Explanation

Breathing is entirely under nervous control. A ‘respiratory centre’, located bilaterally in medulla oblongata and pons Varolii of the brain not only regulates normal breathing, but also automatically adjusts the breathing rate to the varying requirements of body during various stress conditions such as exercise, fear, pain, anger, fever, worry, etc, and in activities like speaking, playing a musical instrument, yogic exercise, etc, because of this oxygen $\left( p_{O_{2}} \right)$ and carbon dioxide $\left( p_{CO_{2}} \right)$ in blood remain almost static in all conditions. Also we may voluntarily hold out breath for sometime, but not for a longer time due to this nervous control.