Anatomy, Physiology, and Pathophysiology of the Orofacial Region
What you must know
Build a working map of the trigeminal territory: the three divisions (V1 ophthalmic, V2 maxillary, V3 mandibular), the trigeminal ganglion, and the brainstem trigeminal sensory nuclear complex - mesencephalic (proprioception), principal sensory (fine touch), and spinal (pain/temperature, subdivided into oralis, interpolaris, caudalis). The caudalis is the "medullary dorsal horn" and is where convergence and central sensitization begin. Know the temporomandibular joint: biconcave disc, upper and lower compartments, lateral pterygoid's role in translation, and the capsule/ligament restraints. Know masticatory muscles (masseter, temporalis, medial and lateral pterygoid) and their actions. Vascular supply to the mandible and the inferior alveolar nerve's course through the canal matter for injury and anesthesia questions.
Physiology and pathophysiology
Nociceptors in muscle, joint capsule, periosteum, and dental pulp signal via A-delta (fast, sharp) and C fibers (slow, aching). Peripheral sensitization lowers threshold after tissue injury; central sensitization in caudalis widens receptive fields and produces referral and allodynia. Sympathetic and descending modulatory systems (periaqueductal gray, rostral ventromedial medulla) can facilitate or inhibit.
Traps
Questions conflate the mesencephalic nucleus (the only primary sensory nucleus in the CNS housing cell bodies of primary afferents) with the principal sensory nucleus. Referred pain is often mislabeled as a nerve lesion. Remember that pulpal pain is poorly localized because of sparse proprioceptive input and convergence.
Rule of thumb
Match the symptom to the level: sharp, well-localized facial pain suggests a peripheral/A-delta process; dull, spreading, referred pain suggests central convergence. Example: pain in the ear with jaw clenching and no otologic findings points to referred myogenous pain, not V3 neuropathy.