The spinal cord enters the central nervous system.In the human body, he is responsible for motor reflexes and transmission of nerve impulses between organs and the brain. The shells of the spinal cord cover it, providing protection. What features and differences do they have?
Structure
Arches of the vertebrae form a cavity calledvertebral canal, and it contains the spinal cord along with the vessels and nerve roots. Its upper part connects with the medulla oblongata (head part), and the lower part - with the periosteum of the second coccygeal vertebra.
The spinal cord looks like a thin white cord,the length of which in humans reaches 40-45 centimeters, and the thickness increases from the bottom up. Its surface is slightly concave. It consists of thirty-one segments, of which pairs of nerve roots leave.
The spinal cord is covered with shells from the outside.Inside it contains a gray and white substance, their ratio varies in different parts. Gray matter has the form of a butterfly, it contains the bodies of nerve cells, their outgrowths contain a white substance that is located at the edges.
In the center of gray matter is a canal.It is filled with cerebrospinal fluid (cerebrospinal fluid), which constantly circulates in the brain and spinal cord. In an adult, its volume is up to 270 milliliters. Likvor is produced in the ventricles of the brain and is updated 4 times a day.
Shells of the spinal cord
Three shells:solid, arachnoid and soft - cover both the head and spinal cord. They have two main functions. Protective prevents the negative impact of mechanical effects on the brain. The trophic function is associated with the regulation of the cerebral blood flow, through which the metabolism in the tissues is carried out.
The spinal cord consists of cellsconnective tissue. Outside, there is a hard shell, beneath it spider's and soft. They do not fit tightly together. Between them there is a subdural and subarachnoid space. To the spine they are attached by plates and ligaments, which prevent the stretching of the brain.
Shells are formed at the beginning of the second monthembryo development. Connective tissue is formed on the neural tube and spreads through it. Later, cells of the tissue are separated to form the outer and inner membranes. After some time, the inner shell is divided into a soft and arachnoid.
Hard shell
The outer hard shell consists of a top andbottom layers. It has a rough surface, on which there are many vessels. In contrast to the similar membrane in the brain, it does not fit tightly to the walls of the spinal canal and is separated from them by the venous plexus, fatty tissue.
The dura mater of the spinal cord representsdense shiny fibrous fabric. It envelops the brain in the form of an elongated cylindrical bag. The covering cells (endothelium) make up the lower layer of the membrane.
It envelops the nodes and nerves, forming cavities,that expand, approaching the intervertebral foramen. Near the head of the shell is connected with the occipital bone. Down it narrows and is a thin thread that joins the tailbone.
The blood passes to the sheath through the arteries,connected to the abdominal and thoracic aorta. Venous blood enters the venous plexus. The shell is fixed in the spinal canal using processes in the intervertebral foramen, as well as fibrous bundles.
Arachnoid
Slotted space with lots ofconnecting bundles separates the hard and spider shells of the spinal cord. The latter has the form of a thin sheet, it is transparent and contains fibroblasts (connective tissue fibers that synthesize extracellular matrix).
The arachnoid membrane of the spinal cord is shroudedneuroglia - cells that provide the transmission of nerve impulses. It does not contain blood vessels. The processes, thread-like trabeculae depart from the arachnoid membrane, interlacing with the next soft shell.
Subarachnoid is located under the shell.space. Inside it contains liquor. It is expanded in the lower part of the spinal cord, in the sacrum and coccyx. In the neck is a partition between the soft and arachnoid membranes. The septum and dentate ligaments between the nerve roots fix the brain in one position, preventing it from moving.
Soft shell
Внутренней оболочкой является мягкая.It envelops the spinal cord. Compared with a similar structure in the brain, it is considered more durable and thicker. The soft shell of the spinal cord consists of loose tissue that is covered with endothelial cells.
It has two thin layers, between whichnumerous blood vessels are located. On the upper layer, represented by a thin plate or sheet, are jagged ligaments, which fix the shell. A membrane of glial cells adjoins the inside, connecting directly to the spinal cord. The sheath forms the vagina for the artery and with it penetrates the brain and its gray matter.
The soft shell is present only inmammals. Other terrestrial vertebrates (tetrapods) have only two - solid and internal. In the course of evolutionary development, the inner shell of mammals was divided into arachnoid and soft.
Conclusion
Spinal cord refers to the central nervousthe system of all vertebrates, including humans. It performs the reflex and conductor functions. The first is responsible for the reflexes of the limbs - their flexion and extension, pulling, etc. The second function is the conduction of nerve impulses between organs and the brain.
Hard, arachnoid and soft shells envelopspinal cord outside. They perform protective and trophic (nutritional) functions. Shells are formed by connective tissue cells. They are separated by spaces that are filled with liquor, a fluid circulating in the spinal cord and brain. Between themselves, the shells are connected by thin fibers and processes.
