Nervous coordination

Question 1

What are the 7 parts of a nerve cell?

Answer 1

Nucleus, cell body, dendrites, axon, Schwann cells, nodes of Ranvier, axon terminal

Question 2

How is the resting potential of a neurone achieved?

Answer 2

Sodium-potassium pump moves 3 Na+ out of the neurone and 2 K+ into the neurone via active transport
Membrane is more permeable to K+ than Na+
Some K+ diffuses out of the neurone
Higher conc. of Na+ outside and higher conc. of K+ inside the neurone

Question 3

What is the voltage of the resting potential of a neurone?

Answer 3

-70mV

Question 4

How is an action potential achieved?

Answer 4

1. Na+ channels open and Na+ ions diffuse in which causes depolarisation
2. If depolarisation exceeds threshold, action potential created
3. Na+ channels close and K+ channels open
4. K+ ions diffuse out which causes repolarisation
5. Eventually hyperpolarisation occurs so K+ channels close
6. Sodium-potassium pump restores resting potential

Question 5

Refractory period definition

Answer 5

Time during which no new action potentials can be generated

Question 6

What are the 3 reasons why refractory periods are important?

Answer 6

1. Allows action potentials to travel in one direction
2. Produces discrete impulses
3. Limits the maximum frequency of action potentials

Question 7

Explain the all or nothing principle

Answer 7

Action potential is an all or nothing response and is always the same size - if threshold is reached you get an action potential, if not reached there is no action potential

Question 8

How does the brain determine the strength of a stimulus?

Answer 8

Stronger stimulus = greater frequency of action potentials to the brain

Question 9

Explain propagation of an action potential along an UNMYELINATED neurone (3 steps)

Answer 9

1. Action potential occurs at section of axon membrane
2. Voltage gated Na+ channels in membrane, adjacently in front of action potential, detect depolarisation and open, also forming an action potential
3. Action potential moves forward in one direction - refractory period behind action potential prevents impulse from being conducted backwards

Question 10

Explain propagation of an action potential along a MYELINATED neurone (4 steps)

Answer 10

1. Myelin insulates axon, preventing ion movements
2. Depolarisations only take place at nodes of Ranvier
3. Saltatory conduction occurs
4. Less depolarisations along whole length of axon membrane

Question 11

What 3 ways can speed up the conduction of action potentials?

Answer 11

1. Myelination - allows saltatory conduction
2. Higher temp. - increases kinetic energy of ions so they diffuse faster through membrane
3. Greater axon diameter - reduces resistance to ion flow

Question 12

What are the 8 parts which make up a synapse?

Answer 12

1. Pre-synaptic neurone
2. Post-synaptic neurone
3. Mitochondrion
4. Synaptic vesicle
5. Synaptic cleft
6. Neurotransmitter receptor
7. Ca2+ channel
8. Neurotransmitter reuptake pump

Question 13

What are the 6 steps to the transmission of an impulse across a CHOLINERGIC synapse?

Answer 13

1. Action potential depolarises pre-synaptic membrane
2. Voltage-gated Ca2+ channels open and Ca2+ ions diffuse in
3. Ca2+ causes synaptic vesicles to fuse with pre-synaptic membrane and release ACh into synaptic cleft
4. ACh diffuses across synaptic cleft and binds to receptors on post-synaptic membrane
5. Na+ channels open and Na+ diffuses into post-synaptic neurone, depolarising it and causing action potentials
6. Acetylcholinesterase hydrolyses ACh so Na+ channels close and no more action potentials are generated

Question 14

What does summation do?

Answer 14

Increases the amount of neurotransmitter released to increase depolarisation so it is more likley to reach threshold

Question 15

Explain spatial summation

Answer 15

More than one pre-synaptic neurone releasing neurotransmitter onto one post-synaptic neurone

Question 16

Explain temporal summation

Answer 16

Several action potentials arrive in a short time from ONE pre-synaptic neurone to ONE post-synaptic neurone, increasing neurotransmitter

Question 17

What is unidirectionality and what 2 things enable synapses to have this?

Answer 17

Action potentials travel in one direction

1. Neurotransmitter is only released from the pre-synaptic neurone
2. Receptors are only on the post-synaptic neurone

Question 18

What effect does Cl- channels on the post-synaptic membrane have and how does this lead to synapse inhibition?

Answer 18

Makes the post-synaptic neurone more negative, more Na+ needed to reach threshold for an action potential

Question 19

What are 3 differences between cholinergic synapses and neuromuscular junctions?

Answer 19

1. Cholinergic synapses are neurone to neurone whilst neuromuscular junctions are neurone to muscle fibre
2. Cholinergic synapses can be excitatory or inhibitory whilst neuromuscular junctions can only be excitatory
3. Cholinergic synapses have less ACh receptors on the post-synaptic membrane whilst neuromuscular junctions have more ACh receptors on the muscle fibre