Section 6: Chapter 15: Nervous Coordination and Muscles

Question 1

What are 5 key features of the hormonal / endocrine system?

Answer 1

• Communication via chemicals called hormones.
• Transmission via blood flow.
• Slow.
• Widespread response.
• Long-lasting.

Question 2

What are 5 key features of the nervous system?

Answer 2

• Communication via nerve impulses.
• Transmission by neurones.
• Fast.
• Localised response.
• Short-lived / temporary.

Question 3

What is the role of a neurone?

Answer 3

To carry nerve impulses around the body.

Question 4

What is the main difference between the structure of a motor and sensory neurone?

Answer 4

Motor neurone has a cell body on the end of it’s axon, sensory neurone’s cell body is in the middle of the axon.

Question 5

What are Schwann cells? (in neurones)

Answer 5

• Surrounds the axon.
• Provides electrical insulation.
• Involved in nerve regeneration.

Question 6

What is the myelin sheath? (in neurones)

Answer 6

• Covers axon.
• Rich in the lipid myelin.
• Increases speed on action potential.

Question 7

What is the node of Ranvier? (in neurones)

Answer 7

• Gaps between myelin sheath.

- Increases speed of action potential.

Question 8

What are dendrons and dendrites? (in neurones)

Answer 8

Small branches that carry nerve impulses to the body.

Question 9

What is a resting potential?

Answer 9

• Charge of a resting axon. -70mV because more positive ions are actively transported out than in (3 NA+ out, 3 K+ in).

Question 10

What is the charge of a resting potential?

Answer 10

-70mV.

Question 11

Why is a resting potential negative?

Answer 11

More positive ions actively transported out than in.

3 Na+ out, 3 K+ in.

Question 12

How are the movements of ions across an axon membrane controlled?

Answer 12

1) Phospholipid bilayer - NA+ and K+ ions can’t diffuse across.
2) Channel proteins - some always open, some have gates (eg/ voltage).
3) Sodium-potassium pump - active transport.

Question 13

Where do sodium ions go when they are actively transported out of an axon?

Answer 13

Surrounded tissue fluid.

Question 14

During a resting potential, is an axon polarised or depolarised?

Answer 14

Polarised.

Question 15

What causes an action potential?

Answer 15

Stimulus detected by a receptor, causing a temporary reversal of charge.

Question 16

What is the charge of an action potential?

Answer 16

+40mV.

Question 17

During an action potential, is an axon polarised or depolarised?

Answer 17

Depolarised.

Question 18

Draw out the graph of an action potential?

Answer 18

https://www.moleculardevices.com/applications/patch-clamp-electrophysiology/what-action-potential#gref

Question 19

Label a graph of an action potential with 6 key words.

Answer 19

Polarised.
Threshold.
Depolarised.
Repolarised.
Hyperpolarised.
Resting potential.

Question 20

Describe the process of an action potential.

Answer 20

1) Resting potential -70mV.
2) Once impulse reaches threshold, some Na+ VG channels open. Na+ move in down chemiosmotic gradient.
3) Na+ enters until action potential / depolarisation has happened (+40mV).
4) Na+ VG channels shut. K+ VG channels open - K+ leave down chemiosmotic gradient.
5) Repolarisation - K+ leaving.
6) Hyperpolarisation - more negative than resting potential.
7) Resting potential reestablished using Na+/K+ pump and leak channels.

Question 21

Does an action potential travel faster in a myelinated to an unmylinated axon? why?

Answer 21

Myelinated because action potential jumps along nodes of Ranvier (saltatory conduction).

Question 22

What is saltatory conduction? (action potential)

Answer 22

Action potential can jump along nodes of Ranvier in a myelinated axon. Faster.

Question 23

What 3 factors affect the speed of an action potential?

Answer 23

1) Myelin sheath - increases speed due to saltatory conduction.
2) Axon diameter - Increased diameter = increased speed.
3) Temperature - increased temp = increased speed because increased ion diffusion.

Question 24

What is the all or nothing principle? (action potential)

Answer 24

Stimulus has to reach threshold to cause action potential.

Threshold not reached = nothing.

Question 25

If an action potential is always 40mV, then how can you tell how big a stimulus is?

Answer 25

1) No. of impulses in a set time/

2) Some neurones have a higher threshold, so larger stimulus.

Question 26

What is the refractory period of an action potential?

Answer 26

• Na+ VG channels shut after action potential.

- Action potential can’t happen for short period of time (refractory period) bc Na+ can’t move in.

Question 27

What is the importance of a refractory period for an action potential?

Answer 27

1) Ensures action potential only unidirectional (one direction).
2) Ensures each action potential separate.
3) Limits no. of action potential in a given time.