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Updated: May 9, 2025
P. Pons. D.G. Dorsal root ganglia. S.G. Sympathetic ganglia. N. Nerve trunks to upper and lower extremities. The arrangement of the neurons of the spinal cord is just the reverse of that in the cerebrum—the center being occupied by a double column of cell-bodies, which give it a grayish appearance, while the fibers occupy the outer portion of the cord, giving it a whitish appearance.
We can understand causally that a chemical disposition in the nerve fibers brings about a chemical excitement in those neurons, but how a mental disposition is to create mental experience we could not understand; and to explain it casually, we should need again a reference to the underlying physiological processes.
Atrophy of the nerve fibers follows death of retinal neurons, but atrophy of some of the nerve fibers may be, and probably is, due to the pressure and traction exerted upon them at the margin of the disc. It is probable that too much importance has been given to this mode of interference with the nerve fibers.
*Nature of the Nervous System.*—The nervous system represents the sum total of the neurons in the body. In some respects it may be compared to the modern telephone system. As the separate wires are massed together to form cables, the neurons are massed to form the gross structures of the nervous system.
Locate and give the approximate number of the sympathetic ganglia. Show how the two portions of the spinal nerves are formed—the one from the mon-axonic and the other from the di-axonic neurons. Enumerate the different agencies through which the brain and spinal cord are protected. What cranial nerves contain afferent fibers? What ones contain efferent fibers?
There was one second of thinking that the memory of his mother had neither dissipated in part nor whole but surely remained as something inappreciably more cohesive and tangible that was either lost or banished and forlorn within the present jungle- thicket growth of neurons, and caught in the weeds and brambles of failed possibilities.
They are also protected from jars resulting from the movements of the body by the general elasticity of the skeleton. *Summary.*—The nervous system establishes connections between all parts of the body, and provides a stimulus by means of which they are controlled. It is made up of a special form of cells, called neurons.
*Sense Organs.*—The sense organs are not parts of the afferent neurons, but are structures of various kinds, in which the neurons terminate. Their function is to enable the sensation stimuli to start the impulses. By directing, concentrating, or controlling the stimuli, the sense organs enable them to act to the best advantage upon the neurons.
*Arrangements of the Neurons.*—Nowhere in the body do the neurons exist singly, but they are everywhere connected with each other to form the different structures observed in the nerve skeleton. Two general plans of connection are to be observed, known as the anatomical and the physiological, or, more simply speaking, as the "side-by-side" and "end-to-end" plans.
The side-by-side plan is seen in that disposition of the neurons which enables them to form the nerves and the ganglia, as well as the brain and spinal cord. The end-to-end connections are necessary to the work which the neurons do.
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