Question

Select the incorrect option

• A. If the blood pH is less, the medullary respiratory center sends nervous impulses to the external intercostal muscles and the diaphragm, to increase the breathing rate.
• B. Neural signals from pneumotaxic centre can reduce the duration of inspiration and can regulate the medullary centre to increase the respiratory rate.
• C. Aortic arch and carotid artery can recognize fluctuations in carbon dioxide and hydrogen ion concentration and hence, can send signals to the medullary rhythm centre.
• D. Chemosensitive area is highly sensitive to carbon dioxide and hydrogen ion concentration.

Answer 1

The correct option is C Aortic arch and carotid artery can recognize fluctuations in carbon dioxide and hydrogen ion concentration and hence, can send signals to the medullary rhythm centre.

Receptors associated with the aortic arch and carotid artery are called the aortic body and the carotid body respectively. The carotid bodies are located on the bifurcation of one of the main arteries of the neck called the carotid artery. Whereas, the aortic body is located on the aortic arch, which is the portion of the main artery (aorta) that bends between the ascending and descending part of the aorta. The aortic body and carotid body can recognize changes in carbon dioxide and hydrogen ion concentration in the blood and send necessary signals to the respiratory rhythm centre for remedial actions. For example, higher hydrogen concentration (low pH) in the blood is detected by any of these chemorecptors. These signals are transmitted to the medullary respiratory centre. The respiratory centre then directs the respiratory muscles like external intercostal muscles and diaphragm to help increase the breathing rate. This results in an increase in pH due to a shift in bicarbonate buffer equation towards release of more carbon dioxide production.
Neural signals from this centre can reduce the duration of inspiration and thereby alter the respiratory rate. It works via the medullary centres. The pneumotaxic center sends signals to inhibit inspiration that allows it to finely control the respiratory rate. Its signals limit the activity of the phrenic nerve (nerves in the neck and passing through the thorax to the diaphragm) and inhibit the signals of the apneustic center (another pons respiratory centre). It decreases tidal volume. The apneustic center sends signals for inspiration for long and deep breaths. It controls the intensity of breathing and is inhibited by the stretch receptors of the pulmonary muscles at maximum depth of inspiration, or by signals from the pneumotaxic center. It increases tidal volume. This is how the apneustic and pnuemotaxic centers work against each other together to control the respiratory rate and rhythm centre help direct the respiratory muscles which leads to a decreased/increased breathing rate.