The efferent pathways consist of a cranial and a sacral part. The cranial part consists of efferent fibres present in the third, seventh, ninth and tenth cranial nerves. The sacral part consists of efferent fibres present in the third, fourth and fifth sacral spinal nerves.
Cranial part
- The oculomotor parasympathetic fibres arise from the Edinger-Westpal nucleus in the midbrain.
- The preganglionic fibres pass along the branch of nerve supplying the inferior oblique muscle and enter the ciliary ganglion.
- This ganglion is small, flattened reddish gray in colour and about the size of a pinhead.
- It is situated near the apex of the orbit in the loose fat between the optic nerve and lateral rectus muscle lying generally on the lateral aspect of the ophthalmic artery.
- The postganglionic fibres leave the ganglion by the short ciliary nerves to be distributed to the ciliary muscle and constrictor pupillae of the iris.
- The facial nerve contains efferent parasympathetic fibres that arise in the superior salivary nucleus of the medulla oblongata. These pass along the facial nerve then in the chorda tympani and ultimately reach the lingual nerve and enter the mandibular ganglion. The postganglionic fibres leave the ganglion and supply secretomotor fibers to the mandibular and sublingual salivary glands. Some of the parasympathetic fibres that are secretomotor fibres travel in the great superficial petrosal nerve, reach the sphenopalatine ganglion and are relayed to the mucous membrane of nose and palate and to the lacrimal gland via the zygomatic branch of maxillary nerve and the lacrimal nerve. The sphenopalatine ganglion is the largest of the cephalic para sympathetic ganglia and is placed deeply in the pterygopalatine fossa close to the sphenopalatine foramen. It is flattened, reddish-gray in colour and is below the maxillary nerve.
- The glossopharyngeal nerve contains efferent fibres which arise in the inferior salivary nucleus of the medulla oblongata, travel in this nerve and its tympanic branch, traverse the tympanic plexus, and enter the lesser superficial petrosal nerve and terminate in the otic ganglion. This ganglion is placed immediately below the foramen ovale on the internal face of the mandibular nerve. It is oval, flattened and reddish-gray in colour. From this ganglion the postganglionic fibres are relayed through the superficial temporal nerve and supply secretomotor fibres to the parotid salivary gland.
- The vagus nerve contains a very large proportion of parasympathetic fibres that arise in the dorsal nucleus of vagus; travel in this nerve and in its oesophageal, pulmonary, cardiac, gastric and intestinal branches. The branches terminate in small ganglia placed in the walls of individual viscera; the postganglionic fibres are relayed finally to the glands and musculature.
- The cardiac nerve fibres are depressor nerves of the heart and with sympathetic branches form cardiac plexus. The fibres terminate in ganglia placed in the walls of the heart and from here postganglionic fibres are relayed to the substance of the auricles and the auriculoventricular bundle and it is through the latter that ventricle are brought under the action of the vagus.
- The pulmonary branches are motor to the bronchial muscles and are bronchoconstrictors.
- The gastric branches are secretomotor to glands and motor to the muscular coat of the walls.
- The intestinal branches have motor action on the glands of the mucous membrane and muscular wall. The relays are in the Auerbach’s and Meissner’s plexuses.
Sacral part
- The sacral part of the efferent parasympathetic fibres are contained in the ventral primary divisions of the third, fourth and fifth sacral spinal nerves.
- The visceral branches containing these fibres form a plexus with the sympathetic pelvic plexus.
- Minute parasympathetic ganglia are located in the walls of the viscera and from here the postganglionic fibres are relayed to the organs.
- They supply rectum, urinary bladder, uterus, pelvis and external genitalia.
