Introduction

Abstract

The special sensory systems are concentrated in the head. This major “information center” is rich in general sensory receptors (touch, pressure, temperature, pain) by the largest cranial nerve — th\e trigeminal — that has (at least in humans) also the largest ganglion, called after Gasser (Hassler and Walker 1970; Ferner 1970). Its three divisions, the ophthalmic, maxillary and mandibular nerves, innervate the skin of the face and anterior scalp, the conjunctiva and the cornea, the mucous membranes of the mouth, the nose and the paranasal sinuses, the anterior two thirds of the tongue, the teeth, the meninges of the anterior and middle cranial fossae, including the tentorium, and, possibly, the anterior wall of the external auditory meatus, and a small portion of the external surface of the tympanic membrane (Cushing 1904; Brodal 1965; Lang 1981; Samii and Janetta 1981; Leblanc 1992; Roda and Blanton 1994). The central processes of the trigeminal ganglion cells comprise the radix sensoria (portio major) of the trigeminal nerve and terminate in the principal sensory nucleus and the nucleus of the spinal tract (Cajal 1909; Windle 1926a,b; Sjoqvist 1938; Szentagothai and Kiss 1949; Astrom 1953; Torvik 1956; Kerr 1963, 1970a; Zhukova 1966; Westrum and Black 1968; Rustioni et al. 1971; Grant and Arvidsson 1975; Gobel and Höckfield 1977; Westrum and Canfield 1977; Marfurt 1981b; Westrum et al. 1981; Arvidsson 1982; Falls and Alban 1986; see the exhaustive review of Capra and Dessem 1992; for the distribution of trigeminal primary afferent projections to “non-trigeminal” areas of the central nervous system see also Marfurt and Rajchert 1991). Small numbers of fibers from the intermediate, glossopharyngeal and vagus nerves also join the spinal tract (Brodal 1947; Torvik 1956; Kerr 1962; Rhoton et al. 1966).