Central chemoreceptors
Also known as: medullary chemoreceptors, retrotrapezoid nucleus
Chemosensitive neurons near the ventral surface of the medulla that respond to the H+ concentration of brain extracellular fluid/CSF — and therefore to arterial PCO2 — providing most of the drive to breathe.
Overview
CO2 crosses the blood–brain barrier freely, whereas H+ and HCO3− cross slowly. In the brain interstitial fluid and CSF, CO2 is hydrated to H+ and HCO3−; because CSF contains little protein, it is poorly buffered and its pH changes sharply with PaCO2. The resulting H+ stimulates chemosensitive neurons (notably in the retrotrapezoid nucleus) on the ventrolateral medullary surface, close to the exits of CN IX and X, which drive the respiratory centres.
Central chemoreceptors account for ≈70–80% of the ventilatory response to a rise in PaCO2; ventilation increases ≈2–3 L/min per mmHg rise. They do not respond to hypoxia (which depresses central neurons). With sustained hypercapnia (e.g. COPD) the choroid plexus raises CSF HCO3− over 1–2 days, normalising CSF pH and blunting the CO2 drive; conversely, at altitude CSF HCO3− falls, allowing ventilation to stay high (acclimatisation).
- Location
Ventrolateral surface of the medulla oblongata.
Function
- Sense PaCO2 (via CSF pH) and drive ventilation to keep PaCO2 ≈40 mmHg.
- Physiology
Normal CSF pH ≈7.32; response latency ≈1–2 min (slower than peripheral chemoreceptors).
Clinical significance
Chronic CO2 retention
In chronic hypercapnic COPD the central drive is blunted by renal and CSF bicarbonate compensation, so peripheral hypoxic drive and V/Q effects become important; high-concentration O2 can worsen hypercapnia, so target SpO2 is 88–92%.
Apnoea test in brain-stem death
Absence of any respiratory effort despite PaCO2 rising above ≈60 mmHg (and pH < 7.30) confirms loss of brainstem respiratory function.
Test yourself
Central chemoreceptors in the medulla respond most directly to which stimulus?
- Decreased arterial PO2
- Increased H+ concentration in the cerebrospinal fluid
- Decreased arterial O2 content
- Increased plasma bicarbonate
Answer: Increased H+ concentration in the cerebrospinal fluid
CO2 diffuses across the blood–brain barrier and is hydrated to H+ and HCO3− in poorly buffered CSF; the H+ stimulates central chemoreceptors. Charged H+ and HCO3− in blood cross the barrier poorly. Central chemoreceptors do not respond to hypoxia — that is the role of the carotid and aortic bodies.
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.