Chapter 36. Regulation of Respiration
In an experimental system, the pre-BÖTC is eliminated and its main function is taken over by outside electrical stimulation. The investigator has full control of firing amplitude and rate, and can directly measure the downstream muscle response. While the investigator tried many different patterns and measurements, which of the following best substituted for normal pre-BÖTC activity during quiet respiration?
A. Rhythmic bursts of ~2 s of impulses and 5 s of rest that resulted in contraction of expiratory muscles
B. Large single neuron impulses every 10–12 s directed at dorsal respiratory group (DRG) and resulting in inspiratory muscle contraction
C. Large single neuron impulses every 10–12 s directed at ventral respiratory group (VRG), and resulting in inspiratory muscle contraction
D. Rhythmic bursts of ~2 s of impulses and 5 s of rest that resulted in contraction of inspiratory muscles
E. Rhythmic bursts of ~2 s of impulses and 5 s of rest directed at the DRG, and resulting in expiratory muscle contraction
The correct answer is C. The pre-BÖTC is the rhythmic or pattern generator for the control of breathing. The rhythmic firing is largely communicated through the phrenic nerve for contraction of the diaphragm and control of inspiration. Expiration occurs as the diaphragm relaxes and is not a target for activation of the pre-BÖTC, ruling out A and E. The activation pattern generated by the pre-BÖTC includes many neurons and many firings, ruling out B and C. The DRG and VRG can provide upstream input to the pre-BÖTC to regulate the firing pattern but do not contribute downstream of the pre-BÖTC for muscle contraction, further ruling out B and C.
A professor and his student meet up in a gym and sit in adjoining stationary bikes and begin a light conversation. As time goes by, the chitchat is replaced by determination and the two find themselves pedaling their bikes at exceptional speeds. The extensive work of the leg muscles requires anaerobic respiration and results in raised levels of circulating lactic acid, which in turn increases ventilation. Eventually the student realizes that it is hopeless to keep up the pace and returns to a more normal cadence and more chitchat about current events. Which of the following is true concerning the transduction of the net increase in lactic acid to increased ventilation?
A. Acid sensing in receptors responsible for the transduction are located in the medulla oblongata.
B. Acid sensing in receptors responsible for the transduction are located in the carotid bodies.