Describe how the mechanism of ventilation is controlled. Describe the roles of the phrenic nerves and medulla in generating a basic breathing rhythm.

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Describe how the mechanism of ventilation is controlled.Describe the roles of the phrenic nerves and medulla in generating a basic breathing rhythm.

Introduction

The tidal flow of air  into and out of the lungs is caused by differences in pressure between the thorax and the atmosphere.Air always moves from an area of higher pressure to an area of lower pressure.A ventilation mechanism ensures that a constant supply of fresh air is available to provide enough oxygen for gas exchange and to remove carbon dioxide.

There are two processes of breathing- inhalation and exhalation

Inhalation

Air moves from high to low pressure.Hence the pressure in the lungs is low.The diaphragm muscle contracts and flattens.The external intercostals muscles contract and pull the rib cage out and up.The volume in the lung  increases.This reduces the pressure in the lungs and air moves from the atmosphere(high pressure) to the lungs(low pressure)

          Process of breathing in

Exhalation

In this process the pressure in the lungs must be higher than the pressure in the atmosphere so that air move in an opposite direction to that in inspiration.The diaphragm muscle relaxes and rises up.The internal intercostals muscles contract and the ribs are pulled downwards and inwards.These movements reduced the volume of the lungs.Since the volume decreases ,pressure increases.Hence air moves out of the lungs to the atmosphere.

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Process of breathing out

Ventilation brings oxygen into the lungs for gas exchange and removes carbon dioxide.Since the amount of oxygen we need varies depending on activity ,there must be a mechanism which controls the breathing process.

The rhythmic sequence of  and  is brought about by alternating series of signals from the inspiratory and expiratory  cells in the  center of the (medulla).During the phase in which the inspiratory nerve cells are activated, the expiratory nerve cells do not discharge, and conversely.Complex circuits and networks of   are responsible for this mechanism. Signals from  located in ...

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