An essay on the mechanism of breathing and its control.

Essay by dizzielizzie13 January 2003

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An essay on the mechanism of breathing and its control

The basic mechanisms involved in inspiration and expiration are as follows;


The contraction of the diaphragm and external intercostals muscles leading to an expansion of the lungs. This expansion means there is an increase in the volume of the thorax and a decrease in intrapulmonary pressure. A pressure gradient is therefore established from the atmosphere to alveoli, hence air being suck into the lower pressure in the lungs called inspiration or breathing in.


This involves the relaxation of inspiration muscles and contraction of internal intercostals muscles decreasing the size of the lungs. This decrease in the volume of the volume of the thorax leads to an increase intrapulmonary pressure. A pressure gradient is established from alveoli to atmosphere, with air being pushed out to the atmosphere into the lower pressure. We call this expiration or breathing out.

Control of the ventilation mechanism

The ventilation rate is controlled by a respiratory system situated in the hindbrain.

In this centre there, there are three separate areas

1.the medullary rhythmicity centre, controlling the basic rhythm of ventilation and made up of an inspiratory centre and expiratory centre, located i the medulla oblongta

2.the apneustic area, located in the pons, capable of activating the inspiratory system and prolonging its action.

3.the pneumotaxic area, also located in the pons, acting on the inspiratory centre to turn it off when the lungs become overstretched or full of air.

During normal breathing impulses from the Inspiratory Centre stimulate the contraction of external intercostals muscles and diaphragm, and inhibit the expiratory system for about 2 seconds. The effect of this is the inflation of the lungs and inspiration. After 2 seconds nerve impulses from the expiratory centre stimulate the internal intercostal muscles and abdominal muscles...