The nerve impulse

Question 1

What is a nerve impulse?

Answer 1

A self-propagating wave of depolarisation that travels along the surface of the axon membrane

It is a temporary reversal of the electrical potential difference across the axon membrane.

Question 2

What are the two states of electrical potential difference in a nerve impulse?

Answer 2

Resting potential and action potential

These states represent the electrical charge differences across the axon membrane.

Question 3

What prevents sodium and potassium ions from diffusing across the axon membrane?

Answer 3

The phospholipid bilayer of the axon plasma membrane

This bilayer is selectively permeable to ions.

Question 4

What are intrinsic proteins?

Answer 4

Proteins that span the phospholipid bilayer of the axon membrane

They contain channels called ion channels for ion movement.

Question 5

What are ion channels?

Answer 5

Channels within intrinsic proteins that allow ions to move through the axon membrane

Some channels have gates that can open or close.

Question 6

What is the function of the sodium-potassium pump?

Answer 6

To actively transport potassium ions into the axon and sodium ions out of the axon

It helps maintain the resting potential of the axon.

Question 7

What is the resting potential of an axon typically around?

Answer 7

-65 mV

The resting potential can range from -50 to -90 mV.

Question 8

What does it mean for an axon to be polarized?

Answer 8

The inside of the axon is negatively charged relative to the outside

This is due to the distribution of ions across the membrane.

Question 9

How many sodium ions are moved out of the axon for every two potassium ions moved in by the sodium-potassium pump?

Answer 9

Three sodium ions

This unequal movement contributes to the resting potential.

Question 10

What creates a chemical gradient in the axon?

Answer 10

The difference in concentration of sodium and potassium ions inside and outside the axon

More sodium ions are in the tissue fluid, and more potassium ions are in the cytoplasm.

Question 11

What happens to sodium and potassium ions during the resting potential?

Answer 11

Sodium ions begin to diffuse back into the axon and potassium ions begin to diffuse out

However, most gates for sodium are closed while those for potassium are open.

Question 12

Fill in the blank: The sodium-potassium pump transports sodium ions ______ and potassium ions ______.

Answer 12

out of the axon; into the axon

This action is crucial for maintaining the resting potential.

Question 13

What happens to the axon membrane’s permeability to potassium ions?

Answer 13

The axon membrane is 100 times more permeable to potassium ions.

Question 14

What is the result of potassium ions diffusing out of the axon?

Answer 14

It increases the potential difference between the negative inside and the positive outside of the axon.

Question 15

What types of gradients affect the movement of potassium and sodium ions?

Answer 15

Chemical gradient and electrical gradient.

Question 16

What happens to the outside of the axon as potassium ions diffuse out?

Answer 16

The outside of the axon becomes more positive.

Question 17

What prevents further outward movement of potassium ions?

Answer 17

Attraction to the negative inside and repulsion from the positive surrounding tissue fluid.

Question 18

What is established when the chemical and electrical gradients are balanced?

Answer 18

An equilibrium with no net movement of ions.

Question 19

Fill in the blank: The axon membrane is _______ more permeable to potassium ions.

Answer 19

100 times

Question 20

True or False: The electrical gradient works against the movement of potassium ions out of the axon.

Answer 20

True

Question 21

What is an action potential?

Answer 21

A temporary reversal of the charges on the axon membrane, resulting in a positive charge of around +40 mV

The action potential is a key process in neuronal signaling.

Question 22

What is the resting membrane potential inside the axon before depolarization?

Answer 22

-65 mV

This is the typical charge inside a resting axon.

Question 23

What happens to the membrane during depolarization?

Answer 23

The membrane becomes depolarised, with a charge change to around +40 mV

Depolarisation is essential for the propagation of action potentials.

Question 24

What causes the depolarization of the axon membrane?

Answer 24

The opening or closing of voltage-gated channels due to changes in membrane voltage

These channels respond to the electrical state of the membrane.

Question 25

What are voltage-gated channels?

Answer 25

Channels that change shape and open or close depending on the voltage across the membrane ## Footnote They play a crucial role in the generation of action potentials.

Question 26

Fill in the blank: The negative charge of -65 mV inside the membrane becomes a positive charge of around _______.

Answer 26

+40 mV ## Footnote This change is a defining feature of an action potential.

Question 27

True or False: Depolarization of the axon membrane leads to a negative charge.

Answer 27

False ## Footnote Depolarization results in a positive charge inside the membrane.

Question 28

What initiates the action potential in a neuron?

Answer 28

A stimulus received by a receptor or nerve ending ## Footnote The energy from the stimulus is essential for triggering the action potential.

Question 29

What channels are open at resting potential?

Answer 29

Some potassium voltage-gated channels (permanently open) are open, while sodium voltage-gated channels are closed.

Question 30

What triggers the opening of sodium voltage-gated channels?

Answer 30

The energy of the stimulus causes some sodium voltage-gated channels in the axon membrane to open.

Question 31

What happens when sodium ions diffuse into the axon?

Answer 31

They trigger a reversal in the potential difference across the membrane.

Question 32

What effect does the initial influx of sodium ions have on sodium channels?

Answer 32

It causes more sodium channels to open, leading to an even greater influx of sodium ions by diffusion.

Question 33

What is the approximate action potential value established during the process?

Answer 33

+40 mV.

Question 34

What happens to the sodium ion channels once the action potential is established?

Answer 34

The voltage gates on the sodium ion channels close, preventing further influx of sodium ions.

Question 35

What occurs after the sodium channels close during action potential?

Answer 35

The voltage gates on the potassium ion channels begin to open.

Question 36

What happens to potassium ions when the potassium voltage-gated channels open?

Answer 36

More potassium ions diffuse out, causing repolarisation of the axon.

Question 37

What is hyperpolarisation in the context of action potential?

Answer 37

The inside of the axon becomes more negative relative to the outside due to the outward diffusion of potassium ions.

Question 38

What restores the resting potential after hyperpolarisation?

Answer 38

The gates on the potassium ion channels close, and sodium-potassium pumps restore sodium ions out and potassium ions in.

Question 39

What is the resting potential value re-established after repolarisation?

Answer 39

-65 mV.

Question 40

Fill in the blank: The process of returning to resting potential after an action potential is called _______.

Answer 40

repolarisation.

Question 41

True or False: At resting potential, sodium voltage-gated channels are open.

Answer 41

False.