The Mechanism of Rapid Response: Understanding the Reflex Arc

Reflex actions are the way the body responds rapidly to painful situations or the threat of painful situations. The reflex are is the mechanism by which the response occur The reflex arc is the name given to the pathway (or circuit) along which the initial stimulus and the corresponding response message travel There are five parts to a reflex arc:

1.) The Receptor, which receives the initial stimulus
2.) The Sensory (afferent) Nerve, which carries the impulse to the spinal cord or brain
3.) The Intermediate Nerve Fibre (the adjustor or interneuron), which interprets the signal and issues a response
4.) The Motor (efferent) Nerve, which then carries the response message from the spinal cord to the muscle or organ
5.) The Effector Organ itself, which carries out the response

Proprioceptors and the Control of Movement

Proprioceptors are specialized receptors located throughout the body within tendons, muscles and joints that provide sensory information about the state of muscle contraction, the position of body limbs, and body posture and balance This feedback and control over muscles is provided primarily by the afferent input from two sensory receptors:

1.) Golgi Tendon Organs (GTOS)
-Sensory receptors that terminate where tendons join to muscle fibre -Serve as a kind of tension detection device for the muscle system by helping to protect the muscle from excessive tension that would otherwise result in damage to the muscle and/or the joint

2.) Muscle Spindles
Lie parallel to the main muscle fibre
Help to maintain muscle tension by detecting changes in muscle fibre length and responding to it by sending a message to the spinal cord, leading to the appropriate motor response Contains two afferent and one efferent nerve fibre

Involved in the reflex contraction of muscles (the stretch reflex) The means by which muscles constantly and automatically adjust to the changing demands placed on them by providing constant feedback.