The nervous system is the most complex and interesting in the whole body. The brain, spinal cord, and nerve fibers provide the integrity of our body and support its functioning. One of the main functions of the nervous system is to protect the body from external stimuli. This is possible due to the presence of spinal reflexes.
What is a reflex?
Reflex is an automatic response of the body to an external stimulus. Historically, it is one of the most ancient reactions of the nervous system. The reflex act is involuntary, that is, it cannot be controlled by consciousness.
The sequence of neurons and their processes that provide a certain reflex are called reflex arcs. It is necessary for conducting an impulse from a sensitive receptor to a nerve ending in the working organ.
The structure of the reflex arc
The reflex arc of a motor reflex is called the simplest, since it consists of onlyof two nerve cells or neurons. Therefore, it is also called two-neuron. Impulse conduction is provided by the following departments of the reflex arc:
- The first neuron is sensitive, with its dendrite (short process) it extends to peripheral tissues, ending with a receptor. And its long process (axon) stretches in the other direction - to the spinal cord, enters the posterior horns of the spinal cord, and then into the anterior ones, forming a connection (synapse) with the next neuron.
- The second neuron is called a motor neuron, its axon stretches from the spinal cord to the skeletal muscles, ensuring their contraction in response to a stimulus. The connection between a nerve and a muscle fiber is called the neuromuscular junction.
It is thanks to the transmission of a nerve impulse along the reflex arc that the existence of spinal motor reflexes is possible.
Types of reflexes
In general, all reflexes are divided into simple and complex. The spinal reflexes discussed in this article are classified as simple. This means that only neurons and the spinal cord are sufficient for their implementation. The structures of the brain do not take part in the formation of the reflex.
Classification of spinal reflexes is based on what stimulus causes a given reaction, as well as depending on the bodily function performed by this reflex. In addition, the classification takes into account which part of the nervous system is involved in the reflex response.
The following types of spinalreflexes:
- vegetative - urination, sweating, vasoconstriction and dilation, defecation;
- motor - flexion, extensor;
- proprioceptive - ensuring walking and maintaining muscle tone, occur when muscle receptors are stimulated.
Motor reflexes: subtypes
In turn, motor reflexes are divided into two more types:
- Phase reflexes are provided by a single flexion or extension of the muscles.
- Tonic reflexes occur with numerous consecutive flexion and extension. They are necessary to maintain a certain posture.
In neurology, another classification of types of reflexes is most often used. According to this division, reflexes are:
- deep or proprioceptive - tendon, periosteal, articular;
- superficial - skin (checked most often), reflexes of the mucous membranes.
Methods for determining reflexes
The state of the reflex can tell a lot about the work of the nervous system. Hammer reflex testing is an important part of a neurological exam.
Deep (proprioceptive) reflexes can be determined by lightly tapping the tendon with a hammer. Normally, there should be a contraction of the corresponding muscles. Visually, this is manifested by extension or flexion of a certain part of the limb.
Skin reflexes are elicited by rapidly holding the handle of the neurological hammer over specificareas of the patient's skin. These reflexes are historically newer than deep ones. Since they were formed later, even with the pathology of the nervous system, it is this type of reflex that disappears first.
Deep reflexes
The following types of spinal reflexes are distinguished, which originate in the tendon receptor:
- Biceps reflex - occurs with a light blow to the tendon of the biceps muscle of the shoulder, its arc passes through the IV-VI cervical segments of the spinal cord (SM), the normal reaction is flexion of the forearm.
- Triceps reflex - occurs when the tendon of the triceps (triceps) is struck, its arc passes through the VI-VII cervical segments of the SM, the normal reaction is the extension of the forearm.
- Cacarporadial - caused by a blow to the styloid process of the radius and is characterized by flexion of the hand, the arc passes through the V-VIII cervical segments of the CM.
- Knee - is caused by a blow to the tendon under the patella and is characterized by leg extension. The arc passes through the II-IV lumbar segments of the spinal cord.
- Achilles - occurs when a hammer hits the Achilles tendon, its arc passes through the I-II sacral segments of the spinal cord, the normal reflex reaction is plantar flexion of the foot.
Skin reflexes
Surface or skin reflexes are also important in neurological practice. Their mechanism is similar to deep reflexes: muscle contraction that occurs when receptor endings are stimulated. Only in this case, irritation does not occur with the help of a hammer blow,but with a stroke of the handle.
The following types of skin spinal reflexes are distinguished:
- Abdominal, which, in turn, are divided into upper, middle and lower reflexes. The upper abdominal reflex occurs when the receptors of the skin area under the costal arch are irritated, the middle one is near the navel, the lower one is under the navel. The arcs of these reflexes close at the level of VIII-IX, X-XI, XI-XII thoracic segments of the SM, respectively.
- Cremastery - is the pulling of the testicles up due to the contraction of its muscles in response to irritation of the skin area of the inner thigh. The arc of the reflex passes at the level of I-II lumbar segments of the CM.
- Plantar - flexion of the fingers of the lower extremities with dashed irritation of the skin of the sole, the level of the reflex - from the V lumbar segment to the I sacral.
- Anal - located at the level of the IV-V sacral segments and is caused by dashed movements on the skin of the near-anal region, which leads to a contraction of the sphincter.
The most widely used in neurological practice is the definition of abdominal and plantar reflexes.
Pathology of spinal reflexes
Normally, reflexes should be lively, single-phase (that is, without oscillatory movements of the limb), of moderate strength. The condition when reflexes are increased in strength or activity is called hyperreflexia. When the reflexes, on the contrary, are reduced, they speak of the presence of hyporeflexia. Their complete absence is called areflexia.
Hyperreflexia occurs when the centralnervous system. Most often, this pathological symptom occurs with the following diseases:
- strokes (ischemic and hemorrhagic);
- infectious inflammation of the central nervous system (encephalitis, encephalomyelitis);
- cerebral palsy;
- brain and spinal cord injuries;
- new growths.
Hyporeflexia, in turn, is one of the manifestations of the disruption of the peripheral nervous system. This condition is caused by diseases such as:
- polio;
- peripheral neuropathies (alcoholic, diabetic).
However, a decrease in the reflex activity of the nervous system can also occur when the central nervous system is damaged. This occurs when a pathological process occurs in the segment of the spinal cord where the reflex arc passes. For example, if the V cervical segment of the CM is affected, the biceps reflex will be reduced, while other deep reflexes that close on the lower segments will be increased.
Vegetative reflexes
Probably autonomic reflexes are the most complex type of spinal reflexes. Their function cannot be determined using a conventional neurological hammer, however, they provide the vital functions of our body. Their occurrence is possible due to the function of a specific formation in the brain - the reticular formation, in which the following centers of regulation are located:
- vasomotor, providing activityheart and blood vessels;
- respiratory, which regulates the depth and frequency of breathing through the centers innervating the respiratory muscles;
- food, which increases the motor and secretory functions of the stomach and intestines;
- protective centers, when irritated by which a person coughs, sneezes, experiences nausea and vomiting.
The study of the reflex activity of the nervous system is an important part of the neurological examination of the patient, which allows you to establish the localization of damage, which contributes to timely diagnosis.
