Which cranial nerve is responsible for innervating the muscles of mastication and carries sensory fibers from the anterior two-thirds of the tongue?

Explanation

## Trigeminal Nerve (CN V) — Motor and Sensory Functions **Key Point:** The trigeminal nerve (CN V) is the only cranial nerve that provides motor innervation to the muscles of mastication (masseter, temporalis, medial pterygoid, lateral pterygoid). ### Motor Component The motor division of CN V innervates: - Muscles of mastication (4 muscles) - Mylohyoid - Anterior belly of the digastric - Tensor veli palatini - Tensor tympani ### Sensory Component CN V provides sensory innervation to: - **Anterior two-thirds of the tongue** — via the lingual nerve (branch of CN V3) - Face and scalp (via three divisions: ophthalmic, maxillary, mandibular) - Cornea, conjunctiva, and mucous membranes of oral and nasal cavities **High-Yield:** CN V is the ONLY cranial nerve with both motor and sensory innervation to the tongue region. The anterior two-thirds sensation is CN V (trigeminal), while the posterior one-third is CN IX (glossopharyngeal). **Mnemonic:** **MAD** — **M**asseter, **A**nterior belly of digastric, **D**ental innervation = CN V motor functions. ### Comparison with Other Cranial Nerves | Cranial Nerve | Motor to Tongue | Sensory from Tongue | Taste | | --- | --- | --- | --- | | CN V (Trigeminal) | No | Anterior 2/3 | No | | CN VII (Facial) | No | No | Anterior 2/3 | | CN IX (Glossopharyngeal) | Stylopharyngeus only | Posterior 1/3 | Posterior 1/3 | | CN X (Vagus) | Pharyngeal & laryngeal muscles | Epiglottis & pharynx | Epiglottis | | CN XII (Hypoglossal) | Tongue muscles | No | No | **Clinical Pearl:** Lesion of CN V results in loss of sensation over the face and inability to clench the jaw (masseter paralysis), whereas CN VII lesion causes facial droop but preserved jaw clenching.