Electrical activity in the nervous system

Question 1

Define graded potential

Answer 1

A graded potential is proportional to a stimulus. It is a change in electrical potential of a membrane, and the summation of these causes an action potential.

Question 2

Define resting membrane potential

Answer 2

The electrical charge of a membrane at rest, around -70mV

Question 3

Define action potential

Answer 3

A change in electrical activity

Question 4

Define voltage gated channel

Answer 4

A ion channel that is activated if there is a change in electrical activity near it.

Question 5

Define threshold

Answer 5

The electrical charge that needs to be reached if an action potential is to occur. Around -55mV.

Question 6

Define depolarisation

Answer 6

An increase in positive charge of the membrane when the sodium voltage gated channels open, causing an influx of sodium into the axon to increase the charge to +30mV.

Question 7

Define repolarisation

Answer 7

A decrease in charge of the membrane when the sodium voltage gated channels close and the potassium voltage gated channels open.

Question 8

Define hyperpolarisation

Answer 8

An overshoot in charge as a result of the slower movement of potassium out the axon than potassium moves in.

Question 9

Define relative refractory period

Answer 9

The period when the potassium channels are still open when a greater stimulus is required to cause another action potential to occur.

Question 10

Define absolute refractory period

Answer 10

The period after a neurone firing when another action potential cannot be generated, no matter how big the stimulus.

Question 11

Define temporal summation

Answer 11

When a single neurone sends an impulse one after another to reach threshold and cause an action potential

Question 12

Define spatial summation

Answer 12

When many neurones send impulse to reach the threshold and cause an action potential

Question 13

Describe the stages of the propogation of an action potential from the stimulus to the re-uptake pump

Answer 13

1. A resting potential of -70mV is present across the membrane.
2. A stimulus causes a neurotransmitter acetylcholine to bind to the ligand gated channels on the dendrites of the neurone.
3. This causes a sudden influx of sodium ions into the cell body, stimulating local depolarisation and a graded potential.
4. If the threshold is reached (-55mV) then an action potential will occur. This is as a result of summation at the axon hillock.
5. The change in electrical potential around the voltage gated ion channels causes them to open, causing depolarisation in the axon, reaching +30mV.
6. The sodium channels close and the potassium open, causing repolarisation where potassium leaves the axon. This makes the axon charge more negative.
7. There is a slight overshoot, called hyperpolarisation because the rate of potassium diffusion out the cell is slower than that of the sodium.
8. The action potential reaches the axon terminal.
9. Here, this stimulates voltage gated calcium channels to open, causing the synaptic vesicles which contain the neurotransmitter acetylcholine, to move down to the pre-synaptic membrane via exocytosis.
10. The vesicles fuse with the membrane and release the contents into the synaptic cleft. The neurotransmitter binds to receptors on the postsynaptic membrane, causing a post synaptic potential to be conveyed into the next neurone.
11. The acetylcholine is recycled by acetylcholinesterase and moves back into the vesicles.

Question 14

Define synaptic transmission

Answer 14

The process by which communication between two neurones/or an effector at a synapse can occur

Question 15

Define chemical synapse

Answer 15

Communication between two neurones involving a neurotransmitter

Question 16

Define electrical synapse

Answer 16

An electrically conductive link between 2 neurones

Question 17

Define Pre-synaptic facilitation

Answer 17

The action of the pre-synaptic membrane to release more neurotransmitter to move the post-synaptic membrane closer to threshold

Question 18

Define pre-synaptic inhibition

Answer 18

The action of the pre-synaptic membrane to release less neurotransmitter to move the post-synaptic membrane further away from threshold