Features Peculiar to the Trigeminal Innervation

Summary The aspects of trigemina! sensory structure and function which are uniquely different from spinal systems are reviewed in this paper. In the periphery, several unique arrangements of sensory receptors are seen, and appear to have unique sensory functions. The receptors in the cornea, the nasal mucosa, and the tooth pulp are morphologically unspecialized and are associated with “protopathic” sensory experiences. The important sensory functions of the mammalian vibrissae are also discussed, as well as their relationship to the anatomically distinctive cortical “barrels”. Aspects of trigeminal proprioception are also of interest. The absence of spindles in some muscles and the unique central organization of trigeminal proprioceptive afférents in the jaw and extraocular muscles are of functional significance in the motor function of the jaw and the eye. Trigeminal afférents are also involved in several complex autonomie reflexes. Characteristic changes in cardiovascular and respiratory function are elicited by various patterns of trigeminal sensory stimulation. These reflexes include the diving reflex, the oculo-cardiac reflex, naso-cardiorespira-tory reflexes, and the trigeminal depressor response. The clinical significance of these reflexes is discussed. Several coordinated behavioral responses including suckling are also elicited from trigeminal afférents. The evidence implicating trigeminal afférents in eating and drinking behavior is presented.