The pons, a saddle-like mass of coarse fibers,
connects the medulla with the higher brain centers. The medulla, or spinalbulb, just below the pons and at the upper end of the spinal cord, is a
switching center for nerve impulses to and from higher brain centers.
It also
contains centers which, as we will see, work through the autonomic nervous
system to control heart action, changes in artery walls, breathing, and other
activities that go on without our conscious effort. The cerebellum, or little
brain, is divided into hemispheres like the cerebrum. The front and back areas
control muscle tone. Equilibrium is the concern of an area behind the back
lobe. The two main hemispheres coordinate voluntary movements.
It is characteristic of the intricate organization of
brain and nervous system that the cerebellum receives nervous messages from the
balance mechanism of the inner ears, from the muscles and joints, and from
centers deep in the brain, and then sends impulses to the muscles adjusting
their tone and coordinating their action. Are you able, with eyes closed, to
touch the tip of your nose? Can you both rub your stomach and pat your head
simultaneously? Then your cerebellum is still at work.
Protection for the Brain
The brain is an excellent example of built-in
protection provided by nature for a vital organ, Despiteprocesses in the brain,
brain tissue itself is quite sturdy stuff, tough and resilient. It is protected
against injury in a number of ways. A tough bony cage, the skull, surrounds the
brain completely. It takes a very strong blow to break the skull. The skull
itself is protected by the scalp, which can absorb some tough blows. The scalp
is made up of five layers which medical students remember by an acrostic: S is
for skin (and hair in which in women constitutes considerable protection), and
the skin of the scalp is the thickest in the body; C is for the cutaneous
tissue, a layer under the skin; A is for the aponeurosis, a tough layer of
fibrous tissue which helps the scalp slide around; L is for some loose tissue;
Still more protection is provided
Inside the
brain are four reservoirs, the ventricles, which contain cerebrospinal fluid.
This fluid circulates around the brain. Thus, the brain practically floats on
and in fluid. And engineers will tell you that this is an ideal "shock
absorber" system. Finally, inside the bone of the skull the brain is
wrapped in layers of tissue. One of these layers, the dura mater, is
particularly tough and helps protect the brain against blows. But nature cannot
provide infinite protection, and it has not foreseen the demands of modern
society. It did not anticipate that man would ride motorcycles at 100 miles an
hour, and might hurtle over the handle-bars.
Or that children would go out on hard turf and play
football. Or those workmen would walk under skyscraper construction projects
where a bolt falling from the fortieth floor would develop the speed of anartillery projectile. So we need additional protection: adequate helmets for
motorcyclists and athletes, steel hats for workmen exposed to possible head
injuries. Parents must realize, too, that babies fall off beds and, at some
stage, jump out of cribs. These must be guarded against and a baby doctor can
advise. Beyond protecting the brain from injuries, you can protect it so there is
no interference with its efficient operation.
