What Is a Reflex Hammer?

Tendon reflex, also known as deep reflex, actually refers to the involuntary muscle contraction that occurs when the tendon is rapidly pulled. It is actually a type of muscle stretch reflex (the other is muscle tension). The diameter of the afferent fibers reflected by the tendon is thick (12 to 20 microns) and the conduction speed is faster (more than 90m / s). Tendon reflexes are single synaptic reflexes with a short latency (about 0.7 ms). For example, the knee reflex, tapping the quadriceps tendon under the knee joint, the quadriceps contraction occurs once. Tendon reflexes are single synaptic reflexes in the body. The tendon reflexes are muscle spindles, with the center at the anterior horn of the spinal cord. The effectors are mainly fast muscle fibers that contract muscles faster. If the tendon reflex weakens or disappears, it indicates that the reflex arc is damaged, while the tendon reflex is hyperactive, indicating a high central lesion. In clinical practice, tendon reflexes are often used to understand the functional status of the nervous system.

Tendon reflex, also known as phased reflex, refers to the sudden contraction of the muscles caused by tapping the tendon. The degree of muscle contraction of the two limbs is usually compared to determine whether a tendon reflex is increased (hyperactive), decreased, or disappeared. In the clinic, changes in tendon reflexes have diagnostic significance and are a commonly used neurological examination item ^[1]

Tendon reflexes are single synaptic reflexes, which mainly occur in the fast muscle fiber components that contract rapidly in the muscle. Tendon reflexes that are often checked clinically include: biceps reflex, triceps reflex, radial reflex, knee reflex, Achilles tendon reflex, etc. Tendon reflex asymmetry is an important sign for localization of nervous system damage. The strength of tendon reflexes can be described by disappearance (-), attenuation (+), normal (++), enhancement (+++), and clonic (++++) ^[2]

At the position of the tendons of the proximal and distal bones, a quick percussion with a percussion hammer elicits reflexes.

(1) Biceps tendon reflex

[Clinical manifestations] The examiner pressed the biceps tendon slightly above the elbow joint with his thumb, tapped the examiner's thumb, and appeared

NINDS National Association for Neurological Disorders and Stroke proposes a 5-point scale.

(Level 0-4), level

0 reflection disappears

1 Reflection is below normal; includes only a little reaction or intensified test

2 Reflection is slightly lower at half of normal range

3 Reflection is slightly higher at half of normal range

4 Increased reflection above normal; includes

The magnitude of the muscle reflex depends on the completeness of the upper and lower motor neurons that conduct the reflex. A reflexed lower motor neuron includes its peripheral nerves and spinal cord segments. Any of these lesions will cause the reduction and disappearance of related reflexes. The upper motor neuron cortical spinal cord descends to dominate the reflexes. Any lesion in this conduction pathway can Resulting in increased reflexes; spinal cord disease: due to the presence of both upper and lower motor neurons, reflexes at the level of damage may disappear (lower motor neuron response) and reflexes below the level of damage increase (upper motor neuron response).

It is worth mentioning that the increase and disappearance of the reflex itself does not determine the neurological disease, so it must be bilaterally contrasted and contrasted up and down. Very few people in the normal population may have hyperreflexia. In fact, the enhancement and disappearance of reflexes are only meaningful when accompanied by one of the following clinical symptoms: The disappearance of reflexes is accompanied by other manifestations of damage to the lower motor neurons, such as weakness, atrophy, and beam tremor. Increased reflexes are accompanied by other manifestations of upper motor neuron damage, such as paralysis, spasm, and positive Babinski sign. The amplitude of the reflection is asymmetric, which suggests that either the side with low reflection is damage to the lower motor neuron, or the side with high reflection is damage to the upper motor neuron. Compared with slightly higher spinal cord reflexes, the reflexes are abnormally higher, which further suggests that there is damage between the spinal cords with reduced reflexes and the spinal cords with increased reflexes.