With fromNerve endingsThe nerves that transmit impulses to the center are called afferent nerves.Equivalent to allsensory nerve。In fact, the afferent nerve is called the afferent fiber or afferentneuronIs more accurate.The entire pathway of transmitting impulses from any sensory site to the central nervous system is called the afferent pathway.Most of the autonomic nerves belong to the efferent nerves, but some nerves such as the great artery nerve, carotid sinus nerve, and pulmonary branches of vagus nerve are afferent nerves
Chinese name
Afferent nerve
Foreign name
afferent nerve
Definition
A nerve that transmits impulses from nerve endings to the central nervous system
The afferent nerve is composed of sensory nerve fibers, which directly contact the posterior horn of gray matter.The biggest difference between the afferent nerve and the efferent nerve is that the afferent nerve has an "alpha" shaped ganglion.Afferent nerves describe the relative connections between structures, also known assensory nerveYuan;Transmitting nerve stimulation from receptors or sensory organs tocentral nervous system。The shape of the afferent nerve cell body is smooth and round, and the structure contains a longDendriteAnd a shorteraxon, and specificInterneuronconnect.
Histological characteristics
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It is composed of afferent nerve fibers, surrounded by connective tissue membrane, in which there are fibroblasts, histiocytes and adipocytes.There are blood vessels in the outer membrane and the inner nerve fascicle.One end of the nerve is distributed in the receptor from the sensory fiber end, and the other end is connected with the brain or spinal cord.The receptors generate excitation after feeling the stimuli inside and outside the body, and convert them into nerve impulses, which pass through the afferent nerves into the center, causing sensation or reflex.
connective tissue：It is composed of cells and intercellular substance.The number of cells is small, but there are many kinds, non-polar, scattered in the cytoplasm.The number, morphology and function of cells in different types of connective tissue are also different.There are relatively many cell stroma, including matrix and fiber.The matrix is in a homogeneous state, some of which are flowing liquids, or viscous colloidal substances, and some are solids.The fibers are filamentous, which can be generally divided into collagen fibers, elastic (force) fibers and reticular fibers.
Connective tissue is a kind of homologous tissue, which is derived from mesenchymal cells of mesoderm in embryonic stage.Mesenchyma is also composed of cells and cell stroma, which mainly exists in the embryonic stage.Mesenchymal cells are astrocytes with many processes, and the processes connect to each other into a network. The nucleus is large, the nucleolus is obvious, and the cytoplasm is less, and it is basophilic.
Mesenchymal cells are poorly differentiated and have a strong ability to differentiate in many ways.All kinds of connective tissue cells, vascular endothelial cells and smooth muscle cells are derived from embryonic mesenchymal cells.In some tissues of the adult body, such as reticular connective tissue, some mesenchymal cells with differentiation potential, also known as undifferentiated reticular cells, are still retained.
Connective tissue exists in various forms, including liquid blood, fibrous and solid cartilage and bone, to adapt to complex functional activities.
At present, there is no perfect and unified classification method for connective tissue.Generally, according to the morphology and structure, it can be divided into four categories: intrinsic connective tissue, cartilage, bone and blood.Inherent connective tissue is divided into loose connective tissue, dense connective tissue, reticular connective tissue, fat connective tissue and mucus connective tissue.
The functions of connective tissue are complex. Different types of connective tissue have different functions. They have both division of labor and multiple abilities. In general, they have the functions of connection, support, protection, defense, repair, nutrition and transportation.
Fibroblast：Fibroblasts, also known as fibroblasts, are the main cells in fibrous connective tissue that can produce fibers and stroma. Their morphology and structure depend on their functional status.When the function is active, that is, fiber and matrix are produced, the cells are star shaped or spindle shaped, and the cell body is large, extending a number of short and thick cytoplasmic processes.There are many cytoplasm and weakly basophilic.The nucleus is large, oval, and the chromatin particles are small and sparse, so the staining is shallow, with 1~2 obvious nucleoli.Under the electron microscope, the cytoplasm is rich in rough endoplasmic reticulum and free ribosomes. There are many mitochondria, developed Golgi complexes, and secretory vesicles. There are microfilament bundles and microtubules in the cytoplasm near the cell membrane.Microtubules are associated with the transport of secretory vesicles.The microfilament bundle contains actin, myosin and tropomyosin, which is the structure of cell movement. Under the action of microfilament, cells can slide along the surface of attachments.When the cell function is inactive or inactive, it can be called fibrocyte.These cells are smaller, less prominent, and more slender.The cytoplasm is less, weakly eosinophilic, and lightly stained.The nucleus is smaller, darker, and the nucleolus is smaller.Under the electron microscope, the organelles are reduced and underdeveloped.Some people think that fibroblasts are immature cells, commonly seen in the formation of fibrous connective tissue and granulation tissue;Fibroblasts are mature cells commonly found in the connective tissue that has been formed.The morphology of fibroblasts is not only related to their functional status, but also to their surrounding environment. For example, when the cells are squeezed by dense fiber bundles, the cell bodies elongate and are parallel to the fibers. The cytoplasm forms several thin winged processes that extend between collagen fibers, and the nucleus becomes slender, such as tendon cells.Fibroblasts can produce collagen fibers, elastic fibers and reticular fibers, as well as proteoglycans and glycoproteins of matrix.The proteins that make up various fibers are synthesized in cells, released outside cells, and then polymerized into fibers.The protein part of matrix proteoglycan is produced by rough endoplasmic reticulum, and the polysaccharide part is produced by smooth endoplasmic reticulum and Golgi complex.Fibroblasts play an important role in the regeneration of connective tissue.When the wound is healed, the fibroblasts at the edge of the wound actively undergo mitosis.Undifferentiated mesenchymal cells also divide and differentiate to form fibroblasts.The newborn fibroblasts produce fibers and matrix, which together with the newborn capillaries form granulation tissue to fill and repair wounds.Recent studies have proved that fibroblasts in granulation tissue have new characteristics, similar to smooth muscle cells. There are many microfilaments and dense bodies in the cytoplasm, which can be called muscle fibroblasts.Some people believe that these variant fibroblasts play a key role in the contraction of granulation tissue and the closing of wound edge.
Histiocyte：The cell bodies vary in size and are long oval or irregular in shape. The diameter of the long axis can reach more than 20~50 μ m, and the edges are mostly irregular and paper torn.The nucleus is round or oval, and the chromatin in the nucleus is thick reticular, often with 1~2 clear blue nucleoli.The cytoplasm is rich, light blue, with a few astrophilic particles, sometimes containing phagocytic pigment particles, fat droplets, blood cells, bacteria, etc.
fat cells：Adipocytes are connective tissue cells that store large amounts of fat.The fat it stores is mainly neutral fat, namely triglyceride, which is clustered into drops in the cytoplasm.According to the size and number of fat drops, fat cells are divided into single bubble fat cells and multi bubble fat cells.Monovesicular adipocytes constitute most of the adipose tissue, that is, white (yellow) adipose tissue, and are often distributed in loose connective tissue individually or in groups.Because of its large number and wide distribution, the so-called fat cell usually refers to this kind of cell.The distribution of polyvesicular adipocytes is limited, forming brown adipose tissue.Adipocytes are derived from mesenchymal differentiated adipoblasts.The shape of adipocytes is similar to that of fibroblasts, but fat can accumulate in their cytoplasm.At first, there were some scattered small fat drops in the cells, and then the small fat drops fused into a large fat drop, so the cells took the shape of typical single bubble fat cells.Postnatal new adipocytes are usually found around small blood vessels with undifferentiated mesenchymal cells.
Adipocytes are spherical or extruded into polygons with large volume and diameter up to 120 μ m.There is a big fat drop in the center of the cytoplasm, which occupies most of the cell volume, so this kind of cell is also called a single bubble fat cell.The rest of the cytoplasm is squeezed to the periphery of the cell by lipid droplets, forming a thin layer, and the nucleus is also squeezed into a flat circle, located on one side of the cell.In HE. In the stained paraffin sections, the fat drops have been dissolved, and the fat cells are ring shaped.Fresh tissue was made into frozen sections and stained with fat soluble dye Sudan Ⅲ. The fat drops were bright red.Under the electron microscope, in addition to a large central fat drop, there are also some small fat drops. The cytoplasm around the fat drop contains mitochondria, a small amount of endoplasmic reticulum, free ribosomes and many pinocytosis vesicles. There is a small Golgi complex near the nucleus.
Adipocytes are the "fat bank" for storing fat. The body stores or uses fat from the fat bank according to the demand for heat.The data of studying fat metabolism with isotope shows that the fat in fat cells is constantly metabolized and renewed even under the condition of heat balance.The fat stored by adipocytes is mainly triglyceride, which is synthesized by α - phosphoglycerol, the intermediate product of fatty acid and glucose metabolism in adipocytes from different sources, under the catalysis of enzymes, and then incorporated into the central fat drop for storage soon after synthesis.Some data show that mitochondria and endoplasmic reticulum are the synthesis pool of triglycerides, and the central lipid droplet is the storage pool.When the stored fat is used, the activated hormone sensitive lipase (triglyceride lipase) will hydrolyze triglycerides into fatty acids and glycerol, and release them into the blood circulation.The fat metabolism of adipocytes is regulated and controlled by hormones and nerves.Insulin can promote lipogenesis and inhibit lipolysis.Catecholamine, growth hormone, thyroxine, adrenocorticotropic hormone and glucagon are lipolytic hormones.Hormones activate triglyceride lipase and promote triglyceride hydrolysis through the second messenger of fat cells.
