The nervous signal that is transmitted to the inspiratory muscles (mainly the diaphragm) begins weakly and increases steadily in a ramp manner for about 2 seconds in normal respiration → then ceases abruptly for ± 3 seconds (expiration) → repeat;
it causes a steady ↑ in the volume of the lungs during inspiration, rather than inspiratory gasps.
Two qualities of the inspiratory ramp are controlled:
Control of the rate of increase of the ramp signal - during heavy respiration, the ramp increases rapidly → fills the lungs rapidly.
Control of the limiting point at which the ramp suddenly ceases - method for controlling the rate of respiration; the earlier the ramp ceases = the shorter the duration of inspiration. this method also shortens the duration of expiration → the frequency of respiration is ↑.