CTR - 7 - AP

Question 1

What is depolarisation?

Answer 1

A decrease in potential difference between the inside and outside of the cell. (inside less negative than RMP)

Question 2

What is hyperpolarisation?

Answer 2

An increase in potential difference between the inside and outside of the cell. (inside more negative than RMP)

Question 3

What is repolarisation?

Answer 3

Return to RMP from either direction

Question 4

What is overshoot

Answer 4

When the inside of the cell becomes positive due to reversal of membrane potential polarity

Question 5

What is this? A decrease in potential difference between the inside and outside of the cell.

Answer 5

Depolarisation

Question 6

What is this? An increase in potential difference between the inside and outside of the cell.

Answer 6

Hyperpolarisation

Question 7

What is this? Return to RMP from either direction

Answer 7

Repolarisation

Question 8

What is this? When the inside of the cell becomes positive due to reversal of membrane potential polarity

Answer 8

Overshoot

Question 9

What cells are excitable cells?

Answer 9

Muscle and nerve cells

Question 10

What are excitable cells?

Answer 10

Allow an action potential to propagate along it

Question 11

What are the two ways a change in membrane potential can be achieved?

Answer 11

1 - altered membrane ion permeability

2 - anything that alters ion concentrations on either side

Question 12

What are the two types of potentials?

Answer 12

Graded potentials (sub threshold potentials)

Action potentials

Question 13

How is a GP/AP generated (in broad terms)?

Answer 13

Increase in Na+ permeability –> sodium moves into cell –> if this reaches the threshold potential –> depolarise the cell

Question 14

A _________ stimuli causes _________ potentials.

Answer 14

subthreshold stimuli –> sub threshold/graded potentials

suprathreshold stimuli –> APs

Question 15

What is the threshold which must be reached?

Answer 15

-50 mV

Question 16

The strength of a GP is proportional to the ________.

Answer 16

strength of the stimulus

Question 17

The_________ is proportional to the stimulus strength.

Answer 17

GP strength

Question 18

What happens to GP strength? Why?

Answer 18

Loses strength moving through the cell

Due to leakage of charge across membrane

Question 19

What happens to GP strength in dendrites?

Answer 19

As there are NO voltage gated channels –> current leaks –> decreases GP strength

Question 20

Do dendrites have voltage gated channels? Consequence of this?

Answer 20

NO! Current leaks –> decreases GP strength

Question 21

The GP must _____________ at the trigger zone!

Answer 21

be above threshold (-50 mV)

Question 22

What is another name for the trigger zone?

Answer 22

Axon hillock

Question 23

What does a suprathreshold GP do at the trigger zone?

Answer 23

Triggers an AP

Question 24

What does a subthreshold GP do at the trigger zone?

Answer 24

Does not trigger an AP

Question 25

Do subthrehsold stimuli result in APs?

Answer 25

No (subhreshold stimulus --> sub threshold GP --> no AP)

Question 26

Do suprathrehsold stimuli result in APs?

Answer 26

Yes (supra threshold stimulus --> suprathreshold GP --> AP)

Question 27

What happens to the strength of a supra threshold GP in the ______?

Answer 27

Dendrite. It decreases, but not enough to fall below threshold (-50mV) --> AP!

Question 28

What happens to the strength of a subthreshold GP in the ______?

Answer 28

Dendrite. It decreases, below threshold (-50mV) --> no AP!

Question 29

The movement of K+ out of a cell results in

Answer 29

hyperpolarisation

Question 30

The movement of Na+ into a cell results in

Answer 30

depolarisation

Question 31

Chemically-Gated channels are also known as ______.

Answer 31

receptor-mediated

Question 32

Voltage-gated channels are also known as _________.

Answer 32

Electrically stimulated

Question 33

Duration of AP

Answer 33

4 milliseconds

Question 34

What are the three states of the sodium channel? What happens to the gates?

Answer 34

Resting - activation gate closed Activated - activation gate open Inactivated - inactivation gate closed

Question 35

What is the function of the absolute refractory period? Why does it exist?

Answer 35

Gates on Na+ channel have not reset Assures one way propagation - so that the AP reaches the effector organ

Question 36

Refractory periods limit ____________.

Answer 36

the rate of propagation

Question 37

How do APs code behaviour

Answer 37

frequency

Question 38

How does increased stimulus frequency affect APs?

Answer 38

Increased frequency (not size!)

Question 39

What is the structural difference between the axon and dendrite

Answer 39

Axon has voltage gated sodium channels Dendrite does not

Question 40

What factors affect the rate of propagation?

Answer 40

Diameter of axon - smaller diameter (greater resistance --> slower speed) - larger diameter (less resistance --> higher speed) Degree of myelination - presence of myelin sheath (acts as an insulator --> prevents charge from leaking from axon)

Question 41

What is the difference between continuous conduction and saltatory conduction. How much faster is one of these?

Answer 41

Continous = non-myelinated axons - channels are immediately adjacent - to ensure voltage does not decay - must regenerated AP at every voltage gated ion channels - SLOW Saltatory conduction = myelinated axons (acts as insulator) -channels separated by myelin sheaths (channels in nodes of ranvier) -APs only generated in nodes of ranvier (decreased number of regeneration points) FAST

Question 42

What are the two types of conduction?

Answer 42

Saltatory (fast) and continuous (slow)

Question 43

What is multiple sclerosis caused by? What cells does it affect?

Answer 43

Demyelination of nerves in CNS (not PNS) due to auto-immune disease Affects oligodendrocytes

Question 44

What are some symptoms of MS?

Answer 44

muscle, weakness, fatigue, difficulty walking, loss of vision

Question 45

How is MS treated?

Answer 45

Anti-inflammatory drugs (prevent immune cells destroying myelin)

Question 46

How do local anaesthetics works?

Answer 46

Blocking voltage gated Na+ channels (no Na+ entry) --> no AP.