Nervous Control Of Respiration

The basic rhythm of respiration is controlled by groups of neurons in the medulla oblongata and pons, called the respiratory centre. This respiratory centre is divided into 3 functional areas;

• The medullary rhythmicity area controls the basic rhythm of respiration and is further subdivided into two areas;
• 1. The inspiratory area determines the basic rhythm and is also responsible for the contraction of the diaphragm. The inspiratory area sends signals to the diaphragm via the phrenic nerves.
• 2. The expiratory centre is usually inactive during normal respiration, however during forceful expiration e.g. during exercise, it is activated by nerve impulses from the inspiratory area. Impulses from the expiratory centre cause contraction on the internal intercoastals and abdominal muscles, resulting in a forced expiration.
• The pneumotaxic area is found in the superior portion of the pons, and helps to coordinate the transition between expiration and inspiration by turning off the inspiratory area before the lungs become too full. The net result is that the pneumotaxic area helps to facilitate expiration.
• The apneustic area also helps to coordinate the transition between inspiration and expiration by activating the inspiratory area and inhibiting expiration. It is found in the anterior portion of the pons and only works when the pneumotaxic area is inactive. The net result is that the apneustic area helps to facilitate inspiration.

How does the respiratory centre know when the body needs to inspire?

The respiratory centre receives messages from the chemoreceptors involved in the chemical control of respiration via a negative feedback loop. The chemoreceptors detect high levels of CO₂ and H⁺ and low levels of O₂ and send nerve impulses to the respiratory centre. The respiratory centre interprets these signals and stimulates the appropriate area to bring about inspiration.

Bibliography
Tortora & Grabowski (2000) Principles Of Anatomy & Physiology. 9th Edⁿ.New York. John Wiley & Sons Inc.