Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment. These act to detect the changes in pH of nearby

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...

(CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues. An increase in carbon dioxide causes tension of the arteries, often resulting from decreased CO₂ output (

hypercapnia Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous p ...

), indirectly causes the blood to become more acidic; the cerebrospinal fluid pH is closely comparable to plasma, as

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

easily diffuses across the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of the central nervous system where ne ...

. However, a change in plasma pH alone will not stimulate central chemoreceptors as are not able to diffuse across the

into the CSF. Only CO₂ levels affect this as it can diffuse across, reacting with H₂O to form carbonic acid and thus decrease pH. Central chemoreception remains, in this way, distinct from peripheral chemoreceptors. The central chemoreception system has also been shown experimentally to respond to hypercapnic hypoxia (elevated CO₂, decreased O₂) and aqueous

sodium cyanide Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its hi ...

injection into the whole animalSolomon IC, Edelman NH, Neubauer, JA. Pre-Bötzinger complex functions as a central hypoxia chemosensor for respiration ''in vivo''. J Neurophysiol. 83(5):2854-68, 2000. and ''in vitro'' slice preparation. These methods can be used to mimic some forms of

hypoxic hypoxia Generalized hypoxia is a medical condition in which the tissues of the body are deprived of the necessary levels of oxygen due to an insufficient supply of oxygen, which may be due to the composition or pressure of the breathing gas, decreased lu ...

and they are currently being studied including the detection of variation in arterial CO₂ tension acting as a quick-response-system for short term (or emergency) regulation. This system utilizes a negative feedback system, therefore if the pH of the cerebral spinal fluid does not compare to an ideal “set” level, then the receptor will send an error signal to the effectors and appropriate action may be executed.

Peripheral chemoreceptor Peripheral chemoreceptors (of the carotid and aortic bodies) are so named because they are sensory extensions of the peripheral nervous system into blood vessels where they detect changes in chemical concentrations. As transducers of patterns of v ...

s (carotid and aortic bodies) and central chemoreceptors (medullary neurons) primarily function to regulate respiratory activity. This is an important mechanism for maintaining arterial blood pO2,

pCO2 ''p''CO2, pCO2, or P_\ceis the partial pressure of carbon dioxide (CO2), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO2 as a function of its ...

, and pH within appropriate physiological ranges. For example, a fall in arterial pO2 (

hypoxemia Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the bod ...

) or an increase in arterial pCO2 (hypercapnia) leads to an increase in the rate and depth of respiration through activation of the chemoreceptor reflex. Chemoreceptor activity, however, also affects cardiovascular function either directly (by interacting with medullary vasomotor centers) or indirectly (via altered pulmonary stretch receptor activity).

Respiratory arrest Respiratory arrest is a sickness caused by apnea (cessation of breathing) or respiratory dysfunction severe enough it will not sustain the body (such as agonal breathing). Prolonged apnea refers to a patient who has stopped breathing for a long pe ...

and

circulatory shock Shock is the state of insufficient blood flow to the tissues of the body as a result of problems with the circulatory system. Initial symptoms of shock may include weakness, fast heart rate, fast breathing, sweating, anxiety, and increased t ...

(these conditions decrease arterial pO2 and pH, and increase arterial pCO2) dramatically increase chemoreceptor activity leading to enhanced sympathetic outflow to the heart and vasculature via activation of the vasomotor center in the medulla.

References

External links

*
Overview at cvphysiology.com
{{Respiratory physiology Sensory receptors Respiratory physiology

See also

References

External links