13.4 Nervous transmission

Question 1

what is the resting potential?

Answer 1

the potential when no impulse is being transmitted

-70 mV

Question 2

what is the charged composition of a membrane under resting potential?

Answer 2

outside of the axoplasm is MORE positively charged than the inside of the axoplasm which makes the membrane polarised

Question 3

how is a resting potential generated?

Answer 3

Na+ ions are pumped out of the axoplasm
K+ ions are pumped into the axoplasm

Na+ voltage gated channels are closed so Na+ ions cannot diffuse back into the axoplasm

K+ voltage gated channels are opened at resting potential so many K+ ions diffuse out of the axoplasm

means that there are more positive ions outside the axoplasm than inside

therefore the membrane is polarised

Question 4

how many Na+ ions are pumped OUT?

Answer 4

3

Question 5

how many K+ ions are pumped IN?

Answer 5

2

Question 6

how are Na+ and K+ ions pumped in or out?

Answer 6

using a Na/K pump

Question 7

what are the intrinsic proteins which exist in the axon membrane?

Answer 7

Na+ voltage gated channel
K+ voltage gated channel
K+ channel (leaky channel)
Na/K pump

Question 8

what is the order of events in generating action potential?

Answer 8

1. resting potential
2. start of depolarisation
3. depolarisation
4. end of depolarisation and start of repolarisation
5. repolarisation
6. hyperpolarisation
7. resting potential

Question 9

what happens between -70mV and -55mV?

Answer 9

stimulus arrives as an electrical impulse which causes Na+ voltage gated channels to open

Na+ ions diffuse INTO the axoplasm down the electrochemical gradient

makes the membrane less polarised

Question 10

what happens between -55mV and +40mV?

Answer 10

DEPOLARISATION

change in polarisation causes more Na+ voltage gated channels open

this allows more Na+ ions to move INTO the axoplasm down the electrochemical gradient
this causes an increase in the potential difference

Question 11

what happens between +40mV and -70mV?

Answer 11

REPOLARISATION

the Na+ voltage gated channels close which stops Na+ ions diffusing into the axoplasm

the K+ voltage gated channels open which allows K+ ions to diffuse OUT of the axoplasm which causes a decrease in the potential difference

Question 12

what happens between -70mV and -90mV?

Answer 12

HYPERPOLARISATION

the K+ channels are still open so more K+ ions move OUT of the axoplasm

potential difference continues to decrease as axoplasm becomes more negative

Question 13

what happens between -90mV and -70mV?

Answer 13

K+ voltage gated channels are closed

the Na/K pump pumps OUT Na+ ions into the tissue fluid and K+ ions INTO the axoplasm

resting potential is restored

Question 14

what is the refractory period?

Answer 14

a short period of time when the axon cannot be excited again. the Na+ gated channels are CLOSED which prevents Na+ ions entering the axoplasm meaning an action potential cannot be generated

Question 15

what does a refractory ensure?

Answer 15

that action potentials don’t overlap and instead pass as discrete impulses

ensures action potentials as unidirectional

Question 16

what is saltatory conduction?

Answer 16

when an electrical impulse jumps between nodes which makes impulse transmission faster and easier

Question 17

why does having a myelinated neurone allow for saltatory conduction?

Answer 17

myelinated axons mean there are less places for voltage gated channels to be kept open as only the nodes of Ranvier are exposed to the tissue fluid

Question 18

why does a non-myelinated neurone transmit impulses slower?

Answer 18

no nodes of ranvier so action potentials need to be generated along the whole axon

makes transmission slower

Question 19

what factors affect the speed of action potential movement?

Answer 19

• myelination
• axon diameter
• temperature

Question 20

how does myelination affect the speed of action potential movement?

Answer 20

myelinated neurones allow for saltatory conduction which is faster than in conduction in non-myelinated neurones

Question 21

how does the axon diameter affect the speed of action potential movement?

Answer 21

bigger the axon diameter, the faster the impulse is transmitted as there is less resistance to the flow of ions

Question 22

how does the temperature affect the speed of action potential movement?

Answer 22

higher the temp, the faster the nerve impulse due to the kinetic theory. however, once temp has passes optimum, proteins such as the Na/K pump denature which stops the generation of resting potential

Question 23

what is the all or nothing principle?

Answer 23

a stimulus needs to exceed a threshold value otherwise no response is triggered

Question 24

what happens with a larger stimulus?

Answer 24

the larger the stimulus the more frequently action potentials are generated

Question 25

when an action potential is generated when is the Na/K pump active?

Answer 25

ALL THE TIME

Question 26

why may depolarisation and repolarisation be faster in certain neurones?

Answer 26

presence of more Na+ and K+ voltage gated channels

steeper Na+ gradient

steeper K+ gradient