no
pain.

Scattered along the entire length of the spinal cord, especially in the
upper part, are groups of nerve cells which preside over certain specific
functions of animal life; that is, definite collections of cells which
control definite functions. Thus there are certain centers for maintaining
the action of the heart, and the movements of breathing; and low down in
the cord, in the lumbar regions, are centers for the control of the
various abdominal organs.

Numerous other reflex centers are described by physiologists, but enough
has been said to emphasize the great importance of the spinal cord as an
independent nerve center, besides its function as a conductor of
nervous impulses to and from the brain.

280. The Brain as a Reflex Center. The brain, as we have just
stated, is the seat of consciousness and intelligence. It is also the seat
of many reflex, automatic, and coordinating centers. These give rise to
certain reflex actions which are as entirely independent of consciousness
as are those of the spinal cord. These acts take place independently of
the will, and often without the consciousness of the individual. Thus, a
sudden flash of light causes the eyes to blink, as the result of reflex
action. The optic nerves serve as the sensory, and the facial nerves as
the motor, conductors. The sudden start of the whole body at some loud
noise, the instinctive dodging a threatened blow, and the springing back
from sudden danger, are the results of reflex action. The result ensues in
these and in many other instances, without the consciousness of the
individual, and indeed beyond his power of control.

281. The Importance of Reflex Action. Reflex action is thus a
marvelous provision of nature for our comfort, health, and safety. Its
vast influence is not realized, as its numberless acts are so continually
going on without our knowledge. In fact, the greater part of nerve power
is expended to produce reflex action. The brain is thus relieved of a vast
amount of work. It would be impossible for the brain to serve as a
"thinking center" to control every act of our daily life. If we had to
plan and to will every heart-beat or every respiration, the struggle for
life would soon be given up.

The fact that the gray cells of the spinal cord can originate a countless
number of reflex and automatic activities is not only of great importance
in protecting the body from injury, but increases vastly the range of the
activ