A nurse in a provider's office is preparing to test a client's cranial nerve function. Which direction should the nurse include when testing cranial nerve V (trigeminal) to assess motor function?

A nurse in a provider's office is preparing to test a client's cranial nerve function. Which direction should the nurse include when testing cranial nerve V (trigeminal) to assess motor function?

• A. Close your eyes.
• B. Tell me what you can taste.
• C. Clench your teeth.
• D. Raise your eyebrows.

Answer: (C)

The key idea is to assess the motor function of the trigeminal nerve by activating the jaw muscles. Asking the patient to clench their teeth engages the muscles of mastication—the masseter and temporalis—which are innervated by the mandibular division of the trigeminal nerve. Having the patient bite down (and, if appropriate, apply gentle resistance) lets you evaluate strength and symmetry of these muscles. A normal finding is a strong, equal bite with no jaw deviation. Weakness, asymmetry, or deviation suggests dysfunction of the trigeminal motor pathway or the masticatory muscles. Other options don’t test trigeminal motor function: closing the eyes assesses the facial nerve’s ability to close the eyelids; tasting checks gustatory function carried by the facial and glossopharyngeal nerves; and raising the eyebrows also tests facial nerve motor control.

The key idea is to assess the motor function of the trigeminal nerve by activating the jaw muscles. Asking the patient to clench their teeth engages the muscles of mastication—the masseter and temporalis—which are innervated by the mandibular division of the trigeminal nerve. Having the patient bite down (and, if appropriate, apply gentle resistance) lets you evaluate strength and symmetry of these muscles. A normal finding is a strong, equal bite with no jaw deviation. Weakness, asymmetry, or deviation suggests dysfunction of the trigeminal motor pathway or the masticatory muscles.

Other options don’t test trigeminal motor function: closing the eyes assesses the facial nerve’s ability to close the eyelids; tasting checks gustatory function carried by the facial and glossopharyngeal nerves; and raising the eyebrows also tests facial nerve motor control.