Nervous system

Structural and functional elements of the nervous system is the neuron (see Nervous tissue), with the dendrites, the body and the axon. The nervous system of vertebrates and human divided into the Central nervous system including the brain (see) and the spinal cord (see), and peripheral, which consists of nerve fibers and components (see Nerves), outside of the Central nervous system. On some peculiarities of the structure and function of the nervous system is divided also by somatic and autonomic nervous system (see), the latter in its turn is divided into the sympathetic and parasympathetic.
One of the basic physiological processes that serve to implement all functions of the nervous system, is spreading excitation (see). Appearing in the body of the neuron, the institution is distributed under AXONE to the next neuron or to effector cells (secretory, muscle). The transfer of excitation from the axon of one neuron to another, or on the effector is via synapses (see).
The nervous system operates on the principle of reflex (see). The structural basis of it is the reflex arc that includes receptors, afferent fibres of the Central nervous system, efferent fibres, effector.
When exercising the functions of regulating the activity of neurons big role plays the second important physiological process - inhibition (see).
Afferent and efferent fibres that make up the nerve trunks and related to the peripheral nervous system, are axoneme neurons located in different parts of the Central nervous system.
Depending on the thickness and speed of the proceedings, all the nerve fibers divide into three groups (a, b, C). Fiber group And are thick myelinated fibers (diameter 12 - 22 MK) and conduct agitation with the highest speed (up to 160 m/sec).
This group includes as efferent motor fibers originating from the motor neurons of the spinal cord and going to skeletal muscle, and the afferent fibers that conduct excitation from tactile, temperature and pain receptors. Nerve fibres of type b - thin myelinated fibers (diameter 1-3 MK), with the low speed of the proceedings (3-14 m/s)are preganglionarnah fibre vegetative nervous system. Thin bezmalinovic nerve fibers group that has a diameter of about 0.5 microns and low speed of the proceedings (2 - 6 m/s), are postganglionarnyh fibers of the sympathetic nervous system, and the afferent fibres from some pain, Cold, heat receptors and receptor pressure.
For all groups of nerve fibers there are General laws of initiation. The normal initiation of a nerve fiber is possible only if its anatomical and physiological integrity, ensure the integrity of the mechanisms of the proceedings. All the nerve fibers in the nerve trunk spend excitation in isolation from each other. They have the ability to conduct agitation in any direction, but in the body due to unilateral conductivity synapses excitation always extends in one direction: from the dendrites or body of a neuron in AXONE to the effector or to another neuron. Structural and physiological features of nerve fibers allow him to carry out the excitation pulses with high frequency (up to 1000 Hz), which is why the nerve fiber is almost neutomimy.
The functions of the Central nervous system (brain and spinal cord) are determined by the nature of morphological links between neurons and their functional relationship. Possible to identify some General principles of work of the Central nervous system.
The arrival of numerous excitations from neurons of different departments or different receptors to one neuron of the Central nervous system referred to as the principle of convergence. The most studied and widely represented in the Central nervous system is the "multi-touch" convergence, which is characterized by the meeting and interaction on the neuron two or more afferent excitations (visual, auditory, tactile, temperature). Especially distinctly multi convergence is evident in the reticular formation (see), the neurons which converge and interact excitation occurs when somatic, visceral, auditory, visual, vestibular, cortical and cerebellar irritation. Multi convergence takes place also in the "non-specific" the nuclei of the thalamus, the median centre, the caudate nucleus, the hippocampus and some other structures of the Central nervous system.
In a bark of the big hemispheres, along with numerous effects multitouch convergence installed many other types of convergence: "touch-biological" convergence, "Multibanka" convergence, "afferent-efferent" convergence.
Central nervous system suffers from a number of properties that reflect the peculiarities of propagation of an excitation and the relationship between neurons: the principle of irradiation, the principle of multiplication (multiplication), the principle of prolongation (prolonged action).
Clusters of neurons at various levels of the Central nervous system clearly marked morphologically and functionally United, called the nucleus. The set of neurons or nerve nuclei necessary for the implementation of one or another specific functions of the organism, are called centers of nervous system. At the level of lumbar Department of a spinal cord are reflex centres defecation, urination, erection, ejaculation, and also centers of regulating the tone of skeletal muscles of lower limbs. At the level of the cervical spinal cord is the Central governing the work of muscles of a pupil and an eyeball, and some centers of the autonomic nervous system, regulating the activity of the heart and clearance bronchi.
In the medulla emit such vital centers, as the center of breathing, sosudodwigatelny centre. There are centers of sucking, chewing, swallowing, salivation and other
At the level of the mid-brain centers are located reflex regulation of muscle skeletal muscles. Diversity tonic reflexes carried out, can be divided into static defining the position of a body in space, and stato-kinetic aimed at preservation of balance when moving body.

In structures related to the intermediate brain, such as the hypothalamus (see), the thalamus and the limbic system (see Subcortical functions)are the centers performing and more General regulatory, integrative functions of the body: the state of hunger, satiation, thirst, maintaining a constant temperature, some of the instincts, and primitive movement acts.
Supreme regulator of all body functions, establishing a thin adequate relationships of an organism with the environment, is the bark of the big hemispheres. Different areas of the cortex, where various types of somatic and visceral sensitivity, are the final link analyzer systems (see Analyzers). In the back Central gyrus of a bark of the big hemispheres presents superficial and muscular-articular sensitivity. Localization tactile stimuli, the positioning of the various parts of the body in space is a function of this area of the cortex. In the superior temporal gyrus along the edge of the rear third of the lateral grooves is hearing the region. Next to it - vestibular area. Visual stimuli are perceived by the respective area, which occupies medial surface of the occipital lobe of the cerebral cortex. The forward Central gyrus is an area of the output of motor excitation to the periphery to the muscles of body parts. Within it you can select groups of neurons, the initiation of which leads to the reduction of certain muscle groups.
The destruction of the areas of the cortex, which is the place of representation of the various functions, leads to their violation. On this basis talk about localization specific function in a bark of the big hemispheres, considering separate areas of the cerebral cortex of the higher centers of these functions.
Many of the school by I. P. Pavlov to study conditioned reflexes, as well as modern fine electrophysiological study of the functions of the cerebral cortex of the brain showed that there are no clear borders of the localization areas of particular functions. Depending on the situation and formed behavioral reactions of the organism regulation of this or that function can neurons lying in different areas of the cerebral cortex. Function always localized dynamically depending on the complexity and nature of the reactions of the whole organism. Holistic nature of behavioral acts of the body is achieved by combining the "centre and periphery." It is based on the formation of functional systems, representing the totality of the Central and peripheral units, United in the moment for the final, biologically useful, adaptive effect of the organism.