Inferior salivatory nucleus

At a glance

English

Inferior salivatory nucleus

Latin (TA2)

Nucleus salivatorius inferior

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the inferior salivatory nucleus

The inferior salivatory nucleus is one of two salivatory nuclei in the brainstem. It is a loose cluster of preganglionic parasympathetic neurons in the reticular formation of the dorsal brainstem, close to the junction between the pons and the medulla oblongata. It lies just below the superior salivatory nucleus, which serves the facial nerve, and above the top of the dorsal vagal nucleus. These three cell groups form a broken column of general visceral efferent neurons, the parasympathetic outflow of the hindbrain. Its cells are small and not sharply bounded, so the nucleus is identified more by its connections than by its outline.

Its axons leave the brainstem in the glossopharyngeal nerve (cranial nerve IX). They separate from that nerve below the skull in its tympanic branch, which climbs into the middle ear and joins the tympanic plexus on the promontory. From there the fibres gather as the lesser petrosal nerve, which leaves the middle ear, enters the middle cranial fossa, and passes down through or near the foramen ovale to the otic ganglion, just below the skull base beside the mandibular nerve. In the ganglion the fibres synapse. Postganglionic fibres then hitch a ride on the auriculotemporal nerve, a branch of the mandibular nerve, which carries them into the parotid gland.

The nucleus is controlled from higher centres, especially the hypothalamus and the nucleus of the solitary tract. The solitary nucleus receives taste and other sensory input from the mouth, so the sight, smell or taste of food leads, through these connections, to a flow of watery saliva from the parotid. Its output is both secretomotor, stimulating the gland cells, and vasodilator, increasing blood flow through the gland.

Interruption of the pathway anywhere along its course, for example in a fracture or surgery of the middle ear, reduces parotid secretion on that side. Cutting the tympanic nerve or plexus (tympanic neurectomy) has been used to treat drooling. After parotid surgery, regenerating secretomotor fibres from the auriculotemporal nerve may wrongly grow into sweat glands of the cheek, so that the skin sweats and flushes while eating: Frey syndrome.

Function and supply

Begins at

Preganglionic parasympathetic neurons in the dorsal reticular formation at the pontomedullary junction, below the superior salivatory nucleus and above the dorsal vagal nucleus.

Ends at

Its axons run in the glossopharyngeal nerve, tympanic nerve and lesser petrosal nerve to synapse in the otic ganglion; postganglionic fibres reach the parotid gland through the auriculotemporal nerve.

Function

Parasympathetic secretomotor and vasodilator supply to the parotid gland, driving salivation.

Blood supply

Branches of the vertebral and posterior inferior cerebellar arteries supplying the dorsal medulla.