Control of Respiration
A) Respiratory Centre
Respiratory muscles contract as a result of nerve impulses from centers in the brain and relax in the absence of these nerve impulses. Clusters of neurons located bilaterally in the medulla oblongata and pons are collectively called the Respiratory Centre. This area is further divided into 3 main areas: 1) Medullary Rhythmicity Area : is control of the basic rhythm of respiration. There is an area for inspiration and expiration. Nerve impulses for inspiration are normally the only active ones during quiet breathing. If forceful exhalation is initiated, the expiratory area is activated. 2) Pneumotaxic Area : helps coordinate the transition between inhalation and exhalation. This area is located in the upper Pons and transmits inhibitory impulses to the inspiratory area of the medullary rhythmicity area. 3) Apneustic Area : also helps coordinate the transition between inhalation and exhalation, located in the lower pons. The difference is that this area sends stimulatory impulses to the inspiratory area that activate it and prolong inhalation. This promotes long, deep inhalation. Activation of the pneumotaxic area overrides signals from this area. The basic rhythm and coordination of the respiratory centre can be modified by input from other areas of the brain and receptors in the PNS. Cerebral cortex connection allows horses to voluntarily alter their pattern of breathing such as refusing to breath for short period of time. This prevents water or irritating gases from entering the lungs. Buildup of CO2 and acids stimulate the inspiratory center to strongly send impulses to muscles of inspiration.
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