Intro To ANS

Question 1

Summarise the basic dominance of each PNS and SNS pathways.

Answer 1

SNS: pupil dilation, less baroreceptor firing when low body fluid so BP drops to stimulate SNS

PMS: cephalic secretions and gastric motility, vagus nerve

Question 2

What is the structure and role of the transmitters released from pre and post ganglionic fibres in SNS and PNS

Answer 2

Parasympathetic: always ACh, long preganglionic and short post ganglionic. Localised, little divergence 1:1 pre vs post

Sympathetic: short preganglionic, long post ganglionic, coordinated response, very divergent 1:20 pre vs post

1. Preganglionic > ACh > post ganglionic > NA > effector
2. Preganglionic > ACh > post ganglionic > ACh > drives secretions only (sweat)
3. Preganglionic > adrenal medulla secretes NA/A

Question 3

Describe the 2 different receptors

Answer 3

Cholinergic receptors: nicotinic (pre ganglionic - ion channel receptor) and muscarinic (post ganglionic - G protein coupled receptor activating intracellular machinery). Muscarinic receptor: M1-Neural M2-Cardiac M3-exocrine eg in stomach

Adrenoreceptors: at all effector organs innervated by post ganglionic sympathetic stimulated by A/NA (G-protein coupled > more selective) so in the heart B1 in the nodal tissue increases HR.

Question 4

Describe the biosynthesis, release and metabolism of ACh, A, NA

Answer 4

ACh: acetyl CoA + choline > into vesicle via choline acetyl transferase > released via Ca+ into synaptic cleft > onto receptor and then broken down via acetylcholine esterase > into choline and acetate.

Adrenaline: same thing as ACh

NA: tyrosine > DOPA via tyrosine hydroxylase > dopamine via DOPA carboxylate > NA via dopamine hydroxylase > into synaptic cleft via Ca+ > degraded via COMT > metabolised via MAO-A