The unifying activity of all organs and ensuring its interaction with the environment.
Nervous system
Central (CNS) - brain, spinal cord
Peripheral (PNS) - nerves, nerve nodes
Somatic (voluntary regulation)
Autonomous (involuntary regulation) - sympathetic, parasympathetic
Divisions of the nervous system
Central - represented by the spinal cord and the brain, which are protected meninges consisting of.
Peripheral - formed by nerves and nerve nodes.
Autonomous (vegetative) - controls work internal organs, does not obey the will of a person, consists of two sections: sympathetic and parasympathetic.
Sympathetic department - strengthens and accelerates the work of the heart, narrows the lumens, and expands the lumens, enhances the secretion of sweat glands.
Parasympathetic - slows down and weakens the contraction of the heart.
Nervous system consists of nerve tissue, which is formed by neurons surrounded by neuroglia. Neurons are mononuclear cells made up of axons and dendrites. Axons - long branches, dendrites are short. Nerve cells form constant contacts with other cells. The place of contact is the sine.
The brain and spinal cord are composed of gray matter (a collection of nerve cell bodies) and white matter (formed by the processes of nerve cells). There are three types of neurons: sensory, motor, and intercalary.
Sensory neurons transmit impulses from the senses and internal organs to the brain. Intercalary neurons form white matter spinal cord The motor conducts an impulse from the brain to the working organs.
Conducting nerve impulses along the long process of the cell - essential function neuron. The nerve impulse arising in the neuron runs along the entire length of the process. The endings of the long processes approach other nerve cells, forming specialized contacts.
The function of such contacts is to transfer influence from one nerve cell to another. A nerve impulse that arrives along a long process to the next nerve cell can cause either excitement or inhibition in it. If a neuron is excited, its own nerve impulse arises in it, which, having reached the end of the long process, can excite a whole group of subsequent neurons that are in contact with it. And, which are part of the nerves, carry to the muscles and glands. In some cases, a nerve impulse, having reached a neighboring neuron, not only does not excite it, but, on the contrary, temporarily complicates the development of excitation in it or even inhibits it. This process is called nerve cell inhibition. Inhibition does not allow excitement to spread infinitely in the nervous system. Due to the interaction of excitation and inhibition at each moment of time, nerve impulses can be formed only in a strictly defined group of nerve cells. This ensures the coordinated activity of nerve cells. Excitation and inhibition are two of the most important processes in neurons. According to their functions, all nerve cells can be divided into three types: sensitive neurons transmit nerve impulses to the brain from the organs of vision, hearing, etc., as well as from internal organs. Most of neurons are of the type of intercalary. It is their bodies that form the bulk of the gray matter of the brain. They are, as it were, inserted between sensitive neurons, making a connection between them.
Executive neurons form response nerve impulses and transmit them to muscles and glands.
; there are over one hundred billion neurons in humans. A neuron consists of a body and processes, usually one long process - an axon and several short branched processes - dendrites. Axons are unbranched processes of a neuron, starting from the cell body with an axonal mound, can be more than a meter long and up to 1-6 microns in diameter. Among the processes of a neuron, one, the longest, is called an axon (neurite). Axons extend far from the cell body (Fig. 2). Their length varies from 150 μm to 1.2 m, which allows axons to function as communication lines between the cell body and a far-located target organ or brain region. Signals generated in the body of a given cell pass along the axon. Its terminal apparatus ends on another nerve cell, on muscle cells(fibers) or on cells glandular tissue... Along the axon, the nerve impulse moves from the body of the nerve cell to the working organs - muscle, gland or the next nerve cell.
The impulses follow the dendrites to the cell body, along the axon - from the cell body to other neurons, muscles or glands. Thanks to the processes, neurons contact each other and form neural networks and circles along which nerve impulses circulate. The only process along which the nerve impulse is directed from the neuron is the axon.
The specific function of the axon is to conduct an action potential from the cell body to other cells or peripheral organs. Its other function is axonal transport of substances.
Axon development begins with the formation of a growth cone in a neuron. The growth cone passes through the basement membrane surrounding the neural tube and is guided through connective tissue the embryo to specific target areas. Growth cones move along strictly defined paths, as evidenced by the exact similarity of the location of the nerves on both sides of the body. Even foreign axons, which grow into a limb in places of normal innervation under experimental conditions, use almost exactly the same standard set of paths along which growth cones can freely move. Obviously, these pathways are determined by the internal structure of the limb itself, but the molecular basis of such a guiding system is unknown. Apparently, axons grow along the same predetermined paths in the central nervous system, where these paths are probably determined by the local characteristics of the glial cells of the embryo.
The specialized area of the cell body (usually the soma, but sometimes the dendrite), from which the axon departs, is called the axonal hillock. The axon and axonal hillock differ from the soma and proximal dendrites in that they lack the granular endoplasmic reticulum, free ribosomes, and the Golgi complex. The axon contains a smooth endoplasmic reticulum and a pronounced cytoskeleton.
Neurons can be classified by the length of their axons. In neurons of the 1st type according to the Golgi, they are short, terminating, like dendrites, close to the soma. Golgi type 2 neurons are characterized by long axons.
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