Muscle cells are fibrous, not branched, with obvious striations, many nuclei, and are located below the cell membrane.There are many filamentous myofibrils parallel to the long axis of muscle cells.Each myofibril has alternating bright bands (I bands) and dark bands (A bands).The bright zone is slightly stained, while the dark zone is deeply stained.There is a brighter line in the middle of the dark band called H-line.There is an M line in the middle of the H line.In the middle of the bright belt, there is a darker line called Z line.The section between two Z lines is called a sarcomere, which is about 1.5~2.5 microns long.The light band of adjacent myofibrils is on the same plane, and the dark band is also on the same plane, so that the myofibrils show alternating light and dark stripes.
Skeletal muscles are arranged in bundlesmuscle cellsConstitutive.Each cell is different in length, closely arranged and complementary in length.Each cell is surrounded by a thin reticular membrane, called endocardium;Each muscle bundle is wrapped by a connective tissue membrane composed of glial fibers and elastic fibers, called fascicle membrane;On the outside of each muscle, there is another layer of thick connective tissue, called adventitia.The connective tissue of each membrane is continuous with each other, and the blood vessels and nerves distributed to the muscle enter along the connective tissue membrane.Skeletal muscle contraction is controlled by consciousness, so it is also called“Voluntary muscle”。The characteristic of contraction is fast and powerful, but not lasting.
motion
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1. Classify or describe according to shape
Skeletal muscle shortening produces movement, and the force generated by contraction is pulling force rather than pushing force.However, in some special cases, such as the bulge of the tympanic membrane to balance the air pressure on both sides of the tympanic membrane when the "popping sound acts on the ear", and the phenomenon of the muscle vein pump, etc., are all related to the effect of muscle abdominal expansion during muscle contraction.
Most skeletal muscles can make bones move, while some muscles can move other parts of the body such as eyes, lips and scalp.The orbicularis oris muscle surrounds the mouth and plays an important role in pronunciation and sucking.Although the tongue has no bones or joints, the hyoid bone only constitutes its base, but it can also move
2. Classification according to unit of motion
Primordial muscleThe main muscles that cause specific movements of the body can produce intentional movement by actively contracting;
Antagonistic muscleA muscle that opposes the action of a prime mover.During the contraction of the original muscle, the antagonist muscle gradually relaxed to ensure the smooth movement process;
Synergist muscleWhen the prime mover passes through more than one joint, the synergetic muscle contraction can prevent one (some) of the joints from interfering with the movement of the prime mover.In short, synergists play a role in assisting the movement of the original muscles;
Fixed muscleWhen the movement occurs in the distal part of the limbs, the fixing muscles play the role of stabilizing the proximal part of the limbs.
classification
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Oblate muscle:Muscle fibers are parallel, often with aponeurosis, such as: external oblique abdominis;
Feather muscles:The muscle bundles are arranged in feather shape, and can be divided into hemifeather, feather or polyfeather muscles, such as deltoid;
Spindles:Spindle shaped (muscle belly is thick and round, and both ends gradually become thin), for example: biceps brachii;
Square muscle:It is square and has 4 approximately equal sides, for example, the pronator;
Circus or sphincter:Distributed around openings or holes in the body.Narrow these openings when muscles contract, for example, orbicularis oculi can close the eyelid fissure.
physical exercise
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In childhood and adolescence, we should pay attention to properly increase physical exercise, improve the toughness of the whole body's skeletal muscles, exercise appropriately for middle-aged and elderly people, and try to do aerobic exercise without hurting muscles, such as swimming, playing tai chi, etc.
