Lecture 3

Question 1

Incoming signals can do two things to the polarity of the nerve cell membrane. What are they?

Answer 1

Depolarise it - causing membrane potential to rise from resting potential (-70mV).
Hyper-polarise it - lowering the membrane potential further, reducing the chance of an action potential occurring.

Question 2

What is a threshold potential? (both value and description)

Answer 2

The critical level of depolarisation of the cell membrane, whereby any additional depolarisation causes an action potential to be triggered in the axon.
-55mV.

Question 3

Where is an action potential initiated in a nerve cell?

Answer 3

Trigger zone of the axon hillock.

Question 4

5 stages of an action potential in a nerve cell? (1 being at initial resting state)

Answer 4

1. ) Initial resting state - retention of K+ in the cell.
2. ) Threshold - Na+ flows in through voltage-gated ion channels.
3. ) Depolarisation phase - large influx of Na+.
4. ) Repolarisation phase - inactivation gate closes, preventing influx of more Na+, K+ ion channel opens, allowing flux of K+.
5. ) Undershoot - membrane potential temporarily goes below expected.

Question 5

What phrase describes an action potential’s longevity, and why?

Answer 5

Self-propagating, as there is no loss in signal intensity as it travels down the axon.

Question 6

What does ‘all or none’ refer to?

Answer 6

Each stimulus produces either a full action potential, or none at all.

Question 7

What is saltatory conduction, and how fast is it?

Answer 7

Impulses jumping between Nodes of Ranvier due to myelinated axons.
Up to 150m/sec.

Question 8

How is the intensity of a signal conveyed?

Answer 8

By the frequency of nerve impulses.

Question 9

What is a refractory period?

What does it explain?

Answer 9

A short time after an action potential has occurred when another cannot be stimulated.
(Explains unidirectional movement.)

Question 10

2 types of synapse, and which is more common?

Answer 10

Electrical (gap junctions)

Chemical - more common.

Question 11

What are transmitters stored in?

Answer 11

Membrane bound synaptic vesicles.

Question 12

What is the amount of transmitter in one vesicle known as?

Answer 12

Quantum.

Question 13

What an action potential arrives at a synapse, what happens?

Answer 13

Influx of Ca2+, fusion of vesicles with pre-synaptic membrane, release of transmitter into synaptic cleft.
Transmitter binds to receptor on post-synaptic membrane.

Question 14

What two effects can transmitters have?

Answer 14

Excitatory.

Inhibitory.

Question 15

There must be a mechanism to terminate transmitter activity. What 2 methods are capable of doing this?

Answer 15

Catabolism.

Uptake of neurotransmitter into axon terminal or glial cells.

Question 16

What effect do auto receptors typically exhibit?

Answer 16

Inhibition - stopping transmitter release.

Question 17

Where are enzymes required for synthesis of transmitter molecules typically found?

Answer 17

In cytoplasm and synaptic vesicles.

Question 18

4 criteria for transmitter substances?

Answer 18

• Synthesised in neurone.
• Present at presynaptic terminals and packaged in vesicles.
• Endogenous substance at reasonable concentration mimics action of endogenously released transmitter.
• Specific mechanism exists for removing transmitter from synaptic cleft.

Question 19

Four well known biogenic amines? Their functional class? Secretion sites?

Answer 19

• Noradrenaline, Excitatory or inhibitory, CNS and PNS.
• Adrenaline, Excitatory or inhibitory, CNS and PNS.
• Dopamine, Usually excitatory, sometimes inhibitory, CNS and PNS.
• Serotonin, Typically inhibitory, CNS.

Question 20

Four well known amino acids? Their functional class? Secretion sites?

Answer 20

• GABA, inhibitory, CNS and invertebrate neuromuscular junction.
• Glycine, inhibitory, CNS.
• Glutamate, excitatory, CNS and invertebrate neuromuscular junction.
• Aspartate, excitatory, CNS.

Question 21

Two well known neuropeptides? Their functional class? Secretion sites?

Answer 21

• Substance P, excitatory, CNS and PNS.

- Met-enkephalin, typically inhibitory, CNS.

Question 22

Where is acetylcholine (ACh) found, and what is it involved in?

Answer 22

The brain, at neuromuscular junction and in autonomic ganglia.
Involved in learning and memory.

Question 23

In what disease is there a deficiency of brain ACh?

Answer 23

Alzheimer’s disease.

Question 24

What is acetylcholine synthesised by?

Answer 24

Choline acetyl transferase.

Question 25

What are the 2 types of receptors for acetylcholine? (and where are they found?)

Answer 25

Nicotinic (neuromuscular junction, brain, autonomic nerves).

Muscarinic (smooth muscle, exocrine glands, brain).

Question 26

What enzyme stops acetylcholine transmitter? And where is it found?

Answer 26

Acetylcholinesterase.

Attached to extracellular side of synaptic membranes.

Question 27

What is an agonist?

Answer 27

Substance that binds to a receptor and stimulates it (mimicking transmitter).

Question 28

What is an antagonist?

Answer 28

Substance that binds to a receptor but doesn’t stimulate it (blocking transmitter).

Question 29

One example of a nicotinic agonist?

Answer 29

Nicotine.

Question 30

One example of a nicotinic antagonist?

Answer 30

Curare.

Question 31

One example of a muscarinic agonist?

Answer 31

Muscarine.

Question 32

One example of a muscarinic antagonist?

Answer 32

Atropine.

Question 33

What is the neuromuscular junction responsible for the initiation of?

Answer 33

Muscle contraction.

Question 34

Where are nicotinic acetylcholine receptors found in vertebrates?

Answer 34

Neuromuscular junction.

Question 35

What enzyme combines Acetyl-CoA and Choline?

Answer 35

Choline acetyl transferase.

Question 36

What are inhibitors of acetylcholinesterase often used to treat?

Answer 36

Alzheimer’s disease.

Question 37

When was Alzheimer’s first discovered, and by whom?

Answer 37

1907. Alois Alzheimer.

Question 38

What characterises Alzheimer’s?

Answer 38

Progressive loss of short term memory, until patient is left completely demented.

Question 39

Neuropathological changes involved in Alzheimer’s?

Answer 39

Loss of brain weight, enlargement of ventricles, numerous senile plaques, neurofibrillary tangles (NFTs) in the brain, degeneration of cholinergic nerve cels and loss of cholinergic marker enzymes.

Question 40

What do NFTs consist of, and where are they found?

Answer 40

Consist of tau (microtubule associated axonal protein), accumulate in cell bodies and dendrites.