Final answer:
The type of muscle fiber that is served by both a sensory and a motor axon, and also functions as a stretch receptor, is the muscle spindle.
Step-by-step explanation:
The muscle spindle, a specialized type of muscle fiber, uniquely serves both sensory and motor functions. Positioned within skeletal muscle tissue, it acts as a stretch receptor, detecting alterations in muscle length.
Comprising sensory and motor axons, the muscle spindle functions as an essential component in regulating muscle tone.
When the muscle undergoes stretching, the activated muscle spindle receptor triggers a reflexive contraction, ensuring the muscle maintains its length and preventing potential over-contraction or tearing.
This intricate mechanism contributes to the precision of muscle control and coordination within the body, safeguarding against detrimental effects associated with excessive muscle strain.