**Core Concept**
Chemoreceptors are specialized sensory receptors that detect changes in the chemical composition of the blood, particularly in the levels of oxygen, carbon dioxide, and pH. They play a crucial role in regulating breathing and maintaining acid-base balance.

**Why the Correct Answer is Right**
Chemoreceptors are located in the medulla oblongata, specifically in the vicinity of the respiratory centers. The carotid bodies, which are the primary chemoreceptors, are located in the carotid bifurcations, while the aortic bodies are located in the aortic arch. These chemoreceptors contain type I and type II pneumocytes, which release neurotransmitters such as serotonin, dopamine, and acetylcholine in response to changes in blood pH, pCO2, and pO2. This triggers a reflex increase in breathing rate to compensate for the changes.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because the chemoreceptors are not located in the hypothalamus, which is primarily involved in regulating body temperature, hunger, and thirst.
* **Option B:** This is incorrect because the chemoreceptors are not located in the spinal cord, which is primarily involved in transmitting sensory information from the body to the brain.
* **Option C:** This is incorrect because the chemoreceptors are not located in the cerebellum, which is primarily involved in coordinating muscle movements and maintaining balance.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that chemoreceptors are sensitive to changes in blood pH, pCO2, and pO2, and that their stimulation triggers a reflex increase in breathing rate. This is a critical concept in understanding the regulation of respiration and the pathophysiology of respiratory disorders.

**Correct Answer:** C. The medulla oblongata.