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Origin of Cerebral or Cranial Nerves

nerve, nuclei, sensory, motor, brain and mixed

ORIGIN OF CEREBRAL OR CRANIAL NERVES According to Sommering there are twelve pairs of cerebral nerves (nervi cerebrales), but to this must be added the nervus intermedius (pars intermedia) which, though associated with the facial nerve in the facial canal, is.of itself a true mixed nerve. The remnant of a nervus terminalis should also be included. The first, second and eighth cerebral nerves are purely sensory; six of them, the third, fourth, sixth, seventh, eleventh and twelfth, are purely motor; while the fifth, the intermediate, the ninth and tenth are mixed nerves and contain both efferent and afferent fibers.

Cerebral Nerves, Nervi Cerebrales (Figs. I I r and 133).— 1. Olfactory (nn. olfactorii)—special sense of smell.

2. Optic (n. opticus)—special sense of sight.

3. Oculomotor (n. oculomotorius)—motor.

4. Trochlear (n. trochlearis)—motor.

5. Trigeminal (n. trigeminus)—motor and common sensory.

6. Abducent (n. abducens)—motor.

7. Facial (n. facialis)—motor.

Intermediate (n. intermedius)—special sense of taste, secretory and trophic. The glossopalatine nerve.

8. Acustic (n. acusticus)—special senses of hearing and equilibrium.

9. Glossopharyngeal (n. glossopharyngeus)—Special sense of taste, common sensory, secretory, trophic and motor. Io. Vagus (n. vagus)—motor, vasomotor, viscero-motor, inhibitory, secretory, trophic and common sensory. Ir. Accessory (n. accessorius)—motor.

12. Hypoglossal (n. hypoglossus)—motor.

Robert Bean suggests certain changes in the treatment and nomenclature of cranial nerves, most of which could be adopted with advantage, viz.: "Masticator nerve" instead of motor root of trigeminal, to indicate its supply of the muscles of mastication; " glossopalatine nerve" in place of intermediate nerve, because this better describes its distribution to tongue and palate (and glands); " acustic nerve" should be limited in meaning to the nerve supplying the cochlea, which alone is a nerve of hearing; and the nerve distributed to the vestibule and semicircular canals, whose function is equilibrium, should be considered an independent nerve, " the vestibular nerve" (Anat. Rec., Vol. 7).

All cerebral nerves are connected with the brain and, when their functions were not understood, these points of connection were indiscriminately called origins; but with our present knowl edge of the functions and development of the pure sensory and the mixed nerves such use of the term "origin" is not ad missible. Pure sensory nerves and the sensory roots of mixed nerves take their origins from ganglia situated wholly outside the brain. From those ganglia the dendrites grow outward to the peripheral distribution of the respective nerves; the axones grow centrally into the brain, where they arborize and end in groups of cell-bodies forming nuclei. Such nerves conduct impulses from the periphery to these nuclei, hence the name applied to them is terminal nuclei (nuclei terminales) (see the blue nuclei, Fig. 133). The motor nerves and the motor roots of mixed nerves take their origins inside the brain from groups Of cell-bodies also called nuclei. The axones grow outward from these4atter nuclei toward the periphery; they conduct impulses from the nuclei to the muscles or to the secreting cells in their respective areas of distribution, hence the nuclei of motor nerves and motor roots are genetic nuclei (nuclei origines) (see the red nuclei, Fig. 133). Thus it is seen that the brain connection of a motor nerve is its true origin, while this connection is the real termination of a sensory nerve.

In fishes the bodies of certain peripheral sensory neurones are found inside the spinal cord, the ganglion cells of Rohon