A neuron, being a structural and functional unit of the nervous system, is a highly specialized cell that is able to generate and conduct electrical impulses. During the evolutionary process, neurons have lost the ability to divide, and therefore can not multiply. This is where the popular expression “nerve cells cannot be restored” came from.
A neuron, the structure and functions of which are very different, also has a diverse shape and size, depending on the location of the cell. The largest neurons - giant pyramidal cells - are located in the brain in the cerebral cortex and in the cerebellum. Obviously, the large sizes of these cells are due to the complexity of their functions.
The main function of nerve cells is to ensure the adaptation of a living organism to changing environmental conditions, and a person with their help has acquired the ability to think.
The structure of a neuron only at first glance seems simple. Each cell consists of a body or catfish and processes - dendrites and axons. Axon is a long non-branching process whose function is to transmit a nerve impulse from one cell to another. Moreover, only one such process can depart from the body of one cell, this is the morphological feature of the axon. But the number of dendrites, departing from the soma of one nerve cell, may, on the contrary, be large. They, interacting with axons or with other dendrites, take a nerve impulse. But nevertheless, the main receptive field of the neuron is dendrites. Axonal endings are able to secrete special substances - mediators, to which the dendritic membrane reacts. As a rule, each neuron has several dendrites that branch strongly, thus providing a large number of information inputs. Information enters the cell through specialized contacts called spines. They allow neurons to perceive a nerve signal.
The structure of the neuron also includes an axonal knoll - a section of the cell soma, which performs an integrative function using a multilayer membrane. She, covering the body of the cell, provides the formation, distribution and transmission of the electrotonic potential from the soma to the axon knoll. The function of the soma is mainly informational, but it still performs a trophic function, which consists in ensuring the growth and development of processes in the process of ontogenesis of the body.
According to the number of processes, neurons are monotube (unipolar), bipolar (bipolar) and multiparticle (multipolar). Only neurons of the brain that are located in the nucleus of the trigeminal nerve and control the proprioception of the masticatory muscles can be called truly unipolar. Otherwise, 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 it to fulfill the 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 incorporates proteins that perform a number of functions: moving molecules and ions in the cell against the concentration gradient, providing selective membrane permeability, recognizing foreign molecules and ensuring the occurrence of chemical reactions on the membrane surface.
The complex structure of the neuron and the variety of functions it performs allows us to classify nerve cells in many ways:
- by the type of chemical structure secreted by their axons of substances;
- by type of sensitivity to the action of various stimuli;
- by type of functional activity.