Reflex Loops and Muscle Tone

Abstract Amuscle Stretch Reflex (aka myotatic reflex or deep tendon reflex) is a simple circuit that requires the following: muscle spindle cells, large sensory afferent fibers, spinal cord interneurons, motor neurons, motor efferent fibers, and a paired agonist–antagonist muscle group. In this chapter,we will use the patellar reflex (aka knee extensor reflex) as a prototypical muscle stretch reflex to learn about spinal reflexes. The common muscle stretch reflexes we test are at the biceps (C5, C6), triceps (C7, C8), patella (L3, L4), and achilles (S1). Also, in this chapter, we will discuss the related anatomy of muscle tone.