The Autonomic Nervous System 2 (neurotransmitter synthesis)

Question 1

General process of amine neurotransmitter synthesis, release, and removal?

Answer 1

Precursor molecule to neurotransmitter
Transmitter packaged into vesicle
Action potential arrives, increasing intracellular calcium, vesicle fuses and exocytoses
Transmitter binds with receptor on effector cell/post-synaptic terminal
Removal by uptake or metabolism by local enzyme system

Question 2

What is the reaction that forms acetylcholine?

Answer 2

Choline + acetyl coenzyme A –> acetylcholine + coenzyme A

Question 3

What enzyme catalyses the formation of acetylcholine?

Answer 3

Choline acetyl transferase

Question 4

What is the reaction involving breakdown of acetylcholine?

Answer 4

Acetylcholine –> choline + acetate

Question 5

What enzyme catalyses the breakdown of acetylcholine?

Answer 5

Acetylcholinesterase

Question 6

What is the overall “lifecycle” of acetylcholine?

Answer 6

Produced from choline + acetyl coenzyme A
Packaged into vesicles
Released into synapse, binds with receptors on post-synaptic terminal
Removed by breakdown into choline and acetate
Choline recycled into presynaptic terminal to begin cycle again

Question 7

Process of noradrenaline production?

Answer 7

Tyrosine enters the cell
Tyrosine –> DOPA
DOPA –> dopamine
Dopamine enters vesicle –> noradrenaline

Question 8

Enzymes involved in stages of noradrenaline production?

Answer 8

Tyrosine hydroxylase
DOPA decarboxylase
Dopamine beta-hydroxylase

Question 9

Mechanisms of noradrenaline removal?

Answer 9

Reuptake into neurone where it is broken down into metabolites by monoamine oxidase A (MAO-A)
Uptake into effector cell, degradation by COMT

Question 10

Overall “lifecycle” of noradrenaline?

Answer 10

Production from initially extracellular tyrosine to DOPA to dopamine (enters vesicle) to noradrenaline
Vesicle fusion/exocytosis of noradrenaline
Either binds with receptor on postsynaptic terminal and reuptake into presynaptic neurone where it is metabolised by monoamine oxidase A
OR taken up by effector cell where it is degraded by COMT

Question 11

Distinctions of sympathetic, parasympathetic and adrenal medulla activity?

Answer 11

Sympathetic - Diffuse system allowing stimulation of multiple parts of the body at once (mass discharge)
Parasympathetic - Relatively discrete system innervating individual target tissues via specific nerves
Adrenal Medulla - Chromaffin cells synapse with pre-ganglionic fibres and release catecholamines directly into the blood

Question 12

What is the “fight or flight” response and what physiological effects accompany it

Answer 12

Mass sympathetic discharge in response to alarm or stress

• Increased arterial BP
• Increased blood flow to active muscles
• Increased blood glucose concentration
• Increased respiration

Question 13

Acute stress response effects and mechanism?

Answer 13

Stress acts on the hypothalamus and brain steam leading to sympathetic stimulation of adrenal medulla - catecholamine release into blood
Tachycardia
Splanchnic bed vasoconstriction (GI)
Increased metabolic rate
Sweating
Pupil dilation
Increased blood glucose
Increased mental awareness

Question 14

Ratio of adrenaline and noradrenaline released by adrenal medulla in percentage?

Answer 14

80% - Adrenaline

20% - Noradrenaline