Sarcolemma n. The thin, transparent, extensible membrane spanning every striated muscle fiber Source: modified by Maria Victoria Gonzaga, invernessgangshow.net, from the occupational of OpenStax, CC BY-SA 4.0..

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Sarcolemma Definition

What is the sarcolemma? that is the thin, transparent, extensible plasma membrane of the muscle cell. It consists of a cell membrane (plasma membrane) and also an outer coat made up of a thin layer the polysaccharide (glycocalyx) material with countless thin collagen fibrils. Etymologically, what execute you median by sarcolemma?Sarco’ comes from the Greek (sarx) an interpretation “flesh”, and also ‘lemma’ comes from the Greek meaning “sheath”.

Sarcolemma (biology definition): the thin, transparent, extensible membrane extending every striated muscle fiber. That is structure and also design is vital in receiving and also conducting stimuli. At every finish of the muscle fiber, the outer layer that the sarcolemma fuses through tendon fibers, which consequently collect right into bundles to type muscle tendons. Etymology: native sarco– + Greek lemma, definition “husk”. Synonyms: myolemma.
Figure 1: What carry out you median by sarcolemma? The muscle cell membrane is dubbed the sarcolemma. Source: CNX OpenStax.

Characteristics that Sarcolemma

The sarcolemma anatomy have the right to be identified as the plasma membrane of a muscle cabinet or the plasma membrane of a muscle fiber. Muscle cells are also known as muscle fibers as result of their long, cylindrical shape.

The sarcolemma is extended by a glycocalyx. How carry out we define glycocalyx? The glycocalyx is a coating extending the cabinet membrane. The is written of glycosaminoglycans (GAGs), proteoglycans, and other glycoproteins the consist of acidic oligosaccharides through sialic acids at the terminal position. Proteins linked with the glycocalyx function as transmembrane proteins that assist link the membrane come the cytoskeleton that the cell. This keeps the structure of the membrane secure and permits signal transduction between the intracellular and also extracellular components.

The sarcolemma deserve to be excited electrically causing the activation of muscle fibers by signals from motor nerves. The sarcolemma has ion-conducting pathways and also channels with which sodium, potassium, calcium, and chloride circulation selectively and non-selectively.

These membrane pathways can open in response to particular molecules (ligands), transmitters, or when changes in voltage occur. The sarcolemma supplies naturally developing regulatory procedures to close this pathways.

Just external the sarcolemma, in call with the glycocalyx is the basement membrane. This offer to prevent further diffusion of electrolytes and 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 actually two layers. The first is the plasma membrane, i m sorry is a framework of comparable biochemical ingredient to the general plasma membrane discovered 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 rich in collagen fibrils and proteins that allow the muscle fibers to adhere come it. The cytoskeleton of the muscle cell, which is composed of a large amount the the protein actin, is linked to the basement membrane with transmembrane proteins in the plasma membrane. The ends of the muscle fibers fuse v tendon fibers, which subsequently collect right into bundles to kind muscle tendons. This attaches muscle fibers to the bone.

There are 3 class of connective tissue in muscles. These space the epimysium, the perimysium, and also the endomysium. The outermost class of connective tissue neighboring a skeletal muscle is the epimysium. The perimysium wraps around bundles of muscle fibers (fascicles) and also the endomysium wraps around the individual muscle fibers. So, what is the difference between the sarcolemma vs endomysium? that is essential not to confuse these terms. The sarcolemma is the cabinet membrane of the muscle fiber, and the endomysium is the connective tissue layer end the muscle fiber. number 2 shows the places of the 3 class of connective tissue.

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

To know the structure and role of the sarcolemma, us must an initial understand the framework of striated muscle tissue. Within muscle fibers, myofibrils are found running the length of the cell. Myofibrils deserve to be defined as devices of a muscle cell made up of organized proteins consist of of sarcomeres. Hundreds to hundreds of myofibrils can be uncovered in every muscle fiber.

There are 2 types of myofibrils that space either made up of special filaments or thin filaments. The protein actin predominantly creates the thin filaments together with proteins tropomyosin and troponin. The protein myosin forms the thick filaments. These filaments overlap to type patterns that deserve to be regarded under a microscopic lense (striations).

Actin and myosin are the proteins involved in muscle contraction. This thin and also thick filaments kinds to kind 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 the same physical properties in any direction). The A band includes an H-zone where no overlap between the thin and thick filaments occurs. It is composed only the the special filament and permits muscle convulsion by ending up being shorter.

A sarcomere is a structure unit of striated muscle tissue. Sarcomeres are repeating devices that occur between each Z line (or Z disc). The Z heat is the boundary in between each sarcomere. The sarcomere is composed of myofibrils. The M line is in the facility of the sarcomere and is the attachment site for the special filaments. The M line is created of proteins myomesin, titin, obscurin, and obsl1. Figures 3 and also 4 display the structure of a sarcomere denote the different filaments and also bands.

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

Now we have actually looked at the structure of the muscle tissue. We deserve to understand an ext about the plasma membrane the the muscle cells. As discussed earlier, the plasma membrane the a skeleton muscle fiber is called the sarcolemma. The sarcolemma invaginates into the cytoplasm that the muscle cell (sarcoplasm). This develops membranous tubules the pass across the muscle cells. This are referred to as transverse tubules (or ‘T tubules’). The T- tubules save on computer extracellular fluid, i beg your pardon is high in both calcium and also sodium ions.

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Inside the muscle fibers, the T-tubules lie close come enlarged areas of the sarcoplasmic reticulum known as terminal cisternae. Two terminal cisternae discovered on either side of a T-tubule is recognized as a triad. There room thousands the triads in each muscle fiber. The sarcoplasmic illusion is found surrounding the myofibrils and also is made up of membrane-bound tubules. The sarcoplasmic reticulum features as a calcium store. More information regarding the sarcolemma duty is explained in an ext detail below. Figure 5 reflects the anatomical partnership of the T-tubules, terminal cisternae, and the sarcoplasmic reticulum, and also a microscopic image of a triad.

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