Pontine corticonuclear fibers

Pontine corticonuclear fibres are descending cortical fibres that terminate in or influence cranial motor systems within the pons. They are principally associated with motor control involving:

• Motor nucleus of the trigeminal nerve (CN V) – supplies the muscles of mastication and other branchial motor derivatives.

• Abducens nucleus (CN VI) – participates in the control of horizontal eye movements through its motor neurons supplying the lateral rectus and interneuronal connections coordinating conjugate gaze.

• Facial motor nucleus (CN VII) – supplies the muscles of facial expression and other branchial motor derivatives.

Clinical correlate

Most pontine cranial motor nuclei receive bilateral corticonuclear fibres. A clinically important exception is the part of the facial motor nucleus controlling the lower facial muscles, which receives predominantly contralateral corticonuclear input. Consequently, a unilateral lesion of the corticonuclear pathway above the facial nucleus typically produces weakness of the contralateral lower face, while forehead movement is relatively preserved because the upper facial muscles receive substantial bilateral cortical input.

Pontine corticonculear fibres Vs. corticopontine fibres

Pontine corticonuclear fibres should not be confused with corticopontine fibres. Corticonuclear fibres influence cranial motor systems, whereas corticopontine fibres terminate in the ipsilateral pontine nuclei and form part of the corticopontocerebellar pathway.

Autonomic motor nuclei of pons

The autonomic motor nuclei, such as the superior salivatory nucleus, associated primarily with CN VII, is a preganglionic parasympathetic nucleus involved in secretomotor control of the lacrimal, submandibular and sublingual glands and glands of the nasal and palatal mucosa. It is subject to higher descending influence from cerebral cortex; however, this regulation occurs through broader descending autonomic hypothalamospinal pathways, and therefore it should not be regarded as an equivalent direct target of the voluntary corticonuclear motor fibres.