At the physical level, ida and pingala correspond to the two aspects of the autonomic nervous system. Pingala coincides with the sympathetic nervous system and ida with the parasympathetic nervous system. The sympathetic nervous system is responsible for the stimulation and acceleration of activities concerned with the external environment and the deceleration of the organs which tend to utilize a lot of energy internally. The sympathetic nerves speed up the heart, dilate the blood vessels, increase the respiration rate and intensify the efficiency of the eyes, ears and other sense organs.
The parasympathetic nerves directly oppose the sympathetic nerves because they reduce the heartbeat, constrict the blood vessels and slow the respiration. This results in introversion. The flow of prana in ida and pingala is completely involuntary and unconscious until controlled by yogic practices.