*

Sarcolemma n. The thin, transparent, extensible membrane covering every striated muscle fiber Source: modified by Maria Victoria Gonzaga, lungemine.com, from the job-related of OpenStax, CC BY-SA 4.0..

You are watching: The cell membrane of a muscle cell is called the


Sarcolemma Definition

What is the sarcolemma? that is the thin, transparent, extensible plasma membrane of the muscle cell. It is composed of a cabinet membrane (plasma membrane) and an outer coat comprised of a slim layer of polysaccharide (glycocalyx) product with plenty of thin collagen fibrils. Etymologically, what execute you median by sarcolemma?Sarco’ originates from the Greek (sarx) definition “flesh”, and also ‘lemma’ comes from the Greek an interpretation “sheath”.


Sarcolemma (biology definition): the thin, transparent, extensible membrane covering every striated muscle fiber. That is structure and also design is crucial in receiving and conducting stimuli. At every end of the muscle fiber, the external layer of the sarcolemma fuses with tendon fibers, which consequently collect into bundles to type muscle tendons. Etymology: indigenous sarco– + Greek lemma, an interpretation “husk”. Synonyms: myolemma.
*
Figure 1: What perform you typical by sarcolemma? The muscle cell membrane is referred to as the sarcolemma. Source: CNX OpenStax.

Characteristics that Sarcolemma

The sarcolemma anatomy can be characterized as the plasma membrane the a muscle cell or the plasma membrane that a muscle fiber. Muscle cell are additionally known as muscle fibers because of their long, cylindrical shape.

The sarcolemma is extended by a glycocalyx. How execute we specify glycocalyx? The glycocalyx is a coating spanning the cabinet membrane. The is composed of glycosaminoglycans (GAGs), proteoglycans, and also other glycoproteins the consist the acidic oligosaccharides through sialic mountain at the terminal position. Proteins associated with the glycocalyx function as transmembrane proteins that aid link the membrane come the cytoskeleton that the cell. This keeps the framework of the membrane certain and enables signal transduction between the intracellular and extracellular components.

The sarcolemma deserve to be excited electrically bring about the activation the muscle fibers by signal from motor nerves. The sarcolemma includes ion-conducting pathways and also channels through which sodium, potassium, calcium, and chloride flow selectively and also non-selectively.

These membrane pathways deserve to open in an answer to details molecules (ligands), transmitters, or when changes in voltage occur. The sarcolemma uses naturally developing regulatory procedures to close this pathways.

Just outside the sarcolemma, in call with the glycocalyx is the basement membrane. This offer to prevent additional diffusion the electrolytes and also maintaining support and shape because that the muscle fibers.


Sarcolemma Structure

Is sarcolemma a connective tissue? No, it is no connective tissue. The sarcolemma is the plasma membrane.

The sarcolemma is explained as having two layers. The first is the plasma membrane, i beg your pardon is a structure of comparable biochemical composition to the general plasma membrane uncovered in eukaryotic bio cells. The 2nd layer is the glycocalyx, i beg your pardon is in contact with the basement membrane. The basement membrane is wealthy in collagen fibrils and proteins that permit the muscle yarn to adhere come it. The cytoskeleton the the muscle cell, which is composed of a huge amount that the protein actin, is associated to the basement membrane through transmembrane protein in the plasma membrane. The ends of the muscle yarn fuse v tendon fibers, which consequently collect right into bundles to type muscle tendons. This attaches muscle yarn to the bone.

There space 3 great of connective tissue in muscles. These room the epimysium, the perimysium, and also the endomysium. The outermost great of connective tissue neighboring a bones muscle is the epimysium. The perimysium wraps about bundles that muscle fibers (fascicles) and also the endomysium wraps around the individual muscle fibers. So, what is the difference in between the sarcolemma vs endomysium? it is essential not to confuse this terms. The sarcolemma is the cabinet membrane that the muscle fiber, and also the endomysium is the connective organization layer end the muscle fiber. figure 2 shows the places of the 3 layers of connective tissue.

*
Figure 2: The class of Muscle Connective Tissue. Credit: Dustin Peters, “Muscular Sytem”. SlidePlayer.

To know the framework and role of the sarcolemma, us must an initial understand the framework of striated muscle tissue. Within muscle fibers, myofibrils are found running the size of the cell. Myofibrils have the right to be explained as systems of a muscle cell made up of organized proteins consists of sarcomeres. Hundreds to countless myofibrils can be discovered in each muscle fiber.

There room 2 varieties of myofibrils that are either comprised of special filaments or thin filaments. The protein actin predominantly creates the slim filaments in addition to proteins tropomyosin and also troponin. The protein myosin forms the thick filaments. These filaments overlap to type patterns that can be regarded under a microscope (striations).

Actin and myosin room the proteins associated in muscle contraction. These thin and thick filaments kinds to type bands well-known as A-bands and I-bands. “A” represents Anisotropic (because the filaments are stronger in one direction than the other) and “I” stands for isotropic (because they have actually the very same physical nature in any kind of direction). The A band consists of an H-zone wherein no overlap between the thin and thick filaments occurs. It consists only that the special filament and permits muscle contraction by coming to be shorter.

A sarcomere is a structural unit that striated muscle tissue. Sarcomeres are repeating units that occur between each Z line (or Z disc). The Z heat is the boundary in between each sarcomere. The sarcomere is created of myofibrils. The M line is in the facility of the sarcomere and also is the attachment site for the special filaments. The M line is written of protein myomesin, titin, obscurin, and obsl1. Figures 3 and also 4 present the structure of a sarcomere describe the various filaments and bands.

*
Figure 3: Striated muscle as soon as viewed under a microscope indicating the sarcomeres and the location of the I and also A bands. Source: amendment by Maria Victoria Gonzaga, lungemine.com, native the photograph of bones muscle in light microscopic lense at 400x magnification by Alexander G. Cheroske, CC BY-SA 4.0, and the electron micrograph of the banding that a muscle fiber by Purves et al., Life: The scientific research of Biology, 4th Edition, by Sinauer Associates and also WH Freeman.
*
Figure 4: The structure of a Sarcomere. Credit: Open learning Initiative, CC BY-NC-SA.

Now we have looked at the structure of the muscle tissue. We can understand much more about the plasma membrane of the muscle cells. As pointed out earlier, the plasma membrane the a skeleton muscle fiber is dubbed the sarcolemma. The sarcolemma invaginates into the cytoplasm of the muscle cabinet (sarcoplasm). This forms membranous tubules the pass throughout the muscle cells. These are dubbed transverse tubules (or ‘T tubules’). The T- tubules save on computer extracellular fluid, which is high in both calcium and also sodium ions.

See more: Uh Oh Uh Oh Uh Oh Oh No No By Speakrs, Uh Oh, Oh No No Lyrics

Inside the muscle fibers, the T-tubules lie close to enlarged areas of the sarcoplasmic reticulum recognized as terminal cisternae. 2 terminal cisternae found on either side of a T-tubule is recognized as a triad. There space thousands of triads in each muscle fiber. The sarcoplasmic illusion is discovered surrounding the myofibrils and also is made up of membrane-bound tubules. The sarcoplasmic reticulum features as a calcium store. Much more information about the sarcolemma duty is explained in more detail below. Figure 5 reflects the anatomical connection of the T-tubules, terminal cisternae, and also the sarcoplasmic reticulum, and also a microscopic photo of a triad.

*
Figure 5: in-depth schematic the a sarcomere denote the T-tubules, sarcoplasmic reticulum, a triad, and the terminal cisternae. Credit: Biomedcentral.com.