Sarcolemma
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The name sarcolemma is used to describe the cell membrane of a muscle fibre or muscle cell. The membrane is designed to receive and conduct stimuli. Alterations in the sarcolemmal membrane stability and repair system can lead to muscular dystrophy. Current mechanism of muscular dystrophy: Lack of functional dystrophin means that the sarcolemma is not attached to the cytoskeleton. Therefore during contractions the sarcolemma is not “in sync” with the interior of the cell. The looseness of the sarcolemma permits membrane calcium channels to open. Rise in internal [Ca++] activates proteolytic enzyme calpain, which now digests proteins including contractile proteins, rendering the muscle much weaker.
Sarcolemma will invaginate into the cytoplasm of the muscle cell, forming membraneous tubules called transverse tubules. Sarcoplasmic reticulum is the enlargements of smooth endoplasmic reticulum found in muscle cells on either side of the transverse tubules. The triad of transverse tubules surrounded by two smooth ER cisternae transmit altered membrane permeability down the tubules. The nuclei lie just inferior to the sarcolemma at the periphery.
This membrane is extensible and encloses the contractile substance of a muscle fiber.
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[edit] See also
skeletal muscle/general: epimysium, fascicle, perimysium, endomysium, muscle fiber, myofibril
sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin), tropomyosin, troponin (T, C, I)
neuromuscular junction, intrafusal muscle fiber, extrafusal muscle fiber, motor unit, muscle spindle, sliding filament mechanism
myoblast, satellite cells, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule
