Definition: Autonomic Nervous System (ANS)

The Autonomic Nervous System (ANS) is a major division of the human Nervous System (NS) and is part of the Peripheral Nervous System, PNS. The ANS controls the predominantly automatic and self-regulatory functions of our blood vessels, most of our internal organs, various tissues and our endocrine glands and it is controlled by the part of the brain called the hypothalamus. 

The ANS is in turn subdivided into three main areas: The Sympathetic, Parasympathetic and Enteric Systems.

  • The Sympathetic Nervous System (SNS), also known as the orthosympathetic nervous system, the main function of which is concerned with arousal and brings about catabolic processes. The SNS becomes activated in response to something exciting, or a perceived threat or stress, sometimes switching on a startle reflex and the 'fight / flight' reaction, both of which which send energy to our limbs for action and take energy away from our digestive system. The SNS also brings about the release of adrenalin and other hormones associated with both excitement and stress. These are primitive but entirely natural responses that enable us to react quickly, for instance to jump out of the way of a bike that suddenly comes up onto the pavement next to us. However, the SNS can become over-active during periods of high or prolonged stress, often resulting in physiological and psychological strain or illness.
  • The Parasympathetic Nervous System (PSNS) is dominant during quiet, peaceful times and brings about anabolic processes. The PSNS can become activated for instance, when a stressful situation ends, or the person uses a coping strategy in order to calm down. The PSNS and the Enteric System are predominantly involved with our digestive system and the conservation of energy, so when someone practices the Alexander Technique Lying Down Procedure, for instance, you will often hear a gentle tummy-rumble, which is a sound to be welcomed as it indicates that their nervous system is calming down and the PNS is activated, so their gut can function again.

These two main divisions of the Autonomic Nervous System are antagonistic, creating opposing reactions in our bodies. However the SNS and PSNS do, for the most part, balance their functioning to bring about homoeostasis in our system. They also work together at times of strong emotions, such as during sexual activity or extreme fear.

The main reactions brought about by the SNS and PSNS are as follows:

SNS~ Preparation for Action

  • Increased heart rate and blood pressure
  • Secretion of saliva and dilation of the pupils of the eye
  • Dilation of blood vessels in our limbs to help us run or fight, for instance
  • Digestion and Peristalsis (the contractions in our stomach and gut) slows down 
  • Breathing rate increases
  • Strong emotions

PSNS ~ Calming Processes

  • Decreased heart rate and blood pressure 
  • Saliva increases and pupils contract
  • Energy comes away from our limbs and their blood vessels contract
  • Digestion commences and peristalsis speeds up
  • Breathing slows and calms down 
  • Milder emotional reactions
Much of the work that takes place in Alexander Technique lessons reduces the activity of the SNS and encourages the calming processes brought about by the activation of the PSNS.

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