ACTION POTENTIALS

Question 1

How is the resting membrane potential established?

Answer 1

The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion. … Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential.

Question 2

How is that done? with Na+ & K+?

Answer 2

Na+/K+ -ATPase has a role to generate ion gradients which uses energy from ATP breaking to ADP producing a lot of energy to drive active transport across the membrane
3 Na+ out
2 K+ in

Question 3

the potential of k?

Answer 3

-90mV

Question 4

the potential of Na?

Answer 4

65 mV

Question 5

What is the resting membrane potential?

Answer 5

-70mV

Question 6

Do all cells have a membrane potential?

Answer 6

Yes all cells have a membrane potential, ionic gradients are important in all cells

Question 7

Where do rapid changes occur in cells?

Answer 7

Rapid changed to occur in excitable cells like neurons, myocytes and pancreatic cells

Question 8

What is membrane potential?

Answer 8

It is the voltage of the inside of the membrane relative to the outside (equilibrium)

Question 9

What is hyperpolarisation?

Answer 9

it is when the inside of the membrane becomes more negative because of the opening of voltage-gated K+ ions (lets K+ out) the mV goes below resting potential when exposed to stimuli

Question 10

What is depolarisation?

Answer 10

where the inside of the membrane becomes more positive due to the opening of the voltage-gated Na+ channels, it lets Na+ in, the more channels open mean more depolarisation. The mV goes higher than resting potential when exposed to stimuli

Question 11

What is the threshold voltage?

Answer 11

The threshold voltage is -50 to -55mV

Question 12

what does it mean when it’s an all or nothing process?

Answer 12

The generation of an action potential is all or nothing process, once this threshold is reached a full action potential must be generated

Question 13

How fast is the generation of an AP?

Answer 13

Very fast: 1-2 milliseconds and high frequency

Question 14

What is the magnitude independent on?

Answer 14

The magnitude is independent of the strength of the original stimulus

Question 15

Summary of steps

Answer 15

Resting potential –> threshold is reached –> sodium channels are open (the depolarization stimulus) –> produces the action potential –> repolarisation

Question 16

What are voltage-gated Na+ and K+ channels

Answer 16

a gate that opens when a change in voltage occurs

Question 17

What occurs during the resting stage?

Answer 17

In the resting stage (-70mV) the ion gated sodium and potassium channels and the cell’s selective permeability are inactivated resulting in no movement

Question 18

What occurs in Na+ channels

Answer 18

When depolarisation occurs, to let Na+ ions in. It has a three-step stage where the gate remains closed, once stimulated, the voltage-gated Na+ ion channels opens where Na+ can enter the cell. Once the stimulus strength is sufficient an action potential is produced. Once the action potential is produced the voltage-gated Na+ channels inactivate, facilitating repolarization to the resting potential. The channel’s a gate (activation gate) is closed at rest and activates in several steps to an open state after depolarization.

Question 19

How does the Na+ channel become inactivated?

Answer 19

The peptide that sits on the end of the channel, in short time blocks the channels then it eventually closes (the tail moves) There are three processes, you cannot skip them! This Na+ process is faster!

Question 20

What occurs in the voltage-gated K+ channels?

Answer 20

Repolarisation occurs, where the K+ channels open and K+ ions rush out of the cell, generally this process is slow. There are only two steps open and closed. The Na+ channels are inactive ans it start to close

Question 21

What occurs in an action potential! LABEL

Answer 21

LLL

Question 22

What occurs in the undershoot?

Answer 22

A small hyperpolarisation occurs, it needs Na+/K+ ATpase to restore Na_ and K+ concentration

Question 23

What happens in absolute refractory period?

Answer 23

Absolute refractory period: during this time it is absolutely impossible to send another action potential. The inactivation (h) gates of the sodium channels lock shut for a time, and make it so no sodium will pass through. No sodium means no depolarization, which means no action potential. Absolute refractory periods help direct the action potential down the axon, because only channels further downstream can open and let in depolarizing ions.

Question 24

What occurs in relative refractory period?

Answer 24

Relative refractory period: during this time, it is really hard to send an action potential. This is the period after the absolute refractory period, when the h gates are open again. However, the cell is still hyperpolarized after sending an action potential. It would take even more positive ions than usual to reach the appropriate depolarization potential than usual. This means that the initial triggering event would have to be bigger than normal in order to send more action potentials along. Relative refractory periods can help us figure how intense a stimulus is - cells in your retina will send signals faster in bright light than in dim light, because the trigger is stronger.

Question 25

Can an another AP occur?

Answer 25

Another AP can occur during the relative refractory period if only a larger stimulus is applied because the larger stimulus can open up most of the closed ion channels

Question 26

What does the refractory period do?

Answer 26

it limits firing frequency and limits neuron firing

Question 27

Does AP have a direction?

Answer 27

Yes it does, it can only travel is one direction along the axons, not backwards

Question 28

What does local anesthetic do to the AP?

Answer 28

it does this through blocking voltage-gated Na+ channels. This primarily occurs through the prevention of the ‘inactivated state’ of the channel to its ‘closed’ state; thereby preventing the channels to reopen.

Question 29

LABEL POST AND PRE SYNAPTIC NEURONS

Answer 29

LLL

Question 30

Steps?

Answer 30

The AP is generated as Na+ flows inwards across the membrane one location, then the depolarisation of the membrane spreads to the neighboring region, reinitiating the AP there where the AP is already complete, the membrane is repolarising as K+ flows outwards.

Question 31

What are the factors that influence AP conduction speed?

Answer 31

1) axon diameter- the larger the diameter, there is less resistance which produces a faster conduction speed
2) Temperature- a chemical reaction occurs faster at warmer temperatures
3) the degree of myelination, the myelin insulates the membrane of the axon, it makes it have a faster conduction speed
* * the conduction of speed is affected more by myelination than by axon diameter

Question 32

What is saltatory conduction?

Answer 32

Saltatory conduction is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.

Question 33

What does unmyelinated nerve fibers produce?

Answer 33

Unmyelinated nerve fibers produce smooth conduction

Question 34

What does myelinated nerve fibers produce?

Answer 34

Myelinated nerve fiber produce saltatory conduction with NOR