The elongated part of neuron cytoplasm (cytoplasm) is called "nerve fiber", also called "neurite".The thickness of nerve fibers varies from a few tenths of a micron (1 micron is equal to 1/1000 mm) to 100 microns in diameter.Some are very short, only a few microns;Some are very long, up to about 1 meter.It is surrounded by insulating myelin sheath, called myelin sheath fiber;Those without obvious myelin sheath are called unmyelinated fibers.The fibers are filled with semi fluid nerve plasma, which contains microtubules, microfilamentsmitochondrionEndoplasmic reticulum, which can maintain the growth and transportation of neurites.Many parallel nerve fibers gather into bundles, which are called nerves.
Chinese name
nerve fiber
Foreign name
nerve fiber
Distribution
In the space between all organs and tissues of human body
The main function of nerve fibers is to transmit nerve impulses.The conduction velocity of various nerve fibers is different, about 3-120 meters per second.The afferent fibers transmit the nerve impulses of receptors to the central nervous system;Transmitting the impulses of the central nervous system to the effector organs is called efferent fiber.All fiber bundles composed of afferent fibers are called sensory nerves;All fiber bundles composed of efferent fibers are called motor nerves;The fiber bundle with both afferent and efferent fibers is called mixed nerve.In addition, in the process of transmitting impulses, nerve fiber terminals will release differentNeurotransmitter。According to the difference of neurotransmitters released, it can be divided into cholinergic nerve fibers, adrenergic nerve fibers and purinergic nerve fibers.
2、 Morphology of nerve fibers in skin scar
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（1） Hypertrophic scar:
Hierarchical scanning and three-dimensional reconstruction showed that the internal structure of nerve fibers was incomplete, and there were longitudinal or transverse fracture surfaces locally
It appears, is damaged or even disintegrated, has irregular swelling and distortion thinning, and the degree of pathological changes observed on different levels of optical sections and different rotation angles is different.
（2） Mature scar:
Stratified scanning showed that the internal structure of nerve fibers was relatively complete, without obvious pathological changes;Three dimensional reconstruction showed that the continuity of nerve fibers was enhanced, the thickness was uniform, there was little distortion and swelling, the branches were reduced, and the morphology was close to normal nerve fibers.The reason for this morphological change may be that excessive inflammatory reaction and hypoxia in hypertrophic scar have abnormal stimulation on nerve endings, which leads to degeneration of regenerated nerve endings and sensory abnormalities;With the maturity of the scar, some fibers could not establish contact with a certain number of target organs and eventually degenerated, and recovered close to the normal level of innervation.
Hypertrophic scar (HS) is a common pathological healing result. With the formation of scar, the number of nerve fibers in the early stage of HS increases significantly, and with the maturity of scar, the number of nerve fibers decreases gradually.However, no matter in the early or late stage, the innervation of HS tissue is always more intensive than that of normal skin tissue.However, the positive area ratio of nerve fibers in hypertrophic scars was significantly higher than that in normal skin, while that in mature scars was significantly lower than that in normal skin, suggesting that nerve fibers may have some relationship with scar hyperplasia.Therefore, it is speculated that early wound healing requires more nerve involvement to regulate wound healing by some mechanism, while a large number of cytokines stimulate nerve fiber proliferation;After scar formation, with the stability of the local environment, the inflammatory reaction subsides, and the stimulation factors are reduced. At the same time, scar remodeling or restructuring can improve the structure and strength of the tissue, gradually restore the original structure and function of the tissue, and the nerve fibers are gradually reduced.
