Final answer:
Muscle spindles are specialized structures within skeletal muscles that detect muscle length and provide sensory information to neurons in the spinal cord.
Step-by-step explanation:
The specialized structure within skeletal muscles that senses muscle length and provides sensory information to neurons in the spinal cord is called muscle spindles. Muscle spindles are stretch receptors that detect the amount of stretch or lengthening of muscles.
They contain sensory neurons that send signals to the spinal cord through the dorsal nerve root and provide information about muscle length to the central nervous system. These signals help regulate muscle contraction and maintain bodily position.