The Myotatic Reflex

The Myotatic Reflex (sometimes myotactic reflex) is probably our body’s most important and unrecognised defence mechanism. When it comes to making it safely through the day, nothing comes close to the myotatic reflex.

Muscles constantly monitor their own length and tension, and feed back changes in length or tension to the spinal cord. Without the myotatic reflex, controlled movement would be impossible.

The myotatic reflex starts in the muscle spindle, which constantly and spontaneously produces afferent impulses to the spine (and therefore the brain) – at a rates between 5 and 50 times per second.

Any change in tension or stretch in the muscle will increase this feedback to spine and produce an rapid increase in muscle tone.

When a muscle is stretched, the muscle spindles are activated, which sends a signal through afferent sensory neurons to the spinal cord. The spinal cord then sends a signal back to the muscle through motor neurons, which causes the muscle to contract. This reflex contraction helps to resist the stretch and maintain appropriate muscle tone and contraction.

The myotatic (or stretch) reflex helps to protect the muscle from being overstretched, and also helps to maintain muscle length, which is important for proper muscle function and movement. The reflex works in conjunction with the opposing muscle group, the antagonist, to create balance and stability in muscle tone and movement.

By limiting the stretch of muscles, the myotatic reflex protects ligaments and joints from overstretching which prevents sprain, strain, tearing and dislocation.

The stretch reflex can be graded based on the intensity of the stretch and the degree of muscle contraction. For example, if a muscle is stretched quickly, the reflex contraction will be stronger than if the muscle is stretched slowly. 

The myotatic reflex helps us walk down stairs.

As you step down on a stair, the quadriceps muscle, which is located in the front of the thigh, has to lengthen or “eccentrically contract” to control the descent of the body. Eccentric contractions generate high-force and helps to slow down the descent of the body and control the landing on the stair. The amount of contraction generated in the quadriceps has to be just enough to stop us tumbling down the stairs or leaping in the air.

As the quadriceps muscle is stretched, the muscle spindles are activated, which sends a signal to the spinal cord, triggering a reflex contraction in the muscle, to help resist the stretch and maintain muscle tone. The amount of contraction will be proportional to the input so that the same result can be achieved whatever load the person is carrying.

This process is aided by the coordination of other muscle groups involved in lower body movement.

In addition to its role in maintaining muscle tone and preventing injury, the stretch reflex also plays a role in posture, balance and coordination. 

The Myotatic Reflex is what causes the knee-jerk reflex. A sudden increase in quadriceps length induces a quick firing at the anterior motor neuron.

The myotatic reflex prevents damage to joints. When it is working properly, joints are protected from excessive movement or strain.

If the myotatic reflex is inhibited, the joint will be damaged – causing pain initially, and osteoarthritis in the long term.

Eliminating abnormal inhibition of the myotatic reflex is the ultimate aim of afferentology. Only when muscles have their full nerve supply are they able to provide the support and feedback the body needs for repair and healing.