5.1 Nervous transmission & potentials

Question 1

what is potential difference? what is it measured in?

Answer 1

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

Question 2

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

Answer 2

resting potential

-70mv

Question 3

in resting state what is the membrane said to be?

Answer 3

polarized

Question 4

when does an action potential occur?

Answer 4

when the p.d across an axon is temporarily reversed

Question 5

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

Answer 5

+40mv

depolarized

Question 6

when is the axon in resting potential?

Answer 6

when no impulse is present

Question 7

when is there an action potential?

Answer 7

when an impulse is being transmitted

Question 8

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

Answer 8

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

Question 9

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

Answer 9

some voltage gated sodium ion channels to open

membrane more permeable to sodium ions

Question 10

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

Answer 10

an electrochemical gradient

make inside axon less negative

Question 11

3. as some channels open sodium diffuses in causing a change in charge, what does this do?

Answer 11

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

Question 12

4. When the p.d reached +40mv what happens to the channels?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

HYPERPOLARISATION

Question 15

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

Answer 15

3 sodium ions out
2 potassium in
returns to resting potential

Question 16

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

Answer 16

the threshold value

Question 17

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

Answer 17

insufficient numbers of sodium channels open

Question 18

what does insufficient numbers of open sodium channels prevent?

Answer 18

full depolarisation of the axon

Question 19

once the threshold value is reached what is generated?

Answer 19

the action potential

Question 20

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

Answer 20

the same size

Question 21

what does the size of the stimuli affect?

Answer 21

the number of action potentials generated in a given time.

Larger stimulus = more frequently action potentials are generated

Question 22

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

Answer 22

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

Question 23

what is repolarisation?

Answer 23

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

Question 24

what does hyperpolarisation involve?

Answer 24

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

Question 25

what is the refractory period?

Answer 25

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

Question 26

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

Answer 26

action potential could be initiated backwards

action potentials could overlap

Question 27

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

Answer 27

an action potential to be generated

Question 28

2. when does an absolute refractory period occur? what can not happen?

Answer 28

after an action potential has been generated.

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

Question 29

3. when can an action potential be generated?

Answer 29

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

Question 30

4. what is the normal resting state?

Answer 30

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

Question 31

what does the myelinated sheath do?

Answer 31

insulates the axon making the action potential move faster

Question 32

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

Answer 32

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

Question 33

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

Answer 33

saltatory conduction

Question 34

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

Answer 34

the greater the diameter of the axon the faster the impulse

Question 35

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

Answer 35

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

Question 36

how does temperature affect the speed of an impulse?

Answer 36

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