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

Human central nervous system

The central nervous system (CNS) is represented by the brain and spinal cord; it regulates all body processes and serves as the control center for all human systems.

The meninges surround the brain and spinal cord. They consist of connective tissue formations.

Functions of the meninges
1). Serve to protect nervous tissue from mechanical damage	20. They are a barrier that prevents the penetration of microbes and various substances into the brain	3). Contains blood vessels involved in the secretion of cerebrospinal fluid

Shell image diagram:

brain

spinal cord

Spinal cord and its structure

The spinal cord has the form of a cord 45 cm long and 1 cm in diameter. In the center there is a canal filled with cerebrospinal fluid.

Location of the spinal cord in the spinal canal

The spinal cord consists of 31-32 segments:

1. 8 cervical (C1-C8);

2. 12 chest (Th1-Th12);

3. 5 lumbar (L1-L5);

4. 5 sacral (S1-S5);

5. 1-2 coccygeal;

6. The lumbosacral nerves follow the canal for a considerable distance and form the cauda equina.

Structure of a spinal cord segment

Consists of:

pathways in the white matter, dorsal root (sensitive), spinal ganglion, mixed spinal nerve, gray matter, anterior root (motor), central canal.

Cross section of the spinal cord

1. Soft shell of the spinal cord;

2. Posterior median sulcus;

3. Anterior median fissure;

4. Anterior spinal artery;

5. Dorsal root - axons of sensory neurons, the bodies of which are located in the spinal ganglia;

6. Posterior horn - interneurons;

7. Lateral horn - nuclei of the sympathetic system;

8. Anterior horn - bodies of motor neurons;

9. Anterior root - axons of motor neurons.

Functions of the spinal cord

Brain structure		Functions of the spinal cord
Gray matter	Interneurons	Reflex function - takes part in motor reactions. Here are the centers of unconditioned reflexes (knee reflex, etc.); vegetative centers of reflexes of urination, defecation, reflex activity of the stomach.
	Cell bodies and dendrites of motor neurons
White matter	Axons of neurons forming descending tracts	Conductor function - conduction of nerve impulses. There is communication between different parts of the spinal cord; connection of the brain with other parts of the central nervous system; connection of receptors with executive organs.
	Neuronal axons forming ascending tracts

Cerebrospinal fluid

Cerebrospinal fluid is produced by the choroid plexuses of the ventricles of the brain; its composition is similar to blood plasma. Its volume is 120-150 ml.

Functions of cerebrospinal fluid
1). It is a shock absorber - protects the brain and spinal cord from shocks and shocks	2). Ensures the delivery of nutrients to all parts of the central nervous system and the removal of metabolic products	3). Maintains a certain level of osmotic pressure (60-140 mm water column)

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Source of information: Rezanova E.A. Human biology. In tables and diagrams./ M.: 2008.

Features of anatomy

The spinal cord is a unique organ of the human body, so it is not surprising that it has its own characteristics. It is located along the spine, and this anatomy allows you to effectively protect this extremely important and sensitive organ from any mechanical influences from the outside. But it is shorter in length than the entire ridge, so the ratio of the spinal cord segments does not correspond to the numbering of the sections of the column itself. Complete agreement is observed only in preschool children.

The spinal cord begins at the back of the head and ends at the lumbar level, approximately at the level of L1-L2. In women the cord is slightly shorter than in men. In general, its length reaches 43–45 cm. The spinal cord ends in a cone, from which a terminal filament extends, surrounded by a nerve outlet.

The entire cord along its entire length is unequal in thickness, as it has two seals in the cervical and lumbosacral regions. This is due to the need to place a large number of neurons responsible for the functioning of the lower and upper extremities.

Spinal nerves

Two pairs of roots emerge from each segment of the brain: anterior and posterior. These are the beginnings of the spinal nerves connecting the central nervous system with organs.

The dorsal roots have thickenings (nodes) in which the bodies of sensory neurons lie.

Rice. 2. Spinal cord roots.

The axons of these neurons travel to the organs and form sensory nerves.

The anterior roots are formed from the axons of motor neurons, the bodies of which lie in the gray matter. From these roots originate motor nerves that transmit signals to the organs.

Functions

The spinal cord performs 2 functions:

reflex;
conductor.

Reflex function

A reflex is the body’s response to any irritation from the external or internal environment.

spinal cord reflexes are carried out without the participation of human consciousness, automatically.

Rice. 3. Reflex arc of the spinal reflex.

A reflex arc can only include 2 neurons:

sensitive;
motor.

But more often, between these neurons there is one or more intercalary neurons, which are located in the gray matter.

All gray matter neurons are divided into 2 types:

motor (3%);
insertional (97%).

Conductive function

Impulses are carried out by white matter, consisting of bundles of nerve fibers.

Along the ascending paths there are impulses from receptors that perceive information from the internal environment of the body and the external world.

Along descending pathways, signals from the brain are sent to all organs.

When the spinal cord is ruptured, the victim develops paralysis of the limbs and cannot control them. If the injury is at the neck level, the arms and legs are paralyzed; if it is at the chest or lower back level, only the legs are paralyzed.

Thus, the structure and functions of the spinal cord correspond to each other.

The bundles of fibers that make up the white matter are like wires through which signals constantly flow from the brain to the organs and back.

Neurons of the gray matter are intermediaries between the motor and sensory areas of the reflex arc.

Segment structures

The structure of the segments in the spinal cord is paired, and they are connected to the organs by nerves. The anterior and posterior roots provide the transmission of information, and their main task is to stimulate muscle contraction. Only the dorsal roots are sensitive; they are the ones that are activated by receptor stimuli. The spinal cord is not homogeneous in cross section, but is a substance consisting of white and gray matter.

Segmental structure of the spinal cord with the designation of roots in different sections

White matter

The white matter of the spinal cord is represented by processes of nerve cells that make up the pathways. It is located on the periphery of the gray matter and is formed from nerve bundles. The white matter contains descending ascending fibers that pass into the brain. They transmit information coming from receptors. Their location is natural: on the side of the back there are ascending ones, on the abdominal side there are outgoing ones. The white matter is delimited by the grooves of the spinal cord into:

anterior - make up the descending pathways.
lateral - there are both ascending and descending paths.
posterior cord - make up the ascending pathways.

White matter contains projection, association and commissural nerve tracts. The first provide communication with the brain.

Gray matter

Gray matter consists of interneurons and motor neurons. They provide motor reflexes and communication between neurons. In total, it occupies approximately 18% of the total volume of the spinal cord, and includes approximately 13.5 million neurons. This is a special device that contains some functions of the central nervous system. Thanks to two-way communication, irritation can pass through both ascending and ascending pathways. The response is a contraction of muscle tissue and a motor response.

Do you know that:

The spinal cord stops growing at the age of 5 years.
In the process of evolution, it was the spinal cord that appeared first, and only then the brain.
People with spinal cord injury cannot sweat below the injury site. Therefore, in hot weather they need to be in the shade or otherwise cool their body to avoid overheating.
The spinal cord relaxes all the muscles of the body during sleep. This function allows a person not to repeat the movements that he performs in his sleep.

What are the segments?

The sections of the spinal cord differ from those used to conventionally divide the areas of the spine. Their length varies; the fewest elements are found in the coccygeal part. The segments are connected to certain areas in the body by nerve conductors. In general, the brain is divided into the following segments:

Prognosis for spinal cord myelitis

Neck – 8.
Chest – 12.
Sacral – 5.
Lumbar – 5.

The main length falls on the thoracic segments of the spinal cord, after which 23.2% is allocated to the neck and only 7.3% to the lower back. They are posterior and anterior nerve roots that alternate regularly. They are located above the vertebrae with the same number. Their main task is to report movements and be responsible for muscle contractions. Therefore, the anterior nerve roots are also called motor, and the posterior - sensitive.

The intervertebral foramen contains the roots of each individual segment. Their direction is not the same, because the spinal column is filled with the brain. In the cervical region they lie horizontally, in the thoracic region they are directed diagonally, and in the lower part they are almost vertical.

The shortest segments are the neck segments, and the longest ones are in the lower back and sacrum. In the lower part they form the so-called “horse tail” - this is a bunch of roots located below the 2nd vertebra.

A visual representation of what a spinal cord segment looks like in cross section

Basic functions of the spinal cord

The segmental structure of the spinal cord allows it to effectively cope with assigned tasks. Their well-coordinated communication ensures a high speed of impulse transmission and perception of information coming from the environment. The main functions of the spinal cord are conductive and reflex. They ensure the ability of the organ to perform all the necessary actions for the normal functioning of the body.

The segmental apparatus is connected with almost all internal organs and ensures human activity and the functionality of each system. The first function allows you to receive complete information about the world around you: what effects are on the skin or body, whether it hurts or not. The “communication” is two-way, since the brain not only reacts to events around it, but also gives commands what needs to be done. The conduction function ensures mental and motor activity.

The reflex function is no less important. The concept itself explains what it is. Thanks to the spinal cord, if the hand feels pain or burning when exposed to fire receptors, the person quickly pulls it back reflexively. During the examination, neurologists check the knee reflex and other body reactions to stimuli; if they are absent, this helps to diagnose hidden disorders in a timely manner.

The spinal cord has a rather complex structure, since it is responsible for the most important functions in the body, namely: digestion, urination, blood circulation, breathing, sex life, motor activity and many others. It is thanks to the reflexes for which he is responsible that a person is saved in moments of danger. It consists of many segments that help transmit impulses from the periphery towards the brain. Thanks to their coordinated work, a person’s muscles contract and he feels the world around him.

Location Features

The skeletotopy of the areas is individually variable, since the lower part of the lumbar region can be located in adults from the lower third of the body of the 9th thoracic vertebra to the disc between L1-L2. Because of this, a certain feature appears. When the upper processes are directed in the transverse direction, the further down the canal, the higher the exit site is located relative to the intervertebral foramen.

Each segment of the spinal cord is responsible for its part of the periphery. This could be muscle tissue, internal organs or skin. The division into such sections is almost identical in all people, so it is not difficult for doctors to identify the location of the lesion based on the specific sensitivity of a particular area. The relationship can be seen in more detail in the table:

Department	Number of spines	Related department
Cervical	8	Skin and muscles in the neck, upper limbs, diaphragm
Chest	12	Skin on the chest, back and abdomen
Lumbar Sacral Coccygeal	5 5 1	Lower body, legs, feet, pelvic organs

For example, when a patient complains of discomfort in the navel area, there is a high probability that the pathology is hidden below the 10th thoracic vertebra. The doctor will check for the presence of a lesion in this particular part of the body.