Module 3: Action potential Flashcards

1
Q

What is depolarisation?

A
  1. Inside of membrane becomes more positive, Na+ coming into neuron
  2. more positive
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2
Q

What is repolarisation?

A
  1. return to resting membrane potential from being depolarised
  2. back to normal
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3
Q

What is hyperpolarisation?

A
  1. inside becomes more negative, K+ leaving neuron
  2. more negative
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4
Q

what triggers an Action potential in neurons?

A

a local or graded potential that is large enough to trigger the positive feedback cycle

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5
Q

what is the general threshold to trigger an action potential?

A

~50mV

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6
Q

describe the features of an action potential

A
  1. fast (1-2 ms)
  2. travel long distances without diminishing
  3. initiated in axon hillock
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7
Q

describe the ion flow of an action potential

A
  1. 70mV: both channels closed
  2. ripple of current causes a positive feeback cycle until the threshold is reached
  3. on reaching -50mV threshold all Na+ channels open and flood the neuron, rapidly depolarising it to +30mV
  4. once at +30mV the Na+ channels become inactive and the K+ channels open
  5. K+ channels cause repolarisation, dropping the voltage
  6. once voltage reaches -70mV the Na+ channels become closed
  7. K+channels still open, neuron becomes hyperpolar and K+ channel closes
  8. passive facilitated diffusion occurs due to the leak channels and the resting membrane potential is achieved again
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8
Q

when does NA+ channel close?

A
  1. open
  2. closed
  3. inactivated
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9
Q

describe how the sodium channel is positioned in the closed position

A

the gate is closed, the ball is at rest, no ions can pass through but it is ready to open again at the next action potential

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10
Q

describe how the sodium channel is positioned in the inactivated position

A

the gate is open, the ball is blocking the channel so sodium ions cannot pass through. It isn’t able to open again until it moves to the closed position at the end of repolarisation

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11
Q

describe how the sodium channel is positioned in the open position

A

gate is open and ball is at rest, sodium ions can pass down heir gradient as they wish

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12
Q

when do potassium channels become open in an action potential?

A

at the peak of the action potenetial

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13
Q

when do potassium channels become closed in an action potential?

A

when the action potential becomes hyper polarised (lower than -70mV)

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14
Q

what is the positive feedback cycle in an action potential?

A

when a local or graded potential is big enough to cause a ripple effect within the Na+ channels, opening enough to trigger more opening, which floods the neuron with positive ions, making it depolarise more and more until an action potential is achieved

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15
Q

what is action potential propagation?

A

the process of the action potential travelling from the axon hillock to the end of the axon

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16
Q

what is an absolute refractory period?

A
  1. when all the Na+ channels are open or inactive no more action potentials can be generated
  2. limits firing frequency
  3. action potential travel in one direction
17
Q

what is a relative refactory period?

A
  1. action potential generated if a large stimulus is applied
  2. some Na+ closed
18
Q

what affects the speed of an action potential?

A
  1. diamter of the axon: thicker is faster
  2. temperature: not relevant humans as we are hod blooded, but faster the warmer
  3. degree of myelination: more myelination faster action potential AKA saltatory conduction
19
Q

what is saltatory conduction?

A

when the myelination of an axon enables the action potential to jump along the axon to the next node of Ranvier, speeding up the pace