General Anatomy
General Anatomy tests regional and systemic structure with a strong head-and-neck emphasis: skull and jaw bones, the temporomandibular joint, muscles of mastication, cranial nerves, and the blood supply of the face and teeth. Items often ask about the consequence of a nerve lesion.
Core rules
- The trigeminal nerve (CN V) has three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3). V3 is the only division carrying motor fibers, supplying the muscles of mastication, mylohyoid, anterior digastric, tensor veli palatini, and tensor tympani.
- Muscles of mastication: masseter elevates; temporalis elevates and retracts; medial pterygoid elevates and assists protrusion; lateral pterygoid protrudes and depresses the mandible.
- The facial nerve (CN VII) supplies muscles of facial expression; it does not supply the muscles of mastication.
- The temporomandibular joint is a synovial, bilateral, modified hinge joint with an articular disc; the lateral pterygoid attaches to the disc and condyle.
- The maxillary artery supplies the face and teeth; the inferior alveolar artery enters the mandibular canal.
Worked example
A patient has numbness of the lower lip and chin, weakness of jaw closure, and reduced sensation on the anterior two-thirds of the tongue. These findings localize to the mandibular division of the trigeminal nerve: the mental nerve carries lower lip and chin sensation, motor fibers supply the masseter and other masticatory muscles, and the lingual nerve carries general sensation from the anterior tongue. Taste on that region remains intact because taste travels with the chorda tympani of the facial nerve.
Traps
- Do not confuse facial expression (CN VII) with mastication (CN V3).
- The lateral pterygoid is the only masticatory muscle that depresses and protrudes.
- Distinguish origin from insertion when naming muscle actions.