agyidegek

Agyidegek, or cranial nerves, are twelve pairs of nerves that emerge directly from the brain and brainstem rather than the spinal cord. They innervate the head and neck regions, and in the case of the vagus nerve also thoracic and abdominal viscera. They carry sensory information (such as smell, vision, hearing, balance) and motor commands (eye movements, facial expressions, chewing, swallowing, speech), with several also providing autonomic (parasympathetic) functions.

The twelve cranial nerves are numbered I through XII and have diverse roles. I is the olfactory nerve (smell); II is the optic nerve (vision); III is the oculomotor nerve; IV is the trochlear nerve; V is the trigeminal nerve (facial sensation and mastication); VI is the abducens nerve (lateral eye movement). VII is the facial nerve (facial expression and taste on the anterior two-thirds of the tongue); VIII is the vestibulocochlear nerve (hearing and balance); IX is the glossopharyngeal nerve (taste on the posterior tongue and swallowing); X is the vagus nerve (parasympathetic control of much of the thorax and abdomen, with duties in swallowing and voice); XI is the accessory nerve (sternocleidomastoid and trapezius muscles); XII is the hypoglossal nerve (tongue movement).

Origin and course: most agyidegek arise from the brainstem (midbrain, pons, or medulla), with the first two nerves originating as forebrain structures. They pass through specific openings in the skull, such as the foramina for the optic canal, superior orbital fissure, foramen rotundum/ovale, stylomastoid foramen, and jugular foramen, to reach their targets.

Clinical relevance: lesions can cause distinctive deficits—loss of smell or vision, double vision, facial weakness or numbness, difficulty swallowing, hoarseness, or impaired tongue movement—informing localizing diagnosis and management.