The Trigeminal nerve is probably usually pretty annoyed. It’s actually the largest and most complex of ALL the cranial nerves, and yet it’s often confused with the facial in terms of function or damage… plus the Vagus gets ALLLL the love and attention from SLPs. Anyway. The trigeminal has both sensory and motor responsibilities. It provides sensation to the interior and exterior jaw and TMJ, surface and deeper structures of the face, the mucous membrane of the upper mouth, palate and tongue, the pharnx and palate, as well as pain/temperature/touch and proprioception to the cheeks, lips, and jaw (as well as the forehead, eyes, eyebrows and nose-but trying to stick to swallowing here). It’s motor duties include mastication, jaw side to side movement and closure. It also helps out with up and forward movement of the larynx, backing movement of the tongue to the velum, tensing of the soft palate, and constriction of the posterior pharyngeal wall. See? All that work and no respect.
To assess, take a look at the patient for jaw symmetry at rest and while chewing, and have the patient “hold mouth closed and don’t let me open” and then “keep your mouth open and don’t let me close”. Make notes of any weakness or asymmetry, weakness or tremors of the jaw. Checking sensation should involve temperature (cold cotton swab) to lower gum, mandible, anterior tongue on both sides. Also check the soft palate during phonation and note and flaccidity.
Functionally, these patients can have difficulty with biting and chewing, coordinated bolus formation and transfer (can be a little messy or take longer) and may complain of unexpected pain in the face, or loss of feeling in the tongue so you may also see some injuries to the tongue if they have bitten themselves.
The trigeminal originates in the pons, and extends through the midbrain in the upper medulla, so damage to that area of the brain should trigger the expectation of trigeminal impairment. Check out some references below for more info!