Sympathetic and Parasympathetic nervous system & Human Stress Response

Summary

Explaining the Sympathetic and Parasympathetic nervous system & Human Stress Response.

Sympathetic and Parasympathetic nervous system

The body functions that are regulated automatically, like digestion, heart rate, breathing, hormone regulation, liver function etc... are regulated by the autonomic nervous system (ANS). The ANS has two branches that work in conjunction: the sympathetic nervous system (SNS) (promotes activity in the body/ fight or flight mode) and the parasympathetic nervous system (PNS) (promotes relaxation/ rest & digest).

Sympathetic nervous system (activating) 

The Sympathetic Nervous System, in conjunction with such stress hormones as adrenaline and cortisol, initiate a series of changes in the body, including raising blood pressure, heart rate, and blood sugar levels. These changes help a person deal with a crisis situation. They mean more energy and more blood and oxygen flowing to the large muscles of the trunk, arms, and legs, allowing the person to run from danger or do battle (the so-called “fight-or-flight” response).

• Diverts blood flow away from the gastrointestinal (GI) tract and skin via vasoconstriction

• Blood flow to skeletal muscles and the lungs is enhanced (by as much as 1200% in the case of skeletal muscles)

• Dilates bronchioles of the lung through circulating epinephrine, which allows for greater alveolar oxygen exchange

• Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for enhanced blood flow to skeletal muscles

• Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and enhances far vision

• Provides vasodilation for the coronary vessels of the heart

• Constricts all the intestinal sphincters and the urinary sphincter

• Inhibits peristalsis

• Stimulates orgasm

Parasympathetic nervous system (relaxing/rest & digest)

The PNS, in contrast, tends to slow the heart and lower the blood pressure, allowing recovery after a stressful event. Blood flow diverted away from the intestines and reproductive organs, whose function isn’t essential in an emergency, returns. In contrast to fighting or flight, these more restorative functions can be thought of as “rest and digest.” They are also sometimes dubbed the relaxation response.

• Dilating blood vessels (vasodilation) leads to the GI tract and increases blood flow.

• Constricting the bronchiolar diameter when the need for oxygen has diminished

• Dedicated cardiac branches of the vagus and thoracic spinal accessory nerves impart parasympathetic control of the heart.

• Constriction of the pupil and contraction of the ciliary muscles, facilitating accommodation and allowing for closer vision.

• Stimulating salivary gland secretion and accelerates peristalsis, mediating digestion of food and, indirectly, the absorption of nutrients

• Sexual. Nerves of the peripheral nervous system are involved in the erection of genital tissues via the pelvic splanchnic nerves 2–4. They are also responsible for stimulating sexual arousal.

The Human Stress Response

Strong and deep breathing techniques activate the sympathetic nervous system. 

Slow & subtle breathing promotes the Parasympathetic nervous system. 

The human stress response is a mechanism of the human body that provides a better chance of survival when the body is under threat and mobilizes neural and hormonal networks to optimize cognitive, cardiovascular, immunological and metabolic functions.

A stressful situation — whether something environmental, such as a looming work deadline, or psychological, such as persistent worry about losing a job — can trigger a cascade of stress hormones that produce well-orchestrated physiological changes. A stressful incident can make the heart pound and breathing quicken. Muscles tense and beads of sweat appear.

This combination of reactions to stress is also known as the “fight-or-flight” response because it evolved as a survival mechanism, enabling people and other mammals to react quickly to life-threatening situations. The carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses helps someone to fight the threat off or flee to safety. Unfortunately, the body can also overreact to stressors that are not life-threatening, such as traffic jams, work pressure, and family difficulties.

Over the years, researchers have learned not only how and why these reactions occur but have also gained insight into the long-term effects chronic stress has on physical and psychological health. Over time, repeated activation of the stress response takes a toll on the body. Research suggests that chronic stress contributes to high blood pressure, promotes the formation of artery-clogging deposits, and causes brain changes that may contribute to anxiety, depression, and addiction... More preliminary research suggests that chronic stress may also contribute to obesity, both through direct mechanisms (causing people to eat more) or indirectly (decreasing sleep and exercise).

Techniques to counter chronic stress

Many people are unable to find a way to put the brakes on stress. Chronic low-level stress keep the glands that produce stress hormones simulated ( the hypothalamic, pituitary and adrenal glands). Much like a motor that is idling too high for too long. After a while, this has an effect on the body that contributes to the health problems associated with chronic stress.

Persistent epinephrine surges can damage blood vessels and arteries, increasing blood pressure and raising the risk of heart attacks or strokes. Elevated cortisol levels create physiological changes that help to replenish the body’s energy stores that are depleted during the stress response. But they inadvertently contribute to the buildup of fat tissue and to weight gain. For example, cortisol increases appetite, so that people will want to eat more to obtain extra energy. It also increases the storage of unused nutrients as fat.

Fortunately, people can learn techniques to counter the stress response.

“Resetting” the nervous system

By doing strong breathing techniques one can give all systems in the body a good ‘shaking’ and one can in a way ‘reset’ the nervous system.

Relaxation response

Dr. Herbert Benson, director emeritus of the Benson-Henry Institute for Mind-Body Medicine at Massachusetts General Hospital, has devoted much of his career to learning how people can counter the stress response by using a combination of approaches that elicit the relaxation response. These include deep abdominal breathing, focus on a soothing word (such as peace or calm), visualization of tranquil scenes, repetitive prayer, yoga, and tai chi.

Most of the research using objective measures to evaluate how effective the relaxation response is at countering chronic stress have been conducted in people with hypertension and other forms of heart disease. Those results suggest the technique may be worth trying — although for most people it is not a cure-all. For example, researchers at Massachusetts General Hospital conducted a double-blind, randomized controlled trial of 122 patients with hypertension, ages 55 and older, in which half were assigned to relaxation response training and the other half to a control group that received information about blood pressure control. After eight weeks, 34 of the people who practiced the relaxation response — a little more than half — had achieved a systolic blood pressure reduction of more than 5 mm Hg, and were therefore eligible for the next phase of the study, in which they could reduce levels of blood pressure medication they were taking. During that second phase, 50% were able to eliminate at least one blood pressure medication — significantly more than in the control group, where only 19% eliminated their medication.