This is the first of a two component series explaining howmuscles work. In this an initial article I describe the gross structure of skeletalmuscle; in the second article I describe skeletal muscle ultrastructure and also howmuscles develop tension.

You are watching: The fibrous connective tissue that wraps muscle is called

Gross framework of skeletal Muscle

Humans possess three species of muscle—cardiac, smooth, and skeletal—each exhibiting distinctive functional and also anatomical differences, watch below.


Cardiac muscle residesonly in the heart. It share several common features with skeletal muscle asboth appear striated (striped) under low-magnification microscope examinationand both shorten (contract) in a similar manner. Smooth muscle lacks a striatedappearance however shares cardiac muscle’s characteristic of nonconsciousregulation under autonomic nervous system control. Skeleton muscle operatesunder voluntary control, together incurling a 25-lb barbell.

Individuals have the right to easilycontrol the velocity of activity in a barbell curl, the selection of movement duringthe lifting movement, and also the variety of repetitions completed. In golf, theplayer controls all elements of the coordinated and also hopefully perfect timedmovements the the arms, legs, and torso during the backswing and downswing. Adifferent instance exists for both cardiac and smooth muscle organization becauseactivity of these tissues occurs involuntarily,although mediation from main centers deserve to exert part influence. This way ageneral lack of conscious control as to how rapid the heart beats, or howfast food moves with the digestive system, or just how the mile of blood vesselscontract and also expand transparent the day.


The figure below illustrates a cross section of bones muscle structures and arrangement the connective organization wrappings, consisting of the hundreds of cylindrical wells called fibers.

Top: Endomysium covers individual muscle fibers. The perimysium surrounds groups of fibers called fasciculi, and also epimysium wraps the whole muscle in a sheath of connective tissue. The sarcolemma, a thin, elastic membrane covers the surface of each fiber. Bottom: Cross section of the sarcoplasmic reticulum and T-tuble mechanism that surrounding the myofibril.

Each of the body’sapproximately 600-plus skeletal muscles contain various wrappings that fibrousconnective tissue. These long, slender, multinucleated fibers lie parallel toeach other, through the pressure of activity directed along the fiber’s lengthy axis.Their number probably remains mostly fixed by the 2nd trimester of fetaldevelopment. Individual fiber length varies native a few millimeters in the eyemuscles to almost 30 centimeter in the huge antigravity leg muscles (with widthreaching 0.15 mm).

Skeletal Muscle Organization

The endomysium, a well layer of connective tissue, wraps every muscle fiber and also separates it from surrounding fibers. One more layer that connective tissue, the perimysium, surrounding a bundle of as much as 150 fibers dubbed a fasciculus. A fascia the fibrous connective tissue, the epimysium, surrounds the whole muscle. This security sheath tapers in ~ its distal and proximal ends together it blends into and also joins the intramuscular organization sheaths to form the tendon’s dense, solid connective tissue. Tendons connect both end of the muscle come the periosteum, the bone’s outermost covering.

FYI— Tendinitis, a condition of tendon inflammation, most generally occurs indigenous trauma at the patellar tendon of the knee (common in basketball and volleyball athletes) and also other body regions. These encompass the Achilles an ar of the ankle (common in sports requiring high affect during lunging and jumping activities), or in ~ the attachments of the rotator cuff muscles, a team of muscles and their tendons the act come stabilize the shoulder (common in sports that show off high-velocity baseball pitching, shotput, or discuss throwing). Tendinitis likewise can take place from overuse and putting four through too much movements the exceed the joints’ normal selection of motion. In much less severe tendon trauma, typical therapies incorporate nonsteroidal anti-inflammatory medications (NSAIDs), immobilization, ice, and also rest, with progressive return to common physical activities.

The tissues of thetendon intermesh with the collagenous fibers within bone. This develops a powerfullink in between muscle and also bone that stays inseparable except during severestress once the tendon can sever or literally pull far from the bone. As soon as thetendon attaches come the end of a lengthy bone, the bone adapts by enlarging at thatend to create a more stable union.

The force of muscleaction transmits directly from the connective organization harness to the tendons,which climate pull on the bone in ~ the point of attachment. The pressures exerted onthe tendinous attachments under muscular exertion range from 20 to 50 N (197 to492 kg) every cm2 the cross-sectional area—forces often larger than themuscle fibers themselves have the right to tolerate.

The muscle’s origin describes the place where thetendon joins a relatively stable bones part, normally the proximal or fixedend of the lever system or that nearest the body’s midline; the allude of distalmuscle attachment to the relocating bone represents the insertion.

Beneath the endomysiumand neighboring each muscle fiber lies the sarcolemma,a thin, elastic membrane the encloses the fiber’s to move contents. Itcontains a plasma membrane (plasmalemma) and also a basement membrane. In between thebasement and also plasma membranes lie myogenic stem cells recognized as satellite cells, these normallyquiescent myoblasts duty in regenerative to move growth provide possibleadaptations to exercise training and recovery from injury.

Incorporation of satellite cabinet nuclei into existing muscle fibers appears a likely explanation for exercise-induced muscle fiber hypertrophy. The fiber’s aqueous protoplasm or sarcoplasm contains enzymes, fat and glycogen particles, nuclei (approximately 250 every mm that fiber length) that contain the genes, mitochondria, and also other devoted organelles. The sarcoplasmic reticulum, substantial longitudinal latticelike network of tubular channels and also vesicles offers structural integrity to the cell.

Muscles’ chemistry Composition

Waterconstitutes about 75% of skeleton muscle fixed while protein composes20%. The continuing to be 5% consists of salts and other substances, includinghigh-energy phosphates; urea; lactate; the mineral calcium, magnesium, andphosphorus; various enzymes; sodium, potassium, and chloride ions; and also aminoacids, fats, and also carbohydrates. The many abundant muscle protein includetitin, the biggest protein in the body consisting the 27,000 amino acids(accounts for around 10% the muscle mass), myosin (approximately 60% the muscleprotein), actin, and tropomyosin. Each 100 g that muscle tissue has about700 mg the the oxygen-binding, conjugated protein myoglobin.

Muscles’ BloodComposition

Arteries andveins that lie parallel to separation, personal, instance muscle fibers provide a richvascular supply. This vessels divide into plenty of arterioles, capillaries,and venules to kind a diffuse network in and also around the endomysium.Extensive branching of blood ship ensures each muscle fiber an adequateoxygenated blood it is provided from the arterial system and rapid remove of carbondioxide in the venous circulation. Throughout vigorous physical task for anelite endurance athlete, the muscle’s oxygen absorb increases practically 70 timesto about 11 mL every 100 g every minute. The neighborhood vascular bed deliverslarge amounts of blood through active tissues to accommodate this oxygenrequirement. Blood flow distribution fluctuates in rhythmic running, swimming,cycling, and also other similar activities. Circulation decreases throughout the muscle’scontraction phase and also increases during relaxation to carry out an auxiliary“milking action” the moves blood with the muscles and also propels the via thevenous system ago to the heart. In between 200 and also 500 capillaries deliver bloodto each square millimeter of active muscle overcome section, v up come fourcapillaries straight contacting every fiber. In endurance athletes, 5 toseven capillaries surround every fiber; this hopeful adaptation ensures greaterlocal blood flow and adequate tissue oxygenation once needed.

Physicalactivities that call for “straining” (i.e., exerting force versus an immovableobject) current a rather different photo for muscle blood flow. When amuscle generates around 60% the its force-generating volume for severalseconds, elevated intramuscular pressure occludes regional blood flow during thecontraction. V a sustained high-force contraction, the intramuscularhigh-energy phosphates and also glycolytic anaerobic reactions carry out the mainenergy resource for muscular effort.


Trained muscles’ boosted capillary-to-muscle fiber ratio helps to describe improved exercise capacity through endurance training. An amplified capillary microcirculation expedites removal of heat and also metabolic byproducts from active tissues in addition to facilitating delivery of oxygen, nutrients, and hormones. Electron microscopy expose the total variety of capillaries every muscle and capillaries every mm2 of muscle tissue averages about 40% higher in endurance-trained athletes than untrained counterparts. Intensified vascularization in ~ the capillary level proves an especially beneficial during activities that call for a high level that steady-rate aerobic metabolism. Vascular stretch and also shear stress on the vessel walls from boosted blood flow during exercise stimulate capillary development with intense aerobic training.

Source:McArdle WD,Katch FI, Katch VL. Exercise Physiology:Nutrition Energy, and Human Performance.

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Eighth Edition. Wolters KluwerPubl. 2015.