Transcript Nerve Impluses

Biology 12
Neuron Function
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Neurons carry messages as electrical
impulses
It comes from:
▪ Another neuron
▪ A sensory receptor
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Here we are looking at how an impulse
travels within one neuron, down the axon!
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For an impulse to be sent there must be a
difference in electrical charge between the
inside and the outside of the cell.
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Also called an ACTION POTENTIAL
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Sodium (Na+)
Potassium (K+)
 Found inside and outside of
neurons
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Since both are positive….
It`s all relative!
 Positive = more positive ions
 Negative = fewer positive
ions
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Not sending an impulse
Neuron is polarized
When a neuron receives a stimulus, the cell is
ready/armed to transmit the signal by having
a charged difference across the membrane
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Neuron impermeable to Na+
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 Na+ collects outside
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K+ moves freely (permeable)
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Outside is positive
 All Na+ and some K+
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Inside is negative
 Some K+
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Polarized
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When a neuron is excited by a stimulus, the
cell membrane become highly permeable to
Na+ ions
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Na+ channels (gates) open
 Na+ diffuses (moves) into cell
 The negative charge become positive inside the
cell
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Polarity reversed
 Inside positive
 Outside negative
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Depolarized
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Note: Na+ gates are only open for a fraction
of a second
 Na+ gets trapped inside the cell
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Na+/K+ pumps returns membrane to rest
 Na+ moves out
 K+ moves in
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Repolarized
 Outside now +
 Inside now –
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Neuron is now returned to “resting potential”
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Depolarization occurs in a small area
 Affects adjacent gates
▪ Creates “wave” of electricity
▪ Travels length of axon
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Minimum strength stimulus required for
action potential to occur
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NOT all stimuli can cause action potential
 Different for each neuron
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Impulses are all alike once threshold reached
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Different strength of stimuli are detected
depending only on number of impulses sent
 Greater the number of impulses reaching the
brain the great the response
Na+
channel
closes
Na+
channel
opens
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Resting Potential:
http://www.youtube.com/watch?v=YP_P6bYvEjE
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Action Potential
http://www.youtube.com/watch?v=pbg5E9GCNVE
http://www.youtube.com/watch?v=R0TdXkxBOkE
http://www.youtube.com/watch?v=ifD1YG07fB8
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Read pages 418-422
 Page 426 #3, 4, 6, 7, 8, 10, 11