Organic and functional nervous diseases : a text-book of neurology / by M. Allen Starr.

  • Moses Allen Starr
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Organic and functional nervous diseases : a text-book of neurology / by M. Allen Starr. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    CHAPTER III. THE PERIPHERAL NERVOUS SYSTEM. The peripheral nervous system is made up of the twelve cranial and thirty-one spinal pairs of nerves which connect every part of the body with the central nervous system; viz., the cerebral axis and the spinal cord; and also of the sympathetic nervous system with its various ganglia. The nerves, as already shown, are merely prolonga- tions of the neurones; motor nerves being the axones of the motor neurones situated in the anterior gray horns of the spinal cord and in the gray matter of the medulla, pons, and crura cerebri; sensory nerves being the axones of sensory neurones situated in the posterior spinal ganglia and in the ganglia of the cranial nerve roots; sympa- thetic nerves being the axones of the various sympathetic neurones situated in their ganglia. THE HISTOLOGY OF A NERVE FIBRE. When a nerve trunk is dissected, the connective-tissue sheath or perineurium enclosing its fibres torn away, and the individual fibres set free by tearing the finer connective-tissue strands or endoneurium which bind them together, it is possible to distinguish certain parts by means of appropriate methods of staining. There is, first, the axone or axis cylinder. (Fig. 11.) This is made up of a number of primitive fibrils longitudinally arranged and con- tinuous throughout the length of the nerve. The fibrils are cemented together by a substance which appears finely granular. Each axone comes from a single nerve cell; the individual fibrils come from the cell body and from its dendrites. The fibrils pass together in the axone to the periphery and there terminate, the individual fibrils branching out in various directions, and joining with other fibrils from other axones to form a fine plexus within the organ to which the nerve as a whole has gone. It has been thought possible to trace individual fibrils of the plexus into individual epithelial cells in various internal organs and in the skin. Other axones can be traced directly to ter- minal organs, such as the terminal plates upon the muscle and the ter- minal bulbs and corpuscles in the skin. In these no division or branching of the fibrillary constituents of the axis cylinder has been discovered. Their termination in each of the organs of special sense is still different. The diameter of an axis cylinder varies from 2.6/z to 7.5 /;!. It is no longer believed that the longest fibres have the great- est diameter. There is, secondly, the myelin sheath surrounding the axis cylinder.
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