Muscle spindles are supplied by:

A. Alpha motor neuron
B. Beta motor neuron
C. Gamma motor neuron
D. Extrafusal motor neuron
E. None of the above

To determine the correct answer, let's first understand what muscle spindles are and how they function.

Muscle spindles are sensory receptors located within our muscles. They are specialized structures involved in detecting changes in muscle length, as well as the rate and direction of change. They play a crucial role in maintaining muscle tone, coordinating muscle contractions, and providing sensory feedback to the central nervous system.

Muscle spindles are composed of two types of muscle fibers: intrafusal fibers and extrafusal fibers. The intrafusal fibers run parallel to the extrafusal fibers, which are the main contractile fibers responsible for generating force and movement.

Now, let's examine the given options:

A. Alpha motor neuron: Alpha motor neurons are responsible for activating extrafusal muscle fibers. They are involved in the generation of muscle contractions during voluntary movements and are not directly connected to muscle spindles.

B. Beta motor neuron: Beta motor neurons are also associated with activating extrafusal muscle fibers, similarly to alpha motor neurons. They are not directly involved in the function of muscle spindles.

C. Gamma motor neuron: Gamma motor neurons, on the other hand, play a vital role in regulating muscle spindle activity. When activated, gamma motor neurons cause the contraction of the intrafusal muscle fibers within the muscle spindle. This, in turn, ensures the sensitivity and effectiveness of the muscle spindle in detecting changes in muscle length.

D. Extrafusal motor neuron: Extrafusal motor neurons, as mentioned earlier, are responsible for activating the main contractile muscle fibers and are not directly connected to muscle spindles.

Based on this information, the correct answer is:

C. Gamma motor neuron

Gamma motor neurons innervate the intrafusal muscle fibers within the muscle spindle, allowing them to adjust their sensitivity and maintain accurate feedback to the central nervous system regarding muscle length and tension.