Nerve cells and their structure

Nerve cells that form a nerve tissue,There are two types: neurocytes (neurons) and gliocytes (glial cells). Neurons perceive irritation, generate action potential, conduct and transmit nerve impulses, establish contacts among themselves, and gliocytes provide conditions for optimal functioning of neurons, i.e. isolate them, protect them, take part in the metabolism of mediators and release the growth factor of neurocytes.

According to information to date, the human brain contains 25 billion neurons, two-thirds of them are in the cortex, and the number of glial cells is about 10 times higher.

Neuron

Nerve cells contain neurons that arethe main structural-functional element of the nervous system. The neuron is a process cell 4-130 μm in size, consisting of a body and shoots, which are of two types: the axon and dendrites. The outgrowth of a nerve cell - an axon - is otherwise called a neurite. The length of the processes reaches 1.5 m. Axon in the cell is only one, long, slightly branching; on it from the body of the cell is an impulse. Dendrites usually numerous, strongly branch, short. On them, the impulse comes to the body of the neuron. Neurons are characterized by dynamic polarization, they conduct a nerve impulse exclusively in one direction - from the dendrite to the axon. That is, the neuron in its structure resembles a funnel. The body of the cell basically performs the function of trophic in relation to the processes. The shape of the body can be different - from pyramidal to round.

Types of neurons

Nerve cells are divided into several basic types according to the number of processes.

• unipolar - have a single process, only an axon. These cells exist only in embryos as an intermediate stage in the development of neurocytes;
• bipolar - contain an axon and a dendrite. Such nerve cells in man are in the retina of the eye and in the inner ear;
• multipolar - have 2 or moreprocesses, axon and dendrites. This is the most common type of neurons in the body, they are both in the central section of the nervous system, and in the peripheral;
• pseudo-unipolar cells - from the cell bodythere is a single common process involving the axon and dendrite, later it is divided into two separate ones. These bipolar neurons are located in the nodes of the cranial and spinal.

Structure of the nerve cell

The cell is covered by neurilemma, which, in addition to the barrier, receptor and exchange functions, performs a specific function of conducting a nerve impulse.

Nerve cells have a cytoplasm that includescommon organelles (mitochondria, endoplasmic reticulum, cell center, Golgi complex, lysosomes) and organelles of special purpose, so-called neurofibrils. The nucleus of nerve cells is light, round, contains 1 or 2 nucleoli.

Types of cells according to their purpose

In accordance with the functional purpose, nerve cells are classified into sensitive, motor and intercalary cells.

Sensitive neurons are such cells, the bodywhich is located in the ganglia of the peripheral system. Dendrites of these cells end with sensitive endings, and the axon is then sent to the brain stem or to the spinal cord.

Insertion nerve cells are responsible for the transmission of neuron excitation.

Motor or secretory cells are called depending on the structure (muscle fiber or iron) where their axon terminates.

There are also auxiliary nerve cells, so-called, gliocytes, which isolate neurons from each other.

Ependymocytes are similar to epithelial tissues and lining the cavities of the spinal cord and brain. Their function is support and demarcation.

Astrocytes are multistep small cells of a star-shaped form. According to the structure of the appendages, astrocytes are protoplasmic and fibrous.

Nerve fibers are formed from nerve processescells and lemocytes. Outside, the nerve fiber is covered by a thin shell of fibrous, loose connective tissue called the basal lamina.