.
The axis cylinders
arethe extension in the nerve
of the neurofibrils which enter the dendrites fromabove and form a mesh work in the cell body (the main cell of the neuron) andaround its nucleus." Text-Book of Human Physiology, page 628> fromthe blood must take place in the nervous tissue is indicated by the fact thatthe irritability of the nerve diminishes after compression - of the bloodvessels, and returns on restoration of the circulation. When activitygoes on to the point of fatigue then a shrivelling of the cell begins, first inthe nucleus then in the body." Howell believes the energy to be derived from "a metabolism whichconsists essentially in the splitting and oxidation of the complex substance inthe protoplasm of the cell." Some of the veins empty their contentseventually into the vena cava, and others into branches of the jugular. Thespinal cord controls various voluntary and involuntary actions of the humanbody. THE TWOROOTS OF THE SPINAL NERVES, ANTERIOR AND POSTERIOR, differ in function. Theanterior roots supplycentrifugal fibres to: "1.Striated muscles of the trunk and of the extremities under the control of thewill. "3.Motor fibres for the unstriated muscles of the vessels, the vaso-motors. Theposterior roots supply sensory nerves to the skin and internal tissues exceptfor the face and the anterior part and inner portions of the head. Stimulationof the anterior roots varies in their relation to the vertebrae in the different regions. Thesuperior cervical ganglion "is situated in front of the longus capitismuscle and the transverse processes of the 2nd and 3rd cervical vertebrae. Thelast three branches come from the upper part of the ganglion. Thefollowing are from the lower part of the ganglion. (Gray says:"between the base of the transverse process of the last cervical vertebraand the neck of the first rib.") The inferior cardiac nerve,entering into the formation of the cardiac plexus, arises "from theinferior cervical and first thoracic ganglia." Other branches form thesubclavian plexus of which "the inferior thyroid and vertebral plexus arethe largest." Most of the thoracic ganglia "lie in front of the necksof the corresponding ribs. In the middle portion of the thorax they areslightly more external, in front of the transverse processes. Lower downthey lie closer to the bodies of the vertebrae. They may be situatednearer the upper border, or nearer the lower border of the ribs, or in theintercostal spaces." The "greater splanchnic nerve comes fromthe 6th to the 9th thoracic ganglia. The roots pass in front of thebodies of, the dorsal vertebrae. The smaller splanchnic nerve comes fromthe 9th to the llth thoracic ganglia." Thelumbar ganglia "lie on the bodies of the lumbar vertebrae." Thecoccygeal ganglion "lies in front of the anterior surface of thesecond piece of the coecyx." Thehypogastric plexus lies "in front of the body of the fifth lumbarvertebra, and of the promontory, and also in front of the left iliac vein." He believes thatthe function of the "sympathetic system are: "1.Cardio-acceleration and cardio-augmentation through the branches from thecervical ganglia.. "2.Secretory impulses to the salivary glands, the stomach, the pancreas, theliver, the small intestine, the large intestine, the kidneys. "4.Motor impulses to the muscular coats of the stomach and intestines, causingperistalsis and controlling the pylorus and the cardia of the stomach. "5.Motor impulses to the muscularis mucosa of the alimentary canal, causingmovements of the mucosa.
Published: November 30, 2006
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