Parasympathetic Nervous System Anatomy

Anatomy of the Parasympathetic Nervous System

Overview of the Parasympathetic Nervous System

• The parasympathetic nervous system consists of cranial and sacral components.

• Preganglionic fibers in this system are longer than those in the sympathetic nervous system, as ganglia are located near or within target organs. This results in shorter postganglionic fibers.

Cranial Outflow Components

• The cranial outflow includes nerves III (Oculomotor), VII (Facial), IX (Glossopharyngeal), and X (Vagus).

• The vagus nerve is the largest component, with extensive distribution to thoracic and abdominal viscera. It plays a significant role in various bodily functions.

Functions of Cranial Components

• In the eyes, it causes pupil constriction and lens accommodation through ciliary muscle action. It also innervates salivary and lacrimal glands for secretion.

• In thoracic viscera, it decreases heart rate and contractility while causing bronchoconstriction in lungs; it also stimulates mucus secretion in gut glands.

Detailed Look at Individual Cranial Nerves

Oculomotor Nerve (Cranial Nerve III)

• Originates from the midbrain at Edinger-Westphal nucleus; extends to ciliary ganglion to control pupil constriction and lens accommodation.

Facial Nerve (Cranial Nerve VII)

• Superior salivatory nucleus gives rise to two branches: greater petrosal nerve for lacrimal gland secretion via pterygopalatine ganglion, and chorda tympani for submandibular gland secretion via submandibular ganglion.

Glossopharyngeal Nerve (Cranial Nerve IX)

• Inferior salivatory nucleus leads to glossopharyngeal nerve; lesser petrosal branch synapses at otic ganglion for parotid gland innervation.

Vagus Nerve (Cranial Nerve X)

• Originates from dorsal motor nucleus in medulla; has wide distribution without peripheral ganglia, affecting cardiac, pulmonary plexuses, and myenteric plexuses in gut wall with short postganglionic fibers near target organs.

Sacral Component of the Parasympathetic Nervous System

• Arises from spinal segments S2-S4, giving rise to pelvic splanchnic nerves that innervate rectum muscles and bladder wall while inhibiting internal anal sphincter function.

• In males, activation leads to erection while sympathetic nervous system controls ejaculation functions.