As we know from zoology, nervous system starts to form from the birth of multicellular organism. Its main function is to unite the body's cells in a

Neuron structure and functions

As we know from zoology, nervous system starts to form from the birth of multicellular organism. Its main function is to unite the body's cells in a single structural and functional system — a multicellular organism. Such function is called the integrating (combining) one. Because of this function, the cells that form the nervous system have a special structure. They have a large number of branches by which they are interconnected with other cells (diagram 141). Such cells are called neurons.

Neuron — is a highly specialized cell that has lost the ability to divide. Its regeneration processes are limited. This nerve cell often dies, if damaged. For the normal functioning, these cells need a lot of oxygen, nutrients, microelements and so on, so each of them is surrounded by an average of ten satellite cells. They help neurons to perform trophic function and are for their support. These cells form neuroglia that together with the neurons form the nervous tissue.

Human has about 10-15 billion nerve cells. All of them appear in the nervous system during embryonic development and after birth their number is not increased. Only 10-15 million nerve cells form the spinal cord and peripheral nerve plexus (ganglia), and the rest 99.9% are concentrated in the brain. The bodies of the neurons are usually arranged in the central nervous system — the brain and spinal cord and in brain nuclei, forming a gray matter. And the processes of nerve cells with glial cells form a white matter. Taken from http://worldofschool.org

Diagram 141. Schematic structure of the neuron: 1 — dendrites; 2 — core; 3 — the body of the neuron; 4 — fat-like shell; 5 — axon; 6 — the end of the axon

The main functions of the neuron are: getting information from different parts of the body and the environment, its analysis, storage and transmission of commands — nerve impulses — to the working organ. According to its functions neurons are divided into sensory, which perceive information from the internal environment via body receptors and from the environment, motor, which send nerve impulses to the working organs, and intercalary that connect the sensory neurons with motor.

A nerve cell has two types of appendages — dendrites and axons (diagram 141). The ones that absorb information and transmit it toward the nervous cells’ body are called dendrites. They are usually short, numerous, and they form a dendritic tree. Dendrites of sensitive cells can be very long.

Appendage, which transmits information to other cells — is the axon. Mostly it is long. Its end splits, forming axonal tree and ensuring contact with a large number of cells.

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Questions:
  • Determine the relationship of neurons’ structure and functions.

  • What makes nervous tissue?

  • Identify features of the structure and functions of dendrites and axons.

  • What types of neurons do you know?