Nervous coordination-Nerve impulses

Question 1

how is a resting potential maintained?

Answer 1

The membrane is more permeable to K+ ions than Na+ ions
Na+ gated ion channels are closed
There is a higher concentration of Na+ outside the neurone than outside, so Na+ diffuse into the neurone
Higher concentration of K+ inside than outside, K+ diffuse out of the neurone
Na+/K+ pump will actively move 3Na+ ions out for every 2K+ inside
The inside is more negative than the outside

Question 2

What are dendrons?

Answer 2

carry nerve impulses towards the cell body

Question 3

what is the axon?

Answer 3

single long fibre that carries nerve impulses away from the cell body

Question 4

describe the function of Schwann cells

Answer 4

surround the axon by wrapping around many times, protecting and providing electrical insulation

Question 5

what is the myelin sheath

Answer 5

forms covering of axon made up of the membranes of Schwann cells

Question 6

nodes of Ranvier

Answer 6

gaps between adjacent Schwann cells where there is no myelin sheath
gaps are 2-3 micrometers and occur every 1-3 mm
action potential jumps from node to node, this is called saltatory conduction

Question 7

How is an action potential generated? (includes resting potential, generating at AP and what occurs afterwards)

Answer 7

1. resting potential is maintained at -65/-70
2. a stimuli causes some of the Na+ ion channels to open; some Na+ ions diffuse in
3. depolarisation occurs, membrane voltage around -55
4. if stimuli is strong enough, depolarisation reaches the threshold (0), causes MORE Na+ ion channels to open
5. causes influx of Na+, inside becomes more positive than outside
6. AP generated when membrane potential reaches +40
7. after AP is established, the membrane enters the refractory period
8. Na+ voltage-gated ion channels close; causes the K+ channels to open
9. K+ ions diffuse out of membrane; inside becomes more negative
10. As some K+ ions diffuse out, causes more K+ ion channels to open
11. ‘Overshoot’- more K+ diffuse out than needed; inside membrane is more negative than it should be
12. causes K+ ion channels to close, RP is restored by the Na+/K+ pump using ATP
13. axon is repolarised

Question 8

Non- myelinated neurones have a slower rate of conduction than myelinated neurones. explain why

Answer 8

1. waves of depolarisation travel across the entire length of the axon
2. depolarisation only occurs at the nodes of Ranvier in myelinated neurones
3. the impulse jumps from node to node (saltatory conduction)

Question 9

how do waves of depolarisation propagate an action potential along the axon?

Answer 9

Some of the Na+ that diffuse into the neurone causes Na+ channels to open in the next region of the axon
depolarisation occurs

Question 10

what are the factors affecting the speed of an action potential?

Answer 10

1. myelination
2. temperature
3. axon diameter

Question 11

explain how mylination affects the speed of an action potential

Answer 11

1. waves of depolarisation occur along the whole length of the axon
2. depolarisation only occur at the nodes of ranvier
3. impulses jump from node to node

Question 12

how does temperature affect the speed of an action potential

Answer 12

1. speed of an action potential increases as temperarure increases
2. ions diffuse faster
3. he speed only increases until 40C, as the protein channles denature

Question 13

describe the ‘refreactatory period’

hint: 2 points

Answer 13

the time where a second action potential cannot be initiated

result of temporary closer of Na+ channels while resting potential is restored

Question 14

what is the importance of the refractory period?

hint: 4 points

Answer 14

1. allows APs to be propagated in only one direction
2. ensures new APs cannot be generated immediately behind another
3. allows seperation of APs
4. limits the number of APs that can apss along the axon at any one time

Question 15

describe the effect of axon diamater on the speed of an action potential

Answer 15

1. APs are condicted quicker along the axon with larger diameters
2. less resistance to the flow of ions
3. so depolarisation reaches the other arts of the neurone faster

Question 16

explain the importance of the all or nothing principle

Answer 16

stops the brain from being overstimulated by responding to smaller stimuli

Question 17

describe what is meant by the all or nothing principle

Answer 17

1. once the threshold is reached an AP is fired with the same change in voltage
2. if the threshold isnt reached, the action potential isnt fired

Question 18

what are the 3 effects of a neurotransmitter fitting into a receptor?

Answer 18

1. triggering an AP
2. cause a muscle contraction
3. Cause a hormone to be secreted