Neurophysiology

Question 1

Name the two kinds of synapses and briefly explain how they differ.

Answer 1

chemical synapses convert action potentials in the presynaptic neuron to neurotransmitter release which triggers new action potentials in the postsynaptic neuron
- electrical synapses transmit electrical signals between two cells that are connected by gap junctions (no neurotransmitters)

Question 2

Describe the steps in transmission of a message between two neurons (3 marks)

Answer 2

action potentials travel to the synaptic terminus and cause opening of calcium channels and movement of calcium INTO the cell

• increased concentration of calcium in cytoplasm causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft
• neurotransmitter diffuses to postsynaptic membrane and binds to receptors resulting in opening of chemical gated channels
• depending on the kind of channels that open, the result can be depolarisation or hyperpolarization
• if membrane potential reaches threshold and action potential is triggered in the postsynaptic neuron

Question 3

Outline two processes that prevent the action of a neurotransmitter on a synapse
from lasting for more than a few milliseconds.

Answer 3

an enzyme (like acetylcholinesterase) can convert the neurotransmitter to inactive form
- there can be reuptake of the neurotransmitter into the presynaptic neuron

Question 4

Neurotransmitters are synthesized in the ________ of the neuron and released from
the ________.

Answer 4

1) cell body

2) synaptic terminus

Question 5

Explain what an acetylcholine agonist is.

Answer 5

a chemical that binds to acetylcholine receptors and acts like acetylcholine

Question 6

Explain what an acetylcholine antagonist is and give an example.

Answer 6

a chemical that binds to acetycholine receptors and prevents that action of acetylcholine (atropine is an example)

Question 7

A neuron may respond to one or more kinds of neurotransmitters (T/F).

Answer 7

true

Question 8

A neurotransmitter does not have any effect of a cell that lacks receptors for that
neurotransmitter (T/F).

Answer 8

true

Question 9

A neurotransmitter may be excitatory in some cells and inhibitory in others (T/F).

Answer 9

true

Question 10

Norepinephrine causes dilation of blood vessels in skeletal muscles and constriction
of blood vessels of the digestive tract (T/F).

Answer 10

true

Question 11

All synaptic termini that branch from the same neuron will release the same
neurotransmitter (T/F).

Answer 11

true

Question 12

A synapse that responds to acetylcholine is termed a(n) ________synapse.

Answer 12

cholinergic

Question 13

A synapse that responds to adrenaline is termed a(n) ________ synapse.

Answer 13

adrenergic

Question 14

Explain the difference between an ionotrophic neurotransmitter and a metabotrophic
neurotransmitter

Answer 14

metabotrophic synapses involve the activation of metabolic pathways (via the action of 2nd messengers) in receiving cells
-ionotrophic synapses result in the opening or closing of ion channels in the cell membrane of receiving cells

Question 15

List the five main chemical classes of neurotransmitters with an example of each (2
marks).

Answer 15

1) acetylcholine
2) amino acid (e.g. glutamate)
3) monoamines (epinephrine)
4) neuropeptide (endorphin)
5) gas (nitric oxide)

Question 16

Explain why amino acids are able to act as neurotransmitters in the central nervous
system but not in other parts of the body.

Answer 16

• the concentration of amino acids in the blood and interstitial fluids is high and would interefere with the action of the neurotransmitter
• the concentration of amino acids remains low because they are excluded from the nervous system by the blood brain barrier)

Question 17

Monoamines are synthesized from ___________________.

Answer 17

amino acids

Question 18

Describe the role of monoamine oxidase (MAO).

Answer 18

enzymes that inactivate monoamines that are produced from dietary amino acids and prevent them from acting as neurotransmitters

Question 19

Each of the ninety or more neuropeptides is synthesized from a different
______________.

Answer 19

gene

Question 20

Explain why a neurotransmitter may have different effects in different parts of the
body.

Answer 20

the receptor for that neurotransmitter may be linked to different processes within the postsynaptic cell

Question 21

Substances that act on synapses to increase or decrease the effects of the
neurotransmitters that normally act at those synapses are called ____________

Answer 21

neuromodulators

Question 22

Some neuromodulators are released from glial cells.

Answer 22

True