Explain the division and function of …

1. The autonomic nervous system is divided into two main divisions: Sympathetic nervous system 
2. Parasympathetic nervous system

These both are antagonistic in working i.e. they work opposite to each other. This is because of the different neurotransmitters secreted by the axon terminals of the nervous systems. The neurotransmitter of the parasympathetic nervous system is acetylcholine whereas in the case of the sympathetic nervous system is adrenaline/epinephrine. Sympathetic works in the case of an emergency while parasympathetic works under normal conditions.

Examples are:

1. Heart: SNS speeds up the heartbeat whereas the PSNS slows down the heartbeat.

2. Eyes: SNS dilates the pupils whereas the PSNS constricts the pupil or bring it in the normal condition.

3. Lungs: SNS dilates the bronchioles for greater alveolar oxygen exchange while PSNS constricts the bronchioles when oxygen requirement diminishes.