The Achilles tendon or Tendo musculi tricipitis sureae is the strongest tendon in the human body and connects the calf muscles , which are also known as the musculus triceps surea, with the heel .

These calf muscles consist of three muscle groups, the two calf muscles (musculus gastrocnemius) and the soleus muscle. The length of this tendon is about 20 to 25 cm. The calf muscles are controlled by the Achilles tendon. This can create movements such as flexing the foot similar to a ballerina standing on tiptoe, or twisting the foot outward.

The Achilles tendon reflex is triggered by a light tap on the Achilles tendon. A stimulus signal is transmitted via afferent nerve fibers . Afferent nerve fibers are those nerve fibers that transmit incoming signals, in this case the impact on the Achilles tendons, which has occurred from the outside, to the respective destination in the body.

In this case, the afferent nerve is the tibial nerve. It carries the signal to the spinal cord . There the incoming signal is passed on to the efferent nerve fibers. These nerve fibers transmit the signal to the outside. In the case of the Achilles tendon reflex, this also happens through the tibial nerve. The incoming signal from the efferent nerve fibers causes the triceps aurea muscle, i.e. the calf muscles, to contract. This stretches the ankle. This entire process is also described as a reflex arc .

function & task

The Achilles tendon reflex is just one of several reflexes in the human body. It belongs to the group of self-reflexes and often serves to protect the body from damage. The self-reflex is a reflex in which a reaction of the organ concerned to a stimulus is resolved, which means that the reaction takes place exactly where the stimulus arrived. In the case of extraneous reflexes , the reaction takes place at a location other than that of the stimulus input. 

A stimulus is sent from afferent nerve fibers to the spinal cord and then returned via efferent nerve fibers and the affected muscle to elicit a muscle response. In addition to the Achilles tendon reflex, there are a few others, such as the abdominal skin reflex . If the abdominal wall is hit, this immediately leads to a contraction and thus to a hardening of the abdominal wall. This protects the internal organs from damage caused by external blows.

Another intrinsic reflex is the toe flexion reflex . This is also known as the Rossolimo reflex and describes the reaction to a hit on the toes. In response, the toes are flexed. This reflex is normally present only in newborns and indicates a possible nervous or motor system disorder.

A well-known intrinsic reflex is the adductor reflex . This is a reflex triggered by hitting the adductor tendons at the knee joint . The affected leg kicks out. The reflexes are therefore intended to protect certain areas such as the internal organs of the human being, but also, for example, from hot or sharp objects or from falling, which could cause damage.

Diseases & Ailments

Another reason for a defective reflex arc is damage to the spinal cord or the nerve fibers that carry the signals. The Achilles tendon reflex arc is carried by afferent nerve fibers through the spinal cord and efferent nerve fibers. These then pass the signal on to the calf muscle. If this signal transmission is disrupted, this can be due to inadequate signal transmission, i.e. defects in nerve fibers or in the spinal cord. As a result, the signal may not be able to travel from the afferent nerve fibers through the spinal cord to the efferent nerve fibers. 

Damage to the spinal cord can have various causes. Spinal cord trauma is possible, which is damage to the spinal cord as a result of violence such as a car accident.

In addition, a defective Achilles tendon reflex can also indicate a herniated disc , in which the discs between the vertebrae are damaged and lose their cushioning effect.

A defective Achilles tendon reflex can also indicate polio , which is also known as polio. Polio is caused by the poliovirus and causes paralysis due to the infection of nerve cells and spinal cord.

In addition, a non-functioning Achilles tendon reflex can also indicate neurosyphilis . This is damage to the nerves that occurs as a result of syphilis disease that has not healed . This condition was common in the 18th century, but is not common today.