Parasympathetic Nervous System: Anatomy, Nerves & Pathways

Parasympathetic nervous system

ANS division important for maintenance functions such as digestion and urine formation; most of its functions occur during periods of rest.

General role of the parasympathetic nervous system

Maintains body functions during rest and supports processes such as digestion and urine formation.

Parasympathetic activity at rest

Most parasympathetic functions are carried out during periods of rest.

Parasympathetic activity level

Parasympathetic activity is rarely completely silent, although it is generally considered subordinate to sympathetic activity.

Parasympathetic division origin

Called the craniosacral division because preganglionic neurons originate from the brainstem through cranial nerves and from the sacral spinal cord.

Parasympathetic cranial nerves

Oculomotor (III), facial (VII), glossopharyngeal (IX), and vagus (X).

Parasympathetic sacral nerves

Sacral nerves S2–S4 contain parasympathetic preganglionic neurons.

Parasympathetic preganglionic axons

Travel from the CNS to terminal ganglia located near or within their target organs.

Terminal ganglia

Parasympathetic ganglia located near the postganglionic neurons' target cells.

Parasympathetic postganglionic axons

Fairly short because terminal ganglia are located near their target cells.

Parasympathetic preganglionic vs. postganglionic length

Preganglionic axons are relatively long, while postganglionic axons are relatively short.

Vagus nerve (CN X) parasympathetic contribution

Provides about 90% of the parasympathetic innervation to the body.

Vagus nerve parasympathetic distribution

Branches contribute to plexuses that innervate organs.

Cardiac plexus

Network of nerves receiving vagal contributions that innervates the heart.

Oculomotor nerve (CN III) parasympathetic pathway

Preganglionic parasympathetic neurons synapse in the ciliary ganglia.

Ciliary ganglia

Terminal ganglia associated with the parasympathetic fibers of the oculomotor nerve (CN III).

Facial nerve (CN VII) parasympathetic pathway

Preganglionic parasympathetic neurons synapse in the submandibular and pterygopalatine ganglia.

Submandibular ganglia

Terminal ganglia associated with parasympathetic fibers of the facial nerve (CN VII).

Pterygopalatine ganglia

Terminal ganglia associated with parasympathetic fibers of the facial nerve (CN VII).

Glossopharyngeal nerve (CN IX) parasympathetic pathway

Preganglionic parasympathetic neurons synapse in the otic ganglia.

Otic ganglia

Small terminal ganglia associated with parasympathetic fibers of the glossopharyngeal nerve (CN IX).

Parasympathetic cranial nerve-ganglion summary

CN III → ciliary ganglia; CN VII → submandibular and pterygopalatine ganglia; CN IX → otic ganglia.

Parasympathetic sacral neuron targets

Supply the last segment of the large intestine, urinary bladder, and reproductive organs.

Pelvic splanchnic nerves

Branches from the sacral spinal cord that carry parasympathetic fibers and form plexuses in the pelvic floor.

Origin of pelvic splanchnic nerves

Parasympathetic neurons from the sacral region of the spinal cord.

Pelvic splanchnic nerve targets

Structures including the last segment of the large intestine, urinary bladder, and reproductive organs.

Parasympathetic terminal ganglia in pelvic plexuses

Some sacral parasympathetic neurons synapse in terminal ganglia located within pelvic plexuses.

Parasympathetic terminal ganglia in organ walls

Most sacral parasympathetic neurons synapse in terminal ganglia located within the walls of their target organs.

Cranial parasympathetic pathway

Brainstem → parasympathetic cranial nerve → terminal ganglion near target → short postganglionic neuron → target organ.

Sacral parasympathetic pathway

Sacral spinal cord S2–S4 → pelvic splanchnic nerves → terminal ganglia near or within target organs → short postganglionic neuron → target.

Sympathetic vs. parasympathetic ganglion location

Sympathetic ganglia are generally near the spinal cord; parasympathetic terminal ganglia are near or within target organs.

Sympathetic vs. parasympathetic axon lengths

Sympathetic usually has short preganglionic and long postganglionic axons; parasympathetic has long preganglionic and short postganglionic axons.

Craniosacral mnemonic

Parasympathetic = cranial nerves III, VII, IX, X plus sacral nerves S2–S4.