5.1 Nervous transmission & potentials Flashcards

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1
Q

what is potential difference? what is it measured in?

A

difference in electrical charge across the plasma membrane, measured in millivolts

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2
Q

what is the normal resting state of an axon called? what is the p.d. in this state?

A

resting potential

-70mv

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3
Q

in resting state what is the membrane said to be?

A

polarized

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4
Q

when does an action potential occur?

A

when the p.d across an axon is temporarily reversed

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5
Q

when the action potential/nerve impulse occurs what is the p.d of the membrane and what is the membrane said to be?

A

+40mv

depolarized

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6
Q

when is the axon in resting potential?

A

when no impulse is present

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7
Q

when is there an action potential?

A

when an impulse is being transmitted

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8
Q
  1. when a neurone has resting potential what are open and what are closed?
A

some potassium channels are open but voltage gated sodium ion channels are closed

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9
Q

2.a what does the energy of the stimulus trigger? what does this do to the membrane?

A

some voltage gated sodium ion channels to open

membrane more permeable to sodium ions

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10
Q

2.b what do sodium ions diffuse down? what does this make the axon?

A

an electrochemical gradient

make inside axon less negative

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11
Q
  1. as some channels open sodium diffuses in causing a change in charge, what does this do?
A

causes more voltage gated sodium ion channels to open allowing more sodium in (POSITIVE FEEDBACK)

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12
Q
  1. When the p.d reached +40mv what happens to the channels?
A

voltage gated sodium ion channels close
voltage gated potassium ion channels open
axon more permeable to potassium ions

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13
Q

5.a after the potassium channels open, what happens to the potassium ions? what does this result in?

A

potassium ions diffuse out of axon down electrochemical gradient
inside axon more negative

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14
Q

5.b inside of the axon becomes more negative than resting, what is this called?

A

HYPERPOLARISATION

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15
Q
  1. voltage gated potassium ion channels close, what does the sodium potassium pump cause? what happens to the potential of the axon?
A

3 sodium ions out
2 potassium in
returns to resting potential

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16
Q

For an action potential to be generates, the stimulus must be greater than what?

A

the threshold value

17
Q

what would cause a stimulus to be below the threshold value?

A

insufficient numbers of sodium channels open

18
Q

what does insufficient numbers of open sodium channels prevent?

A

full depolarisation of the axon

19
Q

once the threshold value is reached what is generated?

A

the action potential

20
Q

regardless of the strength of the stimuli what is the action potential always?

A

the same size

21
Q

what does the size of the stimuli affect?

A

the number of action potentials generated in a given time.

Larger stimulus = more frequently action potentials are generated

22
Q

what is the cause of depolarisation? what does it cause the axon to become?

A

influx of sodium ions into the axon as energy of stimulus opens voltage gated sodium ion channels
causes the axon to be positively charged

23
Q

what is repolarisation?

A

axon membrane p.d going from positive to negative resulting in resting potential

24
Q

what does hyperpolarisation involve?

A

axon becoming more negative than its resting state due to potassium ions diffusing out

25
Q

what is the refractory period?

A

the period of time when the axon can not be excited again

26
Q

if we didn’t have the refractory period what could happen?

A

action potential could be initiated backwards

action potentials could overlap

27
Q
  1. what does normal resting state allow for in the axon?
A

an action potential to be generated

28
Q
  1. when does an absolute refractory period occur? what can not happen?
A

after an action potential has been generated.

another impulse can not be produced regardless of the strength of the stimuli

29
Q
  1. when can an action potential be generated?
A

in the relative refractory period, only if the stimulus is stronger than the normal threshold value

30
Q
  1. what is the normal resting state?
A

after refractory period when the axon returns to resting, its possible for a further action potential to be generated

31
Q

what does the myelinated sheath do?

A

insulates the axon making the action potential move faster

32
Q

what do ion channels at the nodes of ranvier allow for?

A

the movement of sodium and potassium ions across the membrane at these points an action potential can be generated

33
Q

when the action potential moves from node to node what is it referred to as?

A

saltatory conduction

34
Q

how does the diameter of the axon affect the speed of the impulse?

A

the greater the diameter of the axon the faster the impulse

35
Q

axons with a small diameter have a small sa:v ratio what does this cause?

A

large amount of ions leaking out of the axon making it harder to initiate an action potential

36
Q

how does temperature affect the speed of an impulse?

A

the higher the temperature the faster the speed of the impulse, it affects the rate if diffusion of ions across the axon