DEPARTMENT OF HISTOLOGY AND MEDICAL BIOLOGY OF
MEDICAL TREATMENT AND MEDICAL PROPHYLACTIC FACULTIES
The theme of lecture: " NERVOUS TISSUE " for students of a course of medical prophylactic, medical treatment departments
Tashkent 2012

LECTURE: "NERVOUS TISSUE"
Plan of the lecture:
1. An overview of the nervous tissue
2. Histogenesis
3. Neurons - classification, structure
4. The neuroglia
5. The nerve fibers
6. The nerve endings
7. Synapses.
Nervous tissue forms the nervous system. Structural and functional unit is a nerve cell - the neuron. In the nervous system about 1012 neurons. In the nervous tissue is not normal intercellular substance. His role is performed by neuroglia - cells found between neurons and with them a common source of development.
They perform a reference, demarcation, trophic, protective and secretory functions.
In contrast to the muscle tissue in the nervous tissue is almost no connective tissue.
It is only around blood vessels and forms a lining of the brain.
Histogenesis
Source of neural tissue - the ectoderm and its derivatives: the neural tube and neural crest. Not migrating internal cells of the neural tube (spongioblast) are precursors of ependymal cells lining the subsequently the spinal canal and brain ventricles. The cells of the middle strata of the neural tube form the neuroblasts - precursors of neurons and free (migrating) spongioblast - precursors of glial cells and astrocytes oligodendrocytes. Neural crest cells migrate laterally and ventrally.
In the head section, they form the neurons of the nuclei of cranial nerves, and in the trunk region - neurons and neuroglia ganglia of the peripheral nervous system and pigment cells of the skin.
Neurons as differentiation and specialization are losing their ability to divide, and glial cells retain this ability (proliferative activity). Signs of specialization of neurons are a large number of granular endoplasmic reticulum
(HPP), a well-developed Golgi complex, accumulation of neurofilaments in the cytoplasm, neurotubules and development processes - first, the axon, then the dendrites. Between neurons are contacted in the form synapses.
Neurons - belong to the very large cells (up to 130 microns). Their body is large, has an oval, flattened spindle-shaped, ovoid or pyramidal shape. All neurons have spines, one of which is called neuro or axon, the rest - dendrites. Depending on the number of processes are classified as unipolar neurons, which in humans are found only in the embryonic period, bipolar and multipolar. Among the bipolar neurons distinguish psevdounipolar who have two process away from the body together and then separated in the form of the letter T. The majority of neurons in the nervous system, multipolar, with multiple branching of dendrites and axons the sole, which can also branch out.

For the function are distinguished sensitive (afferent), associative, motor
(efferent) secretory neurons. Afferent impulses form in response to exposure, association provides communication between neurons and transmit efferent stimulation on the working bodies.
The structure of nerve cells . Nucleus neurons in a large, usually located in the center. The chromatin is almost completely decondensed, one large nucleolus.
Many neurons are tetraploid. The cytoplasm has a complete set of organelles: mitochondria, Golgi apparatus, lysosomes, microtubules and microfilaments.
Characteristic of nerve cell structure is a matter Nissl: a basophilic staining clumps in the cytoplasm, which correspond to electron microscopy of the granular EPR with numerous free ribosomes and polyrybosomes. Because of the distinctive look of these lumps called tigroid substance. Basophilia is due to the abundance of rRNA. Numerous ribosomes are continuously synthesized proteins of the cytoplasm, which are sent to processes. Nissl substance is not in the axons.
Another characteristic structure of the cytoplasm - neurofilament, fasciculation, especially numerous in the process. In addition, to maintain the form in the cytoplasm of the neuron are neyrotubules (this is typical of microtubules in diameter 24nm). A well-developed Golgi complex is usually located between the nucleus and axon, there are numerous mitochondria, lysosomes. Also contains two pigment - lipofuscin which accumulates with age, and melanin (especially in the substantia nigra, where it is visible macroscopically).
The neuroglia
As already stated, the cells of the neuroglia play the role of intercellular substance and provide a support function. In the nervous tissue of the brain and spinal cord but not the connective tissue of vascular walls and so it is soft, friable.
The apparent structureless mass, which contains the bodies of neurons, neuroglia cells and capillaries, called neuropil, which is the basis of the gray matter. Electron microscopy revealed that this - weave the cell bodies and processes of neuroglial cells and neurons (unmyelinated). Silver paint has identified three types of neuroglial cells:
1 ) oligodendrocyte - small cells with dendritic spines.
2) Astrocytes - processes which are starlike.
3) the ependymal cells.
4) microglia - a very small cells derived from blood monocytes and macrophages play the role.
Oligodendrocyte - distinguish between light, intermediate and dark cells. In adults, dominated by dark. In these cells, many ribosomes and microtubules, thin unbranched processes. They develop from spongioblasts, cells subependimal layer of the neural tube, are also developing astrocytes. After the completion of their differentiation, they no longer divide.
Oligodendrocyte located in the gray matter around the bodies of nerve cells and form a shell around their branches. In the white matter oligodendrocytes processes in the form of flattened and plate many times wrap around nerve fibers.
Different processes of different fiber wrap. These layers form the myelin membrane fibers.

Astrocytes - some of their processes reach the blood vessels, others - to the surface of neurons, is spread on the surface of the capillary, or neuron, forming astrocyte foot. These pins are also on the basement membrane separating the brain from the pia mater. In the cytoplasm there are dense bodies (lysosomes), and fibrils, the protein is different from the filaments of neurons.
Astrocytes are divided into fibrillar and plasma. In fibrillar - long enough branching processes. These astrocytes located in white matter.
Plasma - branching processes, shorter and more numerous. There are many astrocytes in the corpus callosum. The main feature - support and insulation of neurons.
Ependymal cells - line the spinal canal and brain ventricles. Structure: an elongated body, the surface facing the cavity, there are cilia on the basal end of the long branching processes (supporting unit) in the cytoplasm of large mitochondria, the inclusion of the pigment.
The secretory function: secrete active substances in the brain cavity.
Tanicytes - a kind of ependymal cells, almost no cilia, the long arm goes to the brain and ends in the blood vessels. In the ontogeny of these cells direct migration path of neuroblasts.
Microglia - small cell monocytic origin are in white and gray matter. have long branching processes, a small amount of granular EPS, many lysosomes, they do not share. Play the role of macrophages, are able to move, react to a stimulus change their shape to spherical.
Nerve fibers.
Processes of nerve cells, dendrites and axons, usually coated formed oligodendrocyte, which in this case are called Schwann cells or lemmocytes.
Distinguish between myelin and nerve fibers amyelinate. In the envelope of myelin fibers have a thick layer of myelin. White matter fibers of the brain and spinal cord and peripheral nervous system myelin sheath usually have. Amyelinate fibers are mainly in the autonomic nervous system, and also form some afferent nerve fibers.
Myelinated nerve fibers.
Myelin covers nerve fiber layer is not continuous but is interrupted at regular intervals, which are called nodes of Ranvier . In these areas processes of Schwann cells close to cytolemma and in contact with neighboring Schwann cell processes digitiform grippers. Basal plate, available around the Schwann sheath is not interrupted.
The formation of the myelin sheath. Schwann cell covers the axon, it turns out that he was lying in the gutter, then wound Schwann cell begins to process - the axial cylinder. Moreover, its plasma membrane in contact and form a spiral structure of the two membranes - mesaxon. Initially, between these rings is the cytoplasm, but then she is forced to the cell body and pushed to the periphery.
Thus, the myelin is formed from the plasma membrane lemmocytes and consists mainly of the lipid layers of her. In the peripheral nerves between the constrictions in the myelin sheath are small cracks, which are called Schmidt-notch Lanterman.
This is the place where the formation of myelin, cytoplasm was delayed by rotating the Schwann cells, so these slots are also spirally. Myelin is stained by osmic acid

preparation in a black color at the expense of lipids. In the axial cylinder contains longitudinally arranged neurofilaments and neurotubules, mitochondria, myelin is outside the Schwann cell cytoplasm bounded by plasma membrane and the basal plate.
Remak's fiber.
In these fibers, the axons are immersed in the cytoplasm of Schwann cells.
In each cell there are from 5 to 20 different processes of neurons. In such a fiber
Schwann cells are column and connected end to end on a "depression-ledge." They are surrounded by basal lamina. Cytolemma between axons and Schwann cells have cytolemma intercellular space of 10-15 nm, which contains tissue fluid and glycocalyx. Amyelinate fibers because of such a structure called the fiber cable type. Approximate fold over plasmolemma axons called mezaxon.
Thus, the differences between the myelinated fibers and amyelinate are as follows:
Of nerve impulses.
Inside and outside the plasma membrane has a potential difference. Outside, more positive ions inside - negative. The difference provides the charge resting potential - 70 mV, ie, the membrane is polarized.
In response to various stimuli: mechanical, electrical, chemical, physical, t0 - there is a nerve impulse. In unmyelinated fibers with Na + enters the cytoplasm, increases the positive charge inside the resting potential disappears. As soon as the ion content is equalized on both sides of the membrane, increased permeability plasmolemma for K + ions, and they go out. As a result of: 1) reduced overall positive charge of the cytoplasm, 2) increases the positive charge on the outside, 3) restores the resting potential. Again acts Na + - K + - pump.
Thus irritation amyelinate axon immediately causes membrane depolarization and repolarization then. That is, the transfer of momentum - a wave of depolarization-repolarization, passing through the plasma membrane in one direction.
In the myelin fiber membrane depolarization occurs only in the area of nodes of Ranvier, as the electric current produced between the cytoplasm and the external environment can not pass through the myelin. Current is passed to the next interception, causes depolarization of it, etc. until the next catch. This is the momentum transfer occurs at a higher rate than amyelinate fiber.
The structure of the peripheral nerve.
Peripheral nerve myelin is formed by bundles of nerve fibers and amyelinate. The nerve is surrounded by a connective tissue sheath - epineurium.
Sheaves of nerve fibers that make up the nerve surrounded by connective perinevriem, and each fiber - endoneurium. In the strata of loose connective tissue are blood vessels (in the endoneurium - capillaries). In the epineurium and the outer part perinevriya - arterioles and venules, lymphatic vessels. Most of the peripheral nerve is a mixed type, since they contain afferent and efferent fibers.
Only at the distal end of the nerve fibers are distributed to individual sensory or motor sheaves, proved that the fibers pass from one beam to another.

Perinevry - Outside - the connective tissue surrounding each bundle of nerve fibers and the inner part - several concentric layers of flat perineural cells, inside and outside covered with a thick basement membrane containing type IV collagen, laminin, nidogen, fibronectin.
These epithelial cells are connected by close contact, form the perineural barrier, which controls the transport of molecules through perinevry to nerve fibers.
Regeneration.
If the damage is complete degeneration of the nerve to the peripheral segment. Schwann cells proliferate in the peripheral processes forming bunger tape for the regeneration of the axon, which is growing at a rate of 0.25 mm per day to the site of damage, followed by 3-4 mm. Recovery can also occur through collaterals from the surrounding fibers, leaving them in the hook. Schwann cells produce nerve growth factor.
The nerve endings.
For functions are divided into:
1) effector - motor
2) receptor (sensitive, effector).
By Localization - exteroceptor,
- Interoreceptors,
- Proprioceptors.
On morphology - free and commercial.
By spefichnosti perception - baroreceptors, thermoreceptors, chemoreceptors, mechanoreceptors, pain receptors.
Nervous effector endings:
1) motor
2) secretory
Motor - consisting of a terminal axon branching of motor cells of somatic or autonomic nervous system and the specialized area of muscle fibers. Myelinated fiber to muscle fiber loses myelin sheath and immersed in a muscle fiber with its cytolemma, forming the neuromuscular synapse. Cytolemma between axon and muscle fiber has a synaptic cleft width of ~ 50 nm. Nearby are the neuroglia cells - oligodendrocytes. Presynaptic side contains presynaptic vesicles with acetylcholine, the mitochondria. Neurotransmitter released in the synaptic cleft, causes stimulation of postsynaptic membrane and depolarization. Postsynaptic part
- the part of the muscle fiber, which has no cross-striation, contain many mitochondria, ribosomes, the enzyme acetylcholinesterase that breaks down acetylcholine.
Secretory nerve - terminal extensions with fiber synaptic vesicles containing acetylcholine, ending in glands.
Sensory nerve endings - receptors - the terminal branch of the dendritesensitive neuron.
Divided into:
1) free encapsulated
2) non-free

Free nerve endings - mainly Remak's fiber (afferent), they continue in the epidermis without Schwan-ray cells reach the granular layer. Free nerve endings are also in papillary layer around the hair follicles on the muscle fibers. A special type of nerve endings - is Merkelevy nerve. end - are in the deep layers of the epidermis on the palms and soles. The free nerve endings attached to the modified cells of the epidermis (the cells of Merkel) in sprout layer. Myelinated nerve fibers penetrate the epidermis, lose their Schwann sheath and form a discoid expansion, associated with Merkel cells. These nerve endings are mechanoreceptors - carry the sense of touch.
Encapsulated nerve endings.
These include the receptor nerve endings in the connective tissue. The principle structure of the following: terminal branching of nerve branches
(dendrites) are surrounded by oligodendrocytes and in addition, a connective tissue capsule, so called encapsulated, but the species have their own characteristics depending on their functions.
Among the most common are: 1) lamellar bodies or bodies Vater-Pacini.
They are in the connective tissue of the deeper layers of the skin and internal organs. This oval-shaped formation with a diameter of 1-4 mm and 0.5-1mm. At one extreme, it enters the long myelinated fiber loses its myelin in nodes of
Ranvier, gives a few shoots. Schwann cells form the inner core around these nerve branches, like an onion. The cells of the inner bulb flattened and densely packed.
The outer bulb - cells surrounding the nerve fiber, form about 60 full concentric layers. All cells are desmosomes. Between the layers of individual collagen fibers, interstitial fluid and basement membrane components. Outside - connective tissue capsule, passing in endoneural membrane of the nerve fiber, about 30 concentric layers of fibroblasts and fibrocytes. This body takes the pressure and vibration.
2) Taurus Meissner corpuscles or tactile located in the papillary layer of the skin of fingers and toes, palms, and soles. lips, eyelids, vulva, breasts. Are mechanoreceptors respond to touching the skin (tactile sensitivity). 50-100 mm oval formation. Axis is perpendicular to the skin surface is a cylinder axis, divides into branches 9.2, they have branched into a spiral with Schwann cells. Between
Schwann cells arranged collagen fibers across cells. Around the calf thin connective tissue capsule. A variety of these cells are the genital cells, which are characterized in that the capsule consists of a few axons and then they branch out
3) Taurus Ruffini. Located in the deep layers of the dermis, especially in the soles and joints. Elongated 0.1-2 mm, a diameter of 150 microns.
Nerve fiber forms a clump of terminal branches of the collagen fibers, forming the core of the body (inner bulb). Nerve terminals clavate expanded and contain accumulations of mitochondria and vesicles. Terminals are not covered by
Schwann cells, unlike other encapsulated nerve endings and are separated by a basement membrane from the capsular space, located between the capsule and the inner sleeve. This space is filled with fluid, contains fibroblasts, macrophages, and collagen fibers are woven into the inner flask. A thin capsule composed of 4-5 layers of flattened fibroblasts. These cells respond to the displacement of collagen fibers in the capsular space and the inner tube.

4) Bulbs Krause have a rounded shape, diameter ~ 50 microns are found in the conjunctiva, tongue, vulva. There are 2 types: 1) the terminal twigs and branches are not growing flask-shaped, 2) nerve terminal branches within the cells.
Outside the thin capsule.
5) receptors of muscles and tendons are neuro-muscular and neuro-tendinous spindles respond to changes in muscle fiber length and tension of the tendon. In the nerve-muscle spindle a few muscle fibers, called intrafusal (2 thick and 4 thin) surrounded by connective tissue capsule. Muscle fibers from the outside of the capsule are called extrafusal. The central part of intrafusal fibers is not reduced, as it has no contractile filaments. These fibers are suitable afferent nerve fibers forming and end on muscle fibers. When excessive stretching of muscle fibers of these endings in the spinal cord is a pulse that causes muscle contraction. On intrafusal muscle fibers also end in efferent motor nerve fibers, causing reduction in marginal areas. At the same time stretches the central part and increases the sensitivity of the receptor.
Synapses - the specialized contacts between neurons.
Classification
By way of the momentum transfer:
1) chemical (impulse conduction in one side);
2) electrical (impulse conduction in both sides)
By Localization:
- Axodendyc
- Axoaxonal
- Axosomatical
- Somatosomatical
- Dendrodendrycal.
On the composition of the mediator: - adrenergic (norepinephrine)
- Cholinergic (atsetilhodin)
- Peptidergic
- Purynergic
- Dopaminergic
By Features:
- exciting
- Inhibitory
Structure: there are three components of the synapse: presynaptic, postsynaptic and synaptic cleft. Presynaptic part is formed by the end of the axon cells, the momentum transfer. It contains synaptic vesicles with neurotransmitter, and various organelles, among them many of the mitochondria. Postsynaptic membrane of the postsynaptic part is presented, which has receptors to the mediators, and adjacent areas of the cell cytoplasm, perceptive momentum.
Synaptic cleft - the space between the presynaptic and postsynaptic membranes.