PSIO 532 Study Guide - Midterm Guide: Baroreflex, Skeletal Muscle, Tachycardia
PSL – Cardiovascular System
CENTRAL COMMAND:
Central command refers to the volition or will to exercise. Activation of central command
increases heart rate predominately via reduction in parasympathetic activity. The reduction in
PNS causes the heart rate to go up considerably (tachycardia – due to partial reduction in PNS
mediated by the activation of central command) → sometimes even get an overshoot. Central
command appears to have little control over sympathetic activity.
ARTERIAL BAROREFLEX:
For many years it was thought that since arterial blood pressure increases during exercise the
arterial baroreflex must be "shut off" during exercise otherwise this reflex should oppose any
rise in blood pressure. Rather, recent studies have shown that instead of being turned off
during exercise, the arterial baroreflex is reset to a higher level. Thus, rather than oppose the
rise in arterial pressure, the baroreflex may in fact reinforce the rise in pressure during exercise
→ this is because by resetting it to a higher level, the body will actually think it is at a lower
pressure and the reflex will want to increase the HR to increase the BP to match the higher
level. The set point is being manipulated during exercise to increase the operating point of BP
to a higher level. The mechanisms mediating the resetting of the arterial baroreflex are not
known. One hypothesis is that activation of central command causes
baroreflex resetting.
SKELETAL MUSCLE METABOREFLEX and MECHANOREFLEX:
When oxygen delivery to active skeletal muscle is insufficient for the metabolic demands,
metabolites (i.e. K+, lactate, H+, CO2, etc.) accumulate within the muscle and stimulate group
III and IV afferents within the muscle. Skeleton muscle is loaded with sensory neurons. These
afferents are lightly myelinated to unmyelinated and they sense the change in mechanical
activity and metabolite concentration (mechano-reflex and metabo-reflex) → many of the
afferents respond to both stimuli. While exercising, metabolites in the blood will stimulate
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