Parasympathetic innervation of the eye, head and body

See also Chapter 12.

Key points

■ Parasympathetic fibres are found in cranial nerves III, VII, IX and X. They innervate smooth muscle and glands in the head and body.

■ In response to input from the optic nerve, presynaptic axons from the parasympathetic nucleus of III synapse, in the ciliary ganglion, with postsynaptic fibres; these innervate sphincter muscles of the iris.

■ Glands of the head are innervated by parasympathetic fibres in CNN VII and IX.

■ The vagus nerve is the source of parasympathetic motor fibres to the thoracic and abdominal viscera.

Parasympathetic nucleus of the oculomotor nerve

This nucleus is located just medial to the oculomotor nucleus in the ventral midbrain. It forms the efferent portion of the pupillary light reflex (Figs. 10.8 and 10.9).

Parasympathetic nucleus of the facial nerve

This is a small, ill-defined nucleus located within the reticular formation in the ventrolateral area of the rostral medulla oblongata. It receives afferent fibres from the nucleus of the solitary tract and the spinal nucleus of V. Efferent fibres innervate the palatine, lacrimal and nasal glands, the sublingual and mandibular salivary glands and smooth muscle of the nasal and oral cavities resulting, for example, in reflex secretions.

Parasympathetic nucleus of the glossopharyngeal nerve

This nucleus is located at the rostral end of parasympathetic nucleus of X. Its efferent fibres innervate the zygomatic and parotid salivary glands.

Parasympathetic nucleus of the vagus nerve

This long nucleus is located just lateral to the fourth ventricle and the central canal; it extends from just caudal to the trapezoid body to the level of the pyramidal decussation (see Figs. A23, A24, A27, A28). It is the source of autonomic motor fibres that form the vagus nerve and supply the thoracic and abdominal viscera.

Note that the parasympathetic supply to the pelvic viscera arises from the sacral spinal cord (see Chapter 12).