Nervous tissue - a system of interconnected neurons and glia that provide specific functions perceptual stimuli, excitation pulse generation and transfer it. It is the basis of the structure of the nervous system, providing the regulation of all tissues and organs, and their integration into the body and the relationship with the environment.
The nervous tissue:
1) perception of different stimuli and transform them into nerve impulses;
2) conducting nerve impulses, processing and transfer to the working parts.
Main source - neuroectoderm. Some cells develop from glial cells and microglia from the mesenchyme (from blood monocytes).
Significance of nerve tissue in organism is determined by basic properties of nerve cells (neurons) to percept irritation, to get condition of excitation, to produce impulse and pass it. Nervous tissue is the basis of structure of organs of nervous system providing regulation of the all tissues and organs, their integration in the organism and connection with surroundings.
Nerve cells are classified into:
1) on the morphology;
2) function.
The morphology of the number of processes are divided into:
1) unipolar (psevdounipolyarye) - from one process;
2) bipolar - with two spines;
3) multipolar - more than two branches.
By function are divided into:
1) afferent (sensory);
2) efferent (motor, secretory);
3) associative (intercalated)
4) secretory (neuroendocrine)
A neuron consists of a cell body (perikariona) and processes to ensure a nerve impulse - dendrites, bringing impulses to the body of the neuron and axon (neurite) carrying impulses from the cell body. Dendrites bring impulses to the body of the neuron, receiving signals from other neurons through multiple interneuron contacts. Axon (neuro) - long (a person from 1 mm to 1.5 m) process by which nerve impulses are transmitted to other neurons or cells working parts (muscles, glands). Departs from the axon axon hillock and almost all over covered with glial membrane. Neurocytes can have only one axon and one or multiple dendrites.
The body of the neuron (perikarion) includes the core and the surrounding cytoplasm (except for a part of the process). Cytolemma carries receptor function, because on it are numerous nerve endings (synapses) carrying the excitatory and inhibitory signals from other neurons.
Nucleus neuron usually one large, rounded, with a predominance of light euchromatin, has one (sometimes 2-3) nucleolus.
The cytoplasm of the neuron rich organelles and surrounded plasmolemma who has the ability to generate and conduct nerve impulses due to local current Na + in the cytoplasm and K + out through the membrane voltage-gated ion channels.
In contrast to the nerve cells, neurosecretory cells are able to synthesize and secrete a variety of hormones - neurohormones, they are substances of protein nature, and the work of neurosecretory cells is cyclical. Polenov identified neurosecretory cells in the function of three phases:
-accumulation phase
-phase synthesis
-emptying phase
These phase change each other, after the last phase, the granules appear neurohormones into the blood and cerebrospinal fluid (cerebrospinal fluid). Neurohormones regulate the function of the endocrine glands, which, in turn, release hormones into the blood and regulate the activity of various organs and systems.
Combining neural endocrine regulation mechanisms implemented at the level of the hypothalamus and pituitary. In the media the basal region of the hypothalamus synthesize and secrete two groups of neurohormones: libiriny and statins. These neurohormones to enter the portal system to the pituitary gland. Libiriny will activate the neurosecretory cells of the pituitary gland, and statins - reduce. Once in the pituitary gland, activates the synthesis libiriny tropic pituitary hormones. Tropic hormones fall into the general blood flow, spread throughout the body and find their "target" on the corresponding endocrine glands.
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Types of histological preparations
- Section
- Smear
- Imprint
- Pellicle preparation
- Pinch
Stages of propagating of histological preparation
1) Taking and fixing of material
- physical (by thermal processing fixatives)
- Chemical (by immersion into the formalin and so on)
2) Condensation of material
- impregnation by condensing mediums (paraffin, celloidin etc)
- freezing
3) Preparing of sections on microtome
4) Staining of histological sections by histological dyes
-Acidic (eosin, acid fucsin)
-Basic (azur, hematoxylin)
-Neutral
5) Conclusion of section into preserving medium (Canadian, fir balsam, synthetic medium)
Requirement to histological preparation:
1) To reflect vital structure
2) Be transparent
3) Be contrast
4) Be constant
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