Human spinal cord anatomy. Spinal cord, structure and functions, anatomy of the human spinal canal. What is the spinal cord

The human spinal cord is one of the organs of the central nervous system that performs regulatory functions. The structure of the spinal cord of the brain.

The human spinal cord is located in the spinal canal, where there is a cavity formed by all parts of the spine.

There is no clear boundary between the spinal cord and the brain; therefore, the upper level of the first cervical vertebra is taken as the approximate boundary.

In fact, the spinal cord is formed from white and gray matter, which are surrounded by three membranes: pia mater, arachnoid mater and dura mater. The cavities between them and the spinal canal are filled with cerebrospinal fluid.

The soft shell is represented by connective tissue, in the thickness of which there is a blood network that nourishes the soft tissues. The arachnoid membrane is separated from the soft membrane by a subarachnoid space filled with cerebrospinal fluid and blood vessels. The arachnoid membrane has growths or granulations that protrude into the venous circulatory network, and carries out the outflow of cerebrospinal fluid into the venous network. The dura mater, together with the periosteum, forms the epidural space, where adipose tissue and the circulatory network are located. Fusing with the periosteum of the intervertebral foramen, it forms a sheath for the spinal ganglia.

Human anatomy examines the structure of an organ above the intracellular level. The external is organized by segmentation type. Each segment is connected to the brain and peripheral nerves that innervate a specific area of ​​the human body.

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Lecture 2. Nervous system

Structure and functions

Structure. Anatomically divided into central and peripheral, the central nervous system includes the brain and spinal cord, the peripheral - 12 pairs of cranial nerves and 31 pairs of spinal nerves and nerve ganglia. Functionally, the nervous system can be divided into somatic and autonomic (vegetative). The somatic part of the nervous system regulates the work of skeletal muscles, while the autonomic part controls the work of internal organs.

Nerves can be sensitive (visual, olfactory, auditory), if they conduct excitation to the central nervous system, motor (oculomotor), if excitation along them comes from the central nervous system, and mixed (vagus, spinal), if excitation along one fiber goes to one -, and on others - in the other direction.

Functions. The nervous system regulates the activity of all organs and organ systems, communicates with the external environment through the senses, and is also the material basis for higher nervous activity, thinking, behavior and speech.

Structure and functions of the spinal cord

Structure. The spinal cord is located in the spinal canal from the first cervical vertebra to the first and second lumbar vertebrae, length about 45 cm, thickness about 1 cm. The anterior and posterior longitudinal grooves divide it into two symmetrical halves. In the center runs the spinal canal, which contains cerebrospinal fluid. In the middle part of the spinal cord, near the spinal canal, there is gray matter, which in cross section resembles the outline of a butterfly. The gray matter is formed by the cell bodies of neurons and has anterior and posterior horns. The bodies of interneurons are located in the posterior horns of the spinal cord, and the bodies of motor neurons are located in the anterior horns. In the thoracic region, there are also lateral horns, in which the neurons of the sympathetic part of the autonomic nervous system are located. Surrounding the gray matter is white matter, made up of nerve fibers. The spinal cord is covered with three membranes: the outside is dense connective tissue, then the arachnoid and underneath it is vascular.

31 pairs of mixed spinal nerves arise from the spinal cord. Each nerve begins with two roots, the anterior (motor), in which the processes of motor neurons and autonomic fibers are located, and the posterior (sensitive), through which excitation is transmitted to the spinal cord. The dorsal roots contain the spinal ganglia, clusters of sensory neuron bodies.

Transection of the posterior roots leads to loss of sensitivity in those areas that are innervated by the corresponding roots; cutting of the anterior roots leads to paralysis of the innervated muscles.

The spinal cord lies in the spinal canal and in an adult is a cord 41-45 cm long, somewhat flattened from front to back. At the top it directly passes into the brain, and at the bottom it ends with a conical point, from which the terminal filament extends downwards. This thread descends into the sacral canal and is attached to its wall.

Structure

The spinal cord has two thickenings: cervical and lumbar, corresponding to the exit points of the nerves going to the upper and lower extremities. The anterior and posterior longitudinal grooves divide the organ into two symmetrical halves, each in turn has two weakly defined longitudinal grooves, from which the anterior and posterior roots emerge - the spinal nerves. The exit point of the roots does not correspond to the level of the intervertebral foramina and the roots, before leaving the canal, are directed to the sides and down. In the lumbar region they run parallel to the filum terminale and form a bundle called the cauda equina.

From the spinal cord, formed from the anterior (motor fibers) and posterior (sensory fibers) roots, 31 pairs of mixed spinal nerves depart. The area corresponding to the origin of a pair of spinal nerves is called a nerve segment, or a segment of the spinal cord. Each segment innervates specific skeletal muscles and skin areas.

The cervical and upper thoracic segments innervate the muscles of the head, girdles of the upper limbs, chest organs, heart and lungs. The lower thoracic segments and part of the lumbar segments are responsible for controlling the muscles of the trunk and intra-abdominal organs. From the lower lumbar segment and the sacral segment, nerves extend to the lower extremities and partially to the abdominal cavity.

Gray matter structure

A cross section of the spinal cord has the appearance of a butterfly, which is formed by gray matter surrounded by white matter. The wings of a butterfly are symmetrical sections in which the anterior, posterior and lateral columns (or horns) are distinguished. The front horns are wider than the rear ones. The posterior roots enter the posterior horns, and the anterior roots emerge from the anterior horns. In the center of the gray matter, along its entire length, there is a channel where cerebrospinal fluid circulates, which supplies nerve tissue with nutrients.

Gray matter is formed from more than 13 million nerve cells. Among them, three types are distinguished: radicular, bundle, and intercalary. The anterior roots contain the axons of the root cells. The processes of tuft cells connect the parts of the spinal cord with each other, and the intercalary ones end at synapses within the gray matter.

Neurons with a similar structure are united into the nuclei of the spinal cord. In the anterior horns, ventromedial, ventrolateral, dorsomedial and central pairs of nuclei are distinguished, in the posterior horns - proper and thoracic. In the lateral horns there is a lateral intermediate nucleus formed by association cells.

White matter structure

The white matter consists of processes and bundles of nerve cells that form the organ's conduction system. Constant and unhindered transmission of impulses is ensured by two groups of fibers:

1. Short bundles of nerve endings that occupy different levels of the spinal column are associative fibers.
2. Long fibers (projection) are divided into ascending, which go towards the cerebral hemispheres, and descending, which go from the hemispheres to the spinal cord.

Pathways

Long ascending and descending pathways connect the periphery to the brain using two-way communication. Afferent impulses along the spinal cord pathways are carried to the brain, transmitting to it information about all changes in the external and internal environment of the body. Along descending pathways, impulses from the brain are transmitted to effector neurons of the spinal cord and cause or regulate their activity.

Ascending paths:

1. Posterior funiculi (sensory tracts), which carry signals from skin receptors to the medulla oblongata.
2. Spinothalamic, send impulses to the thalamus.
3. Dorsal and ventral (spinocerebellar) are responsible for conducting excitation from proprioceptors to the cerebellum.

Descending Paths

1. Pyramidal - runs in the anterior and lateral columns of the spinal cord and is responsible for performing movements.
2. The extrapyramidal tract starts from the structures of the brain (red nucleus, basal ganglia, substantia nigra) and goes to the anterior horns and is responsible for involuntary (unconscious) movements.

Spinal cord membranes

The organ is protected by three membranes: hard, arachnoid and soft.

1. The dura mater is located on the outside of the spinal cord and does not fit tightly to the walls of the spinal canal. The resulting space is called the epidural; connective tissue is located here. Below is the subdural space at the border with the arachnoid membrane.
2. The arachnoid membrane consists of loose connective tissue and is separated from the soft membrane by the subarachnoid space.
3. The pia mater directly covers the spinal cord, limited from it only by a thin glial membrane.

Blood supply

The anterior and posterior spinal arteries descend along the spinal cord and are connected to each other by multiple anastomoses. Thus, a vascular network is formed on its surface. Also, the central arteries depart from the anterior spinal artery, which penetrate into the substance of the spinal cord near the anterior commissure. 80% of the blood supply comes from the anterior spinal artery. Venous outflow occurs through the veins of the same name, which flow into the internal vertebral venous plexuses.

Functions

The spinal cord has two functions: reflex and conduction.

As a reflex center it carries out complex motor and autonomic reflexes, and is also the site of closure of reflex arcs, which consist of three links: afferent, intercalary and efferent.

It is connected by afferent (sensitive) pathways to receptors, and by efferent (motor) pathways to muscles and internal organs.

An example is the congenital and acquired reflexes of a person; they are closed at different levels of the spinal cord: the knee at the level of the 3-4 lumbar segment, the Achilles at the 1-2 sacral segment.

Conductor the function is based on the transmission of impulses from the periphery (from skin receptors, mucous membranes, internal organs) to the brain along the ascending pathways and back through the descending pathways.

Similarities and Differences in Brainstem and Spinal Cord Functions

The brainstem is the structure into which the spinal cord passes through the foramen magnum and has a structure similar to it. The similarity lies in their performance of reflex and conduction functions.

They differ in the location of the gray matter: the brain stem is characterized by accumulations of gray matter in the form of nuclei, which are responsible for vital functions: breathing, blood circulation, etc., and in the spinal cord it is in the form of columns. Also, the trunk is an autonomous substance in the regulation of sleep, vascular tone, consciousness, and the spinal cord carries out all actions under the control of the brain.

The spinal cord is a cylindrical, elongated cord with a narrow central canal inside. Its outer shell, as in all parts of the central nervous system, has three layers - experts distinguish between the soft, hard and arachnoid membranes.

Anatomy Basics

The spinal cord is located in a cavity that is formed by the bodies and processes of the vertebrae. Its origin comes from the brain in the foramen magnum (at its lower border). The end of this formation occurs in the area of ​​the I-II lumbar vertebrae. At this point it narrows into the conus medullaris, from which the filum terminale branches downwards. In the upper sections of the thread there are elements of nervous tissue.

The conus medullaris below the second lumbar vertebra is a formation of connective tissue that consists of three layers. The end of the terminal filament falls on the second coccygeal vertebra, at the place of its fusion with the periosteum. The roots of the lower spinal nerves wrap around the terminal filum and form a bundle, which is called "". The length of the adult spinal cord ranges from 41 to 45 cm, and its mass is 34 to 38 g.

Thickenings and grooves

Two sections in this part of the nervous system have noticeable thickenings, namely the cervical and lumbosacral thickening, which are a collection of nerve fibers responsible for the movement of the upper and lower extremities.

Between the symmetrical halves of the human spinal cord there are dividing boundaries - the anterior median fissure and the posterior sulcus. On both sides of the median fissure stretches the anterior lateral groove, from which the motor root originates. This groove separates the lateral and anterior cords of the spinal cord. In the same way, the posterior lateral groove is located behind, which also plays the role of a kind of border.

Roots and substance, their relative position

The gray matter in this part of the central nervous system contains nerve endings - the anterior roots of the spinal cord. At the same time, the dorsal roots of the spinal cord are a collection of processes of sensitive cells that penetrate this part of the nervous system. These cells create the spinal ganglion, located at the junction of the anterior and posterior roots. In total, a person has 62 roots, which extend along the entire length in both directions (31 roots on one side). The part of the organ that is located between two pairs of roots is called a segment. Consequently, each person has 31 segments of the spinal cord - of which 5 segments are in the lumbar region, 5 in the sacral region, 8 in the cervical region, 12 in the thoracic region and 1 segment in the coccyx. The duration of this organ is somewhat shorter than the spinal column, therefore the location of the segment and its serial number do not coincide with the same number of the vertebra.

The SM includes both white and gray matter. In this case, nerve fibers form the white matter of the spinal cord, and the gray matter of the spinal cord is formed by both nerve fibers and nerve cells not only of the spinal cord, but also of the brain.

Gray matter SM

The gray matter of the spinal cord is formed from gray columns, which are interconnected by a transverse plate. This is the name given to the gray commissure, in the middle of which the opening of the central canal is noticeable. A person has two such adhesions: anterior and posterior, located respectively in the anterior and posterior parts of the central canal. If you analyze a cross section of the spinal cord, it is noticeable that the gray columns at the junction resemble the letter “H” or a butterfly with open wings.

In addition, it is easy to see projections that extend away from the gray matter. These are horns. They are divided into paired wide ones, which are located on the front part, and paired narrow ones - the place of their branch is on the back part. The anterior horns contain motor neurons. The anterior roots of the spinal cord are formed from neurites - long processes of motor neurons. The nuclei of the spinal cord are created from the neurons located in the anterior horn. There are five of them: the central nucleus, two lateral and two medial nuclei, from which cell processes extend towards the skeletal muscles.

The dorsal horn has its own nucleus located in the middle - it is formed by intercalary neurons. The processes of these neurons (axons) are directed towards the anterior horn. They pass through the anterior commissure, thus reaching the opposite side of the brain. Large interneurons have branched dendrites and form another nucleus located at the base of the dorsal horn. The intervertebral spinal nodes contain nerve cells, the ends of whose processes are located on the nuclei of the dorsal horns.

The intermediate part of the spinal cord is located between the anterior and posterior horns. In this area, the lateral horns branch off from the gray matter. This phenomenon is observed starting from the VIII cervical segment and ending with the II lumbar segment. These horns have a lateral intermediate substance consisting of nerve cells that are responsible for the sympathetic division of the autonomic nervous system.

White matter SM

The white matter is formed by three pairs of cords: anterior, posterior and lateral. The location of the anterior cord is between the anterior lateral sulcus and the medial sulcus, at the exit of the anterior roots. The lateral funiculus is located in the interval of the posterior and anterior lateral grooves, and the posterior, respectively, in the interval of the posterior median and lateral grooves. The white matter is formed by nerve fibers that carry nerve impulses. The impulses are directed up to the brain or down to the lower parts of the spinal cord. The gray matter also contains intersegmental nerve fibers, which are short in length and connect nearby segments. These fibers form the segmental apparatus of the spinal cord, because it is with their help that the connection between the segments is carried out.

The dorsal roots of the spinal cord are formed from fibers of neurons of the spinal ganglia. Some of these fibers enter the dorsal horn, others are directed in other directions. Another part of the fibers is part of the posterior cords, it is directed to the brain. These are the so-called ascending pathways. The endings of the remaining fibers fall on the neurons of the autonomous parts of the nervous system in the lateral horns or on the intercalary neurons of the dorsal horns.

What are the SM pathways for and their types?

The ascending tracts of the spinal cord are located outside of its bundles. Impulses from sensory and intercalary neurons are sent upward along them. From the brain down towards the motor center of the spinal cord, impulses also follow along these pathways. Sensory neurons are formed by a thin and wedge-shaped bundle, the functions of which are to supply an impulse from the nerve endings on the muscles and joints to the medulla oblongata.

The conduction function of the spinal cord is carried out by bundles. The wedge bundle is responsible for conducting impulses from the upper limbs and upper torso, and the thin bundle carries impulses from the lower body. The anterior and posterior spinocerebellar tracts carry out the conduction function of the spinal cord, as they conduct impulses to the cerebellum from the skeletal muscles. The posterior part of the spinocerebellar tract originates from the cells of the thoracic nucleus, which is located in the medial part of the dorsal horn. The location of the posterior spinocerebellar tract is on the posterior side of the lateral cord.

The branches of interneurons located in the intermedial nucleus, which is located in the dorsal horn, form the anterior part of the spinocerebellar tract. On the opposite side of the horn, the fibers of the intercalary neurons form the lateral spinothalamic tract, which performs the function of conducting pain sensations and temperature sensitivity initially to the diencephalon, after which the impulse is sent to the cerebral cortex.

How does the human spinal cord function?

The red nuclear spinal tract and the lateral corticospinal tract form the descending tracts. Their location is in the lateral funiculus. Some of them fall on the anterior cord and form the anterior part of the corticospinal tract. A person also has a tegmental and vestibulospinal tract.

These pathways perform similar functions to the spinal cord. The red nucleus spinal tract provides involuntary motor impulses. The path originates in the red nucleus, gradually descending to motor neurons localized on the anterior horns. This is where the name of the path comes from. Voluntary motor impulses are provided by the lateral corticospinal tract, which includes neurites of cells of the cerebral cortex. Closer to the bottom, the path becomes thinner, which can easily be explained by the fact that on each part of the SC, part of the fibers of the path end on motor cells located on the anterior horn.

The reflex function of the spinal cord is also provided by the anterior corticospinal tract, the purpose of which coincides with the purpose of the lateral tract, with the exception of the location of the axons of the cells of the cerebral cortex (they are localized in the anterior cord). The tegnospinal tract originates at the top and bottom of the roof of the brain, and its end is at the level of the anterior horns. The direction of the vestibular spinal tract runs from the vestibular nuclei to the forebrain. The functions of the human spinal cord at this level are to maintain the balance of the body.

The blood supply to the brain and spinal cord is closely related. Blood enters the spinal cord through the anterior and paired posterior spinal arteries, as well as through the radicular-spinal arteries.

As in the brain, choroid plexuses form in the corresponding meninges. Each spinal nerve root extending from the brain is accompanied by an artery and a vein - this is how a neurovascular bundle is formed, if the elements of which are damaged, various pathological conditions can develop. Actually, to diagnose a specific condition that manifests itself as a pain syndrome, it is necessary to perform a whole set of diagnostic tests - only their results make it possible to determine which of the links in the neurovascular bundle is damaged as the cause of the patient’s complaints.

That is why doctors of various specialties - neurologists, neuropathologists, vertebrologists, and orthopedic traumatologists - can identify and treat pathological conditions and diseases of the spinal cord. It often turns out that all these specialists must observe such a patient - only in this case can one provide the patient with effective assistance and alleviate his condition. Neglect of complaints that arise causes the development and progression of various diseases that can cause disability or death of the patient.

In general, the functions of this part of the human nervous system correspond to its structure.

The spinal cord is the part of the central nervous system located in the spinal canal. The conditional boundary between the medulla oblongata and the spinal cord is considered to be the place of decussion and origin of the first cervical root.

The spinal cord, like the brain, is covered with meninges (see).

Anatomy (structure). Along its length, the spinal cord is divided into 5 sections, or parts: cervical, thoracic, lumbar, sacral and coccygeal. The spinal cord has two thickenings: the cervical, associated with the innervation of the arms, and the lumbar, associated with the innervation of the legs.

Rice. 1. Cross section of the thoracic spinal cord: 1 - posterior median sulcus; 2 - posterior horn; 3 - side horn; 4 - front horn; 5-central channel; 6 - anterior median fissure; 7 - anterior cord; 8 - lateral cord; 9 - posterior cord.

Rice. 2. Location of the spinal cord in the spinal canal (cross-section) and exit of the spinal nerve roots: 1 - spinal cord; 2 - posterior root; 3 - anterior root; 4 - spinal node; 5 - spinal nerve; 6 - vertebral body.

Rice. 3. Diagram of the location of the spinal cord in the spinal canal (longitudinal section) and the exit of the spinal nerve roots: A - cervical; B - breast; B - lumbar; G - sacral; D - coccygeal.

The spinal cord is divided into gray and white matter. Gray matter is a collection of nerve cells to which nerve fibers approach and depart. In a cross section, the gray matter has the appearance of a butterfly. In the center of the gray matter of the spinal cord is the central canal of the spinal cord, barely visible to the naked eye. In the gray matter, there are anterior, posterior, and in the thoracic region, lateral horns (Fig. 1). The sensory cells of the dorsal horns are approached by the processes of the cells of the spinal ganglia, which make up the dorsal roots; The anterior roots of the spinal cord extend from the motor cells of the anterior horns. The cells of the lateral horns belong to (see) and provide sympathetic innervation of the internal organs, vessels, glands, and the cell groups of the gray matter of the sacral region provide parasympathetic innervation of the pelvic organs. The processes of the cells of the lateral horns are part of the anterior roots.

The roots of the spinal cord exit the spinal canal through the intervertebral foramina of their vertebrae, going from top to bottom over a more or less significant distance. They make a particularly long journey in the lower part of the vertebral column, forming the cauda equina (lumbar, sacral and coccygeal roots). The anterior and posterior roots come close to each other, forming the spinal nerve (Fig. 2). A section of the spinal cord with two pairs of roots is called a spinal cord segment. In total, 31 pairs of anterior (motor, ending in the muscles) and 31 pairs of sensory (coming from the spinal ganglia) roots depart from the spinal cord. There are eight cervical, twelve thoracic, five lumbar, five sacral segments and one coccygeal. The spinal cord ends at the level of the I - II lumbar vertebra, therefore the level of location of the spinal cord segments does not correspond to the vertebrae of the same name (Fig. 3).

White matter is located along the periphery of the spinal cord, consists of nerve fibers collected in bundles - these are descending and ascending pathways; distinguish between anterior, posterior and lateral funiculi.

The spinal cord is relatively longer than that of an adult, and reaches the third lumbar vertebra. Subsequently, the spinal cord lags somewhat behind its growth, and therefore its lower end moves upward. The spinal canal of a newborn is large in relation to the spinal cord, but by 5-6 years the ratio of the spinal cord to the spinal canal becomes the same as in an adult. Growth of the spinal cord continues until approximately 20 years of age, and the weight of the spinal cord increases approximately 8 times compared to the neonatal period.

The blood supply to the spinal cord is carried out by the anterior and posterior spinal arteries and spinal branches arising from the segmental branches of the descending aorta (intercostal and lumbar arteries).

Rice. 1-6. Cross sections of the spinal cord at various levels (semi-schematic). Rice. 1. Transition of the first cervical segment into the medulla oblongata. Rice. 2. I cervical segment. Rice. 3. VII cervical segment. Rice. 4. X thoracic segment. Rice. 5. III lumbar segment. Rice. 6. I sacral segment.

Ascending (blue) and descending (red) pathways and their further connections: 1 - tractus corticospinalis ant.; 2 and 3 - tractus corticospinalis lat. (fibers after decussatio pyramidum); 4 - nucleus fasciculi gracilis (Gaull); 5, 6 and 8 - motor nuclei of cranial nerves; 7 - lemniscus medlalis; 9 - tractus corticospinalis; 10 - tractus corticonuclearis; 11 - capsule interna; 12 and 19 - pyramidal cells of the lower parts of the precentral gyrus; 13 - nucleus lentiformis; 14 - fasciculus thalamocorticalis; 15 - corpus callosum; 16 - nucleus caudatus; 17 - ventrulculus tertius; 18 - nucleus ventrals thalami; 20 - nucleus lat. thalami; 21 - crossed fibers of tractus corticonuclearis; 22 - tractus nucleothalamlcus; 23 - tractus bulbothalamicus; 24 - nodes of the brain stem; 25 - sensitive peripheral fibers of the trunk nodes; 26 - sensitive nuclei of the trunk; 27 - tractus bulbocerebellaris; 28 - nucleus fasciculi cuneati; 29 - fasciculus cuneatus; 30 - ganglion splnale; 31 - peripheral sensory fibers of the spinal cord; 32 - fasciculus gracilis; 33 - tractus spinothalamicus lat.; 34 - cells of the posterior horn of the spinal cord; 35 - tractus spinothalamicus lat., its decussation in the white commissure of the spinal cord.