what causes a graded potential?
- some triggering event allows the response to change the cells membrane permeability
what is the action potential?
everything that occurs following the threshold potential being reached
- the depolarization and the repolarization phases back down to rest
- occurs very rapidly
because the action potential has so much amplitude, what does it reach during depolarization?
0mV and even positive mV membrane potential
- note: membrane potential at rest is -70mV
how fast is repolarization after a depolarization of action potential?
just as rapid as the depolarization
what is an overshoot?
the reversion period (‘reversing’ the potential above 0 mV)
how long is an action potential?
always the same duration
- 1 msec in a nerve cell
what is another name for an action potential?
a spike
when an excitable membrane is triggered to undergo an action potential, we say it?
‘fires’
what is the key to an action potential?
the change in membrane permeability to ions
which gated ion channel uses change of voltage/membrane potential as a mechanism of opening and closing triggering event?
voltage-gated channels
what is the triggering event of a mechanically gated ion channel?
- open in response to mechanical deformation
what is the triggering event of a chemically gated ion channel?
- open in response to some sort of molecule binding to the ion channel specifically neurotransmitters
which gated ion channel opens to initiate action potential?
voltage gated ion channels
what are the two voltage gated ion channels?
- voltage gated K+ (potassium) channels
- voltage gated Na+ (sodium) channels
how does a voltage gated K+ (potassium) channel operate?
simple with one one activation gate that opens once the threshold potential has reached - senses voltage difference and it opens
what are the two differences between Na+ and K+ voltage-gated channels?
- Na+ channels are much faster to respond to change in the membrane voltage / potential
- Na+ channels have in their cytosolic region an activation and an inactivation gates
what happens when threshold potential is reached at the channel level?
- potassium and sodium gates open
- sodium inactivation gate begins to close
- all occurs at the same event once the threshold is reached
- only thing that differs is how quickly these events occur
how fast do the gates of the sodium voltage gated channels open?
activation gate - very rapidly
inactivation gate - quite slow
how fast is the potassium’s gate to open?
quite slow
what has huge implications for the shape and physiology of the action potential?
the rate at which the voltage gated ion channels are opening
what is the state of the voltage gated channels at rest (-70mV)?
- all voltage-gated channels are CLOSED
- Na+ channels are in the configuration with the inactivation gate open but the activation gate closed
the electrical and concentration gradients favour sodium movement into or out of the cell?
into the cell
what leads to greater depolarization of the membrane?
inward movement of Na+ ions
what leads to the positive feedback cycle?
opening of more voltage-gated Na+ channels because of the sodium ions being entered from the already opened voltage gated sodium ion channels
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Module 1 - Lecture 144
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Module 1: Lecture 254
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Module 1: Lecture 351
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Module 1: Lecture 430
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Module 1: Lecture 528
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Module 1: Lecture 622
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Module 1: Lecture 724
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Module 1: Lecture 819
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Module 1: Lecture 927
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Module 2: Lecture 151
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Module 2: Lecture 254
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Module 2: Lecture 353
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Module 2: Lecture 451
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Module 2: Lecture 546
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Module 2: Lecture 643
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Module 3: Lecture 145
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Module 3: Lecture 239
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Module 3: Lecture 347
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Module 3: Lecture 446
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Module 3: Lecture 537
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Module 3: Lecture 633
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Module 3: Lecture 759
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Module 3: Lecture 854
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Module 4: Lecture 156
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Module 4: Lecture 241
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Module 4: Lecture 327
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Module 4: Lecture 425
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Module 4: Lecture 533
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Module 4: Lecture 635
