Introduction to the Autonomic Nervous System:


Within the nervous system is a branch called the ANS (Autonomic Nervous System). This system is responsible for regulating subconscious bodily processes such as organ function, digestion, reflexes and breathing. The ANS is subdivided into sympathetic and parasympathetic nervous systems which usually respond in different ways. 

The sympathetic nervous system activates the 'fight or flight' response, preparing the body for physical and mental activity to respond to perceived threat. This system is found in the sacral region of the spinal cord. Sympathetic neurons accelerate activity such as heart rate by releasing adrenaline into the bloodstream, as well as causing dilation of the pupils in the eyes, muscle contraction, decreased stomach movement and secretions (this is why you may feel a 'knot' in your stomach when feeling nervous because the 'fight or flight'/stress response causes stomach muscles to tighten and causes blood to be redirected away from the stomach to other parts of the body more vital to survival.

On the other hand, the parasympathetic nervous system, found in the lumbar and thoracic regions of the spinal cord, initiates the 'rest and digest' response, controlling the body's response whilst at rest. The rest and digest response acts as a counterbalance to the fight or flight response, restoring the body to a state of calm. Unlike the sympathetic nervous system, the parasympathetic nervous system is slower and consists of longer neuron pathways. Furthermore, the parasympathetic neurons slow down activity in the body by releasing neurotransmitters such as acetylcholine, which has an inhibitory effect on organs. This gives rise to constriction of pupils in the eye, a slower heart rate, relaxing of muscles as well as increased stomach movement and secretions. 

The autonomic nervous system is always working to achieve homeostasis and is not only active during the sympathetic and parasympathetic responses. However, we can experience autonomic imbalances. These imbalances may be instantaneous: we may be confronted with a 'fight or flight' or 'rest and digest' situation very quickly in which either the sympathetic or parasympathetic response becomes dominant. In a highly stressful situation, the sympathetic response becomes dominant. In a relaxed and safe place, the parasympathetic response becomes dominant (although prolonged parasympathetic dominance can cause lethargy). Once one of these responses become dominant, the body tries to initiate the other type of response to counterbalance the effects of the first type of response. In addition, we may also experience long-term autonomic imbalances as a result of chronic stress, which can cause wear-and-tear on the body due to other bodily systems being continuously activated by the nervous system.

By Kumaran Rajaratnam.




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