The Autonomic Nervous System

The Autonomic Nervous System

The Autonomic Nervous System (ANS) is responsible for the regulation of the body’s inner environment, preparing the organism to take action, by orientating it towards potential threats, as well as towards prey or sexual opportunities. It is responsible for the famous fight or flight response, as well as the less-well known freeze response. These responses are taken care of by the Sympathetic Division of the ANS.

At the opposite end of the spectrum is the so-called ‘rest and digest’ response. These are the functions associated with digestive functions, like digesting food, eliminating waste, and general energy conservation. The Parasympathetic Division carries out these functions.

The hormone system, which secretes adrenaline and other stress hormones, which travel to their target organs in the bloodstream, is a vital part of this arrangement.

The ANS is composed of nerves which travel outside the spinal cord and which end on the internal organs, the heart, lungs, blood vessels, liver, kidneys, spleen, etc. They also innervate the eyes, the skin, sweat glands, salivary glands and the sex organs, as well as the sphincters (the valves, if you like) of the urinary bladder and the anus.

The Sympathetic and Parasympathetic operate in a reciprocal fashion, and ideally work in harmony and in an integrated way.

Let us take an example of Sympathetic function.

Late at night on a dark street in dangerous part of town (whatever your dubious reason for being there), you hear loud fast footsteps. Your Sympathetic system will go into overdrive. The first thing you will do is to orientate yourself towards the danger. Your head will turn in the direction of the sounds, your pupils will dilate to gather as much of the available light as possible. If you were a dog your ears would prick up and your hackles would rise. For you it’s goosebumps, and a focusing of your hearing and vision on the presumed threat. Your blood pressure will rise, as will heart rate and force of contraction. You will begin to sweat. Blood will be shunted from your gut where it was beginning to go to work on the Chinese meal you ate earlier. Blood will be transferred to your muscles, in preparation for a fight or flight. Alternatively, you will freeze on the spot, immobilised.

(I had a very poignant experience of this freeze response when I was twelve years old. My nine-year-old brother fell into the sea across the road from our house. I became rooted to the spot, just standing there watching him drown. Luckily a man was nearby and ran down the steps and hauled him onto dry land. For years I felt guilty about my inaction, and wondered if he would have drowned had the man not appeared. I accused myself of cowardice for not having tried to rescue him. Many people who suffer a freeze response in the face of threat feel guilt and a sense of ineptitude, thinking they should have done something constructive. To be honest knowing now that my response was a freeze response does little to assuage the lingering guilt.)

Getting back to our story, your Sympathetic nervous system will instruct your adrenal glands to release adrenaline into the blood stream, which will magnify the effects already mentioned. In an extreme case, you may vomit up the food you ate earlier, to lighten the load. Finally your sphincters will shut tight. This is what happens to men who become shy in a public toilet, when their bladder refuses to cooperate in releasing its contents.

Parasympathetic function is in many ways the opposite.

An example is defecation. You will take yourself to a concealed area and optimise your safety for this vulnerable time (since your Sympathetic system will be shut down). You will probably lock the door of the toilet and relax, perhaps with the paper. Your pulse will slow, your pupils constrict, eyes will water and you will salivate. Blood will shunt to your gut and wave of gut contractions will begin. Finally your bladder and anal sphincters will relax. Were you to be attacked at this time you would be at your most vulnerable, with your Parasympathetic in the ascendant and the Sympathetic asleep.

Some more examples. The erection of the penis and clitoris is mediated by the Parasympathetic, which is why anxiety and is anathema to satisfactory sex. The ejaculation and orgasm on the other hand is mediated by the Sympathetic. Too much drive in that department and the night ends prematurely.

Actually in sexual activity both divisions of the autonomic are aroused equally, with raised pulse, blood pressure, blood flow to the muscles, but increased salivation, secretions and relaxed sphincters (there is a mechanism to prevent passing urine and semen at the same time however).

In cases of extreme fright urination and defecation can occur as the Parasympathetic is aroused in addition to the Sympathetic.

Finally, and this is of central importance when considering how to regulate and balance the ANS, the inspiratory phase of breathing is Sympathetic, and the outbreath is Parasympathetic. To check this for yourself, make a sharp intake of breath. Notice how it arouses you, and produces a slight sense of fear. Now let the breath out with a long Ahhh, and notice the sense of release, of relaxation.

Yawning is great way to fully engage the Parasympathetic response. Notice how a series of hearty yawns relaxes you, causes your eyes and mouth to water, and makes you feel floppy and languid.

With chronic stress the sympathetic system becomes habitually overactive and in states of high anxiety the organism is constantly primed for fight or flight. There is a state of high arousal and there is a sense of impending danger. In such a state there is tendency toward negative thinking, and everything is perceived as potentially threatening. This has survival advantage, since it is more protective to interpret stimuli as potentially dangerous until proven otherwise. Physical symptoms that would otherwise be viewed rationally may be seen as life-threatening and in anxiety states others will be interpreted as being critical or ill-intentioned.

For the purpose of stress management the goal is to regulate and integrate the ANS. The Sympathetic needs to be damped down and the Parasympathetic engaged. One of the most powerful means of accomplishing this is via the breath. In a nutshell the inspiratory phase is reduced in duration, and the outbreath prolonged. Combined with predominantly abdominal breathing this forms the core of the work of pacifying the ANS. More on this later.