Tendon reflex, contraction of a muscle

A tendon reflex is also called a muscle stretch reflex. When the tendon contracts quickly, a stimulus is sent via the central nervous system to the attached muscle. In response, the muscle contracts. A tendon reflex is aimed at restoring balance and posture when necessary. This occurs, for example, in the event of a fall, when we stumble, while walking, etc. When the tendon reflex is absent or too strong, this indicates a problem with the central nervous system. To test a reflex, a tendon hammer or reflex hammer is used.

What is a tendon reflex?

A tendon reflex or muscle stretch reflex is a reflex of the muscles attached to the tendon. A reflex is a reaction of the muscles that occurs involuntarily. There is a stimulus that precedes it. When a tendon is suddenly stretched rapidly, the muscle attached to the tendon will contract quickly.

Difference between tendons and muscles

Everyone knows the muscles. We have more than 600 muscles in our body. The muscles ensure that we can move. But some organs also consist of muscles or are involved in important processes in our body: heartbeat, breathing and digestion. Muscles like the heart are involuntary muscles: we have no control over their rate of contraction. Voluntary muscles include skeletal muscles, for example.

The skeletal muscles are connected to the bones by tendons. This allows us to move bone parts relative to each other. This happens at the level of a joint. Muscles tense, pulling on the tendon and the tendon moves the bone. We can control voluntary muscles ourselves: we largely determine when we contract our muscles. We cannot move the tendons but are controlled by the muscles. The tendons are the connection between muscle and bone.

Stretch the tendon quickly

The tendon can suddenly stretch quickly, for example due to losing balance (falling), running, stumbling, tripping, etc. It is often the tendon on the thigh or arm that is then stretched quickly.

Patellar reflex

A well-known tendon reflex is the patellar reflex. A reflex always has a useful function. The patellar reflex ensures that the balance of the body is quickly restored. When we lose balance, the tendon stretches quickly. This causes the upper thigh muscle to contract quickly and restores the body’s balance. The tendon reflex originates from the Golgi tendon bodies.

Other tendon reflexes

In addition to the well-known patellar reflex, we also distinguish other tendon reflexes. For example, we know the biceps tendon reflex and the triceps tendon reflex. These two reflexes are located in the upper arm. These reflexes are also tested using a tendon hammer.

Tendon hammer

It is possible to test a tendon reflex. A tendon hammer or reflex hammer is used for this. A tendon hammer is a small hammer with which the tendon is tapped. This causes the tendon to stretch. In response to this, the upper thigh muscle will contract. A tendon reflex can be performed on a sitting or supine patient. To test the reflex, the muscle in question must be completely relaxed. The patient always takes a lying or sitting position for this purpose. Moreover, it is useful to distract the patient so that he does not tense the muscle in advance. If the reflex is not expressed, this may indicate incorrect technique, a patient who is too tense or an abnormality in the central nervous system. This can be at the level of the vertebrae or at the level of the brain.

Children often use this technique to provoke the tendon reflex in themselves. It is of course fun to kiss how the lower leg kicks forward on its own. However, it is not recommended that children perform this technique. The kneecap can be damaged if it is hit incorrectly with a hammer or other object. In addition, children often hit using an incorrect method or too hard.

Absence or too strong presence of the tendon reflex

There is no reason to test a tendon reflex. Absence or excessive presence of a certain tendon reflex may lead the doctor to suspect that there is an abnormality in the nervous system. When a tendon contracts rapidly, a stimulus is delivered via the peripheral nerve and the dorsal root to the motor anterior horn cell. The anterior horn cell sends a stimulus to the muscle via the anterior root and the peripheral nerve. In response, the muscle contracts. When something is wrong in the central nervous system, these stimuli are not transmitted correctly. Testing a tendon reflex is often one of the first tests a doctor performs for problems with the central nervous system.

The test must be performed several times and both left and right. The doctor must make a good comparison between both sides. Performing just one test cannot provide a conclusive diagnosis. In addition, the doctor will always place his hand on the muscle in question to be able to feel the contraction. The contraction is not clearly visible in everyone.

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