Question

Explain the process of inspiration and expiration under normal conditions.

Answer 1

Regulation of respiration (inspiration and expiration):

In the brain, the medulla oblongata contains a respiratory centre. This controls breathing. The respiratory centre consists of an inspiratory centre and an expiratory centre. The axons from the nerve cells of these centres lead to the intercostal muscles through the intercostal nerves and the diaphragm via the phrenic nerves. These nerve fibres transmit impulses to the external intercostal and internal intercostal muscles alternately. The walls of the alveoli have sense endings, which are stimulated by changes in the tension of alveolar walls.

When the alveoli are stretched at the height of inspiration the receptors send stimuli to the expiratory centre of the medulla through the vagus nerve which inhibits further inspiration. This sequence of events is called Herring-Bruer reflex. In addition, the medulla contains a pneumotaxic centre, which s connected to the breathing centre and helps to ensure rhythmic breathing. During inspiration, the inspiratory part of the respiratory centre sends impulses to the pneumotaxic centre, which responds by sending impulses to the expiratory part of the respiratory centre. The expiratory centre is then activated and so the inspiratory centre is inhibited reflexly. Thus the respiratory rhythm is controlled by these centres in the brain.