; there are more than 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 non-branching 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 microns 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.
Amyelin fibers: exist in both the central and peripheral nervous systems. Peripheral amyloin fibers are also involved in Schwann cells, but in this case, the spiral winding does not occur. When, at rest, the neuron presents negative external positive and internal electrical charges. The resting neuron is said to be polarized. When faced with a suitable nerve stimulus, the membrane's permeability to sodium increases, which causes these ions to flow into the neuron, causing a polarity reversal. internal environment becomes positive, and the external environment becomes negative.
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.
At the second moment, the membrane becomes permeable to potassium, which migrates into external environment allowing you to return to the primordial potential of "rest". Thus, the membrane becomes positive again on the outside and negative on the inside.
The polarity reversal of the membrane determines the emergence of an action potential that "propagates" along the neuron to generate a nerve impulse. As the nerve impulse propagates, there are successive reversals of polarity and successive returns to a "resting" potential.
Specific function axon - conducting 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 that 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.
In most synapses, nerve impulses are transmitted through chemical mediators that activate receptors in other neurons or effector cells. Synapses are terminal joints installed between one neuron and another, or between a neuron and muscle fiber, or between a neuron and a glandular cell. Between one neuron and another, there is a microsphere called a synapse, in which a neuron transmits a nerve impulse to another through the action of chemical mediators or neurotransmitters.
This dynamic transmission of nerve impulses from one neuron to another depends on highly specialized structures - synapses. They are located at the sites of contact of the axon with dendrites or perichari of other neurons. Although most synapses are established between axon and dendrite or between axon and cell body, there are also synapses between dendrites and between axons. At synapses, the membranes of two nerve cells are separated by a space called the synaptic cleft. These two membranes are firmly adhered to each other.
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.
At the site of the synapse, the membranes are called presynaptic and postsynaptic. The terminal portion of the axons shows a typical structure: there are numerous synaptic vesicles that contain substances called neurotransmitters, which are chemical messengers responsible for transmitting nerve impulses across synapses. These neurotransmitters are released in the presynaptic membrane and bind to receptor molecules in the postsynaptic membrane, facilitating the flow of nerve impulses across the synaptic range.
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.
The unifying activity of all organs and ensuring its interaction with the environment.
Neurotransmitters are contained in microvesicles present at the end of an axon. Since neurotransmitters capable of transmitting a nerve impulse are present only at the ends of the axons, it is concluded that the direction of propagation of the impulse along the neuron has the following path: neuron-axon-axon-end-dendrites the body of the next neuron. Several chemical neurotransmitters have been identified, acetylcholine, norepinephrine, dopamine, gamma-aminobutyric acid, serotonin.
It should also be noted that the brain and other organs of the nervous system are responsible for different types of arch; reflexes and volunteers. Simple reflex arcs were and are very important for the survival of Man, since in general they move away from danger, since, as a result, they are a quick and involuntary automatic response.
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 by the meninges, consisting of.
With regard to voluntary arches, we can say that they imply an extremely demanding course of action in terms of nervous system intervention. Reflex action Reflex actions are involuntary movements controlled by the gray matter of the bone marrow before nerve impulses reach the brain. Among the most famous reflex action It is the patellar reflex, the involuntary movement of the leg when the nerve under the patella is stimulated, and the hand reflex when the touch occurs on something very hot.
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.
Reflex arcs are involuntary responses to sensory stimuli. The stimulus reaches the recipient organ, is sent to Bone marrow through sensory or afferent neurons. In the brain, associative neurons receive information and send out a sequence of actions through motor neurons. Motor or efferent neurons reach the organ.
Voluntary Law There are several areas in the cerebral cortex - visual, auditory, gustatory, motor, etc. - where the received impressions turn into sensations. Thus, we perform actions such as collecting an object, jumping and others that are triggered at will. In these actions - voluntary arcs - brain intervention.
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 are long processes, dendrites are short. Nerve cells form constant contacts with other cells. The place of contact is the sine.
All brain activity occurs through the activity of neurons. A neuron is a cell that makes up the Nervous System, which is why it is also called a Nerve Cell, and neural activity is the connection between neurons. A nerve cell consists of a cell body and small extensions called dendrites, shorter and complete with a cell body and much longer axons.
The cell bodies of neurons are usually found in specific areas of the central nervous system and in nerve ganglia located near the spine. The axons are quite long and in bundles form the nerves that make up the Peripheral Nervous System. The form of communication between neurons is carried out by chemical messengers and electrical stimuli. Chemical intermediaries are called. They are synthesized by the neurons themselves and stored inside the vesicles. These vesicles are concentrated in the terminal of the axons, and when nerve impulses arrive at these terminals, they are released.
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.
The terminal membrane that releases the so-called presynaptic membrane and the one that captures them in another neuron is called the post-synaptic membrane. The axon is surrounded by a myelin sheath made of fat along with a basic protein called myelin, which acts as insulation and facilitates the transmission of nerve impulses.
Electrical communication between neurons distributes chemical neurotransmitters and occurs through the direct passage of ions through open joints. Ionic channels are connected and form functional units called connexins. The transmission of information is very fast through electricity, but it is not as versatile as the neurotransmission of neurotransmitters. After the maturity of the central nervous system, chemical neurotransmissions predominate.
Conducting nerve impulses along the long process of the cell - essential function neuron. A nerve impulse arising in a 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 long process, can excite a whole group of the next neurons in contact with it. And, which are part of the nerves, carry to the muscles and glands. In a number of 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. Everything nerve cells according to their functions, they 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.
This knowledge was fundamental to the study of products capable of acting on mental disorders... For example, antidepressants act primarily alongside the neurotransmitters serotonin, norepinephrine, and dopamine. Neurons are nerve cells responsible for the propagation of a nerve impulse. They make up the nervous system along with glial cells.
There are about 86 billion neurons in the human brain, and it is already known that new neurons are produced throughout life. Neurons have cellular structures such as the nucleus and mitochondria, as well as other cells, but their differentiated form is related to their function.
Executive neurons form response nerve impulses and transmit them to muscles and glands.
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