Resting Potential

Question 1

Receptors?

Answer 1

Some receptors are cells e.g. photoreceptors are receptor cells that connect to the nervous system
Some receptors are proteins on CSM e.g. glucose receptors found on CSM of pancreatic cells

Question 2

What is the resting potential?

Answer 2

The membrane potential is -70mV
The inside of an axon has a charge that is 70mV more negative than the outside
When a neurone is not conducting an impulse, there is a difference between the electrical charge inside and outside of the neurone (resting potential)
More positive ions Na+ and K+ outside compared to inside

Question 3

Establishing a resting potential?

Answer 3

Na+/K+ pump- involves active transport and ATP
Pump moves 2K+ ions in and 3 Na+ ions out
Creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in. Sodium ion channels- inside (high concentration) outside (Low concentration) so K+ ions diffuse out. Na+ ions diffuse in (high concentration outside, low concentration inside)
Cell membrane is more permeable to potassium ions- more K+ ion channels than Na+ ion channels
K+ ion channels are mainly open, but Na+ ion channels only open when you reach a high enough voltage
The Na/K pump returns the membrane to its resting potential and maintains it until the membranes excited by another stimulus

Question 4

What is an action potential?

Answer 4

When the neurones voltage increases beyond a set point from the resting potential -> this generates a nervous impulse

Question 5

What is depolarisation?

Answer 5

An increase in voltage

Question 6

When does depolarisation occur?

Answer 6

When the neurone membrane becomes more permeable to Na+ ions
When there is an increased voltage above the resting potential

Question 7

What is the resting potential?

Answer 7

-70mV

Question 8

What does the stimulus cause?

Answer 8

Enough energy so that the voltage gated sodium ion channels in the axon membrane can open- now we have Na+ ions diffusing into the axon at the same time as the K+ ions diffusing out- slight increase in voltage (start of depolarisation)

Question 9

What is the threshold?

Answer 9

-55mV
Provides more energy for gated Na+ ion channels to open- more Na+ ions diffusing in but the same amount of K+ ions diffusing out
Sharp increase in voltage (depolarisation)

Question 10

What happens when it peaks at 40mV?

Answer 10

The gated Na+ ion channels close when 40mV is reached inside the axon

Question 11

What happens at 40mV with the K+ ion channels?

Answer 11

The K+ ion channels open- 2x the amount of K+ ions diffusing out- causing a decrease in voltage
Continue to happen until you get overshoot
Refractory period- reach -80mV- hyperpolarisation

Question 12

All or nothing principle?

Answer 12

if the depolarisation does not exceed -55mV, an action potential and the impulse are not produced (nothing)
If the stimulus is not large enough to open enough sodium ion channels to go above -55mV- there is no action potential

Question 13

Can the size of action potentials change?

Answer 13

No- only the frequency
Any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage
Bigger stimuli increases the frequency of action potentials- not the size

Question 14

Why is the size of action potentials not being able to change important?

Answer 14

Important as it makes sure that animals only respond to large enough stimuli, rather than responding to every slight change in the environment, which would overwhelm them

Question 15

What is the refractory period?

Answer 15

-80mV
After an action potential has been generated, the membrane enters a refractory period when it cant be stimulated because Na+ channels are recovering and cant be opened

Question 16

Why is the refractory period important?

Answer 16

1) discrete impulses can be produced- meaning that each action potential can’t be generated immediately after one another
2) ensures that action potentials travel in one direction- stops the action potentials from spreading in 2 directions, which would prevent a response
3) limits the number of impulse transmissions- prevents over reaction to a stimulus and therefore overwhelming the senses