6.2 Nerves

Question 1

Dendron definition

Answer 1

Extensions of the cell body which bring electrical impulses towards the cell body

Question 2

Axon definition

Answer 2

Long fibre which takes nerve impulses away from the cell body

Question 3

How is a resting potential maintained?

Answer 3

• Phospholipid bilayer is impermeable for Na+ or K+ to diffuse
• Na+/K+ pumps actively transport ions in/out (3/2 ratio)
• K+ channel proteins open at rest and so allow facilitated diffusion of K+ back out

Question 4

What is myelin?

Answer 4

Lipid

Question 5

How is an action potential formed?

Answer 5

• When generator reaches threshold
• Lots of Na+ channel proteins open = rapid diffusion in
• At top, Na+ close, K+ open, K+ rapid diffuse out

Question 6

What is the resting potential voltage?

Answer 6

-70mv (outside more +ve inside more -ve)

Question 7

How do action potentials move along a neuron?

Answer 7

Na+ that enter diffuse sideways
Causes depolarisation in adjacent section
“Wave of depolarisation”

Question 8

What factors affect speed of conduction of action potentials?

Answer 8

Myelination
Axon diameter
Temperature

Question 9

How does saltatory conduction work?

Answer 9

If a neurons cytoplasm has conducted enough charge to depolarise next node, impulse jumps to next node

Question 10

How does axon diameter affect speed of action potential conduction?

Answer 10

Larger axon diameter = Quicker conduction

- Less resistance to flow of ions than in cytoplasm of smaller axon

Question 11

What is a cholinergic synapse?

Answer 11

One that uses Ach

Question 12

How is Ach transmitted across a cholinergic synapse?

Answer 12

1) Action potential arrives and synaptic knob of pre-s neruon
2) Stimulates voltage-gated Ca2+ to open
3) Ca diffuses into pre-s knob
4) Influx pushes synaptic vesicles to move to pre-s membrane
5) Vesicles filled with neurotransmitter fuse with pre-s membrane and release Ach into cleft
6) Ach diffuses across cleft and binds to specific cholinergic receptors on post-s membrane
7) Cause Na+ channels to open

Question 13

Which enzyme breaks down Ach?

Answer 13

Acetylcholinesterase (AChE)

Question 14

What are the types of neurotransmitters?

Answer 14

• Excitatory = Depolarise post-s membrane

- Inhibitory = Hyperpolarise post-s membrane

Question 15

What is summation?

Answer 15

Where the effect of neurotransmitters from many neurons (or one) are added together

Question 16

Why is summation beneficial?

Answer 16

Synapses process information more accurately and can tune the response accordingly

Question 17

What are neuromuscular junctions?

Answer 17

Synapses between neurons and muscles

Question 18

How are neuromuscular junctions different to normal cholinergic synapses?

Answer 18

• Post-s membrane has folds that form clefts filled with AchE
• Post-s membrane has more receptors than other synapses
• Ach always excitatory
• Specific