Classification

Autonomic Nervous System

The organs (the "viscera") of our body, such as the heart, stomach and intestines, are regulated by a part of the nervous system called the autonomic nervous system (ANS). The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body. In most situations, we are unaware of the workings of the ANS because it functions in an involuntary, reflexive manner. For example, we do not notice when blood vessels change size or when our heart beats faster. However, some people can be trained to control some functions of the ANS such as heart rate or blood pressure.

The ANS is most important in two situations:

1. In emergencies that cause stress and require us t"fight” or take "flight" (run away and

2. In non emergencies that allow us t "rest" and "digest."

Fig. 2.1 Sympathetic and parasympathetic neurons with ganglion.

Fig. 2.2 Classification of nervous system

Autonomic is a combination of two words autos (self) and nomos (regulating). Thus ANS has a property to regulate organ functioning automatically. Thus it could maintain the homeostasis of an organ to exist. The two subp arts of ANS, parasympathetic nervous system participates in conserving the energy while sympathetic nervous system participated in utilizing the energy.

If any system innervates only by parasympathetic or sympathetic system then their effect is controlled by their own mechanism or by some third system while, if both are innervating to same system then their activity is controlled by the activity of other system. The above can explained by the following example Heart an organ innervates by both parasympathetic and sympathetic nervous system so if sympathetic system gets activated means energy is utilized in the form of heart contraction or increased heart beat to relax the myocardial muscle parasympathetic system gets activated and relax the myocardial muscle as the demand for oxygen by the body is decreased but do remember that in normal condition they are in the state of dynamic equilibrium i.e. myocardial muscle have specific rate of muscle contraction and muscle relaxation for normal demand biological system.

Now again a question arises in the mind that why this dynamic equilibrium is shifted tone side the answer is, supposing you are doing vigorous exercise means you are utilizing energy i.e. Your sympathetic system is in activated stage and why after 10 or 15 minutes your breath becomes normal, because parasympathetic system starts superseding the sympathetic system to conserve the energy beyond the needed amount.

1.2 The ANS regulates:

Muscles

• In the skin (around hair follicles; smooth muscle)
• Around blood vessels (smooth muscle)
• In the eye (the iris; smooth muscle)
• In the stomach, intestines and bladder (smooth muscle)
• Of the heart (cardiac muscle)

Glands

The ANS is divided into three parts:

• The sympathetic nervous system
• The parasympathetic nervous system
• The enteric nervous system.