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Updated: June 21, 2025
They are connected on either side by the right and left sympathetic nerves which extend vertically from ganglion to ganglion. The sympathetic ganglia receive nerves from the central division of the nervous system, but connect with glands, blood vessels, and the intestinal walls through fibers from their own cell-bodies.
This is the plan in the cerebrum and cerebellum, and here are found devices for increasing the surface: the cerebrum having convolutions, the cerebellum transverse ridges. That of collections of cell-bodies into rounded masses. Such masses are found in the bulb, the pons, the midbrain, and the base of the cerebrum. That of arrangement in a continuous column. This is the plan in the spinal cord.
Control of Arteries.—Changes in the rate and force of the heart’s contractions can be made to correspond only to the general needs of the body. When the blood supply to a particular organ is to be increased or diminished, this is accomplished through the muscular coat in the arteries. These, like the controlling neurons of the heart, have their cell-bodies in the bulb.
*Side-by-side Connections.*—On separating the ganglia and nerves into their finest divisions, it is found that the nerves consist of axons, while the ganglia are made up mainly of cell-bodies and dendrites. But the axons, in order to connect with the cell-bodies, must terminate within the ganglion, so that they too form a part of it.
It thus appears that the entire control of the circulation is effected in a reflex manner through the nerve centers in the bulb. These centers are stimulated by conditions that relate to the movement of the blood through the body. *Respiration.*—Efferent fibers connect the different muscles of respiration with a cluster of cell-bodies in the bulb, called the respiratory center.
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.
Most of these have their cell-bodies in the gray matter of the cord, while their fibers pass into the spinal nerves by the ventral roots. They may be stimulated by impulses either from the intermediate neurons, or from branches of the afferent neurons. Their impulses reach and stimulate the muscles.
The ventral-root divisions, of the fibers of mon-axonic neurons, the cell-bodies of which are in the gray matter of the cord. The first convey impulses to the cord and are called afferent neurons; the second convey impulses from the cord and are known as efferent neurons. A division of this pathway reaches the brain.
Fibers that convey excitant impulses to the heart to quicken its movements. b. Fibers that convey inhibitory impulses to the heart to retard its movements. The cell-bodies of the excitant fibers are found in the sympathetic ganglia, but fibers from the bulb connect with and control them.
The lowest cell-bodies develop from one cell; the enormous majority of organic beings are many-celled and among the lower forms these take on similar, and among the higher forms greater variations of, groupings and activities. In the human body for example are bones, muscles, nerves, sinews, ligaments, cartilage, skin, all either made up of cells or originating in them.
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