Autonomic Nervous System Introduction Quiz

See Actions of the Autonomic Nervous System. Option C is correct. The autonomic nervous system works as a chain of two neurones, the pre-ganglionic neurone, whose cell body lies in the brainstem or spinal cord, and the post-ganglionic neurone, whose cell body lies in a ganglion (a collection of nerve cell bodies outside the central nervous system). All pre-ganglionic neurones, both sympathetic and parasympathetic, release acetylcholine (ACh), which acts on nicotinic receptors on the post-ganglionic neurone. The post-ganglionic neurones then differ. Sympathetic ones release noradrenaline, which acts on adrenoceptors, whereas parasympathetic post-ganglionic neurones release acetylcholine again, but this time it acts on muscarinic receptors on the target organ. Nicotinic and muscarinic receptors are named after the substances nicotine and muscarine, which each bind one type of receptor. Muscarinic receptors are G-protein coupled receptors (receptors that signal through an attached G protein inside the cell). So the pairing to remember for parasympathetic nerves at the organ is acetylcholine on muscarinic receptors.

• Pre-ganglionic neurones: all release acetylcholine onto nicotinic receptors.
• Parasympathetic post-ganglionic neurones: release acetylcholine onto muscarinic receptors at the organ.
• Sympathetic post-ganglionic neurones: release noradrenaline onto adrenoceptors.