NERVOUS SYSTEM
HONORS ANATOMY & PHYSIOLOGY
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excitable characteristic of nervous tissue
allows for generation of nerve impulses
(action potentials) that provide
communication & regulation of most body
tissue.
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together with endocrine system:
responsible for maintaining homeostasis
Nervous Tissue & Homeostasis
NERVOUS
ENDOCRINE
rapid responder
 action potentials
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slow, prolonged
response
 releases hormones
Differences in Nervous & Endocrine
Control of Homeostasis
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total mass of 2 kg (~3% of total body mass)
Skull
Spinal Cord
Spinal Nerves
Cranial Nerves
Ganglia
Enteric Plexus
Special Senses & other Sensory Receptors
Structures of the Nervous System
Major Structures of the Nervous
System
3 basic functions:
1. Sensory
2. Integrative
3. Motor

Functions of the Nervous System
sensory receptors detect internal & external
stimuli
 sensory (afferent) neurons carry this
sensory information to spinal cord & brain
thru cranial & spinal nerves

Sensory Function
integrate: process
nervous system takes information from
sensory neurons & processes that
information, analyzes it, stores some of it &
makes decisions for appropriate responses
 served by interneurons (connect 1 neuron
to another neuron
 Perception:
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◦ conscious awareness of sensory stimuli
◦ occurs in brain
Integrative Function
served by motor (efferent) neurons
 carry info from brain/spinal cord 
effectors (muscle or gland) thru cranial or
spinal nerves
 results in muscles contraction or gland
secreting
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Motor Function
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What terms are given to neurons that carry
input  spinal cord & brain?
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What terms are given to neurons that carry
output out of the brain & spinal cord?
Quick Quiz
Organization of the Nervous System
2 cell types
1. Neurons
2. Neuroglia
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Histology of the Nerrvous System
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nerve cells that possess electrical
excitability:
◦ ability to respond to a stimulus & convert
it into an action potential
◦ stimulus: any change in environment that
is strong enough to initiate an action
potential
Neurons
Direction Action Potential Travels

electrical signal that propagates along
surface of neurolema (membrane)
◦ begins & travels due to movement of ions
between interstitial fluid & inside of
neuron thru specific ion channels
◦ once begun it travels rapidly @ constant
strength
Action Potential
Parts of a Neuron
contains nucleus, cytoplasm, typical
organelles,
 + Nissl bodies clusters of RER
◦ make materials for:
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 growth of neuron
 regenerate damaged axons in PNS
Parts of Neuron: Cell Body
general term for any neuronal process or
extension that emerges from cell body
 most neurons have 2:
1. Dendrites
2. Axons
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Nerve Fiber
“little trees”
 input portion of neuron
 usually, short, tapering, highly branched
 their cytoplasm contains Nissl bodies,
mitochondria
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Dendrites
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propagates action potentials 
◦ another neuron
◦ muscle fiber
◦ gland cell
Axon
joins cell body @ cone-shaped elevation:
axon hillock
 part of axon closest to hillock = initial
segment
 jct of axon hillock & initial segment where
action potential arises so is called the
trigger zone
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Parts of an Axon
axoplasm: cytoplasm of an axon
 axolemma: plasma membrane of axon
 axon collaterals: side branches along length
of axon (most @ 90°)
 axon terminals: axon divides into many fine
processes
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Parts of an Axon
site of communication between 2 neurons
or between a neuron & effector cell
 synaptic end bulbs: tips of some axon
terminals swell into bulb-shaped structures
 synaptic vesicles: store neurotransmitter
◦ many neurons have >1 neurotransmitter,
each with different effects on postsynaptic
cell
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Synapse
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2 types:
◦ for moving materials from cell body  axon
terminals
slow
1.
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1-5 mm/d
replenishes new axoplasm to developing or
regenerating axons
fast
2.
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200 – 400 mm/d
moves materials to/from cell body
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organelles or membranes needed in axon terminal
Axonal Transport
Functional Classification
Structural Classification
use # processes
extending from cell
body
1. Multipolar neurons
2. Bipolar neurons
3. Unipolar neurons
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Sensory
Interneurons
Motor
Types of Neurons
several dendrites with 1 axon
 includes most neurons in brain & spinal
cord
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Multipolar Neurons
1 main dendrite & 1 axon
 retina, inner ear, olfactory area of brain
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Bipolar Neuron
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are sensory neurons that begin in embryo
as bipolar
during development axon & dendrite fuse
then divide into 2 branches (both have
characteristic structure & function of an
axon)
1 branch ends with dendrites (out of CNS)
2nd branch ends in axon terminal (in CNS)
cell bodies of most found in ganglia
Unipolar Neuron
Unipolar Neuron
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found in cerebellum
Purkinje Cells
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in cerebral cortex of brain
Pyramidal Cells
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~50% vol of CNS
“glue”
do not generate or propagate action
potentials
multiply & divide in mature nervous
systems
glioma:
◦ brain tumors derived from glial cells
◦ very malignant, grow rapidly
Neuroglia (Glia)
ASTROCYTES
2. OLIGODENDROCYTES
3. MICROGLIA
4. EPENDYMAL CELLS
1.
Glial Cells of the CNS
star-shaped
 largest & most numerous of glial cells
 functions:
1. physically support neurons
2. assist in blood-brain-barrier (bbb)
3. in embryo: regulate growth, migration,
&interconnections between neurons
4. help maintain appropriate chemical
environment for propagation of action
potentials
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Astrocytes
“few trees”
 smaller & fewer branches than astrocytes
 Functions:
1. form & maintain myelin sheath on axons
in CNS
2. 1 oligo. myelinates many axons
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Oligodendrocytes
small cells with slender processes giving off
many spine-like projections
 function:
1. phagocytes
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remove cellular debris made during normal
development
remove microbes & damaged nervous tissue
Microglia
single layer of cuboidal to columnar cells
 ciliated & have microvilli
 function:
1. line ventricles of brain & central canal of
spinal cord
2. produce, monitor, & assist in circulation
of cerebrospinal fluid (CSF)
3. form bbb
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Ependymal Cells
Schwann cells
 Satellite cells
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Neuroglial Cells of the PNS
functions:
1. myelinate axons in PNS
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2.
1 Schwann cell myelinates 1 axon
participate in axon regeneration
Schwann Cells
flat cells that surround cell bodies of
neurons in PNS ganglia
 functions:
1. structural support
2. regulate exchange of materials between
neuronal cell bodies & interstitial fluid
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Satellite Cells
myelin sheath: made up of multilayered
lipid & protein (plasma membrane) covering
 function:
1. electrically insulates axon
2. increases speed of nerve impulses
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Myelination
Myelinated & Unmyelinated Axons
gaps in myelin sheath
 1 Schwann cell wraps axon between nodes
of Ranvier
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Nodes of Ranvier
Sheath of Schwann = Neurolemma
amount increases from birth to maturity
 infant‘s responses slower & less
coordinated as older child or adult in part
because myelination is a work in progress
thru infancy
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Myelin
loss of myelin sheath
 see in disorders:
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◦ multiple sclerosis
◦ Tay-Sachs
◦ side effect of radiation therapy & chemotherapy
Demyelination
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contains:
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neuronal cell bodies
dendrites
unmyelinated axons
axon terminals
neuroglia
Gray Matter of the Nervous System
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composed of:
◦ myelinated axons
White Matter of the Nervous System