08 Respiration and Circulation - part 04 - Regulation of Breathing

 

08 Respiration and Circulation - part 04 - Regulation of Breathing


Regulation of Breathing :
  • Respiration is under dual control : nervous and chemical. 
  • Human adults breathe about 12 times/minute while a new born about 44 times/ minute. 
  • Normal breathing is an involuntary process. 
  • Steady rate of respiration is controlled by neurons located in the pons and medulla and are known as the respiratory centres. 
  • It regulates the rate and depth of breathing. 
  • It is divided into three groups : 
  1. dorsal group of neurons in the medulla (inspiratory center),
  2. ventro lateral group of neurons in medulla (inspiratory and expiratory center) and
  3. pneumotaxic center located in pons (primarily limits inspiration, slow wave sleep and rapid eye movement sleep). 
  • Apneustic center in the medulla is antagonistic to the neumotaxic center. It controls non rapid eye movement sleep and wakefullness.
  • During inspiration when the lungs expand to a critical point, the stretch receptors are stimulated and impulses are sent along the vagus nerves to the expiratory centre. 
  • It then sends out inhibitory impulses to the inspiratory center.
  • The inspiratory muscles relax and expiration follows. 
  • As air leaves the lungs during expiration, the lungs are deflated and the stretch receptors are no longer stimulated.
  • Thus, the inspiratory centre is no longer inhibited and a new respiration begins. These events are called the Hering-Breuer reflex.
  • The Hering-Breuer reflex controls the depth and rhythm of respiration. 
  • It also prevents the lungs from inflating to the point of bursting.
  • The respiratory centre has connections with the cerebral cortex which means we can voluntarily change our pattern of breathing.
  • Voluntary control is protective because it enables us to prevent water or irritating gases from entering the lungs. 
  • But the ability to stop breathing is also limited by the build up of carbon dioxide in the blood.

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