Revision of sympathetic control of the circulation

Question 1

Principal neurotransmitters

Answer 1

Acetycholine

Noradrenaline

Question 2

Parasympathetic neurotransmitters

Answer 2

ACh is the neurotransmitter released from both pre-ganglionic and postganglionic tissues. The post ganglionic neurones are found within the tissue where the ACh acts on muscarinic receptors.

Question 3

Sympathetic neurotransmitters

Answer 3

ACh is released from the pre-ganglionic neurone acting on nicotinic receptors. NAd is then released from the postganglionic neurone and acts on alpha and beta receptors in the tissues.

Question 4

Sympathetic neurotransmission

Answer 4

After release from sympathetic neurones, NAd acts on specific adrenergic receptors, classified as either alpha or beta.
Alpha 2 receptors are found on the pre-synaptic neurone and are involved in a negative feedback regulation of noradrenaline release.

Question 5

Major cardiovascular effects of sympathetic stimulation

Answer 5

In the heart, B receptor stimulation brings about increases in both heart rate (positive chronotropy) and force of contraction (positive inotropy).
In most of the resistance blood vessels (primarily arterioles), alpha receptor stimulation brings about vasoconstriction.