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The sarcolemma is the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
 of a muscle cell. It consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils. At each end of the muscle fiber, this surface layer of the sarcolemma fuses with a tendon fiber, and the tendon fibers in turn collect into bundles to form the muscle tendons that then insert into bones.






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The sarcolemma is the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
 of a muscle cell. It consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils. At each end of the muscle fiber, this surface layer of the sarcolemma fuses with a tendon fiber, and the tendon fibers in turn collect into bundles to form the muscle tendons that then insert into bones. The membrane is designed to receive and conduct stimuli.

Alterations in the sarcolemma membrane stability and repair system can lead to muscular dystrophy
Muscular dystrophy

Muscular dystrophy refers to a group of genetics, hereditary muscle diseases that weaken the muscles that move the human body. Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cell and biological tissue....
. The mechanism of one type of muscular dystrophy, for example, is lack of functional dystrophin
Dystrophin

Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane....
. This means that the sarcolemma is not attached to the cytoskeleton
Cytoskeleton

The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within the cytoplasm. The cytoskeleton is present in all cells; it was once thought this structure was unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton....
. Therefore during muscle contraction, the sarcolemma is not synchronized with the interior of the cell. The looseness of the sarcolemma permits membrane calcium channel
Calcium channel

A Calcium channel is an ion channel which displays selective permeabiltiy to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels....
s to open. The rise in internal calcium ions causes activation of the proteolytic enzyme calpain
Calpain

Calpains are a family of calcium-dependent, non-lysosome cysteine proteases expressed ubiquitously in mammals and many other organisms. Calpains constitute the C2 family of protease clan CA in the MEROPS database....
, which digests proteins including contractile proteins, rendering the muscle much weaker.

The sarcolemma invaginates into the cytoplasm of the muscle cell, forming membranous tubules called transverse tubules (t-tubules). Sarcoplasmic reticulum is the enlargement of smooth endoplasmic reticulum
Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
 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 adjacent to the sarcolemma, at the periphery of the fiber.

This membrane is extensible and encloses the contractile substance of a muscle fiber.

See also

  • Cell membrane
    Cell membrane

    The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....