thalamus
• hypothalamus
• optic tracts
• optic chiasm
• infundibulum
• posterior pituitary
• mammillary bodies
• pineal gland
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
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
Brain Stem
Three Parts
1. Midbrain
2. Pons
3. Medulla Oblongata
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
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
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)
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
Types of Sleep
Slow Wave
Rapid Eye Movement (REM)
• person is tired
• some areas of brain active
• decreasing activity of
• heart and respiratory rates
reticular system
irregular
• restful
• dreaming occurs
• dreamless
• reduced blood pressure and
respiratory rate
• ranges from light to heavy
• alternates with REM sleep
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
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
Structure of a Peripheral Nerve
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 efferent fibers
• carry motor impulses from
CNS to skeletal muscles
General somatic afferent fibers
• carry sensory impulses to
CNS from skin and 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
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
Cranial Nerves
Cranial Nerves I and II
Olfactory (I)
• sensory
• fibers
transmit
impulses
associated
with smell
Optic (II)
• sensory
• fibers
transmit
impulses
associated
with vision
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
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
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
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
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
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
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)
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
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
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
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
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
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
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
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
Sympathetic Division
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
Parasympathetic Division
Autonomic Neurotransmitters
Cholinergic Fibers
• release acetylcholine
• preganglionic
sympathetic fibers
• preganglionic
parasympathetic
fibers
• postganglionic
parasympathetic
fibers
Adrenergic Fibers
• release
norepinephrine
• postganglionic
sympathetic
fibers
Actions of Autonomic
Neurotransmitters
• 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
Actions of Autonomic
Insert figure 11.39
Neurotransmitters
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
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
Clinical Application
Cerebral Injuries and Abnormalities
Concussion
• brain jarred against cranium
• loss of consciousness
• temporary loss of memory
• mental cloudiness
• headache
• recovery usually complete
Cerebrovascular Accident
• stroke
• sudden interruption in blood
flow
• brain tissues die
Cerebral Palsy
• motor impairment
at birth
• caused by blocked
cerebral blood vessels
during development
• seizues
• learning disabilities
TABLES FOR
CHAPTER 11