Action Potential and Nervous Impulse Flashcards

1
Q

Define action potential

A

The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell

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2
Q

What is the threshold?

A

to generate an AP an axon requires a stimulus of a certain minimum strength raising the MP to a certain level = the threshold

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3
Q

What is an axon hillock?

A

Last part of the nerve cell body, connects to axon

needs to depolarise in order for the entire axon to depolarise

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4
Q

What are the stages of an AP?

A
  1. resting membrane potential.
  2. depolarising stimulus.
  3. voltage-gates Na+ channels open, Na+ enter cell, voltage gated K+ channels being to open slowly. Membrane depolarises to threshold.
  4. rapid Na+ entry depolarises cell.
  5. once Na+ channels are open they are prone to inactivate (close). Na+ channels close and slower K+ channels open.
  6. repolarisation: K+ moves from cell to ECF.
  7. K+ channels remain open and additional K+ leaves cell, hyperpolarising it.
  8. voltage gated K+ channels close, some K+ enters cell through leak channels.
  9. cell returns to resting ion permeability and resting membrane potential
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5
Q

How can membrane current be measured?

A

Voltage-clamp = enables membrane currents to be measured at set MP. Decide on MP, measure current by measuring movement of different ions

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6
Q

Describe hyperpolarisation

A

more K channels open than at RMP, recovery = slowly K channel close

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7
Q

What is the refractory period?

A

aka hyperpolarisation. Refractory period – second action potential cannot occur here.

ARP = absolute refractory period – no matter how much stimulus no AP.

RRP = relative refractory period – strong stimulus should be able to initiate AP

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8
Q

Outline recovery

A

when Na open they are prone to close = inactivation – need to recover before they can open again – this is achieved by hyperpolarisation

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9
Q

What is the structure of a voltage gated Na+ channel?

A

1 peptide, 4 repeats. 1 α subunit. Pore region dictates what ion flows through the channel. 4th membrane spanning domain (voltage sensor) has a lot of AA+ve = creates voltage field – if you change the MP you change the voltage field = conformational change = pore open – flow of ions = channel susceptible to inactivation

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10
Q

What is a particle plug?

A

once the pore is open inactivation particle can enter and block = membrane has to hyperpolarise for particle to be removed

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11
Q

Describe local current theory

A

when Na+ flow in, +ve charges repel any other +ve charges and attract –ve charge = set up local current = injection of current = charge spread along axon = once you get depolarisation you get passive depolarisation of adjacent cell by pushing it to threshold

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12
Q

What is capacitance?

A

ability to store charge, rises with size, larger tissue can hold more electrons = more charge

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13
Q

What is myelination?

A

Axon through middle. Folding of schwann cell. Gaps = node of ranvier = high conc of Na+ channels found. Without myelin depolarisation spread wouldn’t go far enough to initiate next depolarisation.

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14
Q

What is saltatory conduction?

A

AP jumps node to node = much faster conduction velocity. Myelin good insulator – causing local circuit current to depolarise next node above threshold

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15
Q

Describe demyelination

A

AP arrives at damaged myelin – poor working local circuit = no depolarised to threshold = no AP e.g. multiple sclerosis (CNS) Landry-Guillain-Barre syndrome (peripheral NS)

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16
Q

What is action potential membrane resistance?

A

amount of ion channels open

lower resistance = more open = higher loss of local current = limiting the spread of local current effect

17
Q

In terms of resistance and capacitance, what does the myelin sheath aim to do?

A

increase resistance = less channels open = lower loss of local current = increasing spread of local current effect

decrease capacitance = lower storage of charge = shorter to charge up = faster spread of local current

18
Q

What are nodes of ranvier?

A

Folding of schwann cell myelinate an axon, the gaps = node of ranvier = high conc of Na+ channels found

19
Q

What allows for an AP to be propagated?

A

local currents

20
Q

Give an example of a disorder affecting the CNS

A

multiple sclerosis

all CNS nerves, demyelinating

21
Q

Give an example of a disorder affecting the PNS

A

Landry-Guillain-Barre syndrome

autoimmune disorder affecting PNS = rapid-onset muscle weakness caused by the immune system damaging the PNS

22
Q

What is conduction velocity?

A

propagation speed of impulse: larger diameter = higher conduction velocity

23
Q

How many ions need to flow to generate an AP?

A

very little due to large diff in ion conc

24
Q

What cells myelinate in the CNS?

A

oligodendrocyte

25
Q

What cells myelinate in the PNS?

A

schwann cells