0 ns 5 nerve impulses
TRANSCRIPT
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Biology 12
Nerve Impulse
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Biology
Main idea:Transmission of a Nerve
Impulse Is how the nervous message movesalong the length of a neuron
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Biology
Nerve impulse is
An electrochemical message Created by the movement of IONS
across the cell membrane (sodium
potassium)
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Biology 2007
Transmission of a signal THINKING!!!
How is a signal transmitted down/along neuron? All or None response
Think Dominoes!
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Biology
Nerve Impulse is.
Tricky!!!!! VOCAB-
Resting Potential
Action Potential Sodium & Potassium Gates (passive)
Sodium &Potassium Pumps (active)
Depolarization
Repolarization
Recovery
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Biology
Nerve Impulse
Order of the Impulse 1- Resting Potential
2-Action Potential
3- Recovery
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Biology 2007
1- Resting Potential
There is a greater concentration of sodium ionsoutside the neuron & a greater concentration of
potassium ions inside the neuron.
Inside the neuron has a relatively negative
charge.
Resting potential is -65 mV
Think KIN (potassium in)
Na+ Na+ Na+ Na+ Na+ Na+ Na+Na+ Na+ K+ Na+ Na+
Cl
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K+ Cl- Cl- Cl-
K+
aa-
K+ Cl- Cl-
aa-aa-aa
-
aa- aa-
K+
K+ +
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Biology
1- Resting Potential
Resting potential is maintained by thesodium-potassium pumps. (active
transport)
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Biology
2 Action potential
A) Depolarization - a Stimulus causes the Na+channels to open (change in pH, electric shock,pressure, light)
Na+ ions diffuses into cell
charges reverse at that point on neuron
cell becomes depolarized (+ 40 mV)
+ + + + + + ++ + + + + + +
+ + + + + + ++ + + + + + +
+
+
Na+
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Biology
How does a nerve impulse travel?
Wave: nerve impulse travels down neuron change in charge opens other Na+ gates
in next section of cell
voltage-gated channels
Na+ ions continue to move into cell
wave moves down neuron = action potential
+ + + + + + + + + + + +
+ + + + + + + + + + + +
+ + +
+ + +
Na+
wave
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Biology 2007
2- Action Potential
B) Repolarization: K+ channels open up K+ ions diffuse out of cell
Restoration of the same potential as resting (- 65
mV)
Causes the channels to close behind impulse
+ + + + + + + + + + +
+ + + + + + + + + + +
+ + + +
+ + + +
Na+
K+
wave
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Biology 2007
3- Recovery
After firing a neuron has to re-set itself Na+ needs to move back out
K+ needs to move back in
Sodium Potassium pumps work to re-establish
the ion distribution of resting potential
+ + + + + ++ + + + +
+ + + + + ++ + + + +
+ + + +
+ + + +
Na+Na+Na+Na+
Na+ Na+
Na+
K+K+
K+K+ Na+ Na
+Na+
Na+Na+
Na+Na+
Na+Na+
Na+
Na+
K+K+K+
K+K+K+K+ K+
wave
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Biology 2007
Neuron is ready to fire again!!!
Na+ Na+ Na+ Na+ Na+ Na+ Na+Na+ Na+ Na+ Na+ Na+ Na+
Na+ Na+ Na+ Na+ Na+ Na+ Na+Na+ Na+ Na+ Na+ Na+ Na+
K+
K+ K+ K+ K+
K+
aa-
K
+
K
+
K
+aa-
aa-aa-
aa- aa-
+ + + + + + + ++ + + + + + +
+ + + + + + + ++ + + + + + +
resting potential (- 65 mV)
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Biology 2007
Action potential - all together!
1. Resting potential2. Stimulus reaches threshold potential3. Na+ channels open; K+ channels closed4. Na+ channels close; K+ channels open
5. Recovery - Na+ / K+ pumps
http://www.psych.ualberta.ca/~ITL/ap/ap.htmhttp://www.psych.ualberta.ca/~ITL/ap/ap.htm -
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Biology 2007
Myelin sheath
signal
direction
Schwann cells insulate neuron (Na+ / K+ cannot
enter cell)
Na+ / K+ can only enter at the
nodes of ranvier
Increase speed of impulse
signal hops from node to node
150m/sec (330mi/hr)
(vs. 5m/sec)
myelinsheath
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Biology 2007
Multiple Sclerosis
T cells attack
myelin sheath
loss of signal