Question

Chemosensitive area in respiratory centre of the medulla is affected by

A) Less $CO_2$ and $H^+$

B) Less $O_2$ and $H^+$

C) Excess $CO_2$ and $H^+$

D) Excess $O_2$ and $H^+$

Answer 1

Hint: The brain is a complex organ divided into three main parts: the cerebrum, cerebellum, and brainstem. The brainstem itself consists of the pons, midbrain, and medulla oblongata. Below the brainstem is the origin of the spinal cord.

Complete answer:

The medulla oblongata is an important part of the autonomic nervous system, and is hence very essential for life. Respiration, cardiac function, vasodilation, sneezing, vomiting and swallowing are all under the regulation of this structure. As the main respiratory centre, the medulla controls the muscles for inspiration and expiration and responds to changes in certain chemical concentrations in the blood, mainly $CO_2$ and $H^+$. This is essentially a positive feedback mechanism which adjusts breathing as the concentration of these chemicals is increased. 

> A fall in $CO_2$ and $H^+$ does not elicit a feedback response in the chemo sensitive area. Option A is incorrect.

>The medulla chemosensitive area is not affected by changes in $O_2$ concentration, therefore both option B and D are incorrect.

> Rise in $CO_2$ and $H^+$ concentration however stimulates the chemosensitive area which sends a message to the respiratory centre resulting in an increase in expiration rates, so that the $CO_2$ is sent out of the body. Option C is the correct answer.

Hence the correct answer is option ‘C’

Note: While respiration is an involuntary process which continues whether we are awake or asleep, as mammals we are also able to override this control. This temporary shift to voluntary functioning allows us to hold our breaths, blow up balloons, and so on.