Contents
Have you ever wondered why we need a spinal cord? Everything is clear with the head: it is responsible for cognitive functions, receives and distributes impulses throughout the body, thanks to which all our systems work. What does the spinal cord do? This is a kind of link between the brain and the peripheral nervous system. And if something happens to him, the body stops working fully.
What is the spinal cord
The spinal cord, together with the brain, is part of the central nervous system of the human body. Both of them begin to form even in the early stages of embryo development. Around the 20th day of pregnancy, some folds form on the body of the embryo, which eventually turn into what experts call the fetal neural tube. It represents the germ of the future central nervous system. During the development of the tube, its front part will turn into the brain, and the back will serve as the basis for creating the spinal cord.
Humanity has been studying the structure and role of the spinal cord since antiquity. For example, the ancient Greek physician Galen studied the central nervous system of animals and gladiators, analyzing how different types of injuries affect the functionality of the body. Modern scientists already know for sure that the spinal cord is a cylindrical bundle of nerve fibers that is connected to the brain and runs through the spine from the neck to the lower back. Scientists also know that in the body of an adult, this organ can reach 40-45 cm in length, 1-1,5 cm in width and weigh about 35 g. It has the shape of a thick-walled tube with a narrow channel inside, somewhat flattened in the anterior-posterior direction, located inside the spinal canal, which is divided into segments (they correspond to the sections of the spine):
- 7 cervical;
- 12 chest;
- 5 lumbar;
- 5 sacral;
- 3-4-coccygeal.
Interestingly, in the body of an adult, the spinal cord does not occupy the entire cavity of the spinal canal, but only about 2/3 of its length. Experts explain this feature by the fact that the spinal column grows faster than the spinal cord, therefore, as a person grows, this part of the central nervous system takes up less and less space in the spinal canal. That is, in the body of adults, the spinal cord in its lower part reaches only the first lumbar vertebrae.
The spinal cord is covered with three meninges (protective) membranes. The first, located closest to the spinal substance (internal), is called the pia mater of the spinal cord. It consists of a network of vessels that are responsible for the blood supply to the brain. Above it is the middle arachnoid membrane, which contains cerebrospinal fluid – cerebrospinal fluid. By the way, when a spinal cord is punctured, the liquor is taken for analysis, that is, the needle penetrates into the space between the inner and middle shells. The uppermost (outer) shell is hard. It protects the nerve roots that lead to the intervertebral foramens.
If the spinal cord is cut across, you can see that its tube has an oval, almost round shape. The upper layer of this organ consists of white matter, under which is contained a gray spinal substance. In cross section, it has the shape of a butterfly, from which horns of gray matter extend forward, backward and sideways. In the central part of the spinal substance is the intermediate nucleus of the gray matter. This part is the most important. It is responsible for collecting all the information and making decisions about the activation of a particular reaction of the body.
White matter is made up of bundles of nerve fibers called axons. They allow different levels of the CNS to exchange impulses. It is known that each bundle of axons differs in the specifics of the transmitted signals. So, some of them (ascending) transmit information to the brain, while the rest (descending) are responsible for transmitting impulses from the brain to neurons in various muscles and glands located throughout the body. The axons of the white matter are covered with an insulating myelin sheath, which facilitates the rapid and free transmission of impulses. Myelin is whitish in color, hence the name white matter.
The gray substance of the spinal cord is formed from nerve cells and their branched processes – dendrites. This substance is responsible for the perception and processing of information. For example, if we talk about the brain, then it is the gray matter in it that gives a person the ability to think. If we talk about the dorsal, then the horns of the gray matter also process various information messages of the body. Moreover, each horn has its own function.
How does the spinal cord control the body?
Each of the segments of the spinal cord controls the functionality of a particular part of the body. So, the segment of the central nervous system, located along the cervical vertebrae, sends impulses to the back of the head, neck and upper limbs. The thoracic segments are responsible for the functionality of the trunk (thorax, abdominal cavity). The lumbar zone of the central nervous system controls the lower limbs, and the sacrococcygeal segments control the pelvis and internal organs located in this area.
The relationship between segments of the spinal cord and parts of the body is always strictly observed. On each “floor” of the body, nerve endings depart from the brain, distributed over the area controlled by these segments.
The spinal cord is a tube that runs inside the spine, and spinal nerve processes emerge from the intervertebral spaces. Understanding the structure of this part of the central nervous system, it becomes clear how dangerous the slightest violation of the natural positions of the vertebrae is for a person. Any displacement of even one vertebra can lead to compression of the spinal nerves and disruption of the interaction between the CNS departments and the part of the body for which the segment is responsible.
Many people know that spinal injuries are fraught with paralysis. But this is not the only danger that can arise from a spinal cord injury. By and large, most health problems can occur due to misalignment of the vertebrae – even gastritis or ulcers. Just imagine, the vertebra is displaced, pinching the nerve ending, because of which the brain sends the wrong signals to the digestive system and gastric juice begins to be produced in excess, corroding the gastric mucosa. The result is gastritis, and then an ulcer.
Spinal Cord Functions
So, the gray matter of the spinal cord has 3 horns, which actually perform the main functions of this organ:
- analyze sensory signals;
- control internal organs (vegetative function);
- control muscles (motor function).
The collection of sensory signals occurs separately on each “floor” of the body. That is, each segment of the spinal cord accumulates information about what is happening in the territory “controlled” by it. This information is also strictly structured. It concerns three aspects:
- pain, that is, damage to cells and tissues on the “floor”;
- skin sensitivity, that is, about heat, cold, vibrations, etc.;
- muscle sensitivity, that is, the condition of the muscles, tendons and the position of the joints.
The spinal cord receives all information through clusters of nerve cells known as spinal ganglia (spinal nodes). The number of these nodes exactly corresponds to the number of spinal segments – 31. The cells included in the ganglion have a special structure: 1 long dendrite and 1 axon. The dendrite collects information about what is happening on the controlled “floor”, and the axon connects to the posterior horn of the gray spinal substance, to which it transmits the received data. In this area, the primary processing of sensory signals occurs and then the transfer of information to the intermediate nucleus of the gray spinal substance, which determines the further reaction of the body. But here it is worth mentioning another interesting point. The neurons of the intermediate nucleus receive signals not only from the horn, but also from the brain, which also retains the right to vote on what should be the response to the impulse received from the horn.
Let’s use an example to make this information easier to understand. Suppose a person took a glass of boiling water. As a result, sensory fibers send pain information to the spinal cord. Therefore, he is ready to give the signal to throw the red-hot object. But at the same time, another signal comes from the brain that, for example, something valuable is contained in a glass or the dishes themselves are valuable, so you should bring the vessel to the surface. These conflicting signals travel to the nucleus medius of the spinal gray matter, where neurons analyze both options and either trigger or block the response. If the intermediate nucleus approves the reaction, it transmits the corresponding signal to the anterior and lateral horns of the gray substance.
The anterior horns of the spinal gray matter contain so-called motor neurons that cause muscle contractions. Autonomic neurons (sympathetic and parasympathetic nervous system) are concentrated in the lateral horns, which regulate the activity of internal organs.
Sequelae of CNS injury
Even partial damage to the spinal cord can cause disruption of the functionality of various systems and organs.
Bones and joints
Spinal cord injury can lead to impaired absorption of calcium and some other important minerals in the bone tissue. But at the same time, these substances can accumulate in the urinary system, causing the formation of stones. Specialists usually explain such processes by a decrease in human motor activity. In addition, reduced mobility can lead to joint stiffness, including knee, elbow, and shoulder stiffness. To prevent this, there are special sets of exercises for people with disabilities.
urinary system
The urinary system consists of the kidneys, which filter the blood and produce urine, and the bladder, which collects and then removes it from the body. After a spinal cord injury, the kidneys continue to pass urine, but the bladder may not work as well as it used to. After an injury, a person may not feel when their bladder is filled with fluid, or their urinary system, due to the lack of the necessary impulses, may lose the ability to pass urine naturally. As a result, a catheter may be needed to empty the bladder. Another option: urine can, on the contrary, come out involuntarily and a person loses the ability to control this process.
Respiratory system
Even after a spinal injury, human lungs continue to work. However, the ability to inhale and exhale air is controlled by the muscles. Depending on the level of injury, a person may lose the ability to cough or take deep breaths. And they are necessary for the full straightening of the lungs and deep air circulation.
The most important muscle for breathing is the diaphragm. It is a large arcuate muscle that sits just below the lungs. And if the diaphragm is paralyzed due to damage to the spinal cord, special equipment may be needed to maintain respiratory function.
Leather
Spinal cord injury can also affect the skin. The human skin plays a very important role. It protects the body from microbes and other pathogens from the outside world. The spinal cord is an important organ that helps protect the skin from damage. For example, when you sit in one position for a long time, the brain sends signals in the form of a feeling of discomfort, which prompts you to change your position and prevent damage or squeezing of the skin. In the same way, the central nervous system protects against burns, cuts and other possible damage to the skin (for example, a person reflexively pulls his hand away from a hot or cutting object). With spinal cord injuries, such signals may not appear, which at times increases the risk of damage to the skin and, consequently, the penetration of microbes into the body.
Sexual system
After a spinal cord injury in the lumbar or sacrococcygeal segment, the functionality of the reproductive system may suffer. Men usually develop erectile dysfunction, problems with ejaculation and fertility. In women, sensitivity in the genital area may be impaired after an injury, although fertility itself may not be directly affected.
Intestines
It is well known that the digestive system is responsible for the breakdown of food consumed, the absorption of nutrients from it and the excretion of metabolic products. A fairly common consequence of CNS injury is a violation of intestinal motility. That is, the digestive system continues to absorb and digest food, but the process of removing excrement is disturbed. In a healthy body, when the rectum fills up, there is an exchange of impulses between the intestine and the brain. If the spinal cord is damaged, such signals may not be received. As a result, a person loses the ability to control the process of defecation.
autonomic nervous system
The autonomic nervous system regulates the activity of internal organs, blood and lymphatic vessels, as well as endocrine and external secretion glands. Body temperature, blood pressure, digestion and other important functions depend on it. After a spinal injury, some of its functions may be impaired. Quite often (especially if the injury occurs in the thoracic segment) after an injury, the body loses its ability to thermoregulate. What does it mean? If the autonomic nervous system works correctly, then the body temperature remains stable regardless of the weather conditions outside or the indoor microclimate. Due to damage to the spinal cord, body temperature may rise or fall in line with indoor or outdoor temperatures. Thermoregulation disorders are most noticeable in parts of the body located below the area of damage.
Emotions and feelings
Spinal cord injury affects not only the body, but also the emotions of a person. After a spinal injury, many people become depressed, depressed, withdrawn, and angry. Therefore, experts insist that patients with this kind of trauma undergo a course of psychotherapy. Also, people whose spinal injury caused impaired mobility need the support and help of loved ones.
The spinal cord is the most important center on which the performance of the whole organism depends, but at the same time this organ is very vulnerable. Its main defense is the vertebrae through which the nerve canal passes. Between the vertebrae are discs – semi-rigid cartilage, and spinal nerves pass through the narrow space between them. And in these places the central nervous system is the most vulnerable. As we age, the discs between the vertebrae lose their elasticity and become more rigid, which makes them more susceptible to damage, and thus increases the risk of spinal cord injury. Partial or complete rupture of the nerve bundle running inside the spine usually occurs due to a sharp displacement of the vertebrae. According to statistics, this most often happens during car accidents. In second place in terms of the frequency of spinal cord injuries is diving in water bodies head first. If the spinal cord is torn, the segments located below the injury site stop receiving impulses from the brain, due to which sensitivity is impaired and paralysis occurs at the level of these “floors”.