Transection of the spinal cord reveals the reflexes that depend only on spinal cord circuits. These include the stretch reflex and the flexion reflex.
Muscle spindles are complex sensory receptors found in muscle in parallel to regular muscle fibers.
They contain nuclear bag and nuclear chain intrafusal muscle fibers. Group la afferent fibers form primary endings on nuclear bag and chain fibers, and group 11 fibers form secondary endings on nuclear chain fibers. Golgi tendon organs are located in the tendons of muscles and are arranged in series. Ib afferent fibers and are excited both by stretch and by contraction of the muscle. Reflexes are simple, stereotyped motor responses to a stimulus.