Neurology (the study of the nervous system)

The nervous system consists of two departments: somatic and vegetative with both Central and peripheral.
To the Central part of the somatic nervous system includes the brain and spinal cord, peripheral - 12 pairs of cranial nerves and 31 pairs of spinal nerves.
The somatic nervous system innervates the body and some internal organs - tongue, larynx, pharynx, the muscles of the eyeball, the middle ear.
Vegetative nervous system consists of the sympathetic and parasympathetic parts that include aggregations of cells located in the brain, spinal cord, autonomic nerves, joints, and plexus, Innervate the internal organs.
Part of the nervous system consists of billions of nerve cells, combined with glial items in gray and white matter. There is great diversity in form and function of nerve cells, which are the basis of simple and complex reflex arcs, forming pathways (Fig. 452).

the scheme of the structure of various narocito
452. The scheme of the structure of various narocito.
A - unipolar neurotic; - bipolar neurotic; false unipolar cell; Mr. multipolar nerve cell: 1 - dendrites 2 - axon.

Nerve cells (neuronum) are divided into sensitive afferent located in the spinal joints, engines cranial nerves, spinal cord and brain; 2) motor - efferent located in the cerebral cortex, subcortical area of the brain stem, the front horns spinal cord; 3) the associative - uniting input pulses with afferent to the effector neural circuits; 4) neurosecretory (for example, located in the hypothalamus area)that has the property to develop and release into the blood hormones called neurosecretory.
Nerve cell has irregular shape body and two kinds of processes: more numerous, called dendrites, few millimeters in length, and filamentary single process - the axon of length 1 m and more. Cell body has a diameter from 10 to 100 microns and more. The surface of the cell body and dendrites covered synaptic plaques afferent neurons that transmit excitation from one neuron to another (Fig. 453). Diameter of plaques 1 micron, and the gap between the plaque and detritom or cell body (synaptic gap) - 0.02 mm. The plaques are synaptic vesicles containing the mediators that go into the synaptic gap, closing her, with the passage of impulses. With the passage of the pulse mediators are destroyed. Axon is a specialized part of the nerve cells and conducts agitation from dendritic zone to synaptic plaques. In place of a discharge from the axon of cell body has aksonnyj mound. Except for the home Department, axon covered cells satellites that make up neurilemma or myelin sheath. In the Central nervous system cells satellites is oligodendroglia.

the scheme of the structure of neurotica
453. The scheme of the structure of neurotica (neuron) (Cadel)
1 - dendrite; 2 - the synapses; 3 - body cells; 4 - myelin sheath; 5 - motor plaques.

microstructural analysis nerve fibers
454. Schematic illustration of the results of x-microstructural analysis of nerve fibers, i.e. Narita nerve cells. Radially located insulating layers supporting lipid structures. Tangentially are well-conductive protein layers. This structure makes the myelin sheath of multi-cylinder capacitor (Schmidt).

a snapshot of the myelin sheath
455. Electron microscopic picture of the myelin sheath. The scheme is particularly noticeable spiral development of this multiple capacitor (Geren, Robertson).

A very complex structure has myelin sheath of nerve fibers, which provides without weakening the transmission of nerve impulses to a distance of 1.2 m Myelin sheath formed 5-10 protein layers in the form of a cylinder, in the middle of which is the nerve fiber - axon (Fig. 454). In this shell has lipid structure which insulators (Fig. 455). Such design of the myelin sheath is a multi-cylinder condenser, where protein cylinders are filled ions. The myelin sheath is all along the axon and every 2 - 3 mm is interrupted by narrow, free from the myelin sheath areas (interceptions Ranvier). In these places there is diffusion of ions in the axon. In the myelin sheath with the passage of excitation have two weak current. One ponderomotive ion current is passed through the interception of Ranvier in the nerve fiber that blows out the following interception on the outside of the myelin sheath and it returns to the original interception of Ranvier, hinging on adjacent interception. This loop current is only on the surface of the myelin sheath to a depth of two protein cylinders. The path electric current is considerably shorter, namely the interception of Ranvier to the nearest capacitor myelin sheath, where is discharged to adjacent condenser and quickly, ahead of the ponderomotive the movement of ions reaches the next interception (Fig. 456). Such design ensures the speed of pulse AXONE each interception of Ranvier (performing the function of the built-in relay) to the previous level. Therefore, the average velocity of propagation of an excitation increases in dozens of times, with approximately 100 m/S. the Speed of transmission of impulses could be accelerated by thickening of nerve fibers, the diameter of which in the absence of the myelin sheath would increase from 50 to 300 times.
In the cytoplasm of a neuron are the kernel and various inclusions (calf of Niska, the Golgi apparatus, neurofibrillar, thyroideia bullock, mitochondria, and others).

the scheme of transfer of excitation in nerve fiber
456. The scheme of transfer of excitation in nerve fiber (Stampeli).

Nerve cells are classified by the number of processes, their length and speed of impulses. Unipolar cell has only axon and devoid of dendrites, bipolar has axon and dendrite (Fig. 452); multipolar cell includes one axon and many dendrites. The length of the axon allocate donnaconna cells and korotkoperiodnye, length of 1-2 mm, depending on the speed of impulses along axons distinguish between neurons a, b and C. Fiber neurons groups a and b mielenterveys and conduct pulse with greater speed than the fibers With a smaller diameter. Nerve fibers have a variety of nerve endings: afferent - sensitive, efferent - motor and secretory.
Sensitive nerve endings - receptors - begin in the body and internal organs, perceive mechanical, thermal, chemical and other irritations. Caused excitement in the Central nervous system, transforming into a sensation. Receptors have a different shape and structure (Fig. 457). Motor nerve endings belong to the fibers of the cells of the front pillars of the spinal cord, nuclei stem part of the brain; on their end are ACCP-muscle synapses.

types of receptors, nerve endings457. Different types of receptors and nerve endings.
And motor nerve ending (motor plaque) in skeletal muscle (A. Sklansky); B - sensitive nerve ending In vane body of Vater - Pacini; G - sensitive genital body; D - tactile body Meissner; E - sensitive bulb Krause (L. Malinovsky).

Nervous sensitive (afferent) fiber transfer irritation of receptors of the body, organs and senses in the Central nervous system, where the synthesis and analysis. In response to incoming irritation in the Central nervous system is formed stream reply pulses propagating through motor (effector), secretory fibers and cause the muscles or secretions. The nervous system controls and coordinates the functions of all organs and systems. In the nervous system are the mechanisms of adaptation of organisms to the environment when it changes.
Neuroglial elements. In other tissues discretionary, support and protection are the cells and fibers of connective tissue. In the nervous tissue, these functions are helicity (opendemocracy, astrocytes, oligodendroglial), derived cells neural tube, and glial macrophages, emerging from the mesenchyme.