Maximus Gage
Reflexes are the body's intrinsic stimulus-response systems for maintaining homeostasis. Muscle reflexes are tested to assess the integrity of the stretch reflex arc and the activity of alpha motor neurons at any level. They are also used to verify whether nerves are working effectively and communicating with the brain as they should. Testing muscle reflexes can also help identify individual nerve and root lesions, as well as indicate underlying problems with the nervous system.
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What You'll Learn
To check for neurological issues
Muscle reflexes are tested to check for neurological issues. A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. The reflex is an automatic response to a stimulus that does not require conscious thought as it occurs through a reflex arc. Reflex arcs act on an impulse before that impulse reaches the brain.
Reflexes are the body's intrinsic stimulus-response systems for maintaining homeostasis, and when performed and interpreted correctly, they are the most objective evidence of the nervous system's health. For example, in the case of the bulbospongiosus reflex, the normal response is the contraction of the bulbospongiosus muscle. If the reflex is absent, it may indicate a spinal cord injury.
Deep tendon reflexes are commonly used in screening examinations. Asymmetry of reflexes suggests abnormality. For example, if all the reflexes on the left side of the body are hyperactive, and those on the right side are normal, then a lesion is interrupting the corticospinal pathways to that side.
Superficial reflexes are usually elicited by stroking the skin or mucous membranes. An abnormal reflex response will show a combination of diminished or absent superficial reflexes with deep reflexes and pathological reflexes, indicating upper motor neuron level (UMNL) involvement.
Pathological or primitive reflexes are considered typical in infants up to about 6 months of age (or even up to 2 years for certain reflexes) and disappear. These primitive reflexes are pathological if found in adults and indicate an underlying problem with the nervous system.
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To assess motoneuronal excitability
Muscle reflexes are tested to assess motoneuronal excitability. Motoneurons are the nerve cells that stimulate muscle contractions. When a muscle is tested for reflexes, it is stimulated by a sharp blow or tap, and the response is observed. This response is involuntary and nearly instantaneous and occurs through a reflex arc.
The H-reflex is a commonly studied reflex in humans and is used to assess the motoneuronal excitability of single muscles. It is produced by a brief stimulus, such as a sharp blow to the body near the muscle being tested, and the amplitude of the test response gradually increases after a brief unresponsive period. The H-reflex can indicate the excitability of the monosynaptic arc, which is influenced by alpha and gamma motor neurons.
Another reflex that can be used to assess motoneuronal excitability is the tendon jerk or phasic muscle reflex. This is elicited by a sharp blow or tap to the tendon that connects the bone and muscle being tested. The tendon jerk can sample motor cell excitability at various brainstem and spinal cord levels, as muscles are innervated by different segmental levels.
Deep tendon reflexes are also commonly used and can be integrated into the examination of the corresponding body part. Asymmetry of reflexes between the left and right sides of the body suggests an abnormality, which can indicate a lesion interrupting the corticospinal pathways.
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To test for upper motor neuron disorders
Muscle reflexes are tested to check for upper motor neuron disorders. Upper motor neurons are located in the brain and spinal cord, and damage to them can impair mobility. Upper motor neuron lesions can result in muscle weakness, muscle wasting, overreactive reflexes, spasms, and other issues.
Other tests include imaging tests of the brain or spine, as well as lumbar puncture, blood tests, electromyography (EMG), and nerve conduction velocity (NCV) tests. An EMG uses a thin needle to check the activity of muscles when they contract and when they are at rest. It can help check for problems with lower motor neurons and diagnose ALS and PLS. A nerve conduction study, usually combined with an EMG, measures how quickly an electrical current moves through a nerve. It can show how well nerves are sending signals to muscles and if there is any nerve damage.
In addition, transcranial magnetic stimulation methods have been used to investigate the integrity of the motor cortex and its descending pathways. Results indicating delayed central conduction time and reduced motor-evoked potential amplitude point to corticospinal tract damage.
Furthermore, the Jendrassik maneuver can be used to augment hypoactive reflexes. The patient locks their hands together and pulls vigorously apart as a tendon in the lower extremity is tapped, or they push their knees together while the upper limb tendon is tested.
Deep tendon reflexes are also tested, and the patient's reflex history, other reflexes, and associated findings such as muscle tone and strength are considered when interpreting the results. Distracting the patient during the test can enhance the chances of obtaining the reflex.
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To gauge muscle tone and strength
Muscle reflexes are tested to gauge muscle tone and strength. A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. The reflex is an automatic response to a stimulus that does not require conscious thought as it occurs through a reflex arc. Reflex arcs act on an impulse before that impulse reaches the brain.
Deep tendon reflexes are commonly used to test muscle tone and strength. These reflexes are elicited by tapping or striking the tendon with a hammer. The hammer is typically made of rubber to ensure that it does not hurt when tapping the tendon. The force used to tap the tendon should be enough to elicit a reflex without causing pain.
When testing muscle reflexes, it is important to allow the muscle to move freely once it is stimulated. The muscle should be in a neutral position and easily flexed. For example, when testing knee reflexes, the person should be seated with their legs hanging down freely. By comparing the reflexes on two muscles, such as both ankles, it is possible to spot abnormal responses.
There are various specific muscle reflexes that can be tested to gauge muscle tone and strength. For example, the bulbospongiosus reflex tests the contraction of the bulbospongiosus muscle when the dorsum of the penis is tapped. The cremasteric reflex, which tests the L2 level, involves stroking the medial thigh upward and observing the elevation of the ipsilateral testis. The patellar reflex is another example of a muscle reflex, where a sudden stretch of the quadriceps muscle results in a quick contraction.
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To compare left and right-side responses
Muscle reflexes are tested to compare left and right-side responses. This is done to identify any abnormal responses, which could indicate an underlying problem with the nervous system. For example, if all reflexes on the left side of the body are hyperactive and those on the right are normal, it suggests that a lesion is interrupting the corticospinal pathways on the left side.
Reflexes are the body's intrinsic stimulus-response systems for maintaining homeostasis. They are involuntary and nearly instantaneous movements in response to a stimulus. When performed and interpreted correctly, they are an objective way to assess the body's functions.
Deep tendon reflexes are commonly tested, and this can be done in a variety of ways. For example, the Jendrassik manoeuvre is used to augment hypoactive reflexes. The patient locks their hands together and pulls them apart while a tendon in the lower extremity is tapped, or they push their knees together while the upper limb tendon is tested. Another method is to get the patient to put slight tension on the muscle being tested, such as making a fist with one hand while the opposite extremity is examined.
The best position for the patient is usually sitting on the side of the bed or examination table. A reflex hammer is then used to tap the tendon with proper force—enough to elicit a reflex without causing pain. The Babinski reflex hammer is often used, and the tap should be brisk but not painful. The examiner's wrist, not their arm, should be used for the action.
The specific instructions for the patient can be mingled with questions or comments designed to distract them, as this enhances the chances of obtaining the reflex. For example, the patient can be asked to count or name their children.
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Frequently asked questions
Muscle reflexes are tested to check the health of the nervous system.
You can test reflexes by tapping on the tendon that connects the bone and muscle you want to test. A reflex hammer is usually used for this.
The reflex hammer is made of rubber and ensures that the test is not painful for the patient.
Some muscle reflexes that are usually tested during neurological exams include the knee reflex, bicep reflex, and ankle reflex.
Abnormal reflex responses can indicate an underlying problem with the nervous system. For example, the presence of pathologic reflexes in adults is indicative of a loss of cortical inhibition.
