Nervous tissue

It is composed of nerve cells and glial cells

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Nerve tissue is composed of nerve cell and Glial cell They are all cells with processes. Nerve cells are nervous system Structure and functional unit of neuron 。 The number of neurons is huge. They have the ability to receive stimuli, transmit impulses and integrate information. Some neurons also have endocrine function.

Chinese name: Nervous tissue
Foreign name: Nerve tissue

Composition: neuron (i.e. nerve cells) and glia
Neuron function: Receiving stimulation and conducting excitement
Glial action: Support, protection and nutrition

catalog

▪ Myelinated nerve fiber
▪ Unmyelinated nerve fiber

brief introduction

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Nervous tissue

Nerve tissue is human and Higher animal Of Basic Organization One is the main component of the nervous system. Nerve tissue is composed of neurons (nerve cells) and glia. Neurons are the main components of nerve tissue, which have the functions of receiving stimulation and conducting excitation, and are also active basic function Company. Glia plays a supporting, protective and nutritional role in nerve tissue. Human nerve tissue is mainly composed of nerve cells. Nerve cells are also called neurons, including Cell body And protuberance. Generally, each neuron has a long one with few branches axon , several short dendrites with dendritic branches. The process of neuron is also called nerve fiber 。 The small branch at the end of nerve fiber is called Nerve endings , distributed to the dominated organization. After being stimulated, neurons can generate excitation and conduct excitation along nerve fibers.

Nervous tissue^[1]

Nerve regeneration

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Nervous tissue

nerve cell Of Soma yes neuron The center of metabolism and nutrition. Damage to neurite or brain body or axon During disconnection, if the injured part is far away from the cell body, the cell body may undergo retrograde changes, such as cell body swelling, nuclear deviation, Nissl body dissolution, and even nuclear disappearance. In case of slight injury, the cell body will begin to recover after 3 weeks. And damaged nerve fiber Distal axon and myelin sheath At 12~ 24 hours Can gradually appear disintegration and Fat drop This process is called evolutionary reaction.

At the proximal broken end of the injury site, the residual Schwann cells divide and proliferate, forming cell cords to the far side. Injured proximal end axon Grow by budding. Nascent Schwann cell In the cord, under the induction of Schwann cells, the axon grows along the cell cord until it reaches the original axon terminal. The new axon terminal can branch to establish contact with the corresponding cell tissue and restore its function. This process is called nerve regeneration. Generally, there are nerve axons Regenerative capacity It can restore the original function, and the time required is generally about 3-6 months. If the two broken ends are far away from each other with serious injury, too many epileptic scar tissues grow between them, or the distal end is not well docked with each other, regeneration will be affected. Schwann cells peripheral nerve regenerate Repair process It can induce, nourish and promote the growth and maturation of axons. Central nervous system Although the fiber also has regeneration ability Glial cell The proliferation is fast, forming glial migration marks, blocking nerve docking and affecting regeneration.

neuron Soma Or serious injury near the cell body may lead to the disintegration and death of nerve cells, which is generally difficult to repair and regenerate. Nerves can be seen around the injured part Cell mitosis Process, explain nerve cells After injury Under certain conditions, it still has a certain ability to split, but the regeneration conditions and functional recovery are still affected by many factors. Research has proved that Neurotrophic factor Neurotropic factors can support neuron survival and promote Neurite Soluble chemical substances that grow, and which affect nervous system It plays an important role in the development and regeneration of nerve. as nerve growth factor NGF（nerve growth factor）， Fibroblast growth factor FGF（fibroblast growth factor）， epidermal growth factor EGF (external growth factor), etc. Nerve regeneration is still an important research topic.

Constituent organ

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Nerve tissue is a highly differentiated tissue Human nervous system The main components of. It is widely distributed in the human body Tissue and organ It has the function of connecting, regulating and controlling various organs, making the body a harmonious and unified whole. Nerve tissue consists of nerve cells and glial cells.

nerve cell

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Nervous tissue

Nerve cells are the main components of nerve tissue and highly differentiated cells. They are large in number, diverse in shape and complex in structure physiological function It has the characteristics of feeling stimulus and conducting impulse (for analysis and synthesis) to produce response. It is the structural and functional unit of nerve tissue, so nerve cells are also called neuron （neuron）。

Nervous tissue

Glial cell Neuroglial cell is an auxiliary component of nerve tissue, and most cells also have processes. Glial Soma It is generally smaller than the cell body of nerve cells; However, the number is about 10 times that of nerve cells, supporting nerve cells. Nutrition, insulation, protection and repair. Neurons have two parts: cell body and processes, which are divided into axon And dendrites.

structure

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Nervous tissue

1． Soma ： neuron Soma lies in the gray matter and ganglion The common shapes are star shaped, cone shaped, pear shaped and ball shaped. The cell bodies vary in size and diameter from 5 to 150 μ m. The cell body is the metabolic and nutritional center of neurons. The structure of the cell body is similar to that of ordinary cells nucleolus , cell membrane cytoplasm and nucleus 。

(l) Cell membrane: The cell membrane of the cell body and the membrane on the surface of the processes, which are continuous and complete cell membranes. except Synapse The cell membrane of the site has a unique structure, most of which are Unit membrane structure 。 The characteristic of nerve cell membrane is a sensitive and excitable membrane. There are various kinds of recipient (receiver) and ion channel (ionic channel) Membrane protein Constitute. The cell membrane that forms the synapse is thickened. The receptors on the membrane can bind to the corresponding chemical neurotransmitters. When the receptor and acetylcholine transmitter or γ - aminobutyric acid When the transmitter binds, the ions of the membrane permeability And inside and outside the membrane Potential difference When changes occur, the cell membrane produces corresponding physiological activities: excitation or inhibition.

(2) Nucleus: mostly located in nerve Cell body Central, large and round, Heterochromatin Less, more in nuclear membrane Inside, Euchromatin Many, scattered in the middle of the nucleus, so the coloring is shallow, nucleolus 1-2, large and obvious. When the cells degenerate, the nuclei move to the periphery and shift.

two Synapse

neuron Between neurons or between neurons and non neurons（ muscle cells 、 Glandular cell A kind of specialization between Cell junction , called synapse. It is the key structure for the connection between neurons and physiological activities. Synapses can be divided into two types, namely Chemical synapse (chemical synapse) and Electric synapse （electrical synapsse）。 Generally speaking, the synapse refers to the former.

Chemical synapse

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Under light microscope, most Synapse The shape of axon It is not spherical or ring-shaped and attached to another neuron Of Soma or Dendrite The surface, most of which is called Synaptic body (synaptic nucleus) or synaptic button.

Nervous tissue

According to the synaptic sites formed between two neurons, there are different types, most of which are Axo somatic synapse (axio somatic synapse) and axis tree Synapse (axo axonal synapse)- spinous ）， Axoaxial synapse (axo axonal synapse) and Tree tree synapse (dendroden dritic synapse) and so on. Usually one neuron There are many synapses that can receive information from multiple neurons, such as the spinal cord Anterior horn motor neuron There are more than 2000 synapses. cerebral cortex Pyramidal cell There are about 30000 synapses. cerebellum Purkinje cell Up to 200000 synapses can be found in the Soma And dendrite base, and dendrite tip and axon Minimum starting segments.

Under electron microscope, synapse consists of three parts: Presynaptic Synaptic space and postsynaptic area. Presynaptic cell membrane Slightly thicker than other parts, respectively called Presynaptic membrane and Postsynaptic membrane The narrow gap between the two membranes is called Synaptic space 。

one Synapse Front（ presynaptic Element) The axonal terminals of neurons are bulbous, and the axonal membrane thickens to form presynaptic membrane, which is about 6-7nm thick. Presynaptic Cytoplasm Contains many Synaptic vesicle （synaptic vesicle ）And some Microfilament and microtubule 、 mitochondrion And smooth endoplasmic reticulum. Synapse Vesicle It is a characteristic structure in the front of the synapse, and the vesicles contain chemicals material , called Neurotransmitter （ neurotransmitter ）。 The shape and size of synaptic vesicles in various synapses are quite different, because they contain different neurotransmitters. The common types of synaptic vesicles are: ① spherical vesicles, about 20-60nm in diameter, with clear vesicles, which contain Excitatory neurotransmitter , such as acetylcholine ；② Granular vesicle, which contains electron density High dense particles Particle size It can also be divided into two types: small granules and vesicles with a diameter of about 30-60 nm, usually containing amine neurotransmitters such as adrenaline 、 Norepinephrine Etc; The diameter of large granule vesicles can reach 80~200nm, and the neurotransmitters contained are 5-hydroxytryptamine or Enkephalin Isopeptides; ③ Flat vesicle, about 50nm in diameter, is flat and round, and contains inhibitory neurotransmitters, such as γ - aminobutyric acid Etc.

Glial cell （ neuroglia Cell), referred to as neuroglia, is widely distributed in the central and Peripheral nervous system 。 Ordinary staining can only show the nucleus, and special staining Silver stain The method can display the overall morphology of glial cells. Generally, glial cells nerve cell It is small, with many and irregular processes, and the number is about ten times that of nerve cells. More distributed in neuron Soma , protuberances and the periphery of central nerve capillaries. Glial cells have support. I. Nutrition, protection Myelination And insulation, with splitting, multiplication and Regeneration and repair And other functions.

Glial cell

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Nervous tissue

1． Astrocyte (astrocyte) Yes Glial cell The largest of, Soma It is star shaped, with large round or oval nuclei and light staining. Cytoplasm Interwoven Glial filament （neuroglial filament）。 Many processes radiate from the cell body, and the ends of some processes expand to form foot plates (ends foot ）, attached to blood capillary Basement membrane Or extend to the surface of brain and spinal cord to form glial limitan. Astrocyte About 20% of all glial cells. Astrocyte According to its distribution and structure, it can be divided into two types.

（1） Protoplasmic astrocytes (protoplasmie astrocyte): distributed in central nervous system It is located in the gray matter of the nerve cell body and around its processes. Proplasmal astrocytes have irregular processes, many short and curved branches, and their surfaces are not smooth. There were few glial filaments in the cytoplasm.

（2） Fibrous astrocytes (fiber astrocyte): distributed in white matter Inside, at nerve fiber between. Its protuberances are radial, slender and straight, with few branches and smooth surface. Cytoplasm There are many interlaced raw fibers ultrastructural Is a kind of Intermediate filament , called glial filament, which contains glial fibrillary acidic protein GFAP ）, immunocytochemical staining technology can Specificity To show such cells.

Astrocyte It contains high concentration of K+, and can absorb certain neurotransmitters (such as γ - aminobutyric acid). It affects neuron Functional activities of. Therefore, astrocytes are important for maintaining nerve cells Microenvironment It plays an important role in stabilizing and regulating the metabolic process. When the central nervous system is injured, astrocytes rapidly divide and proliferate to form Glial scar Form.

nerve fiber

Nerve fiber is composed of neurite (including axon And dendrites) as the axis, outsourcing Glial cell （ Schwann cell or Oligodendrocyte ）。 According to the presence or absence of nerve fibers myelin sheath Wrapping, divided into medullary and Unmyelinated nerve fiber Two.

nerve fiber

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Myelinated nerve fiber

Myelinated nerve fiber （ myelin Ated nerve fiber) axon (or dendrite) myelin sheath 、 Nerve membrane Composition. Myelin sheath ）And neurolemma wrapped around axons in a sheath shape. There is no myelin sheath wrapped at the beginning of the axon. This part is called the axon part far from the beginning of the initial segment. The myelin sheath appears to wrap the axon in segments, similar to the lotus root node, and its discontinuous part, with exposed axonal membrane, can occur Membrane potential Change, call this part nerve fiber Node of nerve fiber, also known as Lang Feijie （Ranvier node）。 A section between two adjacent knots, called Internode body (internode), about 0.5~1mm long, is composed of a Schwann cell The formed myelin sheath and its surrounding nerve membrane constitute. Schwann's nucleus is long oval, located at myelin sheath A small amount of edge Cytoplasm Inside. Myelin sheath is mainly composed of lipid and protein Is composed of, called Myelin (myelin) On routine staining specimens lipid After being dissolved, only the remaining protein is found in a network, which is called neurokeratin network. stay Osmic acid On the infected specimen, the myelin sheath is black, and several funnel-shaped diagonal cracks are also visible Myelin notch (accident of myelin) or Shirley blue cut （Schmidt-Lanterman incisure）。 Under the electron microscope, myelin sheath is arranged in concentric circular lamella with light and dark. Myelin sheath has the function of protection and insulation, which can prevent Nerve impulse Diffusion of. Myelinated nerve fiber Of Nerve impulse conduction , is from a Lang Feijie Jump to the adjacent Langfeijie Skip conduction , long nerve fiber , axon Just thick, myelin sheath Also thick. The internode is also long, conduction velocity Come on. On the contrary, the conduction speed is slow. Most of the brain spinal nerve It belongs to myelinated nerve fibers. The myelin sheath of myelinated nerve fibers in the central nervous system consists of Oligodendrocyte Formation. Several processes of one oligodendrocyte can wrap several axons to form myelin sheath. Its Langfei knot is wide and has no myelin sheath notch Soma It is located between nerve fibers.

Unmyelinated nerve fiber

Unmyelinated nerve fiber (nonyelinated nervefiber) finer axon and Schwann cell Composition, none myelin sheath , None Lang Feijie 。 Under the electron microscope, a Schwann cell with 5~15 axons of different thickness can be seen. The nerve impulse conduction of unmyelinated nerve fibers is along the axon Continuity Conduction conduction velocity than Myelinated nerve fiber Much slower. Autonomic nerve Of Postganglionic fibre And some feelings nerve fiber It belongs to unmyelinated nerve fiber.

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