The spinal cord enters the central nervous system. In the human body, he is responsible for motor reflexes and the transmission of nerve impulses between organs and the brain. The membranes of the spinal cord cover it, providing protection. What features and differences do they have?
Building
The arches of the vertebrae form a cavity called the spinal canal, in which the spinal cord is located along with the vessels and nerve roots. Its upper part is connected to the medulla oblongata (head section), and the lower part is connected to 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 bottom to top. Its surface is slightly concave. It consists of thirty-one segments, from which pairs of nerve roots emerge.
The spinal cord is covered with membranes on the outside. Inside it contains gray and white matter, their ratio varies in different parts. The gray matter has the shape of a butterfly, it contains the bodies of nerve cells, their processes contain whitesubstance that is located at the edges.
A canal is located in the center of the gray matter. It is filled with cerebrospinal fluid (CSF), which constantly circulates in the brain and spinal cord. In an adult, its volume is up to 270 milliliters. Liquor is produced in the ventricles of the brain and is updated 4 times a day.
Sheaths of the spinal cord
Three membranes: hard, arachnoid and soft - cover both the brain and spinal cord. They perform two main functions. Protective prevents the negative impact of mechanical effects on the brain. The trophic function is associated with the regulation of cerebral blood flow, due to which the metabolism in tissues is carried out.
The membranes of the spinal cord are made up of connective tissue cells. Outside is a hard shell, under it is arachnoid and soft. They don't fit tightly together. Between them there is a subdural and subarachnoid space. They are attached to the spine by plates and ligaments that prevent the brain from stretching out.
Shells are formed at the beginning of the second month of embryo development. Connective tissue is formed on the neural tube and spreads along it. Later, tissue cells separate to form the outer and inner membranes. After some time, the inner shell is divided into soft and cobweb.
Hard shell
The outer hard shell consists of top and bottom layers. It has a rough surface on which many vessels are located. Unlikea similar membrane in the brain, it does not adhere 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 is a dense shiny fibrous tissue. It envelops the brain in the form of an elongated cylindrical bag. The covering cells (endothelium) make up the bottom layer of the shell.
She envelops the nodes and nerves, forming cavities that expand, approaching the intervertebral foramina. Near the head, the shell is connected to the occipital bone. From top to bottom, it narrows and is a thin thread that joins the coccyx.
Blood passes to the sheath through arteries connected to the abdominal and thoracic aorta. Venous blood enters the venous plexus. The shell is fixed in the spinal canal with the help of processes in the intervertebral foramens, as well as fibrous bundles.
Spidershell
A slit-like space with a large number of connective bundles separates the hard and arachnoid membranes of the spinal cord. The latter has the appearance of a thin sheet, it is transparent and contains fibroblasts (connective tissue fibers that synthesize the extracellular matrix).
The arachnoid of the spinal cord is shrouded in neuroglia - cells that ensure the transmission of nerve impulses. It does not contain blood vessels. Processes, filiform trabeculae, depart from the arachnoid, intertwining with the next soft shell.
Underthe subarachnoid space is located by a cover. Inside it contains liquor. It is expanded in the lower part of the spinal cord, in the region of the sacrum and coccyx. In the neck area there 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
The inner shell is soft. It envelops the spinal cord. Compared to a similar structure in the brain, it is considered to be stronger and thicker. The pia mater of the spinal cord consists of loose tissue that is covered by endothelial cells.
It has two thin layers, between which are numerous blood vessels. On the upper layer, represented by a thin plate or leaf, there are jagged ligaments that fix the shell. Adjacent to the inside is a membrane of glial cells that connects directly to the spinal cord. The sheath forms a sheath for the artery and, together with it, penetrates the brain and its gray matter.
The soft shell is present only in mammals. Other terrestrial vertebrates (tetrapods) have only two - solid and internal. In the course of evolutionary development, the inner shell in mammals was divided into arachnoid and soft.
Conclusion
The spinal cord belongs to the central nervous system of all vertebrates, including humans. It performs reflex and conductive functions. The first is responsible for the reflexes of the limbs - their flexionand extension, jerking, etc. The second function is the conduction of nerve impulses between the organs and the brain.
Hard, arachnoid and soft shells envelop the spinal cord from the outside. They perform protective and trophic (nutritional) functions. The membranes are formed by connective tissue cells. They are separated by spaces that are filled with cerebrospinal fluid - a fluid that circulates in the spinal cord and brain. The shells are interconnected by thin fibers and processes.
