THANKS TO THE autonomic nervous system, the human body pretty much takes care of itself without conscious effort. The weather changes but core temperature is maintained, food gets digested, cycles of sleeping and waking follow upon one another, and the body’s status remains fairly even from one day to the next. It’s a system in a delicate balance, self-regulating in an attempt to keep the entire body stable and healthy.

Buddhists in Java engage in meditation, which has been found to decrease stress and anxiety and promote calm feelings.
Buddhists in Java engage in meditation, which has been found to decrease stress and anxiety and promote calm feelings.

ABOUT ONE in a hundred Americans older than age 65 suffer from Parkinson’s disease, a neurological condition that mysteriously kills off cells in the brain. They include preacher Billy Graham and former Attorney General Janet Reno. Younger people, like actor Michael J. Fox, can also be stricken with the disease. Symptoms of the disease first appear with the onset of small tremors during voluntary movements. Over time, it becomes harder to initiate motion. Finally, muscles grow rigid, and even making the simplest movements takes extended time and effort. The condition is caused when cells in a region of the brain beneath the cortex that produces and stores the neurotransmitter dopamine die. This region, including the basal ganglia and an area called the substantia nigra (because it appears black in autopsies ), plays a key role in coordinat- ing movement.


American physiologist Walter Cannon came up with the word homeostasis to refer to the body’s ability to stay relatively stable while internal and external environments are changing. While homeostasis literally means “unchanging,” the body does indeed change when sensory receptors detect changes in the environment and automatically react, causing the release of appropriate neurotransmitters and hormones to help the body adapt to the world around it. The body then reacts to the changes, those alterations get fed back into the nervous system, and the process repeats itself.

This is known as dynamic equilibrium. It occurs when change after change keeps the body healthy. And it’s complicated. Think of the body’s constant need to adjust heartbeat and respiration, regulate temperature, as well as maintain the smooth functioning of neurons throughout it. Think of how distracting it might be if the brain didn’t adjust to our environment on a regular basis; hearts would beat rapidly long after a moment of fear had passed; the body wouldn’t adjust to changes in temperatute. The unconscious efforts of the brain go by virtually undetected as the body goes about its business.

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