lecture 7 - local potentials & action potentials

Question 1

What are local potentials?

Answer 1

Graded local changes in membrane potentials caused by the opening/closing of ion channels

Question 2

What causes local potentials?

Answer 2

External stimulus causes the opening/opening of ion channels

Question 3

What are the 2 types of local potentials?

Answer 3

Excitatory, Inhibitory

Question 4

What is an excitatory local potential?

Answer 4

Local change in membrane potential that leads to active, regenerative responses in the membrane

Question 5

What is inhibitory local potential?

Answer 5

One which leads to reduced responses or decreased neuronal activity by repolarising the membrane

Question 6

Why are local potentials considered graded?

Answer 6

Because stimuli can generate different sized changes in local potential - the large the stimulus the more channels open and the greater the depolarisation

Question 7

How does the degree of depolarisation of a local potential change with distance from the origin?

Answer 7

Decrease in depolarisation due to outward leak of negative charge

Question 8

Why do graded potentials outlast the stimulus?

Answer 8

The spread passively with a delayed rise and fall with the opening of ion channels

Question 9

What feature of graded potentials allows for input integration?

Answer 9

Temporal and spatial summation

Question 10

Why are graded potentials not good for carrying information long distances?

Answer 10

They get smaller as they spread and cannot regenerate

Question 11

What do ion pumps maintain in a neuron?

Answer 11

Electrochemical gradients

Question 12

At a neuron, what are inputs processed as?

Answer 12

Graded potentials

Question 13

At a neuron, what are signals transmitted as?

Answer 13

Action potentials

Question 14

Where are action potentials generated?

Answer 14

Axon hillock

Question 15

What is the difference from resting membrane potential that must be reached for threshold for an action potential?

Answer 15

approx. 10mV above resting membrane potential (~-60mV)

Question 16

What channels are involved in action potential generation and propogation?

Answer 16

Voltage gated Na+ channels, K+ channels

Question 17

What happens when the axon hillock reaches threshold?

Answer 17

Opening of voltage gated Na+ channels leading to a rapid depolarisation

Question 18

What channels are responsible for the repolarisation after an action potential?

Answer 18

K+ channels

Question 19

What is the name for the period in which it is impossible for another action potential to occur?

Answer 19

Absolute refractory period

Question 20

What is an absolute refractory period?

Answer 20

A period when the axon is repolarising where it is impossible for an action potential to occur

Question 21

What is a relative refractory period?

Answer 21

Period when another action potenial can occur, but only with a greater depolarisation - threshold is greater

Question 22

Why does the membrane hyperpolarise during the repolarisation stage of an action potential?

Answer 22

K+ channels are open and Na+ channels are inactivated so the membrane becomes more permeable to K+ and the membrane potential becomes more negative