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7. Those which restrain impulses are called inhibitory nerves.

Cerebro
Spinal
Nerves

The Cerebro Spinal nerves control both the voluntary and involuntary movements of the body.

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FIG. 6. The spinal cord and the brain showing the branching of thirty-one pairs of spinal nerves.

By voluntary movements are meant conscious acts, directed by thought; they are the smallest part of the nervous activities.

Cord.

By involuntary acts are meant such workings of the body as sustain life, such as will go on without conscious thought;these are directed largely by nerve centers in the spinal cord and the medulla oblongata. Examples of the involuntary movements are the workings of the digestive system, the metabolic activity among the tissues in the breaking down of waste and the assimilation of nourishment and the control of the circulation, of the heart, the breathing, etc.

The Spinal The spinal cord, which is a part of the cerebro spinal nervous system, lies within the spinal canal or the vertebrae. It is continuous with the brain through the medulla oblongata, which is the name given to the upper end of the cord.

It does not occupy the entire opening in the cavity of the vertebræ, (this space is partially filled with blood vessels); neither does it extend the entire length of the spinal column. It extends from the skull, downward about eighteen inches, or to just about opposite the last rib, where

it divides into a bundle of small nerves, resembling a horse's tail. (See Fig. 5 and 6.)

It weighs about 11⁄2 ounces.

The spinal cord sends out thirty-one pairs of spinal nerves, which issue from either side of the spinal column, through small openings between the vertebræ; (See Figures 7, 8 and 9).

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The spinal nerves branch to all parts of the body, with the exception of the head. The nerves controlling the face and the head do not enter the spinal cord, but connect directly with the brain.

It will be readily seen that if a vertebra be out of place, in such a manner as to cause an extreme pressure upon any pair or pairs of spinal nerves, the nerve impulse through these nerves, as previously explained, will be restricted, while the nourishment to the extremities, or to parts of the body controlled by these nerves, may be interfered with. In extreme cases, entire paralysis of the body supplied by such nerves will result. It is only in extreme cases, however, that the vertebræ are forced so far out of position as to interfere with nerve impulse.

This theory of the interference with spinal nerves, by dislocated vertebræ, is the one upon which the school of Osteopathy largely bases its work. It is one principle, also, upon which the physical culturist must work. If the nourishment to any organ be interfered with because

of weakened nerves, attention must be given to regaining perfect freedom and strength of the spinal nerves controlling that organ.

The spinal nerves do not branch out as single nerve trunks, but arise by two roots, one from the anterior portion of the cord, known as the anterior root, and the other from the posterior portion, known as the posterior root;-(there is a small ganglion found upon this root just after it leaves the cord.)

The anterior root contains the motor nerve fibres, which convey motor impulse from the center to the extremities; the posterior root contains the sensory nerve fibres,-or the fibres which convey impression from the extremities. As these two nerve roots leave the spinal cord, they converge toward the vertebral opening, where they coalesce by the mingling of their fibres to form a compound or mixed spinal nerve, which after issuing from the vertebral canal, gives off anterior and posterior branches, each containing fibres from both roots, as well as a third branch to the

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