TSM25: BRAINSTEM AND CRANIAL NERVES 2
10/10/08
LEARNING OUTCOMES
Describe the general organisation of the brainstem cranial nerve nuclei
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Cranial nerve nuclei in the brainstem are all present bilaterally and are either motor or sensory
The motor nuclei fall into one of two categories:
o Somatic motor (SM) – cell bodies of α-motor neurones supplying skeletal muscle
o Visceral motor (VM) – cell bodies of preganglionic parasympathetic fibres supplying smooth
muscle and glands
The sensory nuclei fall into one of three categories:
o Somatic sensory (GS) – synapses of cutaneous and mucosal afferents
o Visceral sensory (VS) – synapses of visceral and taste afferents
o Special sensory (SS) – synapses of special sense afferents
MOTOR CRANIAL NERVE NUCLEI
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Three motor nuclei span the medulla longitudinally; from medial to lateral these are:
o CNXII motor (SM) – in the central gray matter
 Supplies the tongue
o CNX dorsal motor (VM) – also in the central gray matter
 Supplies thoracic and abdominal viscera
o Nucleus ambiguus (SM) – in the reticular formation
 Supplies soft palate, pharynx, larynx (and heart-rate through parasympathetic fibres)
Also more dorsally in the reticular formation at the level of the nucleus ambiguus are these nuclei:
o Superior salivatory (VM) – laterally
 Supplies the lacrimal, sublingual and submaxillary glands
o Inferior salivatory (VM) – medially
 Supplies the parotid gland only
Two motor nuclei are present at the pontine-medullary junction:
o CNVI motor (SM) – medially
 Supplies the lateral rectus muscle of the eye
o CNVII motor (SM) – laterally
 Supplies the muscles of facial expression
There is only one motor nucleus in the pons itself:
o CNV motor (SM) – medial to the chief sensory nucleus (see below)
 Supplies the muscles of mastication
Three motor nuclei are present in the midbrain:
o CNIV motor (SM) – in the periaqueductal gray matter at the level of the inferior colliculus
 Supplies the superior oblique muscle of the eye
o CNIII motor (SM) – in the periaqueductal gray matter at the level of the superior colliculus
 Supplies the remaining four extraocular muscles and levator palpebrae superioris
muscle which raises the eyelid
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Edinger-Westphal (VM) – dorsal to the CNIII motor nucleus
 Supplies the internal muscles of the eye via the ciliary ganglion
SENSORY CRANIAL NERVE NUCLEI
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The general somatic sensory nuclei span the whole brainstem with three divisions:
o Spinal CNV (GS) – laterally in the medulla
 Receives pain and temperature from the face
 Receives general sensory information from CNVII, CNIX and CNX
 Analogous to the anterolateral system in the spinal cord
o Pontine CNV (GS) – more medially at the lower border of the pons
 Receives fine touch from the face
 In part analogous to the dorsal columns system in the spinal cord
o Mesencephalic CNV (GS) – more medially extending up into the midbrain
 Receives proprioception from the face
 In part analogous to the dorsal columns system in the spinal cord
There is only one visceral sensory nucleus which extends longitudinally in the medulla:
o Solitary nucleus (VS) – lateral to the CNX dorsal motor nucleus
 Receives visceral sensory information from the whole body
 Receives taste in the rostal gustatory portion
There are six special sensory nuclei around the rostral medulla and caudal pons:
o Dorsal and ventral cochlear nuclei (SS) – at the level of the inferior cerebral peduncle
 Receive hearing information from cochlear branches of CNVIII
o Superior, inferior, lateral and medial vestibular nuclei (SS) – mostly in the rostal medulla
 Receive balance and orientation information from vestibular branches of CNVIII