Figure 1.

Schematic representation of the volleys and pathways involved in the production of the H-reflex, tendon jerk, F-wave, and V-wave. Only the most critical elements are labeled so see text for a complete description of the factors which can influence each response. (A), #1—electrical stimulus evokes a single afferent volley which recruits motoneurons for the H-reflex according to the size principle; #2—presynaptic inhibition can influence afferent input to the motoneuron; #3—tendon tap evokes multiple volleys which arrive at the motoneuron over 25 ms. (B), #1—a small number of motoneurons may discharge to produce F-waves after antidromic impulses reach their soma; #2—at rest, F-waves are likely to be limited to large motoneurons due to reflex activation of smaller motoneurons and collision with the antidromic volley prior to the soma. (C), #1—in motor axons conducting orthodromic impulses of voluntary drive, voluntary and antidromic impulses will collide; #2—reflex response which travels along motor axons cleared by the collision described in point #1 will contribute to the V-wave; #3—presynaptic inhibition can influence afferent input to the motoneuron.