The nervous system is the most complex and interesting in the whole body. The brain , spinal cord, as well as nerve fibers ensure 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 an organism 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, which provide a certain reflex, are called reflex arcs. It is necessary for conducting an impulse from a sensitive receptor to a nerve ending in a working organ.
The structure of the reflex arc
The reflex arc of the motor reflex is called the simplest, since it consists of only two nerve cells or neurons. Therefore, it is also called two-neural. The pulse is provided by the following sections of the reflex arc:
- The first neuron is sensitive, with its dendrite (short process), it stretches to peripheral tissues, ending with a receptor. And its long process (axon) stretches in the other direction - towards 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 the motor neuron, its axon stretches from the spinal cord to the skeletal muscles, providing their contraction in response to the stimulus. The connection between the nerve and muscle fiber is called the neuromuscular synapse.
Thanks to the transmission of a nerve impulse along a reflex arc, 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 for their implementation, only neurons and the spinal cord are sufficient. Brain structures do not participate in the formation of the reflex.
The classification of spinal reflexes is based on what stimulus causes this reaction, and also depending on the function of the body 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 spinal reflexes are distinguished:
- autonomic - urination, sweating, vasoconstriction and vasodilation, defecation;
- motor - flexion, extensor;
- proprioceptive - providing walking and maintaining muscle tone, occur during stimulation of muscle receptors.
Motor reflexes: subspecies
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 sequential flexion and extension. They are necessary to maintain a certain posture.
In neurology, a different classification of types of reflexes is most often used. According to this division, reflexes are:
- deep or proprioceptive - tendon, periosteal, articular;
- superficial - skin (most often checked), reflexes of the mucous membranes.
Reflex Detection Methods
The state of the reflex can say a lot about the functioning of the nervous system. Checking reflexes with a hammer is an important part of a neurological examination.
Deep (proprioceptive) reflexes can be determined by lightly tapping the tendon with a hammer. Normally, contraction of the corresponding muscles should be observed. Visually, this is manifested by extension or flexion of a certain part of the limb.
Skin reflexes are caused by the rapid grip of a neurological hammer on specific areas of the patient’s skin. These reflexes are historically newer than deep. Since they later formed, then in 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 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 upon impact on the tendon of the triceps (triceps muscle), its arc passes through the VI-VII cervical segments of the SM, the normal reaction is extension of the forearm.
- The metacarpal beam is 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 SM.
- Knee - is caused by a blow to the tendon under the patella and is characterized by extension of the leg. 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
Superficial, or skin, reflexes are also important in neurological practice. Their mechanism is similar to deep reflexes: muscle contraction that occurs when the receptor endings are irritated. 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 with irritation of the receptors of the skin area under the costal arch, the middle one near the navel, the lower one under the navel. The arcs of these reflexes are closed at the level of VIII-IX, X-XI, XI-XII thoracic segments of the SM, respectively.
- Cremaster - is the pulling up of the testicles up due to the contraction of its muscles in response to irritation of the skin area of the inner thigh. The reflex arc passes at the level of I-II lumbar segments of the SM.
- Plantar - flexion of the fingers of the lower extremities with dashed irritation of the skin of the sole, the level of reflex - from the V lumbar segment to the I sacral.
- Anal - is located at the level of IV-V sacral segments and is caused by stroke movements on the skin of the canal region, which leads to a reduction in the sphincter.
The most widely used in neurological practice was 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. A condition where reflexes of increased strength or activity are called hyperreflexia. When reflexes, on the contrary, are reduced, they indicate the presence of hyporeflexia. Their complete absence is called areflexia.
Hyperreflexia occurs when the central nervous system is damaged . Most often, this pathological symptom occurs with the following diseases:
- strokes (ischemic and hemorrhagic);
- infectious inflammation of the central nervous system (encephalitis, encephalomyelitis);
- cerebral paralysis;
- brain and spinal cord injuries;
- neoplasms.
Hyporeflexia, in turn, is one of the manifestations of a malfunction 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 with damage to the central nervous system. This happens when the pathological process occurs in that segment of the spinal cord where the reflex arc passes. For example, in case of a lesion of the V cervical segment of the SM, the biceps reflex will be reduced, while other deep reflexes that close in the lower segments will be increased.
Vegetative reflexes
Probably autonomic reflexes are the most complex variety of spinal reflexes. Their function cannot be determined using a conventional neurological hammer, however, it is they that 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 regulation centers are located:
- vasomotor, providing the activity of the heart and blood vessels;
- respiratory, which regulates the depth and frequency of respiration through the centers innervating the respiratory muscles;
- food, due to which the motor and secretory functions of the stomach and intestines increase;
- protective centers, when irritated, 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.