Unit 1.4d (i)

Question 1

What is a nerve impulse?

Answer 1

It’s a signal that’s transmitted along a nerve fibre

Question 2

What speed do nerve impulses travel at?

Answer 2

120 m/s

Question 3

What is membrane potential?

Answer 3

It’s the mixture of + and - ions and molecules in and outside of the cell creating a charge across its membrane

Question 4

What is the membrane charge referred to as?

Answer 4

Voltage

Question 5

What’s the resting membrane potential?

Answer 5

It’s when there’s no net flow of ions across the membrane apart from the 3Na+ out, 2K+ in (it’s normal state)

Question 6

What allows K+ ions to leak out of the cell?

Answer 6

Potassium channels inside the neurons membrane

Question 7

When K+ ions leak out of cell what happens to the charge?

Answer 7

The outside of the cell develops a positive charge

Question 8

How are nerve impulses transmitted?

Answer 8

A change in the neurons membrane potential

Question 9

What is depolarisation?

Answer 9

The reduction of the negative charge within the cell

Question 10

What is the determining factor as to whether a nerve impulse will occur?

Answer 10

When there is a wave of depolarisation from the original resting membrane potential

Question 11

What happens if the drop in charge reaches -55mV?

Answer 11

The nerve signal is carried along the axon

Question 12

What is action potential?

Answer 12

The temporary reversal of the membrane potential (the inside become positive then returns to resting membrane potential)

Question 13

Why would happen if -55mV was not reached?

Answer 13

There no action potential, so no nerve signal

Question 14

What happens to the membrane when it returns to resting membrane potential?

Answer 14

The membrane is repolarised

Question 15

What triggers depolarisation?

Answer 15

Neurotransmitter

Question 16

What are neurotransmitters?

Answer 16

Chemicals that transmit signals across synapses

Question 17

What’s a synapse

Answer 17

Gap between 2 neurons

Question 18

How do neurotransmitters initiate responses in the next neuron?

Answer 18

They bind to transmembrane receptor proteins found on the surface of the neuron in the synapse

Question 19

What type of receptor are those that are found on the surface of the neuron that neurotransmitters bind to?

Answer 19

Ligand-gated ion channels

Question 20

When do the ligand-gated ion channels open?

Answer 20

When a neurotransmitter binds to it

Question 21

How does the ligand-ion channel opening cause the initial depolarisation of the membrane?

Answer 21

Because Na+ ion can now enter into the cell

Question 22

Do Na+ ions entering the cell move up or down the electrochemical gradient?

Answer 22

Down

Question 23

What happens as more Na+ ions move into the cell?

Answer 23

More voltage-gated ions begin to open until action potential is reached.

Question 24

Which order do these 4 steps - that represent how a change in charge causes more channels to open along the axon towards the next neuron - go in?

Answer 24

1. Depolarisation moves along axon
2. Voltage gated channels along axon open
3. An area depolarises
4. Behind action potential the axon membrane is repolarised

Question 25

Why is resting membrane potential reestablished after the wave of depolarisation?

Answer 25

In preparation for the next nerve impulse

Question 26

Why do the voltage-gated Na+ ion channels close?

Answer 26

When the voltage reaches a critically high level

Question 27

What opens when the voltage gated Na+ channels close?

Answer 27

The voltage gated K+ ion channels

Question 28

Where do the K+ ions go when there voltage gated channels open?

Answer 28

The K+ ions move out of the cell to restore the resting membrane potential

Question 29

What happens to all the channels when the resting membrane potential is restored?

Answer 29

The K+ channels close close and the Na+ channels return to their original configurations

Question 29

What does the Na+/K+ do?

Answer 29

Continues its normal operation to restore and reset the ion gradient

Question 30

Once the action potential reaches the end of the neuron what happens?

Answer 30

A vesicle don’t neurotransmitters fuses with the membrane

Question 31

Once fused with the membrane what does the vesicle containing the neurotransmitter do?

Answer 31

It releases the neurotransmitter into the synapse and it diffuses across to the target cell

Question 32

What triggers the wave of depolarisation in the next neuron?

Answer 32

The neurotransmitter diffusing to the target cell