Page 394 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 379

The cranial nerves 379

4◊◊Lesions of the vestibular division of the labyrinth or of the vestibulo-
cerebellar pathway result in vertigo — a subjective feeling of rotation —
nausea, ataxia and nystagmus.

The glossopharyngeal nerve (IX) (Fig. 210)
The glossopharyngeal nerve contains sensory fibres for the pharynx and the
posterior one-third of the tongue (including the taste buds), motor fibres for
the stylopharyngeus muscle and secretomotor fibres for the parotid gland. It
is attached to the upper part of the medulla by four or five rootlets along the
groove between the olive and the inferior cerebellar peduncle and leaves the
skull by way of the jugular foramen in which it gives off its tympanic branch.
Below the jugular foramen the nerve courses downwards and forwards
between the internal carotid artery and the internal jugular vein to reach the
styloid process. From here it passes along the stylopharyngeus muscle to
enter the pharnyx between the superior and middle constrictors. Here it
breaks up into its terminal branches which supply the posterior one-third of
the tongue and the mucous membrane of the pharynx (including the tonsil).
The tympanic branch, which is continued as the lesser superficial petrosal
nerve, conveys the preganglionic parasympathetic fibres to the otic gan-
glion (parotid secretomotor fibres).
The only other branch of significance is the carotid nerve which arises
just below the skull and runs down on the internal carotid artery to supply
both the carotid body and carotid sinus. This small twig serves as the affer-
ent limb of the baroreceptor and chemoreceptor reflexes from the carotid
sinus and body respectively.

Clinical features

Complete section of the glossopharyngeal nerve results in sensory loss in
the pharynx, loss of taste and common sensation over the posterior one-
third of the tongue, some pharyngeal weakness and loss of salivation from
the parotid gland. However, such lesions are frequently difficult to detect
and rarely occur as isolated phenomena since there is so often associated
involvement of the vagus or its nuclei.

The vagus nerve (X)

The vagus has the most extensive distribution of all the cranial nerves, inner-
vating the heart and the major part of the respiratory and alimentary tracts.

Central connections

The dorsal nucleus of the vagus in the medulla (Fig. 242) is a mixed visceral
afferent and efferent nucleus. It receives sensory fibres from the heart, the
lower respiratory tract and the alimentary tract down to the transverse
colon; in addition it gives rise to preganglionic parasympathetic motor
fibres to the heart and the smooth muscles of the bronchi and gut.