Muscular contraction initiates reflex increases in cardiovascular and ventilatory function. The afferent arm of this reflex arc is comprised of group III and IV muscle afférents. The responses of group III and IV afférents to static contraction have been characterized. We sought to determine whether these afférents are stimulated by locomotion which closely approximates true dynamic exercise. In decerebrate cats, we recorded from 20 group III (mean conduction velocity 15.9+ 1,9m/s; range 3.1 - 28.2m/s) and two group IV afférents (0.95 and 0.80m/s) during locomotion induced by electrical stimulation of the midbrain locomotor region. All 22 afférents had receptive fields located in the triceps surae. Of the 20 group Ills, 18 responded to locomotion. Of those 18, six responded more to locomotion when the triceps were made ischémie during locomotion by occluding the femoral artery than to locomotion when the triceps were freely-perfused. The 12 group Ills that responded similarly to freely-perfused and ischémie locomotion fired during the contraction phase of dynamic exercise, whereas five of the six ischemically-sensitive group Ills discharged irregularly during the step cycle. One of the two group IV afférents studied was stimulated by locomotion under freely-perfused conditions. The response of this group IV to locomotion increased two-fold when the triceps were made ischémie. These results suggest that dynamic exercise does stimulate group III and IV afférents. Group III afférents are predominantly mechanosensitive, with a subpopulation of fibers which display some chemosensitivity.
|Original language||English (US)|
|State||Published - Dec 1 1996|
All Science Journal Classification (ASJC) codes
- Molecular Biology