Brain stem motor nuclei Table 22

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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

* Cranial nerve with branchial arch.

** Cranial nerve conveying fibres from brain stem.

Oc Tr

TM F

SSN ISN

DMNX

Hyp NA

Fig. 2.1 Cranial nerve motor nuclei.

EW: Edinger-Westphal nucleus;

Oc: oculomotor nucleus;

Tr: trochlear nucleus;

TM: trigeminal motor nucleus;

Ab: abducens nucleus;

F: facial motor nucleus;

SSN: superior salivatory nucleus;

ISN: inferior salivatory nucleus;

DMNX: dorsal motor nucleus of X;

NA: nucleus ambiguus;

Hyp: hypoglossal nucleus;

Acc: lateral horn cells in cervical cord giving spinal roots of XI.

Oc Tr

TM F

SSN ISN

Facial Nucleus Brainstem

Fig. 2.1 Cranial nerve motor nuclei.

EW: Edinger-Westphal nucleus;

Oc: oculomotor nucleus;

Tr: trochlear nucleus;

TM: trigeminal motor nucleus;

Ab: abducens nucleus;

F: facial motor nucleus;

SSN: superior salivatory nucleus;

ISN: inferior salivatory nucleus;

DMNX: dorsal motor nucleus of X;

NA: nucleus ambiguus;

Hyp: hypoglossal nucleus;

Acc: lateral horn cells in cervical cord giving spinal roots of XI.

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