Autonomic Nervous System: Carotid Body and Chemoception

Mammalian carotid bodies are small, bilateral organs that detect chemical signals (e.g., O2, CO2, pH, and glucose) in blood and initiate reflexes so as to maintain homeostasis. They are richly vascularized and contain clusters of endocrine-like receptor cells, linked by chemical and electrical synapses. These cells respond to chemical signals by releasing neurotransmitters, including ATP, that excite apposed sensory (afferent) nerve endings. Afferent nerve activity is modulated locally by released autocrine–paracrine mediators and by efferent autonomic nerves that release nitric oxide. This activity ultimately influences brain stem neurons that control a variety of vital respiratory, cardiovascular, and neuroendocrine functions.