Chemoreceptor Firing-Rate Bench

Arterial Blood Gases

PaO₂ (arterial O₂) 95 mmHg

PaCO₂ (arterial CO₂) 40 mmHg

Simulation speed 1.0×

Live Readouts

Membrane potential V_m

−68 mV

Intracellular Ca²⁺

0.05

Afferent nerve firing rate

2.1 Hz

How it works

This bench renders the same glomus-cell (type I carotid body) O2-sensing cascade as a set of quantitative instruments instead of a 3D cell — a Hill-curve plot, a strip-chart recorder and a spike raster, exactly like the traces a physiology lab would actually record from a real cell:

g_K(PaO₂) = g_min + (g_max − g_min) · PaO₂ⁿ / (PaO₂ⁿ + K½ⁿ)
   n = 4, K½ shifted by PaCO₂ (CO₂/pH potentiates O₂ sensing)
V_m → V_hyper + (V_depol − V_hyper) · (1 − g_K/g_max)   (relaxation, τ≈0.25s)
d[Ca²⁺]/dt = k_in·max(0, V_m − V_thr) − [Ca²⁺]/τ_Ca      (τ_Ca=1.4s)
firing rate = f_rest + (f_max − f_rest) · [Ca²⁺] / ([Ca²⁺] + K_m)

Top panel — the O2-sensitivity Hill curve itself: g_K plotted against PaO₂ for the current PaCO₂, with the live operating point marked and the "firing zone" (where V_m would cross the Ca-channel threshold) shaded.
Middle panel — a scrolling strip chart of membrane potential and intracellular Ca²⁺, so you can watch the depolarization and calcium transient develop in real time as you move the sliders.
Bottom panel — a spike raster of individual afferent nerve impulses (each tick is one action potential fired toward the brainstem) with the instantaneous firing-rate curve overlaid.
K⁺ channel blocker — forces g_K near zero regardless of oxygen, proving the channel — not oxygen itself — gates the signal.

Real-world relevance: this cascade is why breathing rate rises within one circulation time of acute hypoxia (high altitude, apnea, lung disease) — it is the fastest chemical sensor in the human respiratory control loop, feeding the nucleus tractus solitarius via the glossopharyngeal nerve.

g_K operating point Membrane potential V_m Intracellular Ca²⁺ Afferent nerve spike