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HUBS > The Action potential - L18 > Flashcards

The Action potential - L18 Flashcards

1
Q

What allows us to do everything? How is info transferred?

A

Through APs

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2
Q

What is inside and outside the cell

A

Salty H2O

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3
Q

Conc. of Na and Cl outside the cell

A

High

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4
Q

Two forces acting on Na+ and K+

A

Chemical and electrical gradients –> electrochem gradients

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5
Q

conc. of K+

A

Lots of potassium inside the cell, less outside

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6
Q

RMP

A

-70mV inside the cell, attracts +ve cell resulting in a attraction of cations

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7
Q

How do ions pass through the membrane?

A

Through ion channels made of proteins

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8
Q

When the cell is at rest, the ion channels are:

A

Closed

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9
Q

When can ions be opened or closed?

A

Selectively, unless they are signalled to

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10
Q

What is a chemically gated ion channel?

A

Channel that is only activated by the presence of a specific chemical
Chemical binds to the extracellular binding site.

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11
Q

How do ions pass down the electrochem gradient?

A

pore opens in the protein which is fluid filled, allowing specific ions to flow through.

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12
Q

How is membrane permeability reduced?

A

The chemical on a chem gates ion channel unbinds and the protein changes shape and closes, preventing flow of the specific ions

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13
Q

What are voltage gated ion channels?

A

Influenced by change in charge of the membrane

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14
Q

Where are vgic common?

A

areas of excitable membrane

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15
Q

Why are vgic important?

A

Generation and conduction of APs and synaptic transmittion

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16
Q

Structure of VGIC at rest

A

the activation gate on the outside of the cell is closed

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17
Q

Structure of VGIC in the refractory period i.e at +30mV

A

The inactivation gate on the inside is closed until the membrane is repolarised

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18
Q

The VGIC has what that allows it to change shape when it detects a change in charge

A

Charged resides on the protein

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19
Q

What is mechanically gated ion channels?

A

Physical change in the membrane causing the opening and closing of protein channels

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20
Q

What do dendrites do?

A

Increase the SA of the cell

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21
Q

Another name for axon

A

Nerve fibre

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22
Q

Channels found at nerve endings

A

Ca2+ VGIC

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23
Q

Type of ion channels found most abundant on the dendrites and cell body of neurons

A

Chem gated ion channels

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24
Q

What is a local potential

A

Localised change in voltage across the membrane after interaction with neurotrans with receptor of another neuron

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25
Q

What type of channels are on the axons?

A

VGIC

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26
Q

What determines the magnitude of the voltage change?

A

The strength of the stimulus

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27
Q

What is a graded AP

A

A small or big change in voltage
*Depends on how much neurotrans was released
*How many channels opened because of neurotrans

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28
Q

What is depolarisation?

A

When positive i.e Na+ moves into cell, the RMP becomes less negative due to opening of ion channels

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29
Q

hat is a local potential?

A

Change in voltage only occurs in one area and doesn’t spread

30
Q

What causes chem gated ion channels to open

A

A chem stimulus i.e through neurotrans like ACh

31
Q

What happens when CGIC open?

A

Cell membrane depolarises locally

32
Q

After threshold, what happens

A

Cell gets repolarised and stimulus is removed through the Na+ K+ pump

33
Q

What is hyperpolarisation?

A

When positive charge leaves the cell or negative charge enters the cell, causing the cell to become inhibitory

34
Q

At +30mV, the cell becomes

A

Excitatory

35
Q

What channels are involved in local potentials

A

CGICs

36
Q

If there are two nerve terminals that are close to one another…

A

Their signals add together to create a larger signal but if they are not actively progagated, the charge dissipates and nothing happens

37
Q

What is another word for the AP of depolarisation?

A

Excitatory postsnaptic potential

38
Q

What is another word for the AP of Hyperpolarisation?

A

Inhibitory postsnaptic potential (IPSP)

39
Q

What is summation?

A

When 2 or more nerve terminals excrete excitatory neurotrans, it results in local potential whose effects add up

40
Q

Effect of local potentials is summed over…

A

Time and space

41
Q

Spatial summation

A

If nerve terminals are close to one another

42
Q

Temporal summation

A

Whether they arrive in time close to one another

43
Q

What is threshold

A

+10mV change from -70mV to -60mV

44
Q

What determines if info is passed as an AP

A

The balance between excitation and inhibition

45
Q

What makes up the axon hillock?

A

Initial segment, segment 2 and 3

46
Q

What is the initial segment

A

The point where the cell body and axon join

47
Q

What is unique about the initial segment

A

Very dense in VG Na+ C
*Where AP occurs
Sensitive to change in membrane potential

48
Q

How is AP generated

A

Balance of excitation and inhibition at every moment in time depolarises the mem —> causes VGIC to open

49
Q

hen does VG Na+ C open at the initial segment

A

When the cell mem potential reaches -60mV

50
Q

What happens as VG Na+ C opens?

A

Positive charge brought into the cell and voltage across mem becomes more positive at that point

51
Q

What causes a bigger voltage change?

A

As more voltage gated Na+ channels open

52
Q

How long does the reversal of the transmem voltage take?

A

2-3 ms

53
Q

What kind of potential brings the cell to threshold?

A

A graded potential

54
Q

What happens to the shape of the VG Na+ C as the cell reaches +30mV?

A

Polarity of voltage across the protein changes causing protein to change shape and the inactivation gate to close (Sodium channel inactivation)

55
Q

What happens at +30mV

A

VG Potassium channels open,
electrical gradient is outwards and takes K+ out while Na+ stops coming in

Causes repolarisation of the cell (cell mem becomes more negative)

56
Q

What happens at -40mV

A

The VG Na+ C has their activation gates close inactivation gates open i.e back to resting position

*Potassium channels begin to close

57
Q

What happens at -60mV

A

*Potassium channels begin to close, Na+ channels begin reactivating and cell brought back into RMP

58
Q

What happens during the absolute refractory period?

A

Another AP cannot be generated no matter how large the stimulus is

59
Q

What happens during the relative refractory period?

A

AP can be generated in response to a v large stimulus only as enough of the Na+ channels that are in resting can be reactivated (not all are in resting)

60
Q

Why does a refractory period occur?

A

Prevents AP from travelling backwards

61
Q

When can another AP be conducted?

A

At -40mV in response to a v big stimulus as Na+ channels will be in their resting state

62
Q

When is the refractory period and for how long

A

From the -60mV to -40mv

Lasts 1ms

63
Q

What happens as the MP at the initial segment depols to +30mV

A

There is flow of charge in the forward, diagonal, backwards and downwards directions, allowing those parts of the axon to come to threshold

64
Q

Why isn’t the AP conducted backwards even though there is a backflow of charge

A

The MP is in its refractory period hence it is not affected

65
Q

Time taken for APs to be conducted along unmyelinated axons

A

1.5m/s

66
Q

How is conducted v increased?

A

Using myelin

67
Q

What is under the myelin

A

A low density of VGICs

68
Q

Why does myelin help to transmit the AP faster?

A

As the charge does not dissipate

69
Q

What happens at the node of Ranvier?

A

The local current from the initial segment causes a graded depol due to the high density of VGICs at the node of Ranvier, which brings MP to threshold

70
Q

How fast does AP travel in an myelinated axon

A

20-100 m/s

HUBS (27 decks)

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