This is the very first of a two component series explaining howmuscles work. In this an initial article I explain the gross structure of skeletalmuscle; in the 2nd article I describe skeletal muscle ultrastructure and howmuscles construct tension.

You are watching: Connective tissue that surrounds a muscle

Gross framework of skeletal Muscle

Humans own three varieties of muscle—cardiac, smooth, and also skeletal—each exhibiting distinct functional and also anatomical differences, watch below.


Cardiac muscle residesonly in the heart. It share several usual features with skeletal muscle asboth show up striated (striped) under low-magnification microscopic examinationand both shorten (contract) in a comparable manner. Smooth muscle lacks a striatedappearance yet shares cardiac muscle’s characteristics of nonconsciousregulation under autonomic nervous system control. Bones muscle operatesunder voluntary control, as incurling a 25-lb barbell.

Individuals deserve to easilycontrol the velocity of activity in a barbell curl, the variety of movement duringthe lifting movement, and the variety of repetitions completed. In golf, theplayer controls all facets of the coordinated and also hopefully perfectly timedmovements of the arms, legs, and also torso during the backswing and also downswing. Adifferent situation exists for both cardiac and also smooth muscle organization becauseactivity of these tissues wake up involuntarily,although mediation from central centers have the right to exert some influence. This means ageneral lack of mindful control as to how rapid the love beats, or howfast food moves v the cradle system, or how the mile of blood vesselscontract and expand transparent the day.


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

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

Each that the body’sapproximately 600-plus skeletal muscles contain miscellaneous wrappings of fibrousconnective tissue. This long, slender, multinucleated yarn lie parallel toeach other, v the pressure of activity directed follow me the fiber’s long axis.Their number more than likely remains greatly fixed by the second trimester of fetaldevelopment. Individual fiber length varies indigenous a few millimeters in the eyemuscles to practically 30 centimeter in the large 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 that from neighboring fibers. An additional layer that connective tissue, the perimysium, surrounds a bundle of approximately 150 fibers referred to as a fasciculus. A fascia that fibrous connective tissue, the epimysium, surrounds the entire muscle. This security sheath tapers at its distal and also proximal ends as it blends into and also joins the intramuscular organization sheaths to form the tendon’s dense, solid connective tissue. Tendons attach both ends of the muscle to the periosteum, the bone’s outermost covering.

FYI— Tendinitis, a condition of tendon inflammation, most frequently occurs native trauma at the patellar tendon the the knee (common in basketball and also volleyball athletes) and other body regions. These incorporate the Achilles an ar of the fishing eye (common in sporting activities requiring high affect during lunging and also jumping activities), or at the attachments of the rotator cuff muscles, a group of muscles and also their tendons the act to stabilize the shoulder (common in sporting activities that indicate high-velocity baseball pitching, shotput, or discuss throwing). Tendinitis likewise can occur from overuse and putting four through excessive movements that exceed the joints’ normal range of motion. In much less severe tendon trauma, usual therapies encompass nonsteroidal anti-inflammatory medications (NSAIDs), immobilization, ice, and also rest, with progressive return to regular physical activities.

The tissues of thetendon intermesh with the collagenous fibers in ~ bone. This forms a powerfullink in between muscle and also bone that continues to be inseparable except during severestress when the tendon deserve to sever or literally pull away from the bone. Once thetendon attaches come the end of a long bone, the bone it is adapted by enlarging in ~ thatend to produce a much more stable union.

The pressure of muscleaction transmits directly from the connective tissue harness come the tendons,which climate pull ~ above the bone at the allude of attachment. The pressures exerted onthe tendinous attachments under muscular exertion variety from 20 come 50 N (197 to492 kg) per cm2 that cross-sectional area—forces often larger 보다 themuscle yarn themselves can tolerate.

The muscle’s origin refers to the place where thetendon joins a reasonably stable skeletal part, generally the proximal or fixedend that the lever system or the nearest the body’s midline; the suggest of distalmuscle attachment to the relocating bone to represent the insertion.

Beneath the endomysiumand surrounding each muscle fiber lies the sarcolemma,a thin, elastic membrane that encloses the fiber’s moving contents. Itcontains a plasma membrane (plasmalemma) and also a basement membrane. In between thebasement and plasma membrane lie myogenic stem cells known as satellite cells, this normallyquiescent myoblasts role in regenerative moving growth carry out possibleadaptations to exercise training and recovery indigenous injury.

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

Muscles’ chemistry Composition

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

Muscles’ BloodComposition

Arteries andveins the lie parallel to separation, personal, instance muscle fibers carry out a richvascular supply. This vessels division into numerous arterioles, capillaries,and venules to form a diffuse network in and around the endomysium.Extensive branching of blood vessels ensures every muscle fiber an adequateoxygenated blood it is provided from the arterial system and also rapid removed of carbondioxide in the venous circulation. During vigorous physical task for anelite endurance athlete, the muscle’s oxygen uptake increases almost 70 timesto approximately 11 mL per 100 g every minute. The local vascular bed deliverslarge amounts of blood through active tissues to accommodate this oxygenrequirement. Blood flow distribution fluctuates in rhythmic running, swimming,cycling, and other similar activities. Circulation decreases throughout the muscle’scontraction phase and also increases throughout relaxation to administer an auxiliary“milking action” that moves blood v the muscles and propels it via thevenous system back to the heart. In between 200 and 500 capillaries provide bloodto each square millimeter of active muscle cross section, v up to fourcapillaries straight contacting every fiber. In endurance athletes, five toseven capillaries surround each fiber; this optimistic adaptation guarantee greaterlocal blood flow and also adequate tissue oxygenation as soon as needed.

Physicalactivities that require “straining” (i.e., exerting force versus an immovableobject) existing a somewhat different snapshot for muscle blood flow. When amuscle generates about 60% the its force-generating volume for severalseconds, elevated intramuscular press occludes regional blood flow during thecontraction. With a continual high-force contraction, the intramuscularhigh-energy phosphates and glycolytic anaerobic reactions provide the mainenergy resource for muscular effort.


Trained muscles’ increased capillary-to-muscle fiber ratio helps to define improved exercise capacity with endurance training. An enhanced capillary microcirculation expedites removed of heat and metabolic byproducts from active tissues in enhancement to facilitating distribution of oxygen, nutrients, and also hormones. Electron microscopy discover the total variety of capillaries per muscle and capillaries per mm2 the muscle organization averages about 40% higher in endurance-trained athletes 보다 untrained counterparts. Enhanced vascularization at the capillary level proves particularly beneficial during tasks that require a high level of steady-rate aerobic metabolism. Vascular stretch and also shear anxiety on the vessel wall surfaces from enhanced blood flow during exercise wake up capillary advancement with intense aerobic training.

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

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Eighth Edition. Wolters KluwerPubl. 2015.