4 Physiology of the nervous system. The value and functional activity of the nervous system.

The nervous system is a combination of anatomically and functionally interconnected nerve cells with their processes that combine and coordinate the activities of all organs and systems of the body in constant interaction with the external environment. Distinguish between the central and peripheral nervous system. The brain and spinal cord belong to the central nervous system, the cranial and spinal nerves and the related roots, spinal nodes and plexuses belong to the peripheral nerve system. Functional division of the nervous system: somatic (subject to the will of man). Regulates the work of skeletal muscles. The motor centers are located in the cerebral cortex. Autonomous (vegetative). Not subject to the will of man. Regulates the work of internal organs, glands, blood vessels and heart). Vegetative centers are located in the hypothalamus. Sympathetic (included during intensive work requiring energy. The bodies of the first neurons lie in the thoracic and lumbar spinal cord. Parasympathetic helps restore energy reserves during sleep and rest. The bodies of the first neurons lie on average, oblong and in the sacral part of the spinal cord.
The main function of the nervous system is the regulation of the vital activity of the organism, the maintenance in it of the constancy of the internal environment, metabolic processes, as well as the implementation of communication with the outside world. The nervous system is the material basis of mental activity: speech, thinking, social behavior.
The nervous system consists of nerve cells, nerve fibers and neuroglia cells.
The nerve cell - the neuron - is a structural and functional unit of the nervous system. A neuron is a cell that can perceive irritation, come into a state of excitement, produce nerve impulses and transmit them to other cells. The neuron consists of the body and processes - short, branching (dendrites) and long (axon). Impulses always move along the dendrites to the cell, and along the axon from the cell. Connections between neurons are called synapses. Synapses can also be neuromuscular. In synapses, bioelectric energy is transformed into chemical energy and is transmitted through chemically active substances - mediators (acetylcholine, noradrenaline). The neuroglia is the connective tissue supporting structure of the nervous system (stroma) that performs a protective function. A nerve fiber is a process of a nerve cell (axial cylinder), covered to a greater or lesser extent with myelin and surrounded by a Schwann shell, which performs protective and trophic functions. In myelinated waves, the impulse moves at a speed of up to 100 m / s.
The accumulation of bodies of nerve cells forms the gray matter of the brain, and their processes - the white matter. A collection of neurons located outside the central nervous system is called a nervous node. Nerve is the stem of the joint nerve fibers. Depending on the function, motor, sensory, autonomic and mixed nerves are distinguished.
The set of neurons that regulate any function is called the nerve center. The complex of physiological mechanisms associated with the performance of a particular function is called a functional system. It includes cortical and subcortical nerve centers, pathways, peripheral nerves, and executive organs.
The basis of the functional activity of the nervous system is reflex. Reflex is the response of the body to irritation. A reflex is performed through a chain of neurons (at least two), called a reflex arc. A neuron that perceives irritation is the afferent part of the arc, the neuron that performs the response is the efferent part. But the reflex act does not end with the simultaneous response of the working body. There is a feedback that affects the tone of the muscles - a self-regulating ring in the form of a gamma loop.
The reflex activity of the nervous system ensures the perception by the body of any changes in the external world.