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Neuro > 1a Membrane And Action Potenials > Flashcards

1a Membrane And Action Potenials Flashcards

1
Q

What is a membrane potential?

A

The difference between the voltage inside and outside the neurone

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2
Q

What is the resting membrane potential?

A

-70mV

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3
Q

When does movement of ions occur?

A

When the concentration of ions is different across the membrane

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4
Q

What are ion channels?

A

Permeable pores in the membrane which open and close depending on the transmembrane voltage

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5
Q

Which are the four main ions involved in mediating membrane potentials?

A

Na+ Cl- Ca2+ and K+

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6
Q

What is a transmembrane potential?

A

The equilibrium potential is the potential at which electrochemical equilibrium has been reached - prevents the diffusion of ions down the concentration gradient

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7
Q

What equitation is used to calculate the equilibrium potential?

A

Nernst Equation

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8
Q

What is the Nernst equation?

A

E = RT/zF ln (Xintracellular/ Xextracellular)

Where Xin is intracellular ion concentration
z = charge of ion

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9
Q

Where is the concentration of sodium ions the highest?

A

Outside the neurone

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10
Q

Where is the concentration of potassium ions the highest?

A

Inside the neurone

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11
Q

Why do membrane potentials not rest at Na/K potentials?

A

Because the neurone has mixed permeability for both ions

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12
Q

What does the size of each ions contribution to membrane potential depend on?

A

How permeable the membrane is to the ion

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13
Q

What does the P in the Goldman-Hodgkin-Katz equation represent?

A

The permeability / probability of the channel opening so 0 is 100% closed and 1 is 100% open

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14
Q

How to increase the membrane permeability for a particular ion?

A

Open the ion hannels

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15
Q

What happens when Na+ ion channels are opened?

A

The membrane potential is shifted in the positive direction (becomes less negative)

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16
Q

What happens when K+ ion channels are opened?

A

Shifts the membrane in the negative direction

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17
Q

What is hypoerpolarisation?

A

When the membrane potential becomes more negative than the K+ reversal potential

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18
Q

What is the summation effect?

A

Exitory + inhibitory impulses

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19
Q

Why do graded potentials decrease with time?

A

As they spread down the axon, they decay as charge leaks from the axon and deer eases the size of the action potential charge

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20
Q

What are the three stages of an action potential?

A
  1. Depolarization
  2. Repolarisation
  3. Hyperpolarisation
    4.
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21
Q

Changes in the membrane potential during an action potential are due to what?

A

Voltage gated ion channels, not pumps - the ions flow out due to diffusion down the concentration gradient which was set up by moving ions via active pumps

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22
Q

Why is the resting membrane potential for neurones closest to K- equilibrium potential?

A

Because the permeability for potassium is greater than sodium

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23
Q

What causes depolarization?

A

The opening of voltage gated sodium ion channels resulting in an influx of Na+

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24
Q

What causes repolarisation?

A

More K+ ion channels opening and K+ flowing out the neurone, returning the potential to be more negative

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25
Q

Are the potassium ion channels open during depolarization?

A

Yes, however not many

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26
Q

What is the absolute refractory period?

A

The period in which it is not possible for another action potential to be generated because the sodium ion channels are inactive

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27
Q

How is the membrane resting potential restored after hyperpolarisation?

A

K+ ions are pumped back into the neurone using an Na+K+ active pump which requires ATP

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28
Q

During the upstroke phase of an action potential what is the relative permeabilities of sodium and potassium ions?

A

Higher permeability for Na+, which results in depolarization

29
Q

Why is the membrane more permeable to Na+ during depolarization?

A

The sodium ion channels open faster than the potassium ones

30
Q

What are the nodes of ranvier?

A

Small gaps of myelin intermittently places along the axon which the action potential jumps between

31
Q

What is the type of conduction where the action potential jumps between the nodes of ranvier?

A

Saltatory conduction

32
Q

What does saltatory conduction do to the speed of the action potential conduction?

A

Increases it

33
Q

What does the myelin sheath do to the action potential?

A

Prevents it from spreading as it has high resistance

34
Q

What is known by the all of nothing mechanism of action potentials?

A

An action potential is only triggered if a certain threshold is reached

35
Q

Hen does further depolarization stop?

A

Until the voltage gated sodium ion channels become inactive

36
Q

What type of neurones will have a faster decay?

A

Small unmyelinated neurones as they have a larger resistance

37
Q

What affect does myelin have on the rate of decay?

A

Slows the rate of decay and increases the distance of decay along the neurone

38
Q

How does the action potential spread down the neurone?

A

When sodium enters, it moves a small distance across the inside of the membrane and it’s positive charge depolarizers some more of the membrane, causing more Na+ voltage gated ion channels go opem

39
Q

What is propagation along an unmyelinated neurone called?

A

Continuous conduction

40
Q

Why is continuous conduction slower than saltatory?

A

Has to spread the whole length of the axon, no nodes of Ranvier

41
Q

Where are most voltage gated channels located?

A

At the nodes of ranvier

42
Q

What are the two factors which control the conduction velocity inside a neurone?

A

Myelination and axon diameter

43
Q

What affect does a high axon diameter have on the condition speed?

A

Increases

44
Q

What else decreases the conduction velocity?

A

Cold, anoxia, compression and some drugs

45
Q

What is an axondendritic synapse

A

Connected to a neuronal dendrite

46
Q

What is an AXOSOMATIC synapse

A

Connected to a neuronal soma

47
Q

What is an axoaxonic synapse?

A

Connected to a neuronal axon

48
Q

What is paracrine signaling?

A

Cell produces a signal to cause changes in nearby cells

49
Q

What is autocrine signaling?

A

Cell secretes an autocrine agent that binds to autocrine receptors on the same cell to trigger a response

50
Q

What type of signaling is found in the neuromuscular junction?

A

Paracrine signaling

51
Q

What neurotransmitter is used in the neuromuscular junction?

A

Acetylcholine

52
Q

Which type of receptors are found on thr sarcolemma?

A

nicotinic acetylcholine receptors

53
Q

What is botulism?

A

When botulin toxin causes the ACh to not be released from the vesicles in the pre-synaptic neurone resulting in muscle weakness

54
Q

What is myasthenia gravis?

A

Antibodies directed against the nAChR on the sarcolemma, therefore ACh is not detected so less muscle movement

55
Q

What is Lambert Eaton syndrome?

A

When there are antibodies directed against the voltage gated calcium channels, so no influx of Na+ therefore no action potential

56
Q

What structure is involved in Ca2+ ion storage?

A

Sarcoplasmic reticulum

57
Q

What happens once ACh binds to nACh receptors on the sarcolemma?

A

This causes an influx of sodium ions which result in an action potential being propagated down into the T tubules

58
Q

What molecule breaks down ACh?

A

Acetylcholinesterase

59
Q

How is Ca2+ released into the space surrounding the muscle myofibril?

A

The action potential is propagated down the t tubules
This causes the DHP receptor to pick up this change in membrane potential and change the shape of the ryanodine receptor which allows Ca2+ influx

60
Q

How is membrane potential measured?

A

A reference electrode is placed outside the cell, and another is placed inside the cell
The voltage inside and out are measured, and the difference between them is the resting membrane potential

61
Q

what is the extracellular and intracellular concentration of Na+?

A

Intracellular - 10
Extracellular - 150

62
Q

what is the extracellular and intracellular concentration of K+?

A

Extracellular = 5
Intracellular = 150

63
Q

What is the definition of flux?

A

The number of molecules that cross a unit area per unit of time (number of particles).
i.e. molecules.m−2.s−1

64
Q

What three things might cause ion channels to open or close?

A

transmembrane voltage, presence of activating ligands or mechanical forces.

65
Q

What is the Goldman-Hodgkin-Katz (GHK) equation used for?

A

To estimate membrane potentials when more than one ion is involved

66
Q

what is the resting membrane potential almost entirely due to?

A

Resting membrane potential due almost entirely to the movement of K+ ions out of the cell

67
Q

When does an action potential occur from a graded potential?

A

Action potentials (AP) occur when a graded potential reaches a threshold for the activation (opening) of many Na+ channels resulting in an “all-or-nothing” event

68
Q

What happens to the activation and inactivation gates during the process of repolarisation?

A

start: activation: open, inactivated: close

later: both closed

69
Q

What happens during the relative refractory period?

A

Some Na+ channels have recovered from inactivation – gate is open

Neuro (9 decks)

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