Action Potential

Question 1

What is extracellular fluid

Answer 1

fluid outside the cell

Question 2

what is intracellular fluid

Answer 2

fluid inside the cell

Question 3

What are afferent signals?

Answer 3

incoming signals from receptors to the brain (sensory to brain)

Question 4

what are efferent signals?

Answer 4

outgoing signals must pass from motor areas to muscle groups (brain to muscles)

Question 5

What is the name for passing of signals among a nerve?

Answer 5

Intra-neuronal information transmission

Question 6

Where is information from other neurons received?

Answer 6

The dendrites

Question 7

What is the name of the cell body?

Answer 7

Soma

Question 8

What is the long ‘tail’ of a neuron called?

Answer 8

Axon

Question 9

What are the gaps called on the axon?

Answer 9

Nodes of Ranvier

Question 10

What are the coverings called on the axon?

Answer 10

Schwann cells (form the myelin sheath)

Question 11

What is the name of the end of the neuron where the message then leaves the neuron?

Answer 11

Axon terminal OR button

Question 12

What do the Nodes of ranvier do?

Answer 12

Allow membrane to contact extracellular fluid

Question 13

What is saltatory conduction?

Answer 13

Allows another action potential to occur at each node of ranvier gap, this repeats the signal at each stage at same intensity so the signal strength remains strong

Question 14

What does the fluid inside and outside the neuron contain?

Answer 14

Electrolytes. These contain positively and negatively charged ions of different chemicals

Question 15

What is the potential?

Answer 15

The difference between the positively and negatively charged ions

Question 16

What chemicals are in the extracellular fluid

Answer 16

Chloride (Cl-)
Sodium (Na+)
Potassium (K+)

Question 17

What chemicals are in the intracellular fluid

Answer 17

Chloride (Cl-)
Sodium (Na+)
Potassium (K+)
Protein (A-) - doesn’t cross membrane

Question 18

Where is there more K+?

Answer 18

intracellular fluid

Question 19

Where are more Na+ and Cl- chemicals located

Answer 19

Outside cell, extracellular fluid. More Na+ outside because of sodium-potassium pump

Question 20

What is the membrane potential?

Answer 20

When the difference between the intracellular fluid and extracellular fluid charge is 70mV.

The inside is negatively charged (-70mV) This stored charge is called the membrane or resting potential.

Footnote: If a positive charge is added across the membrane this is called depolarisation,

Question 21

What are the two forces at play that generate the membrane potential?

Answer 21

Diffusion - the movement of ions from an area of high concentration to an area of low concentration

Electrostatic pressure - opposite charges attract

Question 22

What does the sodium potassium pump do?

Answer 22

Imbalance of Na+ ions wanting to come IN to the cell.
Pumps which is a hole in the membrane wall works to move 3 x Na+ out, and push 2x K+ in.

2 K+ ions move into the cell against diffusion gradient by energetic process of ATP (bodies energy ‘currency’)

3 Na+ ions move outside of cell against diffusion gradient by energetic process of ATP.

Because of this, resting potential (stored charge) of cell is negative (-70mV) which is what we want.

If this didn’t happen, eventually the electrostatic pressure and diffusion would reach balance and there would be no membrane potential

Question 23

What are voltage dependent ion channels?

Answer 23

Channels along membrane wall that open in response to change in membrane potential. Open in response to diffusion and electrostatic charge.

This means the composition of the fluid inside and outside the cell is always changing and the balance of the forces is always changing

Question 24

What are the two voltage dependent ion channels?

Answer 24

Potassium VDI channels
Sodium VDI channels

Work on membrane alonside sodium potassium pumps

Question 25

What are the four stages of an action potential?

Answer 25

1. Resting potential
2. Depolarisation
3. Repolarisation
4. Hyperpolarisation

Each stage is defined by the voltage caused by the movement of ions across the membrane via the VDI channels.

Question 26

What happens if there is a stronger stimuli / input?

Answer 26

Input strength doesn’t change the AP as it is always the same size and duration but a stronger input can lead to more frequent AP release. Increased firing = stronger response

Question 27

What is stage 1: resting potential?

Answer 27

1. neuron is inactive, it is in a state of being ‘ready to fire’ but no stimulus to membrane meaning the stored charge of -70mV remains and this Is called the resting potential

Question 28

What is depolarisation?

Answer 28

Influx of positive charge - membrane potential reaches state of EXCITATION (-55mV). At this threshold;

Na+ VDI channels open…influx of Na+ ions into cell because want to go in because it’s negatively charged and opposites attract, and also there’s less Na+ ions inside so they want to go diffuse across.

Because of this, K+ VDI channels open in response. Outflow of K+ ions from the cell due to diffusion at first (there are less outside so they want to go out), then they go out because the inside is becoming more positive, outside more negative, and because K+ is positive, electrostatic pressure force makes them go out, as the membrane potential becomes positive.

Membrane potential changes from -55mV to +40mV

Question 29

what happens at stage 3, repolarisation?

Answer 29

Na+ channels close, Na+ ions stop going IN to the cell

K+ ions continue to flow out, but fact sodium (+) is not going in, and K+ continues to go out, the membrane potential is going more negative.

K+ channels begin to close slowly at -55mV

Outflow of K+ ions due to diffusion brings the membrane potential back down to -70mV.

Question 30

What happens at stage 4, hyperpolarisation?

Answer 30

K+ channels still closing, allowing K+ ions to continue flowing out of the cell. This brings the inside of the cell more negative and increases the charge difference across the membrane.

The membrane potential falls below the level of the resting potential

Diffusion (and the sodium/potassium pump) then act to return the membrane potential back up to the resting potential (-70mV)

Question 31

What is the refractory period.

Answer 31

Everything after stage 2 depolarisation phase.
A period in which the neuron can’t generate another action potential

It is what makes the hops on the axon (between nodes of ranvier) directional

Question 32

What is the absolute refactory period?

Answer 32

Repolarisation - a new AP is impossible

Question 33

What is the relative refactory period?

Answer 33

Hyperpolarisation - a new AP is possible but would take a very large input of positive charge to get us back to threshold point.

Question 34

Clinical relevence of Action potential. What diseases are caused by issues with AP?

Answer 34

Multiple sclerosis is an autoimmune disease affecting myelination of nerve fibres. Means they are not formed properly and signal transmission via the action potential is impeeded