muscle tissue outline

8/13/2019 Muscle Tissue Outline

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Muscle TissueO Motion results from alternating contraction

(shortening) and relaxation of muscles; theskeletal system provides leverage and asupportive framework for this movement.

O The scientific study of muscles is known asmyology .

O 3 Types of Muscle Tissue O Skeletal muscle

O attaches to bone, skin or fasciaO striated with light & dark bands visible

with scopeO voluntary control of contraction &

relaxationO Cardiac muscle

O tissue forms the wall of the heart.O striated in appearanceO involuntary controlO autorhythmic because of built in

pacemakerO Smooth muscle

O tissue is located in viscera.O attached to hair follicles in skinO in walls of hollow organs -- blood vessels

& GIO nonstriated in appearanceO involuntary

O Functions of Muscle Tissue O Producing body movementsO Stabilizing body positionsO Regulating organ volumes

O bands of smooth muscle calledsphincters

O Movement of substances within the bodyO blood, lymph, urine, air, food and

fluids, spermO Producing heat

O involuntary contractions ofskeletal muscle (shivering)

O Properties of Muscle TissueO Excitability

O respond to chemicals releasedfrom nerve cells

O ConductivityO ability to propagate electrical

signals over membraneO Contractility

O ability to shorten and generateforce

O ExtensibilityO ability to be stretched without damaging

the tissueO Elasticity

O ability to return to original shape afterbeing stretched

SKELETAL MUSCLE TISSUEConnective Tissue Components Each skeletal muscle is a separate organcomposed of cells called fibers .Connective tissue components of the muscleincludeepimysium = surrounds the whole muscleperimysium = surrounds bundles (fascicles)endomysium = separates individual musclecellsAll these connective tissue layers extendbeyond the muscle belly to form the tendon

O Nerve and Blood SupplyO Each skeletal muscle is supplied by a

nerve, artery and two veins.O Each motor neuron supplies multiple

muscle cells (neuromuscular junction)O Each muscle cell is supplied by one motor

neuron terminal branch and is in contactwith one or two capillaries.

O nerve fibers & capillaries are found in theendomysium between individual cells

O Muscle Fiber or MyofibersO Muscle cells are long, cylindrical &

multinucleatedO Sarcolemma = muscle cell membraneO Sarcoplasm filled with tiny threads called

myofibrils & myoglobin (red-colored,oxygen-binding protein)

O Sarcolemma, T Tubules, and SarcoplasmO Skeletal muscle consists of fibers (cells)

covered by a sarcolemmaO The fibers contain T tubules and

sarcoplasmO T tubules are tiny invaginations of the

sarcolemma that quickly spread themuscle action potential to all parts of themuscle fiber.


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O Sarcoplasm is the muscle cell cytoplasm andcontains a large amount of glycogen for energyproduction and myoglobin for oxygen storage.

O Transverse TubulesO T (transverse) tubules are invaginations of the

sarcolemma into the center of the cellO filled with extracellular fluidO carry muscle action potentials down into

cellO Mitochondria lie in rows throughout the cell

O near the muscle proteins that use ATPduring contraction

O Myofibrils & MyofilamentsO Each fiber contains myofibrils that consist

of thin and thick filaments (myofilaments)O Muscle fibers are filled with threads called

myofibrils separated by SR (sarcoplasmicreticulum)

O The sarcoplasmic reticulum encircles eachmyofibril. It is similar to smoothendoplasmic reticulum in nonmuscle cellsand in the relaxed muscle stores calciumions.

O Myofilaments (thick & thin filaments) arethe contractile proteins of muscle

O Sarcoplasmic Reticulum (SR)O System of tubular sacs similar to smooth

ER in nonmuscle cellsO Stores Ca+2 in a relaxed muscleO Release of Ca+2 triggers muscle

contraction

O Filaments and the SarcomereO Thick and thin filaments overlap each

other in a pattern that creates striations(light I bands and dark A bands)

O The I band region contains only thinfilaments.

O They are arranged in compartments calledsarcomeres, separated by Z discs.

O In the overlap region, six thin filamentssurround each thick filament

O Thick & Thin MyofilamentsO shows the relationships of the zones,

bands, and lines as seen in a transmissionelectron micrograph.

O Supporting proteins (M line, titin and Zdisc help anchor the thick and thinfilaments in place)

O Thick & Thin Myofilaments OverlapO The Proteins of Muscle

O Myofibrils are built of 3 kinds of proteinO contractile proteins

O myosin and actinO regulatory proteins which turn contraction

on & offO troponin and tropomyosin

O structural proteins which provide properalignment, elasticity and extensibility

O titin, myomesin, nebulin anddystrophin

O The Proteins of Muscle Myosin

O Thick filaments are composed of myosinO each molecule resembles two golf clubs

twisted togetherO myosin heads (cross bridges) extend

toward the thin filaments

O Held in place by the M line proteins.

O Thin filaments are made of actin, troponin, &tropomyosin

O The myosin-binding site on each actinmolecule is covered by tropomyosin inrelaxed muscle

O The thin filaments are held in place by Zlines. From one Z line to the next is asarcomere.

O Structural ProteinsO Structural proteins keep the thick and thin

filaments in the proper alignment, givethe myofibril elasticity and extensibility,and link the myofibrils to the sarcolemmaand extracellular matrix.

O Titin helps a sarcomere return to itsresting length after a muscle hascontracted or been stretched.

O Myomesin forms the M line.O Nebulin helps maintain alignment of the

thin filaments in the sarcomere.O Dystrophin reinforces the sarcolemma and

helps transmit the tension generated bythe sarcomeres to the tendons.

O Sliding Filament Mechanism Of ContractionO Myosin cross bridges

pull on thin filamentsO Thin filaments slide

inward


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O Z Discs come towardeach other

O Sarcomeres shorten.The muscle fibershortens. The muscle shortens

O O Three Types of Muscle Fibers1) Fast (or White) Fibers Fast contraction after nervous stimulation Large diameter large glycogen reserve few mitochondria densely packed myofibrils Fatigue fast due to mainly anaerobic respiration

O 2) Slow (or Red) Fibers Slower but continuous contraction for extended

periods Smaller diameter (~ half) contain myoglobin more capillaries more mitochondria

O 3) Intermediate Fibers Have attributes inbetween fast and slow types Most skeletal muscles contain mixture of fiber

types.

Overview: How Does Contraction Begin?1. Nerve impulse reaches an axon terminal2.synaptic vesicles release acetylcholine (ACh)

3. ACh diffuses to receptors on the sarcolemma4. stimulus provided by binding of ACh to the

sarcolemma;5. Na+ channels open and Na+ rushes into the cell6. resulting action potential travels along sarcolemmaand into T tubules, triggering release of calcium ionsfrom SR;

7. calcium ions bind to troponin; resulting shapechange causes myosin binding site to be exposed;8. myosin heads bind to actin, and swivel (powerstroke), pulling Z discs closer together, shorteningmyofiber.-the contraction cycle begins

Relaxation Acetylcholinesterase (AChE) breaks down ACh

within the synaptic cleft Muscle action potential ceases

Ca+2 release channels close Active transport pumps Ca2+ back into storage in

the sarcoplasmic reticulum Calcium-binding protein (calsequestrin) helps hold

Ca+2 in SR (Ca+2 concentration 10,000 times

higher than in cytosol) Tropomyosin-troponin complex recovers binding

site on the actin

Neuromuscular Junction (NMJ) or Synapse NMJ = myoneural junction end of axon nears the surface of a muscle

fiber at its motor end plate region (remainseparated by synaptic cleft or gap)

CARDIAC MUSCLE

Striated , short, quadrangular-shaped, branchingfibers

Single centrally located nucleus Cells connected by intercalated discs with gap

junctions Same arrangement of thick & thin filaments as

skeletal

CARDIAC MUSCLE TISSUE - Overview Cardiac muscle tissue is found only in the

heart wall Its fibers are arranged similarly toskeletal muscle fibers.

Cardiac muscle fibers connect to adjacentfibers by intercalated discs which containdesmosomes and gap junctions

Cardiac muscle contractions last longer thanthe skeletal muscle twitch due to theprolonged delivery of calcium ions from thesarcoplasmic reticulum and the extracellularfluid.

Cardiac muscle fibers contract whenstimulated by their own autorhythmic fibers.

This continuous, rhythmic activity is a majorphysiological difference between cardiac andskeletal muscle tissue.


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Appearance of Cardiac Muscle Striated muscle containing thick & thin

filaments T tubules located at Z discs & less SR Physiology of Cardiac Muscle Autorhythmic cells contract without stimulation Contracts 75 times per min & needs lots of O2 Larger mitochondria generate ATP aerobically Extended contraction is possible due to slow

Ca+2 delivery Ca+2 channels to the extracellular fluid stay

open

SMOOTH MUSCLE Smooth muscle tissue is nonstriated and

involuntary and is classified into two types:visceral (single unit) smooth muscle and multiunitsmooth muscle

Visceral (single unit) smooth muscle is found in thewalls of hollow viscera and small blood vessels;the fibers are arranged in a network and function

as a single unit. Multiunit smooth muscle is found in large blood

vessels, large airways, arrector pili muscles, andthe iris of the eye. The fibers operate singly ratherthan as a unit.

Two Types of Smooth Muscle Visceral (single-unit)

in the walls of hollow viscera & small BV autorhythmic

Multiunit individual fibers with own motor neuron

ending

found in large arteries, large airways,arrector pili muscles,iris & ciliary body

Microscopic Anatomy of Smooth Muscle Sarcoplasm of smooth muscle fibers contains

both thick and thin filaments which are notorganized into sarcomeres.

Smooth muscle fibers contain intermediatefilaments which are attached to dense bodies.

Small, involuntary muscle cell -- tapering at ends Single, oval, centrally located nucleus Lack T tubules & have little SR for Ca+2 storage

Microscopic Anatomy of Smooth Muscle Thick & thin myofilaments

not orderly arranged so lacks sarcomeres Sliding of thick & thin filaments generates

tension Transferred to intermediate filaments & dense

bodies attached to sarcolemma Muscle fiber contracts and twists into a helix

as it shortens -- relaxes by untwisting

Physiology of Smooth Muscle Contraction starts slowly & lasts longer

no transverse tubules & very little SR Ca+2 must flows in from outside In smooth muscle, the regulator protein that

binds calcium ions in the cytosol is calmodulin (in place of the role of troponin in striatedmuscle);

calmodulin activates the enzyme myosin lightchain kinase , which facilitates myosin-actinbinding and allows contraction to occur at arelatively slow rate.

Peristalsis Peristalsis alternating contractions and

relaxations of smooth muscles that mix andsqueeze substances through the lumen ofhollow organs

muscle tissue outline

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