Download Peripheral nervous system

Pages 228-237
http://www.youtube.com/watch?v=FR4S1BqdFG4
1. Sensory input—gathering info
◦ Monitor changes occurring inside
& outside the body
2. Integration
◦ Make sense of information &decide
if/what action is needed
3. Motor output
◦ The “response”
◦ activates muscles or glands in
response to the stimulus
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Central nervous system (CNS)
◦ Brain
◦ Spinal cord
Peripheral nervous system (PNS)
◦ Nerves outside the brain and spinal
cord
 Spinal nerves
 Cranial nerves
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Sensory (afferent) division
◦ Nerve fibers that carry information to the
CNS
◦ “On ramp”
Motor (efferent) division
◦ Nerve fibers that carry impulses away from
the CNS
◦ Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
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Just introduced
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Motor neurons/efferent nerves
Central nervous system
Peripheral nervous system
Nervous system
Sensory/afferent nervous system
Guess about what these mean and where on the
web they fit
◦ Somatic nervous system  controls skeletal muscles
◦ Autonomic nervous system  controls _______ muscle
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In the scenario identify the sensory input,
motor effect, and integration (not specifically
stated). Also identify the role of the efferent
and afferent divisions of the nervous system
and explain which specific efferent/motor
division is being used.
Fritz was putting a tray of cookies into the
oven. The top of his hand accidently grazed
the side of the oven and he quickly retracted
his hand out of the oven.
Neurons
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conduct nerve impulses
can’t divide  no mitosis are in G0
phase
2 functions: irritiability & conductivity
 What
do the words polarization
and depolarization mean?
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Dendrites
◦ Can have a few or 60
◦ Receive messages from other
neurons
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Cell body/soma
◦ Metabolic center
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Axon
◦ Can only have ONE
◦ Sends the message from the cell
body
http://www.youtube.com/wa
tch?v=-SHBnExxub8
http://www.youtube.com/watch?v=sjyI4CmBOA0
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Axon hillock (where AP is
generated) and axon terminal
(branches at the end of an
axon that pass the message
along)
Myelin sheath
◦ Not present on every axon
 Pain receptors don’t have myelin
on their axons
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Schwann Cells
◦ Form myelin sheaths around nerve fibers
◦ MS (multiple sclerosis) attacks myelin sheaths,
converts them to hard covers that can’t conduct
electrical impulses  slurred speech, loss of
balance, impaired vision, etc
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What is a Schwann cell?
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What part of the NS does it support?
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What structural part of the neuron
can it form?
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Why is having a myelin sheath an advantage?
***If 2 nerves are equal in diameter
- the nerve with myelin can send an action
potential at a speed of 100 meters/sec.
- the nerve without myelin can send the
action potential at a speed of 1 meter/sec
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What is saltatory conduction?
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Why we need neurons to be able to make an
electrical impulse (action potential)
Remember these are NOT physically connected
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At resting state the neurons
are polarized
◦ - inside of the neuron b/c cell
has proteins that have – charges
 Has K+ but not enough to
balance out the –
◦ + outside of the neuron b/c
more Na+
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Neurons are selectively
permeable
◦ Contain ion channels
 Voltage gated ion channels 
open when there’s a change in
charge
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A stimulus causes Na+ to flow into the
neuron
If enough Na+ flows in, the neuron’s charge
becomes more positive and becomes
depolarized (not as negative) causing the
nerve to send an electrical signal  action
potential AKA nerve impulse
Sodium voltage-gated ion channels open and
Na+ rushes in  make the inside very +
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Once one area is positive, the positive charge
moves down the axon causing more Na+
channels to open
After Na+ enters, the ions channels for Na+ close
but the inside is still very +
Sodium-potassium pumps then use ATP to move
Na+ out of the neuron and K+ in to return the
charges inside and outside of the neuron to
“normal”  repolarization
All or Nothing Response
1 action potential at a time  while neuron is
recovering it is in a refractory period  no nerve
impulses an be generated
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Myelinated fibers carry messages faster
◦ Use saltatory conduction (charge jumps from node of
Ranvier to node of Ranvier)
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Non-myelinated fibers transmit AP’s slower b/c
all ion channels must open and close
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The larger the diameter of the axon the faster the
signal moves
No
my
elin
◦ Squid diameter 500 micometer  56 mph
◦ Human internal organ diameter 1 micrometer  4.5 mph
◦ Nerve to human leg muscle 20 micometers  270 mph…
WOW… thanks myelin
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dhdGNoP3Y9REplM18zWHNCT2c%3D&b=5
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http://184.171.162.94/images/prevjhy.php?u=Oi8vd3d3L
nlvdXR1YmUuY29tL3dhdGNoP3Y9aWZEMVlHMDdmQjg%3D
&b=5
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter14/ani
mation__the_nerve_impulse.html
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/anim
ation__how_the_sodium_potassium_pump_works.html
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http://www.youtube.com/watch?v=FR4S1BqdFG4
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http://www.youtube.com/watch?v=YP_P6bYvEjE
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In groups of 2-4 create an analogy that
parallels the event that take place to create
an action potential/nerve impulse
Consider
◦ the initial locations of Na+ and K+
◦ the movement of Na+ while the action potential is
being created
◦ The movement of K+ immediately after the AP has
been generated
◦ How the levels of Na+ and K+ inside and outside of
the cell is corrected after the AP has been
transmitted
1. A neuron is more negative inside the cell relative to the
outside (polarized)
2. A stimulus makes causes the cell’s charge to reach the
threshold
3. Na+ channels open and sodium floods into the cell in
one section of the axon
4. The Na+ channels in that area close but the region
down the axon gets positive enough to reach threshold
 Na+ channels open and sodium rushes in… this
continues down the axon
5. The K+ channels open and potassium diffuses out
6. The cell becomes repolarized BUT K+ is concentrated
outside and Na+ is concentrated inside… must swap!
7. The sodium-potassium pumps move Na+ our of the
neuron and K+ into the neuron
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Now that we’ve discussed how nerve
impulses are made, explain how an action
potential is generated
You should
◦ explain what happens to the potassium and sodium
ions
 which does each ion starts where
 how does each move
◦ Discuss polarization, repolarization, and
depolarization (use whatever forms of these words
that you need)
◦ Explain what the threshold is
◦ Discuss the all or none firing