Fundamentals Of The Autonomic Nervous System

Question 0

Describe the different pathways pathways via which these two divisions distribute their fibres to and from target organs

Answer 0

Sympathetic (thoraco-lumbar) - nerve fibres have cell bodies in all 12 thoracic sections and the first two lumbar sections
Short pre-ganglion, long post-ganglion
Parasympathetic (cranio-sacral)
Long pre-ganglion, short post ganglion

Question 1

Give an outline of the anatomy of the autonomic nervous system (ANS) and it’s division into the sympathetic and parasympathetic parts

Answer 1

ANS - 2 neurones - pre and post ganglionic
Neurones exert actions via smooth muscle, viscera and secretory glands
Sympathetic - fight or flight (thoraco-lumbar)
Parasympathetic - relaxation (cranio-sacral)

Question 2

Describe the difference in the overall functional roles of these two divisions

Answer 2

Sympathetic (fight/flight/fright) - diversion of blood to muscles and heart, reduced blood to GI tract and skin, increased heart rate and blood pressure, hyperventilation
Parasympathetic (relaxation) - reduced heart rate and force of contraction, promotes digestion and bladder emptying, promotes sleep

Question 3

Describe in detail the transmitters involved at the synapses and end organs of both divisions

Answer 3

Sympathetic:
Pre-ganglion neurones are cholinergic (ACh)
Post-ganglion neurones have nicotinic receptors
Post-ganglion neurones are noradrenergic (noradrenaline)
(Perspiration and ejaculation are cholinergic)
Parasympathetic:
Pre-ganglion neurones are cholinergic
Post-ganglion neurones have nicotinic receptors
Post-ganglion neurones are cholinergic