5th Cranial nerve – Trigeminal nerve motor test

Definition:

The use and interpretation of medical examinations to determine the integrity and adequate function the motor portion of the trigeminal nerve (fifth cranial nerve).

Test procedure:

The trigeminal nerve can be subdivided into three branches: Vi) ophthalmic, Vii) mandibular and Viii) maxillary, with only the later having both motor and sensory functions.

The muscles of mastication (masseter, temporalis, and pterygoids), may be assessed by having the patient clench their teeth and the examiner palpating the tone of the muscles. Light resistance may also be applied, testing a particular vector for approximately five to ten seconds, as pathological muscle fatigue can take a few seconds to ensue.

The jaw jerk reflex may be assessed by gently taping the patient’s jaw, while it is relaxed, with a reflex hammer. A normal reaction would be minimal movement.

Test findings (inc Positive & Negative results):

An exaggerated jaw jerk reflex may be indicative of an upper motor neurone lesion, often pseudobulbar palsy.

When assessing the strength of the muscles of mastication, observe for any signs of asthenia, and/or clonus, hyper/hypotonicity, and atrophy.

Considerations: (1-2)

A weakness of the muscles of mastication may be the result of an upper motor neuron lesion at the pathways synapsing with the trigeminal nerve or it may also be the result of a lower motor lesion at the nucleus of the trigeminal nerve. An exaggerated jaw reflex may be indicative of a lesion of the upper motor neuron pathways.