Neuron, being a structural and functionalunit of the nervous system, is a highly specialized cell that is able to generate and conduct electrical impulses. During the evolutionary process, neurons lost the ability to divide, and therefore can not reproduce. Hence the well-known expression "the nerve cells are not restored" appeared.
Neuron, the structure and functions of which are verydifferent, has also a variety of shapes and sizes, depending on the location of the cell. The largest neurons - giant pyramidal cells - are found in the brain in the cerebral cortex and in the cerebellum. Obviously, the large size of these cells is due to the complexity of the functions they perform.
The main function of nerve cells is to ensure the adaptation of a living organism to the changing conditions of the external environment, and the person with their help has acquired the ability to think.
The structure of the neuron only at first glance seemssimple. Each cell consists of a body or soma and processes - dendrites and axons. Axon is a long unbranched process, the function of which is to transfer the nerve impulse from one cell to another. And, from the body of one cell can only go one such outgrowth, this is the morphological feature of the axon. But the number of dendrites that depart from the soma of one nerve cell may, on the contrary, be large. They, interacting with axons or with other dendrites, take a nervous impulse. But nevertheless, dendrites are the main receptor for the neuron. Axon terminations are capable of releasing special substances - mediators, to which the dendritic membrane reacts. Typically, each neuron has several dendrites that branch strongly, thus providing a large number of information inputs. Information in the cell comes through specialized contacts, called "spinules." They allow neurons to perceive a neural signal.
The structure of the neuron also includes an axon mound -a section of the cell soma, which performs integrative function by means of a multilayer membrane. She, covering the body of the cell, provides the formation, propagation and transmission of the electrotonic potential from the soma to the axon mound. The function of catfish, mainly information, but it still performs a trophic function, which is to ensure the growth and development of processes in the process of ontogeny of the organism.
По числу отростков нейроны бывают одноотросчатые (unipolar), double-stranded (bipolar) and multi-stranded (multipolar). Truly unipolar can be called only brain neurons that are located in the nucleus of the trigeminal nerve and control the proprioception of the masticatory muscles. In the rest, the structure of the neuron determines its functional purpose. Bipolar neurons form the basis of the peripheral nerves of the auditory, visual and olfactory systems.
The special structure of the neuron allows him to performthe most important - the information function due to the special properties of the membrane. It, having an amazingly small thickness of 6 nm, consists of only two layers of lipid molecules. It integrates proteins that perform a number of functions: moving molecules and ions in the cell against the concentration gradient, ensuring selective permeability of membranes, recognizing foreign molecules and ensuring the flow of chemical reactions on the surface of the membrane.
The complex structure of the neuron and the variety of its functions allows to classify nerve cells according to many features:
- the type of chemical structure of substances exuded by their axons;
- according to the type of sensitivity to the action of various stimuli;
- by type of functional activity.
