Muscle tissue is responsible for mosttypes of human body movement.

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I. Types that muscle:

A. Striated muscle - skeletal musculature, striated in appearanceunder microscope. Cells space unbranched and are multinucleate syncytia. Thesemuscles are capable of voluntary, quick, forceful contractions.

B. Cardiac muscle - heart muscle, striated, cells may bebranched. Cardiac muscle cells are either mono- or binucleate cells. They areconnected through one and other by dedicated junctional complexes calledintercalated disks. Cardiacmuscle is capable of involuntary, strong, rhythmic contractions

C. Smooth muscle - this muscle is not striated and also is uncovered inthe walls of the visceral organs. Mononucleate cells. In enhancement tocontraction, smooth muscle cell synthesize collagen, elastin, andproteoglycans (like fibroblasts). These muscle cell are capable of relativelyslow contractions as compared to those of striated or cardiac muscle.

II. Basic systems of muscle cellorganization

A. sarcolemma - plasmalemma the muscle cells. Exterior to thiscell membrane is a well developed basement membrane.

B. sarcoplasm - cytoplasm of muscle cell excluding themyofibrils.

C. sarcoplasmic reticulum - smooth endoplasmic reticulum of muscle cells.

D. epimysium - special layer of collagenous connective tissuethat separates large bundles that muscle.

E. perimysium - collagenous connective tissue that separatessmaller bundles of muscle cells referred to as fascicles.

F. fascicle - bundle of muscle cell bounded by perimysium.

G. endomysium - thinner layer the connective tissue thatseparates separation, personal, instance muscle cells.

III. Skeleton muscle

A. Connective tissue in the kind of epimysium,perimysium, and endomysium surrounds the components of striated muscle asdescribed above.

B. Bones muscle is generally associated tobone via a item of connective tissue referred to as a tendon.

C. As stated above, individual muscle cellsare syncytial (That is tosay, each striated muscle cell includes multiple nuclei (multinucleate).

D. Every individual muscle cabinet is dubbed a musclefiber. In ~ the sarcoplasm of these cells are myofibrils created of repeating sarcomere systems (see below). These sarcomeres room theactual contractile apparatus.

E. The myofibrils are direct arrays ofstructures well-known as sarcomeresthat room arranged in an finish to end repeating pattern. The sarcomeres containfilaments the actin and myosinthat connect to causecontraction of the muscle cells. See below for sarcomere structure.

F. If us look at the membranous surface ar of a skeletal,muscle cabinet we uncover multiple synapses from engine neurons in the main nervous system. This synapsesare referred to as myoneural junctions.Within the swollen ends of the axons that call the muscle cell are smallvesicles referred to as synaptic vesiclesthat save on computer acetylcholine.When a nervous impulse (action potential) get the synapse, the components of these vesicles are released intothe gap between the axon and also the muscle cell and also are responsible for initiatingan electric action potentialin the sarcolemma that reasons the muscle come contract.

IV. The straightforward Sarcomere Unit ofStriated Muscle


A. The simple unit of striated muscle, thesarcomere is diagramed above. It is written of thin actin and also thick myosinfilaments (as well as a variety of other molecules) i ordered it in aninterdigitated straight array. This molecules kind the sarcomere unit, thatconsists of,

A-band (Anisotropic band) - area containing overlapping actin andmyosin filaments accept in H-band region.

H-band - area that myosin filaments where there isno over lap of actin filaments.

I-band (Isotropic band) - thin actin filaments +Z-line.

Z-line - wherein actin filaments the adjacentsarcomeres are anchored.

M-line - formed by connections in between thecentral portions of surrounding myosin filaments.

B. Let"s think about at the muscle cell because that amoment and consider just how it contracts.

C. In skeletal muscle, contraction is undervoluntary control. Ns decide to raise my arm for instance. Worried stimuli inthe kind of electric activity potentials are transmitted follow me motor nerves tothe muscles came to with raising the arm. This impulses reason the relax ofacetylcholine in synaptic vesicles in ~ the myoneural junctions top top the musclecells. This reasons an activity potential in the sarcolemma the is sent along the surface ar of the muscle cell.

D. The bones muscle cell surface containsmany tubular invaginations that prolong through the cell sarcoplasm and aroundthe individual myofibrils. These structures effectively lug the electricalimpulse right into the interior of the cell. In this way, the activity potentialreaches the sarcoplasmic delusion of the cell much much more quickly than it wouldin the electric impulse had to happen from the surface of the cell right into thecytoplasm to with the sarcoplasmic reticulum.

E. The action potential reasons the sarcoplasmicreticulum to relax Ca+2 ions.

F. These bind to a website on the troponinmolecules the the slim actin filaments. This reasons the troponin molecule tochange shape and also expose a site on the actin that can bind the side chains ofheavy meromysin on the special myosin filaments. This binding catalyses areaction that breaks under ATP that is bound come the myosin side chains, thusreleasing power that reasons the hefty meromysin next chain to bend. As thenumerous meromysin side chains tie to the actin filament and also bend with each other inthe exact same direction (the net bending after ~ binding come actin is toward the Mline), the actin and myosin filaments slide over each other. This movementlines up other actin and also heavy meromyosin molecule which deserve to bind and also bend tomove the filaments further. As the task rapidly repeats itself, the overlapof filaments i do not care complete and the I-bands and also H-bands the the sarcomeres becomethinner until the muscle relaxes.

G. This sort of activity in thousands of repeatingsarcomeres of every myofibril in the cell reasons considerable diminish in themuscle cell length.

H. The ATP for every this activity comes fromnumerous mitochondria (called sarcosomes) the are linked with themyofibrils. During contraction, power is initially obtained from ATP andphosphocreatine from stores existing in the sarcoplasm. As activity continues,the mitochondria metabolise glucose derived from glycogen molecules the arestored in the sarcoplasm in order come provide an ext ATP.

I. Oxygen is obviously essential formitochondrial metabolism of glucose. In order to carry out enough oxygen, themuscle cells likewise contain myoglobulin which is one oxygen binding proteinsimilar come hemoglobulin and also has a high affinity for oxygen. This renders itpossible for the muscle cells to have actually a prepared store the oxygen ~ above hand because that theiractivity. It also permits them to traction oxygen out of the blood in ~ a high rate sothat the high metabolic rates can be maintained.

V. Cardiac muscle

A. Unlike skeletal muscle, cardiac muscle cellsare no a syncytium for the most part, though part cells may have actually two nuclei.

B. The framework of cardiac muscle cells issimilar to that of striated skeletal muscle in that myofibrils and sarcomeresare existing with activity mediated by release of Ca+2 native sarcoplasmicreticulum.

C. The major differences between these twomuscle types are that the cardiac muscle cells room branched and are heldtogether by intercalated disks. They room also shorter in length than skeletal musclecells.

1. Intercalated disks are devoted junctional complexes that bindcardiac muscle cells together. These so-called disks space interdigitatingregions that the plasmalemma of nearby cardiac muscle cell that organize the cellstogether. The intercalated disks form the irregular, jagged, dark lines thatare characteristic watched in appropriately stained cardiac muscle sections.

2. This junctional complicated is written of anumber of frameworks that are arranged along surrounding muscle cell plasmalemmasin a repeating array,

a. desmosomes (macula adherens) - previously describedstructures that host cells together. Situated between surrounding myofilaments.

b. fascia (zonula) adherens - whereby the myofilaments the the sarcomeres atthe end of myofibrils adhere come the sarcolemma. Situated where myofilaments endat the muscle cell plasmalemma.

c. gap junctions are current - connectiong between muscle cellsthat allow transfer of ions in between them. This permits the cell to coordinatetheir activities. Activity potentials have the right to spread quickly in between the sarcoplasmicreticulum the cardiac muscle cells via gap junctions. Thus, cardiac muscle cellscan coordinate your movements. The space junctions are situated along theplasmalemmas of adjacent muscle cell in the regions between myofilaments.

D. Cardiac muscle cells likewise have a transversetubule system present, however itis not as regular as the sarcolemma device of skeletal muscle and there arefewer T-tubules.

VI. Smooth muscle

A. This type of muscle consists of long, overlapping,spindle shaped cell that have some features that are similar to thoseof fibroblasts.

B. Smooth muscle cell similarity to fibroblastsis obvious in that they are able to synthesize collagen, elastin, andproteoglycans

C. There space no sarcomere structures, however filamentsof actin and a kind of myosin room present. Thus, convulsion is lot lessorganized and also occurs an ext slowly than it walk in striated or cardiac muscle.Another factor for this slower contraction is that smooth muscle cells execute notcontain a transverse tubule system. (Also check out G. Below)

D. Due to the fact that the actin and also myosin filaments space notconstrained by a sarcomere/myofilament arrangement, the actin and also myosinfilaments room able to accomplish a greater degree of overlap as soon as they contractresulting in a greater level of contraction.

E. When smooth muscle cell are sluggish tocontract, they have actually the ability to remain contracted for lengthy periods of time.

F. The bundles of smooth muscle are arranged asfascicles similar to what is viewed in striated and also cardiac muscle, Thus, aperimysium with endomysium between cells and also epimysium deliniating majority offascicles can be identified. However, in sectioned tissue, this arrangement is oftennot really evident, presumably because the areas of connective tissue are muchthinner 보다 those the cardiac and skeletal muscle.

G. The contaction the smooth muscle cell isinvoluntary and also the neuromuscular junctions regulating contractile rhythms possibly on the bordering epimysium rather than directly on muscle cells. Together aresult, neurotransmitters have to diffuse across this connective organization layerand top top the plasmalemma the the smooth muscle cell in order to initiate theaction potential that causes contraction. This is another reason because that the slowercontraction that smooth muscle cells.

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H. Smooth muscles exhibit spontaneouscontractile activity (doesn"t require nervous stimulation). Thus, theinnervation the is present acts to modify the contractile activity rather thaninitiate it.