Neuroanatomy

The facial or seventh nerve is purely motor. It is accompanied a short distance by a bundle usually called its sensory root or the intermediate nerve.

Customarily, the cranial nerves are described as comprising twelve pairs and each is referred to by number.

The trigeminus is the largest of the cranial nerves with the exception of the optic. It is usually described as the fifth cranial nerve and as possessing both a sensory and a motor root.

The spinal nerves are arranged in pairs, the nerves of each pair being symmetrical in their attachment to either side of their respective segment of the spinal cord, and, in general, symmetrical in their course and distribution.

The fibers of each trochlear or fourth nerve (or patheticus) spring from the cells of a nucleus which lies in the grey substance of the floor of the cerebral aqueduct in hne with the oculo-motor nucleus, but in the region of the inferior quadri-geminale bodies.

The medial branches of the posterior primary divisions of all the lumbar nerves end in the multifidus spinse and those of the three lower nerves send very small branches to the skin of the sacral region.

The oculo-motor or third cranial nerve is a purely motor nerve. Each supplies seven muscles connected with the eye, two of which, the sphincter of the iris and cihary muscle, are within the ocular bulb.

The posterior primary divisions of the upper four sacral nerves escape from the vertebral canal by passing through the posterior sacral foramina; those of the fifth sacral nerve pass out through the hiatus sacralis between the posterior sacro-coccygeal ligaments.

The fibers of the optic nerve are the central processes of the ganglion cells of the retina. Within the ocular bulb they converge to the optic papilla, where they are accumulated into a rounded bundle, the optic nerve.

The posterior primary divisions of all the thoracic nerves divide into medial and lateral branches while in the vertebral groove.

The olfactory nerve-fibers are the central processes of the bipolar olfactory nerve cell-bodies situated in the olfactory region of the nasal mucous membrane. In man, the olfactory region comprises the epithelium upon the superior third of the nasal septum and that upon practically the whole of the superior nasal concha.

The posterior primary division of the first cervical or suboccipital nerve springs from the trunk, between the vertebral artery and the posterior arch of the atlas, passes dorsalward into the sub-occipital triangle, and breaks up into branches which supply the superior oblique, the inferior oblique, and the major rectus capitis posterior muscles, which form the lateral boundaries of the triangle.

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