If You Voluntarily Lift an Object and Have Correctly Judged

Question

If you voluntarily lift an object and have correctly judged its weight,
A) the intrafusal muscle fibers shorten at a rate that maintains constant tension on the stretch receptor.
B) the muscle spindle afferents fire a rapid burst of action potentials.
C) α motor neurons fire action potentials but γ motor neurons do not.
D) γ motor neurons fire action potentials but α motor neurons do not.

Accepted Answer

The intrafusal muscle fibers shorten at a rate that maintains constant tension on the stretch receptor. This is because the gamma motor neurons fire action potentials, which cause the intrafusal muscle fibers to contract. This contraction shortens the intrafusal muscle fibers, which in turn increases the tension on the stretch receptor. The stretch receptor then sends a signal to the alpha motor neurons, which cause the extrafusal muscle fibers to contract. This contraction lifts the object.