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Chapter 8 Lecture Notes
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Chapter 8 - Nervous System
A. the nervous system coordinates the activities of other organ systems
1. monitors internal and external conditions
2. stores and integrates information
3. coordinates the activity of effector organs
B. nerve tissue = neurons + neuroglia (NOOR oh GLEE uh)
1. neurons conduct electrical and chemical signals
a. basic structure
cell body contains nucleus
dendrites carry signal to cell body
axon and collaterals carry signals to other cells
synaptic terminals at ends of axon contain neurotransmitter
myelin surrounds some axons
nodes of Ranvier are gaps in myelin
b. categories
sensory neurons - take signals from receptors to CNS
motor neurons - take signals from CNS to effector organs
(muscle and glands)
interneurons - about 99% of CNS; connect sensory and
motor neurons
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2. neuroglia protect and support the neurons
a. astrocytes (ASS troe sites) - CNS - help maintain blood-brain
barrier, form structural framework for repair
b. oligodendrocytes (OH lih go DEN droe sites) - CNS - form
myelin
c. microglia (MY crow GLEE uh) - CNS - phagocytes
d. ependymal (ep EN dih mull) - CNS - line cavities in CNS, help
produce and move cerebrospinal fluid
e. Schwann cells - PNS - form myelin
3. synapses are where neurons communicate with each other and
other cells
a. presynaptic neuron synaptic terminals contains
neurotransmitters stored in vesicles
b. synaptic cleft = small space between cells
c. postsynaptic neuron membrane contains receptors for the
neurotransmitters and gated ion channels that regulate the
membrane potential
4. basic multi-neuronal structures
 gray matter consists mostly of cell bodies
 white matter consists mostly of myelinated axons
 cortex - thin layer of neuron cell bodies (gray matter) covering the
outside of parts of the brain
 nucleus - clump of neuron cell bodies (gray matter) located in CNS
 tract - bundle of axons in CNS
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 ganglion/ganglia - clump of neuron cell bodies in PNS, surrounded
by c.t.
 nerve - bundle of axons in PNS, surrounded by c.t.
C. neurophysiology
1. action potential – a temporary change in the membrane potential of
a neuron that acts as a signal
neurons maintain a resting membrane potential, then use
temporary changes in potential to send messages along
their membranes and to other cells
an action potential occurs when a small area of neuron membrane
becomes permeable to Na
Na enters the cell and reverses the membrane potential
Na entry is automatically cut off and K exit occurs a millisecond
later
K exit returns the membrane to resting potential
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2. propagation
an action potential occurs in a very small area
each action potential, unless it is blocked by nerve damage or
drugs, causes a new action potential in the adjacent
membrane
this process repeats to the end of the axon
at the synaptic terminal the action potential causes the release of
neurotransmitter, allowing the signal to be sent on to the
next cell
3. channels
the ion channels that let Na into and K out of the cell are gated
that means their opening is controlled by outside factors like
changes in membrane potential (voltage), chemicals, or
mechanical factors
Na and K channels at a synapse are controlled by the
neurotransmitter
Na and K channels in the axon are controlled by changes in
membrane potential
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4. the sodium/potassium pump works constantly to maintain Na and K
gradients so that whenever ion channels open there is enough Na
or K to move across the membrane to generate a signal
D. Organization of the nervous system
central nervous system (CNS) = brain + spinal cord
peripheral nervous system (PNS) = cranial + spinal nerves
afferent/sensory
efferent/motor
somatic - skeletal muscle
autonomic - cardiac m., smooth m., glands
CNS
PNS
sensory
motor
somatic
autonomic
E. spinal cord, spinal nerves
1. functions of spinal cord
a. pathway between body and brain
b. integrates reflexes (automatic and unlearned responses to
sensory information)
c. contains complex patterns used in activities like walking and
running
2. anatomy of the spinal cord
a. gross
length: foramen magnum to L2
below L2 spinal nerves form cauda equina
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consists of columns of white and gray matter
cervical and lumbar enlargements represent extra nerve
tissue needed for handling sensory input from and
motor control of limbs
b. cross sectional
central canal filled with CSF
gray columns - cell bodies of neurons and glial cells
posterior - sensory neurons
lateral - autonomic motor neurons
anterior - somatic motor neurons
white columns - ascending sensory tracts and descending
motor tracts
anterior
lateral
posterior
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3. anatomy of the spinal nerves
spinal nerves carry information into and out of the spinal cord
each nerve has a dorsal root and a ventral root
dorsal root ganglion is in dorsal root and contains cell bodies of
sensory neurons
dorsal root carries sensory information into the spinal cord
ventral root carries motor information from the spinal cord
dorsal and ventral roots join just inside vertebrae to form spinal
nerves
spinal nerves leave through intervertebral foramina
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F. the simplified brain
1. cerebrum
a. functions: consciousness, thinking, planning, conscience,
memory, control of complex movements, awareness,
localization of sensory input, language
b. structure
left and right hemispheres
lobes: frontal, parietal, temporal, occipital
cortical functional areas:
sensory - visual, auditory; somatic (primary)
association - premotor cortex, prefrontal area
motor - primary
speech - Broca’s, Wernicke’s
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c. components
 cortex - thin layer of gray matter; where most cerebral
functions occur
 white matter - connects cortex to other parts of brain:
corpus callosum connects left and right hemispheres
 basal nuclei - deep to white matter; subconscious control of
skeletal muscle
2. diencephalon
a. epithalamus - pineal gland
b. thalamus - processes and screens sensory input to cerebrum
c. hypothalamus - physical response to emotion, water balance,
temperature control, food intake, hormone secretion,
3. brain stem - pathway between spinal cord and diencephalon
a. midbrain - motor responses to visual and auditory input,
controls level of consciousness
b. pons - integrates cerebellum and brainstem, motor control
centers
c. medulla oblongata - cardiac and respiratory control centers
4. cerebellum - coordination of skeletal muscle, posture, balance
5. ventricles cavities lined with ependymal cells
contain CSF
connected to each other and subarachnoid space
2 lateral ventricles in the cerebral hemispheres
interventricular foramina
3rd ventricle in diencephalon
cerebral aqueduct
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4th ventricle between brainstem and cerebellum
4th ventricle continuous with central canal of spinal cord
6. limbic system - structures in the cerebrum and diencephalon;
emotional state, memory storage and retrieval
G. protective systems of CNS
1. meninges (men IN gees) – singl. – meninx (MEN inks)
3 layers of c.t. surrounding brain and spinal cord
continuous with coverings of nerves
shock absorbing
epidural space
dura mater
subdural space
arachnoid
subarachnoid
space
pia mater
spinal cord
filled with adipose
tissue
single layer
brain
no space
blood vessels
contains CSF
blood vessels
contains CSF
attached to neural
tissue
attached to neural tissue
double layer, outer layer fused to
inner surface of cranial bones;
contains veins called dural
sinuses
2. cerebrospinal fluid (CSF)
secreted into ventricles by ependymal cells at specialized
structures called choroid plexuses
fills ventricles and subarachnoid space around brain and spinal
cord
volume = 150 mL
constantly produced
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excess reabsorbed through arachnoid membrane into the superior
sagittal sinus
turnover is about three times a day
main function is to float the brain
3. blood-brain barrier
tight junctions between cells in brain capillaries
blocks movement of many molecules between blood and brain
tissue fluid
loss of integrity can occur with prolonged stress or trauma
H. nerve structure
nerve = bundle of axons surrounded by layers of c.t.
most nerves contain axons of both sensory and motor neurons
cell bodies of sensory neurons are located in ganglia
spinal nerves have dorsal root ganglia
cranial nerves have ganglia in head
cell bodies of motor neurons are located in gray matter
all spinal nerves contain axons of motor neurons whose cells are in the
lateral and ventral gray columns
cranial nerves with significant motor content have axons originating
from nuclei in the brain stem
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I. cranial nerves (table 8-2)
I olfactory - olfactory
II optic - vision
III oculomotor - motor control of intrinsic and extrinsic eye muscles
IV trochlear - motor control of extrinsic eye muscles
V trigeminal - see table
VI abducens - motor control of extrinsic eye muscles
VII facial - see table
VIII vestibulocochlear - hearing and equilibrium
IX glossopharyngeal - see table
X vagus - autonomic motor control of organs of ventral body cavity
including heart
XI – accessory - see table
XII - hypoglossal - see table
J. spinal nerves and plexuses
31 pairs: organized by region of spinal cord
spinal nerves are named for vertebrae: C1-C8*,
T1-T12, L1-L5, S1-S5, Co1
some spinal nerves interconnect to form plexuses just outside the spinal
column
nerves leaving the plexuses contain axons from several spinal nerves
 cervical - neck and diaphragm (phrenic nerve)
 brachial - upper limb
 lumbar - lower limb
 sacral - lower limb (sciatic nerve)
K. autonomic nervous system (ANS)
1. general pathway
preganglionic neurons
ganglia
postganglionic neurons
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2. organization
a. dual innervation - both divisions innervate most of the same
organs
b. divisions have opposing effects
3. divisions
a. sympathetic (“fight or flight”) - prepares the body for
emergencies and exercise
 innervation is widespread
 control tends to be temporary (the sympathetic response)
 preganglionic neurons have their cell bodies in the
thoracic and lumbar lateral gray horns
 they leave as part of spinal nerves and end in the
sympathetic ganglia
 postganglionic neurons have their cell bodies in the
ganglia and terminate in effector organs
b. parasympathetic (“rest and digest”) - conserves energy
 innervation is localized
 duration of control may be brief (digestive organs) or
long-lasting (heart)
 preganglionic neurons have their cell bodies in the brain
stem and sacral lateral gray horns
 they leave as part of cranial (III, VII, IX, X ) or spinal
nerves and end in the parasympathetic ganglia
 postganglionic neurons have their cell bodies in the
ganglia and terminate in effector organs
 the vagus nerve (X) is the major parasympathetic
innervator of organs in the ventral body cavity including
the heart
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4. neurotransmitters and receptors
a. cholinergic neurons use ACh
there are two main types of cholinergic receptors
this allows ACh to cause different effects in different organs
b. adrenergic neurons use norepinephrine (NE)
there are several types of adrenergic receptors
this allows NE to cause different effects in different organs
preganglionic
postganglionic
sympathetic
cholinergic
adrenergic
parasympathetic
cholinergic
cholinergic
5. the adrenal medulla is a modified sympathetic ganglion
its neurons never developed axons
they secrete epinephrine and norepinephrine directly into the
blood during a sympathetic response
this amplifies and prolongs the sympathetic response
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6. specific effects on organs
sympathetic
parasympathetic
pupils
heart rate
heart contraction force
coronary and skeletal muscle
blood vessels
other blood vessels
bronchioles
digestive activity
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