V3 Trigeminal Nerve - Motor
The motor component of the trigeminal nerve (V3)
supplies the muscles of mastication. The largest of
these include the temporalis and masseter muscles.
- palpate the temporalis and masseter muscles on either
side when the patient clenches their teeth.
- ask the patient to open their mouth and repeat this
against resistance. Observe for any deviation of the
jaw to one side.
- with their mouth open, ask the patient to protrude
their jaw to either side against resistance.
- the jaw-jerk reflex is elicited by the examiner
placing their index finger over the middle of the
patients chin with the mouth slightly open and
the jaw relaxed. The index finger is then tapped with
a reflex hammer, delivering a downward stroke. The
afferent impulse for this reflex is the sensory portion
of the trigeminal nerve. The efferent limb is through
the motor (V3) branch of the trigeminal nerve.
- the jaw should not deviate to either side.
- the jaw-jerk is usually absent or weakly present.
- the jaw deviates towards the side of weakness.
- the jaw-jerk is exaggerated and pathologically brisk
with lesions affecting the pyramidal pathways above
the 5th nerve motor nucleus, especially if the lesions