Stimulus Brings Response

It is worth considering briefly how the hu­man nervous system normally and actually operates. The key to this is the recognition that stimulus always brings response In the simplest terms adequate stimulation of a sen­sory end-plate brings a response on the corre­sponding motor end-plate. This is called a simple reflex act. When the knee tendon is tapped, for example, the leg jerks: when light is flashed in the eye, blinking automatically occurs. These things happen rapidly, but not instantaneously. They take measurable time reaction time, measured in fractions of a second. The actual speed of nerve impulses traveling on the none pathways of the hu­man body is 200 to 300 feet a second, depend­ing on temperature and other factors.

More complicated reflex patterns normally occur in the human mind and body. These reflexes may be considered as unconscious reactions to various stimuli. We have, for ex­ample, coordinated chain reflexes, which per­mit us to walk, breathe, and perform other repetitive bodily functions without consciously thinking about them. Then there are ac­quired    or    conditioned    reflexes, learned through    practice    and   expenence    to   be­come habits.

We sometimes tend to think of stimuli as external forces and events a pinprick or a frightening sight, for example. But as anyone knows who has ever been awakened by a nightmare or blushed in shame at the recall of some earlier folly, the stimuli that set off reaction responses may be internal, hidden residents of the unconscious mind. Forgotten (repressed) memories of past experiences are the substance of many of these unconscious stimuli We frequently react to present sym­bols of past fears, dangers, and angers with­out being aware that we are doing so. This is the source of many of our feelings.

While these stress stimuli "distress sig­nals" we might call them are picked up by the central nervous system, the reactions to them are reflected in all parts of the body. The endocrine system, for example, reacts to stress on the nervous system

THE ENDOCRINE SYSTEM

The endocrine system, like the nervous system, operates to regulate and integrate the functions of separate cells, organs, and tissues of the body to act as one harmonious whole. This system comprises at least seven endo­crine or ductless glands which elaborate an even greater number of biochemical sub­stances. These substances are called hor­mones (after the Greek work meaning to "excite" or "awake"). They are discharged directly into the bloodstream for circulation to all parts of the body They do not pass through ducts or channels, like the secretions of the sweat glands, the salivary glands, the mammary glands, and others. Hence the en­docrine organs are called ductless glands, or sometimes   "glands   of   internal   secretion."

Practically all bodily activities are control­led to some extent by the endocrine glands, and   there   is   a   complex   interrelationship function, muscle tone, and resistance to fa­tigue- But even beyond that the hormones are concerned with human feelings and emotions and mediate between mind and body. This is especially apparent in the case of the adrenal glands. It has been justly stated that hor­mones govern "the tides of life."

Reading downward from skull to groin, the seven acknowledged endocrine glands of the human body are (l) pituitary, (2) thyroid, (3) parathyroids, (4) thymus, (5) adrenals, (6) islet cells of the pancreas, and (7) gonads, appearing as testes in the male and ovaries in the female. Their location is shown in the accompanying illustration. Generally speak­ing they are small organs, and their impor­tance and effect are out of all proportion to their size.

When the endocrines are in good working order, they enhance the smooth, normal functioning of the body. When the endocrine system fails to work properly, some strange and damaging results occur. The amounts of hormones produced are very small, but too little or too much secretion operates to pro­duce some bizarre effects. For example, ex­treme endocrine disorders can produce such circus freaks as the giant, the dwarf, the fat lady, the bearded lady, and the "man turning into stone."