Brain stem motor nuclei Table 22

Last Updated on Wed, 13 May 2020 | Cranial Nerves

Axons of cranial nerve motor neurons originate from brain stem nuclei of three types corresponding to the embryological origin of the muscle groups:

1 Somatic nuclei: These are close to the midline, equivalent to spinal cord ventral horn cells. Somatic nuclei are oculomotor, trochlear, abducens and hypoglossal nuclei.

2 Branchiomotor nuclei: These develop lateral to somatic nuclei, between them and parasympathetic nuclei. Branchiomotor nuclei are trigeminal motor, facial motor and the nucleus ambiguus (and probably its cervical extension for the spinal accessory nerve, see Section 16.3).

3 Parasympathetic nuclei: These are the most laterally placed of the brain stem motor nuclei, equivalent to lateral horn cells of the spinal cord. They include Edinger-Westphal, superior and inferior salivatory, and the dorsal motor nucleus of the vagus.

Brain stem motor nuclei thus make up three interrupted columns: somatic motor, branchiomotor (special visceral motor) and parasym-pathetic (general visceral motor). This pattern is a useful basis for further study.

Table 2.2. Cranial nerve motor nuclei.

Nucleus

Position

Cranial nerve

Function

Somatic motor

Oculomotor

Trochlear

Abducens

Hypoglossal

- voluntary

Upper midbrain Lower midbrain Pons Medulla

Branchiomotor (special visceral motor) -Trigeminal Pons

Facial Pons

Nucleus ambiguus Medulla

Oculomotor III Trochlear IV Abducens VI Hypoglossal XII

voluntary*

Mandibular Vc (first) Facial VII (second)

Glossopharyngeal IX (third) ^ Vagus X, various branches (fourth)

Vagus (X), recurrent laryngeal (sixth)

Eyeball movements: extrinsic ocular muscles

Tongue muscles and movements

Chewing, tensor tympani Facial expression, buccinator, stapedius

Muscles of swallowing and phonation

Table 2.2. (cont.)
Nucleus	Position	Cranial nerve	Function
Cervical accessory	Upper cervical	Spinal accessory XI	Sternocleidomastoid, trapezius
nucleus	spinal cord	(see Section 16.3)
Parasympathetic (general visceral motor) -		- involuntary**
Edinger-Westphal	Midbrain	Oculomotor III	Ciliary muscle: lens
			accommodation, etc.; iris
			muscle: pupilloconstriction
Salivatory: superior	Pons	Facial VII	Secretomotor: lacrimal, nasal,
			palate, submandibular, sublingual
			glands
Salivatory: inferior	Upper medulla	Glossopharyngeal IX	Secretomotor: parotid gland
Dorsal motor of	Medulla	Vagus X	Heart, foregut and midgut
vagus			derivatives