Autonomic Nervous System and Stress
The natural balance of opposites in relation to stress is seen very clearly within the human nervous system. The physical reaction of stress in the body is regulated by the autonomic nervous system. This system has two divisions: the sympathetic and the parasympathetic nervous systems.
"A stressor can be defined as anything that throws your body out of homeostatic balance; for example, an injury, an illness, subjection to great heat or cold, or being teacher. The stress response in turn is your body's attempt to restore homeostatic balance." ( Why Zebras Don't Get Ulcers, p. 7, Robert Sapolsky)
The Sympathetic Nervous System
The sympathetic nervous system is a series of nerves originating in the brain and exiting through the spine to nearly every organ, blood vessel, and sweat gland in your body. They even connect to the tiny muscles attached to hairs on your body. Goose pimples are an activation of the sympathetic nervous system. The sympathetic nervous system controls arousal. When a threat or demand is perceived, chemicals are secreted into the blood stream. The main stress chemicals are adrenaline, which puts the entire body on alert, and cortisol, which helps produce the energy required for red alert status. This is done by producing a number of specific reactions in the body:
- Increased sympathetic nervous system activity.
- Increased stress chemicals.
- Increased heart rate.
- Increased blood pressure.
- Increased metabolic rate for increased energy, including the release of glucose from the liver.
- Increased functioning of the endocrine portion of the pancreas related to production and control of glucose.
- Bronchioles dilated for more energy.
- Contraction of muscles, especially the large muscles of the body used for fight-or-flight like the thighs, back, and shoulders.
- Shunting of blood from abdomen to large muscles, resulting in reduction of digestive activity. Shunting of blood from the sexual organs.
- Vasodilation of arteries to working muscles.
- Vasoconstriction of arteries to nonworking muscles.
- Increased alertness.
The Parasympathetic System
When the perceived demand is seen as having been met or the perceived threat is no longer seen as threatening, the second part of the autonomic nervous system is activated. This is the parasympathetic system which allows for energy conservation and relaxation. It has several characteristics:
- Reduction in heart rate, ventilation, and muscle tension.
- Blood flow is increased to the extremities including the hands and feet.
- It is characterized by diaphragmatic breathing.
- It is dominated by the tenth cranial or vagus nerve which is influenced by the brain stem and connects to the respiratory, circulatory, and digestive systems.
- The main relaxation response chemical is acetylcholine which is released at higher levels during meditation.
- It is necessary for sexual excitation.
A balance in the functioning of these two systems is necessary for health at the physiological and psychological levels. The sympathetic functions as the gas pedal, the parasympathetic as the brake. They function in synchrony for a wide range of functions, though they cannot dominate the system simultaneously. In other words, you cannot be completely aroused and relaxed at the same time.
Within the next posts I will be sharing readings on the following topics:
- Autogenic Relaxation
- Breathing Techniques