A reflex is an uncontrolled action that is the body’s response to external irritation. They can be acquired or congenital.
The knee reflex belongs to the group of stretch reactions or unconditioned reflexes. It can be tested by asking the patient to place one knee on top of the other and lightly but sharply hit the area under the patella (the fossa). Normally, the limb will undergo extension. The physiology of the process is based on the fact that when the muscle tendon (quadriceps femoris) is acted upon, it stretches and acts on the leg extensor muscle. This provokes spontaneous straightening of the leg. The importance of the knee reflex in ensuring the function of maintaining posture and balance.
Reflex arc
A reflex is a response of the body’s nervous system to external irritation. The reflex arc of the knee includes the elements:
- Receptors. The ends of axons or bodies of epithelial cells. The nerve fiber signals towards the center. After receiving the stimulus signal, excitation occurs. Receptors are located in the skin and organs. They are the building blocks of the sense organs.
- Nerve fiber. Conducts the signal to the center. The cell bodies of neurons are located near the brain, in the nerve plexuses in the spinal cord.
- Nerve center. The place from which the signal is transmitted from afferent neurons to efferent ones.
- Efferent fiber. It is a long process of a centrifugal neuron.
- Effector. An organ that responds to receptor stimulation.
Possible causes of PR
The etiological factors of the occurrence of pathological reflexes are usually classified as exogenous and endogenous causes that provoke the development of a certain disease.
Exogenous causes:
- these include standard neurotropic;
- nonspecific (can affect both the central nervous system and other internal organs);
- pathogenic viruses;
- microorganisms that negatively affect the body;
- plant toxins;
- microbial toxins;
- chemicals;
- conscientious influence;
- conditioned reflexes.
Endogenous causes are divided into primary and secondary. Primary causes include ischemia, various head and back injuries, swelling of brain tissue, and genetic predisposition.
Secondary ones include those that exist in the nervous system itself under the influence of primary ones and, as a result, become the main cause of the development of pathological processes in the body:
- neuronal disorder;
- certain changes in neurotransmitters;
- change of neuron genome;
- disturbances in interneuronal transmission;
- changes in nervous trophism;
- excessive neuronal activity;
- pathological determination;
- GPUV;
- the presence of antibodies to brain tissue.
Stages of the passage of a nerve impulse
The mechanism of action of the knee reflex is characterized by one connection of neurons. The impulse originates in the region of the proprioceptors of the quadriceps femoris muscle, which serve as sensitive sensors. The impulse is then transmitted to the lumbar region.
The closure of the reflex arc of the knee reflex occurs at the level of L2-L4, from where the impulse goes to the motor neurons, which are located near the anterior horns of the spinal cord. After this, the motor fibers transmit the impulse to the quadriceps muscle, which extends the tibia.
Diagram of the knee reflex reflex arc
The physiology of the knee reflex is as follows. When a stimulus acts, sensory fibers record the impulse. After this, it is transmitted to the efferent centers of the spinal cord, from where, after instant processing of the information, a return signal is sent. When the signal reaches the muscles, it causes them to contract and a part of the body moves. If there is no reaction, then the patient is susceptible to pathology of muscle tissue, brain, and parts of the nervous system.
The reason for the lack of a knee reflex may be the patient’s severe emotional state.
Description of techniques for testing the knee reflex
The neurologist checks the knee reflex by performing actions in the following patient positions:
- The patient is seated on a chair, with one leg crossed over the other.
- The doctor holds the leg of the patient lying on the table at an obtuse angle.
- The patient sits on a chair, legs down.
- The patient is placed on the couch in a supine position, with one leg on the knee of the other.
The neurologist lightly hits the patellar ligament with a neurological hammer, this action leads to extension of the lower leg. At this time, the patient must turn off conscious control of movements. For this purpose, the doctor may suggest that he perform mental operations. The knee reflex is assessed by the magnitude of the deviation of the lower limb. The doctor chooses which method of testing the knee reflex to use.
What if you need other methods?
If the traditional method does not work, there are several other methods for demonstrating the knee reflex:
- The person should be seated on a chair with their toes touching the floor and their legs bent at an angle slightly greater than 90 degrees. The blow must be applied from top to bottom over the retracted patella. As a result, the patella rises;
- the knee of the required leg must be placed on top of the second knee;
- you can use a high seat so that your legs hang in a relaxed state;
- There is also a method when the patient is lowered onto his back with his knees stacked one on top of the other.
There are times when the patient is physically unable to sufficiently relax the limb being examined. Then specialists use methods of disinhibition of the knee reflex, for example, the techniques of Jendrassik and Shvetsov. The patient should also breathe deeply or solve simple mathematical problems out loud.
Deviations
Normally, the knee joint reflex is characterized by an average degree of tendon reactions, which is called normoreflexia. When the functions of the nervous system are impaired, signal transmission is disrupted, which leads to the development of the following conditions:
Hyperreflexia
The test records the maximum extension of the lower leg. This phenomenon is often the result of deviations accompanied by irritation of motor fibers:
- Intoxication.
- Polyneuritis.
- Radiculitis.
Hyperreflexia is also observed in healthy people of a neurotic type.
Reflex changes
There are pathological changes in the nervous system, manifested in changes in the knee reflex. Deviations may be of the following nature:
- Hyporeflexia.
- Areflexia.
- Hyperreflexia.
A neurologist, having noted such phenomena, will conduct a comprehensive examination to make a diagnosis.
Hyperreflexia
The knee reflex is increased (hyperreflexia) - with the slightest impact on the sensitive area, the leg extends as much as possible.
Most often observed with damage to the pyramidal tracts in the anterior part of the spinal cord (anterior horns of the gray matter). The role of these structures is that they inhibit impulses that come from the brain in response to irritation.
This reflex is observed in people of the neurotic type, with some intoxications, neuritis, radiculitis, plexitis (inflammatory diseases of the nerve fibers).
The consequence of increased reflexes will be clonus - pathological movements, which are characterized by rhythmic and rapid contractions of a muscle group due to a stretched tendon. This is a chain of constant tendon reflexes. The most common manifestations are clonus of the patella and foot.
Hyporeflexia
Irritation reactions with this type of pathology will decrease (hyporeflexia) or be absent (areflexia). The phenomenon manifests itself in the fact that when irritated, the knee reacts weakly or does not react at all. Pathology occurs due to a violation of the integrity and conductivity of the reflex arc at one of the stages of impulse transmission through neurons.
Most often, the absence of a reflex indicates an organic disease of the nervous system (there is a pathological formation in the brain). This may also be due to previous infection, intoxication or cachexia (loss of body weight). The listed processes lead to depletion of neurons and improper functioning of these cells. The reaction may temporarily disappear after an epileptic attack, anesthesia, or when a tourniquet is applied. With tabes dorsalis, the reflex will be absent in both legs.
In some cases, areflexia in healthy people will be a variant of the norm (in case of illnesses suffered in childhood associated with damage to the reflex arc).
Components of stretch reflexes
Characteristics of stretch reflexes are dynamic and static components. The statistical component takes effect during muscle stretching. The duration of the dynamic component is short-term and occurs as a result of changes in muscle length.
Types of muscle fibers
Muscle fibers involved in the knee reflex:
What to do if your knee joint pops out?
- Nuclear chain fibers. Due to their structure, they provide a static component. Thin long fibers are characterized by uniform stretching. When they are stretched, the endings of the arc neurons significantly increase the frequency of signals, which is the mechanism of the static component.
- Nuclear marsupial fibers. In the middle they have a bulge around which the endings of nerves are twisted, carrying a signal about the onset of stretching. The middle of the fiber can quickly elongate when stretched. The sides of the fiber resist rapid stretching, but stretching does occur when the fiber is stretched for a short time.
It follows from this that if the fibers are subjected to rapid stretching, the middle will take the lion's share of the stretching; when the side parts are stretched, the middle will contract. The nerve ending initially sends intense signals, then the frequency flow of impulses decreases due to stretching of the side parts, and the middle again becomes shorter.
Tendon stretching as a prerequisite for the manifestation of the knee reflex
An experiment can be conducted to reveal the features of spinal cord reflexes. It is known that tendon stretching leads to extension of the lower limb at the knee. During the demonstration, the reflex will weaken if the leg is pinched by the subject. To distract him, he is asked to clasp his hands.
During the experiment, the tendon is struck with a medical hammer. If the blow does not stretch the tendon, there will be no reaction. From this we can draw conclusions: the knee reflex occurs only if there is tendon stretching, when impulses enter the spinal cord, after which they travel through motor neurons to the spinal cord.
Do deviations need to be treated?
Hyperreflexia and hyporeflexia are not independent diseases; they only signal damage to the central nervous system. It is possible to eliminate dysfunction of each part of the knee reflex in the following ways:
- If the brain is infected, it is treated with antibiotics.
- If mental disorders occur, mental blockers are used.
- When diagnosing radiculitis, treat with anti-inflammatory steroids.
- For paralysis of the legs caused by hemorrhage, post-stroke therapy is carried out.
- In the presence of intoxication, cleansing of the body is indicated.
Establishing the cause of the knee reflex disorder is important to match the sequence of treatment of the disease that caused the pathology. The study of the causes after the designation of knee reflex disorders includes hardware studies and laboratory diagnostics.
When nerve fibers are torn, resulting in paralysis, surgical suturing is performed
A special method of treating knee reflex disorders is massage, as well as therapeutic exercises. Exercises in the pool are useful. If knee sensitivity fails, constant monitoring is required, as the risk of hidden pathologies is increased. Maintaining a healthy lifestyle and eliminating stressful situations contribute to obtaining a positive result in the treatment of knee joint disorders, which lasts for life.