How are nerve impulses generated and transmitted?

Question 1

What is the first step in a nerve impulse being generated?

Answer 1

Resting potential is achieved by:
-Na+/K+ pumps pump 3 Na+ out and 2 K+ in
-Some K+ diffuses out via non-gated K+ channels
-More anions on inside

Question 2

What is the second step in a nerve impulse being generated?

Answer 2

When a stimulus is applied, non-voltage gates Na+ channels open and Na+ starts to enter neuron so it becomes more positive/less negative on inside

Question 3

What is the third step in a nerve impulse being generated?

Answer 3

If enough Na+ for threshold potential of -55mV is reached, the voltage gated Na+ channels open and a large influx of Na+ so becomes more positive on inside

Question 4

What is this step also called and what is it part of?

Answer 4

Depolarisation and part of all or none law

Question 5

What is the fourth step in a nerve impulse being generated?

Answer 5

At +40mV the voltage gated Na+ channels close and the voltage gated K+ channels open so K+ diffuses out of neuron (facilitated) so it becomes negative again on inside (-70mV)

Question 6

What is the fifth step in a nerve impulse being generated?

Answer 6

The voltage gated K+ channels are slow to close so too much K+ leaves and it becomes more negative than -70 mV on inside

Question 7

What is the fifth step known as?

Answer 7

Hyper-polarisation

Question 8

What is the sixth step in a nerve impulse being generated?

Answer 8

Now most Na+ is on inside and most K+ is on outside so are wrong way around therefore Na+/K+ pumps start to pump the Na+ back out (3) and K+ back in (2) so back to resting potential

Question 9

What is the refractory period?

Answer 9

During last step, another action potential can’t happen

Question 10

What is the generator region?

Answer 10

Where the action potential is generated/initiated

Question 11

What is the first step of a nerve impulse being transmitted in a non-myleinated neuron?

Answer 11

Depolarisation occurs at generator region so Na+ enters

Question 12

What is the second step of a nerve impulse being transmitted in a non-myleinated neuron?

Answer 12

Na+ diffuses to ‘next part’ of neuron
-Diffusion is known as the local current

Question 13

What is the third step of a nerve impulse being transmitted in a non-myleinated neuron?

Answer 13

Means it becomes -55mV in ‘next part’ meaning voltage gated Na+ channels open meaning full depolarisation happens here

Question 14

Movement of transmission of action potential non-myleinated

Answer 14

Is repeated all along neuron so is like a mexican wave

Question 15

What is the first step of a nerve impulse being transmitted in a myleinated neuron?

Answer 15

Depolarisation occurs at generator region meaning Na+ enters

Question 16

What is the second step of a nerve impulse being transmitted in a myleinated neuron?

Answer 16

Na+ diffuses but nothing can happen until it reaches next node of Ranvier meaning there is a longer local current

Question 17

What is the third step of a nerve impulse being transmitted in a myleinated neuron?

Answer 17

When Na+ reaches node of Ranvier, it means voltage gated channels open creating depolarisation at node of Ranvier

Question 18

Movement of transmission of action potential myleinated

Answer 18

Action potential appears to jump node to node speeding up transmission

Question 19

What is the jumping node to node called?

Answer 19

Saltatory conduction

Question 20

How are action potential’s spread?

Answer 20

By positive feedback as if increased Na+ on inside there is more voltage-gated Na+ channel so even more Na+ on inside

Question 21

Which direction do action potentials move in and why?

Answer 21

Always go forwards so this is the only direction that Na+ can move in