Transcript Ch. 12 – Nerve Cells

1. CNS vs. PNS
Central Nervous System =
ONLY cells that begin AND
end in the brain and spinal
cord
Peripheral Nervous System =
Nerve tissue of the outer
regions
-originating in brain =
cranial nerves
-originating in spine=
spinal nerves
2. Afferent Division vs. Efferent Division
afferent division= all “incoming”
sensory pathways
efferent division= all “outgoing”
motor pathways
3. Somatic (SNS) vs. Autonomic (ANS)
Somatic
•coordinates movement of
skeletal muscle
•all voluntary movements
are SNS (and some
involuntary)
Autonomic: coordinates smooth muscle, cardiac muscle, glands
•Involuntary control
Efferent ANS:
•Sympathetic responds to immediate threat (“fight or flight”)
•Parasympathetic coordinates normal resting activity (“rest & repair”)
Afferent ANS: called visceral sensory division (viscera=internal organs)
sensory receptor senses stimulus  afferent neuron carries signal to CNS 
 interneuron in CNS (integrator) transmits signal to efferent neuron 
 efferent neuron stimulates the effector (muscle, gland, organ)  effector
performs the necessary response
DUMB!
Many reflexes DO NOT REQUIRE THE BRAIN. (you become aware afterwards)
1. Neurons- excitable and conduct impulses (see handout for structure)
2. Glia- support the neurons – make up most of N.S.
•Oligodendrocytes- holds nerve fibers together,
produces fatty myelin sheath in CNS.
•Astrocytes- star
shape, cover
capillaries in brain to
form “blood/brain
barrier”
•Ependymal cellsproduce cerebrospinal
fluid - ciliated
Schwann cells- wrap
around long nerve
fiber in the PNS to
form myelin sheath
•Microglia- destroy microorganisms and debris
(“immune cells”)
Myelin – fatty substance that
insulates “wiring” (axons) to
conduct efficiently.
White matter- nerve tissue
containing fatty myelin
(axons)
Gray matter- nerve tissue
without myelin (cell bodies)
classified by number of extensions from the cell body:
1.
2.
3.
4.
multipolar – many extensions – (motor neuron)
bipolar – two extensions – (interneuron)
unipolar – one extension – (sensory neuron)
pyramidal- pyramid shape cell body (brain neuron)
-most glial cells can replace/repair themselves
-Neuron repair is EXTREMELY limited (none if cell body is damaged)
-stem cell therapy for paralysis is hopeful! (been done in rats)
Nerve signals travel by impulses called action
potentials – (waves of electrical excitation)
requires electrical membrane resting potential –
charge difference between inside/outside of
cell membrane (like a battery +/-)
this is a polarized cell
Electrical resting potential is created by the Na+/K+ pump.
•pumps Na+ OUT and K+ IN against concentration gradient
(requires energy in the form of ATP)
•KEY!: only 2 K+ come in for every 3 Na+ out
•This creates cell interior that is negative compared to
exterior
•Cell interior is -70 millivolts compared to outside
1.The process starts when a neurotransmitter molecule
crosses a synapse between neuron- neuron OR when a
sensory neuron is stimulated.
2. This signal opens membrane gates allowing Na+ to surge
in depolarizing the neuron (making it more positive)
3. if depolarization is strong enough, more Na+ gates open
and impulse travels down axon as an action potential (peaks
at +30 milivolt)
4. signal travels from dendrite  cell body  axon
5. K+ channels then open behind the action potential
allowing K+ out to re-polarize the cell
6. action potential reaches end of axon stimulating
neurotransmitter to be released to next neuron OR an
effector (muscle, gland, etc.)
Saltatory ConductionThe action potential can “leap” down the axon to the nodes
of Ranvier between the Schwann cell thereby allowing it to
travel much faster.
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Necessary for communication across the gap
between neurons and continuation the signal.
There are many neurotransmitters depending
on location and job in the NS. (see table 12-2)
Some inhibit nerve cells rather than excite
them
Imbalances of these cause problems (i.e.
serotonin= depression, Dopamine=motor
control, psychosis etc.)
http://www.mind.ilstu.edu/flash/synapse_1.swf