Canonical Question

ANS Physiology

V5 H3.i Historical V4 M1.i 3 appearances

Variant family: at least one exam appearance has different scope. The appearance record controls whether this master answer is safe to display on that Past Paper.

Master answer

Parasympathetic Nervous System

The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system (ANS).
Its general function is to control homeostasis and the body’s rest-and-digest response.
Control the body’s response while at rest. Acts as local brake
Activates response of Rest and digest

Parasympathetic (Cranio-sacral) Efferents

Arises from neurons in cranial (III, VII, IX, X) or sacral segments of spinal cord (S2~S4)
Pre-ganglionic neuron
- Long fibre
Ganglia located near or within effector organs
Post-ganglionic neuron
- Short
- Release Acetylcholine

Cranial:

	Ganglion / Target Organ	Effect
CN III	Ciliary ganglion from occulomotor nucleus	• Pupil constriction, lacrimation
CN VII	Chorda tympani Submaxillary ganglion	secretion of saliva
CN IX	Parotid gland	secretion of saliva
CN X	Respiratory: Pulmonary plexus	Bronchoconstriction increased mucous production
	Cardiovascular: – SA node – AV node	↓ inotropy (Atria > Vent) ↓↓↓ Chronotropy ↓ lusitropy (Atria > Vent) ↓↓↓ dromotropy
	stomach to proximal two-thirds of the transverse colon	Increased gastric motility, secretions Relaxation of pyloric sphincter

Sacral:

	Ganglion / Target Organ	Effect
2nd, 3rd, 4th sacral segments	Hypogastric plexus – Descending colon – Rectum – Bladder – Uterus	Contracts muscular wall of rectum Relaxes internal sphincter of anus Contracts detrusor muscle

Effector

Acetylcholine (CCOOCCNH₃)
Formed for Choline and Acetyl CoA
Receptors
- Muscarinic
  - G Protein Coupled
- Nicotinic
  - Ligand gated ion channels
Metabolism
- Acetylcholinesterase

Mooney / JC 2019

Answer by JC, Mooney

Exam appearances

Exam	Exact wording	Relationship	Success
2014B Q04	Outline the anatomy and physiology of the parasympathetic nervous system.	historical_member	—
2017A Q01	Outline the anatomy and physiology of the parasympathetic nervous system.	historical_member	—
2025B Q14	Outline the physiology of the parasympathetic nervous system using the following headings: (a) the anatomical origins and target organ(s) (45% of marks). Responses of the organ(s) are NOT required. (b) nerve fiber classification and characteristics (20% of marks) (c) receptor types, locations and neurotransmitters (35% of marks	variant	61.00%