nerve impulse

Question 1

what is a nerve impulse

Answer 1

self propagating wave of electrical activity which travel along an axon membrane as a response of a stimulus

Question 2

what are the characteristics of the membrane in resting potential

Answer 2

the outside is relatively positive compared to the inside of the membrane at around -70 mv

Question 3

how is this negativity achieved

Answer 3

they are maintained by the sodium potassium pump

Question 4

why cant they travel throgh the other parts of the membrane

Answer 4

the phospholipid membrane is non polar so dont allow ions to pass through

Question 5

how is the sodium potassium pump used

Answer 5

through active transport 3 sodium ions are actively transported whilst 2 potassium ions are actively pumped into the membrane

Question 6

what also occurs with potasium

Answer 6

the pottasium ion channels open which allows pottasium ion to leave the membrane via facilitated diffusion further increasing the negativity

Question 7

how are the ion channels operated

Answer 7

they are voltage gated and can only operate as a result of a stimulus

Question 8

what is nerve stimulation

Answer 8

neurons are stimulated by receptor cells

Question 9

what happens when there is a stimulus

Answer 9

it excites the neuron cell membrane which casue the na ion channel to open which causes facillitated diffusion of na ions

Question 10

what is this called

Answer 10

depolarisation

Question 11

what continue to happens

Answer 11

positive feedback the na ions diffuse across the axon membrane exciting more sections of the reigion which cause the ion channels to open so the membrane become less negative

Question 12

what does the membrane potential reach

Answer 12

rises sharply until 40mv

Question 13

what happens at 40mv

Answer 13

repolarisation

Question 14

what is repolarisation the

Answer 14

the na ions shut and the potassium ions channel open

Question 15

what does the opening of the potasium cause

Answer 15

the potassium ions to facillatedly diffuse out of the mebrane become more negative

Question 16

what happens then

Answer 16

hyperpolarisation

Question 17

why does hyper polarisation occur

Answer 17

because the potassium ions take a long time to close

Question 18

what does this make the membrane and how

Answer 18

too negative because of the overshoot of potassium ions leaving the membrane

Question 19

how is the membrane reset

Answer 19

using the sodium and potssium pump

Question 20

when does the refractory period happen

Answer 20

after the action potential

Question 21

what happens

Answer 21

as the na and ka concentration are being restored no action potentials can be fired

Question 22

why can no action potential be fired

Answer 22

as all the na ions channels are inactive

Question 23

what happens to the cell

Answer 23

it recovers

Question 24

what does it do to the action potential

Answer 24

it ensures they are seperated , and are only sent in one direction

Question 25

when only does action potential occur

Answer 25

when the membrane depolarises and reaches a threashold

Question 26

what is this principle called

Answer 26

the all or nothing principle

Question 27

what do all action potential have

Answer 27

the same size

Question 28

so how is strength of stimulus detected

Answer 28

the amount of action potential at a given time a stronger stimulus will result in more action potential

Question 29

what do different neurones have

Answer 29

different threashold values