Patrick Yerkes
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The nervous system carries information from
one part of the body to another
The nervous system transmit information by
nerve impulses to communicate with other
parts of the body
Main parts of the nervous system are the:
Brain, Spinal Cord, and Nerves
 Regulate homeostasis and responds to disease
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Central Nervous
System (CNS)
 Occupies the midline or
central part of the body
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Peripheral Nervous
System (PNS)
 Nerves extend to the
outlying or peripheral
part of the body
▪ Autonomic Nervous
System (ANS)
▪ Regulate the body’s
involuntary functions
Cells of the Nervous
System
•Two types of cell:
•Neurons
•Nerve cells
•Conduct nerve
impulses
•Gila
•Specialized
connective tissue
cells
•Support neurons
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Neurons consist of three
parts
 Cell body- main part of the
neuron
 Dendrites- branching
projections of the neuron
▪ Processes that transmits
impulses to the cell bodies
 Axon- elongated
projection
▪ Transmits impulses away
from the cell body
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3 main types of neurons
 Sensory- Transmits impulses to the spinal cord and
brain from all parts of the body. Also called Afferent.
 Motor- Transmits impulses away from the brain or
spinal cord. Only conduct impulses to two kinds of
tissues (muscle and glandular epithelial). Also call
Efferent.
 Interneuron- conduct impulses from the sensory
neurons to motor neurons. Also call Central or
Connective Neurons
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Myelin is a white fatty substance formed by a
Schwann Cells that wrap the axons around
the CNS
The fibers are called Myelinated Fibers
Nodes of Ranvier are indentations between
nearby Schwann Cells
The outer cell membrane is the Neurilemma
 Axons in the brain and spinal cord do not have
Neurilemma and decreases healing or
regeneration
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Also called- Neuroglia
Do not specialize in transmitting nerve
impulses
Are support cells
 Greek word Gila means “glue”
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Holds the functions neurons together and
protect them
Regulates nerve function
Common brain tumor is called Glioma
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Gila can be different in
size
 Large cells that look
somewhat like star from
their thread like extensions
are called- Astrocytes
 Microglia- are the smaller
cells, they remain
stationary
▪ When inflamed or
degenerating brain tissue
they will enlarge and act as
micro scavengers
▪ Eat other micros
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Oligodenrocytes- hold nerve fibers together
and serve a more important function which is
to produce fatty myelin sheath that envelops
nerve fibers located in the brain or spinal cord
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Nerve- is a group of
peripheral nerve fibers
bundles together
Peripheral nerve fibers
usually have myelin sheath
 Often look white
Bundles of axons in the
CNS are called tracts
 The axons could be
myelinated and forming
white matter
 Unmyelinated axons and
dendrites are called grey
matter for being grey
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Each axon in a nerve is surrounded by thin
wrapping fibrous connective tissue called
‘endoneurium’
Groups of endoneurium are called ‘fascicles’
Each fascicle is surrounded by a thin fibrous
‘perineurium’
A tough fibrous sheath is called a
‘epineurium’ which covers the whole nerve
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Some nerve impulses are called ‘Action
Potentials’
 Can travel over trillions of routes
 Neurons create the paths
 Routes named Neuron Pathways
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Reflex Arcs are one way streets, the impulse
can only go one way
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A specialized type of neuron pathway is
called the ‘reflex arc’
 The simplest kind of reflex arc is a two- neuron arc
▪ Consist on only 2 types of neurons: Sensory and Motor
neurons
 Three- neuron arc is the next simplest arc
▪ Consist of all 3 neurons: Interneurons, Motor, and
Sensory
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Are the beginnings of
dendrites of sensory
neurons
Often away from the
spinal cord mostly
located in; (in tendons,
skin, or mucous
membranes)
Sensory receptors are
located in the quadriceps
and the patellar tendon
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Reflex response for the
patellar tendon which is
the rubber hammer and
creates a knee- jerk
 Example of a two- neuron
arc
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A group of nerve- cell bodies located in t he
PNS
Near the Spinal cord
Each spinal ganglion contains no sensory
neuron
The axon of the sensory neuron travels from
the cell body in the dorsal root ganglion
 Ends in the dendrites of another neuron in the
grey matter
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A microscopic space that
separates the axon
ending with one neuron
from the dendrites to
another
 This is called a Synapse
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Nerve impulse stops at
the synapse
The neuron axon forms
a synapse called the
‘effectors’
Organs put the nerve
signals to effect
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Effectors are the muscles and glands
 Muscles contract
 The glands secretion
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Only kind of reflexes by these effectors
A response to impulse conduction on the
reflex arc is called a reflex
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Some neurons need 3 neurons
 More complex involves one more sensory and
motor neuron
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In the 3 neuron reflex
 End of the sensory neurons’ axon synapses first
with a interneuron
 Before chemical signals are sent to a second
synapse
 Ending up with a conduction motor neuron
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Applying an irritating
stimulus to the skin of
the thigh
It creates a 3- neuron
reflex response
Causes contractions of
the muscles to pull away
from the leg away from
the irritant
3 neuron contraction is
also called a - withdrawal
reflex
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All interneuron's’ lie entirely within gray
matter of the brain or spinal cord
 Grey matter forms the ‘H’ shaped inner core of
the spinal cord
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3 neuron reflex has 2 synapses
2 neuron reflexes has 1 synapses between a
sensory neuron and the motor neuron
Reflex Arc: Identify
•ID motor
neuron
•Look at its
dendrites and cell
body
•Located in spinal
cord
•Dies in the
muscles
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A nerve impulse is a self- propagation wave of
electrical disturbance that travels along the
surface of a neuron’s plasma membrane.
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Example
 A Spark going to fuse
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First they have to be stimulated ( a change in
the neuron’s environment)
 Temperature, Pressure, and chemical changes are
used as stimuli
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Membrane of a resting neuron has a slight
positive charge on the outside and a negative
charge on the inside
 This occurs from excessive amounts of sodium
ions (NA+) on the outside of the membrane
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When the section of the
neuron is stimulated and
the channels open
The sodium ions (NA+)
flood inside
Causing the membrane
to become positive
temporarily and then
becomes negative
The neuron immediately
recovers the electrical
disturbance stimuli
(Na+)
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If a impulse is traveling
interacts with a section
of a membrane
insulating myelin
 ‘jumps’ around the myelin
called ‘saltatory
conduction’
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Saltatory Conduction can
travel much faster then
the nonmyelinated
sections
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By definition a synapse is a place where
impulses are transmitted from one neuron
called presynaptic neuron to another
postsynaptic neuron.
The presynaptic and postsynaptic neuron
makes up the synapse
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Three structures of the
synapse is: a synaptic
knob, a synaptic cleft,
and the plasma
membrane of a
postsynaptic
Is a tiny bulge at the end of the terminal branch
of a presynaptic neuron’s axon
 Each synaptic knob has many small sacs or
vessels
 Each vessel contains a very some quantity of a
chemical compound called a neurotransmitter
 After the nerve impulse arrives at the synaptic
knob neurotransmitters molecules are released
from the vesicles into the synaptic cleft
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Is the space between the plasma membrane
(of the postsynaptic neuron) and the synaptic
knob
About 2 millionths of a centimeters in width
Has protein molecules embedded in opposite
synaptic knobs
The receptors and neurotransmitters bind
 The binding can cause an impulse in the
postsynaptic neuron by opening the ion channels
in the postsynaptic membrane
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Neurotransmitters Chemicals help neurons
communicate
Around 30 different
compounds have been
identified as
neurotransmitters
Neurotransmitters are
did sent randomly
 They are localized in
certain types of neuron
groups and released in
specific pathways
ACETYLCHOLINE
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CATECHOLAMINE
Released in certain areas in
the Spinal Cord
Also in the neuromuscular
junctions
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 Also called nerve- muscle
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Includes
 Norepinephrine
 Dopamine
 Serotonin
All three of these
transmitters play a role for
 Sleep
 Motor function
 Mood
 Pleasure recognition
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2 ‘morphine’ like
N.transmitters are called
endorphins and
enkephalins
Released in multiple
areas in the spine and
brain in the pain
conduction pathways
Are natural pain killers
Endorphins are released
mainly in intense
exercise
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Pain is normally used as
a warning sign that
draws our attention to
injuries
Hold back against severe
pain because it can stop
us from continuing an
activity that is needed for
survival
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Unlike other transmitters Nitric Oxide
diffuses directly across the plasma
membrane
 Rather then being released in the vesicles
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Nitric Oxide is important for the male sexual
response to create a penile erection
Drugs like Viagra (sildenafil) treats MED or
Male Erectile Dysfunction by promoting the
Nitric Oxide response