Human central nervous system, spinal cord and its functions (Diagram)

March 1, 2019

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The human spine is the basis of the musculoskeletal system. At the same time, it not only performs a supporting function and provides the ability to walk upright, but also represents a fairly flexible axis of the body, which is achieved due to the mobility of the vast majority of its individual parts. In this case, the anterior part of the spine participates in the formation of the walls of the thoracic and abdominal cavities. But one of its most important functions is to ensure the safety of the spinal cord that runs inside it.

general information

The anatomy of the spinal cord differs from the brain in its oblong structure. In Latin the organ is called medulla spinalis. It is a thickened tube with a small channel inside, slightly flattened in front and behind. It is this structure that ensures the normal transportation of nerve impulses from the main organ located in the cranium to the peripheral structures of the nervous system.

Locally, the organ is located in the spinal canal, where soft and bone tissues and nerve endings responsible for many functions of the human body are concentrated. Without a normally functioning spinal cord, natural breathing, digestion, heartbeat, reproductive activity, and any motor activity are not possible.

In humans, it begins to form at about 4 weeks of development inside the mother’s womb. But in what form it is observed in an adult, it appears much later; at first it is a neural tube, gradually developing into a full-fledged organ. It completes its formation within 2 years after birth.

Blood supply

The supply of nutrients is carried out through the blood, which flows through numerous vessels. They extend from the upper part, along the thyroid and vertebral arteries. They start from the aorta and vertebral arteries, of which there are normally about 6–8 in humans. The largest of them provide nutrition to the cervical and lumbar thickening.

The largest radicular-spinal artery is the inferior artery of Adamkiewicz; there are 15–20 posterior arteries in total, but all of them are significantly narrower. Their main task is to provide nutrition to the posterior third of the spinal cord.

All vessels are connected to each other; such joints are called anastomosis. The entire system provides nutrition to different parts of the brain, while being protected from the formation of blood clots. Even if a separate vessel is closed by a plug, the area for which it is responsible will not be left without power; this is what the anastomosis provides. It saves neurons from hypoxia and death.

In addition to the arteries, the spinal cord is also supplied by veins that are connected to the cranial plexuses. This is a whole system of vessels through which blood flows from this organ to the vena cava. Thanks to the presence of special valves, blood is not able to flow back.

Skeletotopy of the spinal cord

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Structure

The local location of the spinal cord along the entire back has its own characteristics. This physiology ensures that the organ performs its basic functions. The organ begins at the level of the 1st cervical vertebra, where it is gently rebuilt into the brain, but there is no clear division in them. At the junction there is a crossover of the pyramidal tracts responsible for the motor activity of the limbs. The spinal cord ends in the region of the 2nd lumbar vertebra, so it is shorter in length than the entire spine as a whole. This feature allows lumbar puncture to be performed at the level of the 3-4 lumbar vertebrae, without the risk of damaging the spinal cord.

What is special about the structure? The oblong tube has two grooves at the front and back. The brain is covered by three membranes:

• Solid. It is the tissue of the periosteum of the spinal canal, followed by the epidural space and the outer layer of the dura mater.
• Cobweb. A thin, colorless plate that fuses with the hard shell in the area of ​​the intervertebral foramen. In the place where there is no fusion, the subdural space is located.
• Vascular. A soft membrane separated from the previous one by a subarachnoid space with cerebrospinal fluid. The membrane is adjacent to the spinal cord and consists mainly of choroid plexuses.

The space between them is filled with cerebrospinal fluid - cerebrospinal fluid. The gray matter is located in the center of the organ. It consists of intercalary and motor neurons. It also contains two types of horns: the anterior ones, which contain motor neurons, and the posterior ones, where interneurons are located.

External characteristics

The external structure of the spinal cord largely follows the contours of the spine, since the structures adapt to its physiological curves. Two thickenings are observed in the area of ​​the neck and lower thoracic, the beginning of the lumbar calving. These places are characterized as exits of the roots of the spinal nerves responsible for the innervation of the arms and legs.

The external structure can be briefly described by the following characteristics:

• The shape is cylindrical, flattened on the front and back sides.
• Visually, the spinal cord looks like an elongated “cord” with processes.
• On average, the length of the organ is 42-44 cm, but directly depends on the person’s height.
• The mass is 34-38 g, which is 50 times less than the organ of the brain.
• There are two grooves in front and behind, which visually divide the organ into two symmetrical parts.
• In the middle there is a canal, which in the upper part communicates with one of the ventricles of the brain. Inferiorly, the central canal expands, forming the terminal ventricle.

The thickness of the spinal cord is uneven and depends on in which part the measurement is taken. The organ also has four surfaces: two rounded lateral, a convex posterior and a flattened anterior. The external structure is in many ways reminiscent of the internal part of the ridge, since the organ fills the entire canal. The organ is reliably protected by bone tissue.

Internal structure

The spinal cord is made up of nerve tissue cells called neurons. They are concentrated closer to the center and form gray matter. According to rough estimates by scientists, the entire organ contains about 13 million cells, which is many times less than in the head section. The gray matter is located inside the white matter, and if you make a cross section, it will be shaped like a butterfly. This is especially clearly visible in the diagram.

Schematic cross-section of the spinal cord

This unique anatomy allows the spinal cord to be divided into several structures. It is arranged as follows:

• Front horns. They are distinguished by their rounded, wide shape and consist of neurons responsible for transmitting nerve impulses to the muscles. It is precisely because they perform such a task that they are called motor. The anterior roots of the spinal nerves begin in the anterior horns.
• Hind horns. They are distinguished by a long, narrow shape and consist of interneurons. They bear this name due to their ability to receive incoming signals from the sensory roots of the spinal nerves, otherwise they are called dorsal roots.
• Side horns. They are present only in the lower segments of the organ, and contain vegetative nuclei responsible for the dilation of the pupils, or the functioning of the sweat glands.

The physiological function of nerve endings is to transmit signals from the brain to the spinal cord, as well as deliver received impulses in the opposite direction. This ensures interconnection at all levels and areas of the nervous system. Nerve fibers are combined into bundles and are present along the entire length of the spinal cord.

Metamer and segmental structure

Each part of the spinal cord is a constituent element of a specific metamere of the body. Moreover, if there is a “piece” of the spinal cord that includes a section of gray matter with a pair of roots, then the metamer includes the spinal segment itself, muscle fiber (myotome), a section of the epidermis (dermatome), a bone component (scletorome), an internal organ (splanchiotome), controlled by this segment. In humans and higher representatives of the animal world, radicular metamerism is observed - the spinal cord is confined to certain parts of the body.

The skin areas of the body consisting of sensory fibers that approach the corresponding segment of the spinal cord are called dermatomes. They are strips of epidermis controlled by sensitive nerve endings. They are located throughout the body and sometimes overlap each other.

Visual representation of the connection between the skin and the spinal cord

Myotomes are muscle groups that receive motor fibers from certain areas of the brain. Thanks to the study and knowledge of their location, the process of damage and diagnosis of spinal cord lesions is greatly simplified. Damage to a certain segment of the spinal cord provokes sensory and motor disorders.

Connection between the spinal cord and muscle fiber

Segmental structure

The spinal cord is conventionally divided into five sections, although it is a single whole. The name of each directly depends on its location in the body. In total, a person may have 31-33 segments, which consist of:

• Cervical area - includes 8 segments.
• Thoracic region - 12 segments.
• Lumbar region – 5 segments.
• Sacral – 5 segments.
• Coccygeal – 1-3 segments.

This division allows us to examine the organ in more detail and simplify the process of diagnosing various pathologies.

White and gray matter

In cross-section, the symmetrical halves can be seen in detail and the anterior medial fissure and connective tissue septum can be seen. The part located inside is darker and is called gray matter (GM), it is located in a lighter substance - white matter (WM). Most of the SV is located in the lumbar region, the least is observed in the thoracic region. What are the main functions of gray matter:

• Transmission of pain impulses.
• Response to temperature changes.
• Closure of reflex arcs.
• Obtaining information from muscle tissue, tendons, ligaments.
• Formation of pathways.

What is the structure of white matter? It consists of myelinated, unmyelinated nerve fibers, blood vessels and a small amount of connective tissue. Its main task is to trigger simple reflexes and provide connections with skeletal muscles.

Functions

Functional anatomy implies that, being part of the central nervous system, the spinal cord performs a reflex and conductive function. In the first case, the body controls the implementation of the simplest actions at the level of reactions contained in the subconscious. A striking example is the initiation of a motor function by withdrawing the hand if the surface is too hot. The limb does this before the person himself understands what happened. The second task of the organ is to transmit nerve impulses to the head section of the central nervous system, along the ascending and descending pathways.

Briefly about the main functions of the spinal cord

Reflex function

This main function of the organ is a response to external irritation. For example, the appearance of a reflex cough due to foreign objects and particles entering the respiratory tract, removing the hand from cactus spines or a source of danger. The impulse enters the spinal canal through motor neurons, which also trigger muscle contraction. This process does not require the involvement of the brain, and the motor reaction occurs without its participation. That is, a person does not even think about his action, often does not realize it.

Children's innate reflexes are checked after birth. They usually include the ability to suck milk, breathe, and jerk their legs. During development, acquired reflexes also appear, which help doctors identify the correct functioning of the arch elements and individual segments of the spinal cord. The test is carried out during a neurological examination. The main emphasis is on the plantar reflex, knee and abdominal. They allow you to check how healthy a person is at one time or another.

Conductor function

Treatment of spinal cord myelitis

Another important function of the spinal cord is conduction. It ensures the transmission of impulses from the skin, mucosal surface, internal organ to the brain and in the opposite direction. The white matter acts as a “conductor”. It is this that carries information about incoming impulses from the outside. Thanks to this ability, a person can characterize any object that surrounds him.

Cognition of the world is carried out through the transfer of information after touch to the brain. It is thanks to this function that a person understands that an object is slippery, smooth, rough or soft. With loss of sensitivity, the patient ceases to understand what is in front of him when touching an object. In addition, the brain receives data about the position of the body in space, tension in muscle tissue or irritation of pain receptors.

Protective role of the cervical spine

The cervical region of the spine is located at the very top of the column and includes the seven upper vertebrae. They have processes with openings containing blood vessels that supply the brain with blood and, accordingly, oxygen and useful elements. If the cervical vertebrae are damaged, brain diseases may occur due to insufficient blood supply. You may experience headaches, dizziness, speech impairment, and spots before your eyes. This disease is called vertebrobasilar insufficiency.

The cervical region protects cerebral circulation and is responsible for the functioning of the eyes, ears, nose, mouth, vocal cords, thyroid gland, shoulders and arms. If there is a violation of the first vertebra of this department, then headaches may occur (and this can develop into a migraine), problems with sleep, and increased blood pressure.

Problems with the second vertebra can cause frequent fainting, problems with hearing and vision, and even allergic reactions that did not exist before may appear. The third vertebra is responsible for the skin of the face, so its displacement can affect the appearance of rashes and acne. Neuritis and neuralgia may occur.

Changes in the fourth cervical vertebra can cause hearing impairment (even loss) or enlarged adenoids. Curvature of the fifth vertebra leads to sore throat, laryngitis and tonsillitis. Pain in the neck, shoulders, and occipital lobe of the brain can occur due to problems with the sixth cervical vertebra.

Mobility of the shoulders and arms (up to the elbows) may be limited due to loss of functionality of the seventh vertebra.

What organs does the spinal cord control?

It is also important to understand which internal organs are connected to the spinal cord and may suffer if a particular area of ​​the spine is damaged. Specific spinal segments control specific parts of the body by transmitting nerve impulses and transmitting responses along motor neurons. What each vertebra is responsible for can be clearly seen in the table.

Damage to the spinal cord in a specific section negatively affects the functioning of these internal organs. In some cases, dysfunction occurs before vertebral compression or displacement is detected.

Risk of organ damage

Due to the characteristic structure of the brain, it is connected to most systems in the body. The integrity of its structure is extremely important for the correct functioning of the musculoskeletal system and the health of internal organs. Any injury, regardless of severity, can lead to disability. Sprains, dislocations, disc damage, vertebral fractures with or without displacement can cause spinal shock and paralysis of the legs, and disrupt the normal functioning of the cords.

Severe injuries result in shock lasting from several hours to several months. In this case, the pathological condition is accompanied by a number of neurological symptoms. These include numbness, sensory disturbances, pelvic organ dysfunction, and inability to control the process of urination and bowel movements.

Treatment of minor spinal injuries is carried out on an outpatient basis, using medications, therapeutic exercises and massage. Severe injuries require surgical intervention, especially if compression of the spinal cord is detected. Cells are quickly damaged and die, so any delay can cost a person’s health. The recovery period after such an intervention is up to two years. Various physiotherapeutic procedures help with this, for example, reflexology, ergotherapy, electrophoresis, magnetic therapy, etc.

The spinal cord is a key element of the human central nervous system, which is connected in one way or another with almost all internal organs and human muscle tissue. The specific structure allows you to transmit impulses and signals, ensure full motor activity, and perform a number of other functions.

Views of Eastern and Western medicine on the role of the spine

If we turn to Eastern traditions in medicine, the entire body can be considered as a family - the spine and internal organs. The spine is then called the husband, because. This is the main musculoskeletal core, which in addition also provides protection for the body. And the internal organs are called the wife, because... they provide the body with oxygen and nutrients.

Eastern doctors believe that it is in the spine that the keys to all human diseases lie, so first of all it is necessary to treat the spine, and then secondary diseases will go away.

Of course, in modern Western traditional medicine, they first pay attention to diseases of the organs and do not always look at problems of the spine. Not every disease will be 100% related to the spine, but it is still better to monitor its health, and to do this, perform simple exercises to prevent spinal diseases. This way you can protect yourself from many unpleasant diseases.