Muscular Tissue

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   ½ Overview and classification of muscles. ½ Skeletal muscles ½ Myofibrils and myofilaments ½ The contraction cycle ½ Motor innervation ½ Sensory innervation ½ Development ,healing & repair ½ Cardiac muscle ½ Structure of cardiac muscle ½ Injury and repair ø
 



½ Smooth muscles ½ Structure of smooth muscle ½ Functional aspects of smooth muscle ½ Renewal repair and differentiation

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¥    ½ Muscle tissue is 
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Skeletal muscle: which is striated and voluntary Cardiac muscle: which is striated and involuntary Smooth muscle: which is non striated and involuntary

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½ ¥     : a muscle cell ½ :C   the plasma membrane of a muscle cell,its external lamina & its surrounding reticular fibers. ½ C µ  the cytoplasm of the muscle cell ½ C µ    : the endoplasmic reticulum of a muscle cell ½ C µ : the mitochondria of a muscle cell ½ C : the contractile or functional unit of muscle

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dense connective tissue layer around their cell membranes called the 
 µ . ½ The cells are grouped together into groups called µµ ½ µµ are surrounded by another layer of dense connective tissue called the  µ . ½ Many fascicles are grouped into a single muscle which is wrapped with a 3rd dense CT layer, the  µ . ø
 

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½ This regular organization

of the myofibrils gives rise to the cross-striation, which characterizes skeletal and cardiac muscle. Sets of individual "stria" within a myofibril correspond to the smallest contractile units of skeletal muscle, the sarcomeres. ø
 

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bundle of contractile proteins found within the muscle cell. ½ Myofibrils are composed of individual contractile proteins called myofillaments. ½ These myofilaments are generally divided into thick and thin myofilaments. ø
 



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½ The light bands are known as {


µ. The I bands are composed mainly oÌ 
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½ In the middle of the 

band is a somewhat lighter area known as the H zone. This zone corresponds to the area where we have myosin not overlapped by actinÆ. ½ In the middle of the H zone we see a dark band known as the M line. ½ The M line is comprised of protein fibers that function to anchor the myosin filaments ø
 

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 ½ Muscle contraction, ½ Cell motility ½ Cell division ½ Cytokinesis, ½ Vesicle and organelle movement, ½ Cell signaling ½ The establishment and maintenance of cell junctions and cell shape

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¥ ½ The actin molecules (or G-actinÆ are spherical and form long chains. ach thin myofilament contains two such chains that coil around each other.

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½ The MYOSIN H D has several

important characteristics: ½ It has TP-binding sites into which

fit molecules of TP. TP represents potential energy. ½ It has CTIN-binding sites into

which fit molecules of CTIN.. ½ It has a "hinge"at the point where it

leaves the core of the thick myofilament. This allows the head to swivel back and forth, and the "swivelling" actually causes muscle ø
 

contraction.



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½ Ca must be available for the reaction b/w actin & myosin. fter contraction Ca must be removed . This rapid delivery and removal of Ca is accomplished by the combined work of the Sarcoplasmic reticulum and the transverse tublar system

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      ½ The sarcoplasmic reticulum

is the endoplasmic reticulum of the muscle cell. There are sac-like regions of the sarcoplasmic reticulum known as terminal cisternae. The terminal cisternae act as calcium storage sites. ½ Two terminal cisternae are associated with a T tubule to form a structure known as a 

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CC  C   C    ½ The SRCOL MM has a

unique feature: it has holes in it. These "holes" lead into tubes called TRNSV RS TUBUL S These tubules pass down into the muscle cell and go around the MYOFIBRILS. ½ The function of TTUBUL S is to conduct impulses from the surface of the cell (SRCOL MMÆ down into the cell ø
 

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  ½ Because skeletal muscle is voluntary muscle, contraction

requires a nervous impulse. So, step › in contraction is when the impulse is transferred from a neuron to the SRCOL MM of a muscle cell. ½ The impulse travels along the SRCOL MM and down the T-TUBUL S.. From the T-TUBUL S, the impulse passes to the SRCOPLSMIC R TICULUM. ½ s the impulse travels along the Sarcoplasmic Reticulum (SRÆ, the calcium gates in the membrane of the SR open. s a result, CLCIUM diffuses out of the SR and among the myofilaments. ½ Calcium fills the binding sites in the TROPONIN molecules. this alters the shape and position of the TROPONIN which in turn causes movement of the attached TROPOMYOSIN molecule. ø
 

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½ Movement of TROPOMYOSIN permits the MYOSIN

H D to contact CTIN.

½ ½ Contact with CTIN causes the MYOSIN H D to swivel ½ During the swivel, the MYOSIN H D is firmly attached to

CTIN. So, when the H D swivels it pulls the CTIN

½ t the end of the swivel, TP fits into the binding site on

the cross-bridge & this breaks the bond between the crossbridge (myosinÆ and actin. The MYOSIN H D then swivels back. s it swivels back, the TP breaks down to DP & P and the cross-bridge again binds to an actin molecule.

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not as long as skeletal muscles cells Often are branched cells Cardiac muscle cells may be mononucleated or binucleated. Nuclei are located centrally in the cell. T M reveals,that myofibrils of the cardiac muscle separate to pass around the nucleus. ôø

½ Outlining a biconical juxtanuclear region in which cell organelles are concentrated ½ Region is rich in mitochondria & contains the golgi apparatus, lipofuscin pigments, and glycogen. ½ In the atria atrial granules are also concentrated in the juxtanuclear cytoplasm ½ Contain two polypeptide hormonesǯ ½ 
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    Æ ½ Both are diuretics, effecting urinary excretion of Na ½ Inhibit Renin by kidney ½ inhibit ldosterone by adrenal gland

½ Cardiac muscle is striated. ½ In addition cardiac muscle contains intercalated discs ø
 

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invariably occur at the ends of cardiac muscle cells in a region corresponding to the -line of the myofibrils It consists of a 
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½ T-tubules are typically

wider than in skeletal muscle, but there is ‡
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 ‡, ½ It is located close to the line. ½ It does not form continuous cisternae but instead an irregular tubular network around the sarcomere with only small isolated dilations in association with the Ttubules. ø
 



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½ The difference b/w initiation of cardiac and skeletal muscle contraction- the long Ȃlasting membrane depolarization and activation of voltage-sensitive Ca channels in the wall of the T tubuleȂ

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" !   ½ Localized injury-------death of tissue-----replaced with fibrous connective tissue------cardiac function is lost at the site of injury------seen in non fatal MI. ½ Confirmation of suspected MI can be made through the detection of TnI &TnT IN TH BLOOD ½ Released In Blood Stream Within 3-›2 hrs ½ Remain elevated up to two wks.

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½     . ½ Smooth muscle cells have a single centrally located nucleus often has corkscrew appearance in LS. (contraction of cell during fixationÆ(differ from fibroblastÆ ½ In noncontracted cell, nucleus is elongated with tapering end. ½ organelles are concentrated at each ô end of nucleus

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½ Smooth muscle cells do not

have visible striations although they do contain the same contractile proteins as skeletal and cardiac muscle, these proteins are just laid out in a different pattern

Interconnected by gap junctions (specialized communication junctionÆ ø
 



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   C ½ Thin filaments ½ actin ½ tropomyosin ½ caldesmon ½ calponin ½ Thick filaments ½ myosin II

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½ desmin ½ vimentin

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C     ½ Smooth muscles cells posses a 
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thin & thick filaments and a   µ
of desmin and vimentin intermediate filament ½ The thin filaments in SM are attached to dense bodies that

are visible among the filamentǯ ½ Dense bodies are distributed through out the sarcoplasm

in a network of intermediate filaments containing the protein µ 
(vascular SM contain µ 
 

Æ which are part of the cytoskeleton of the cell. ø
 



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½ Calmodulin is Ca binding protein ,related to TnC found in

skeletal muscles ,regulate the intracellular concentration of Ca ½ Calcium does not bind to troponin but, rather, to a protein called calmodulin. The calcium-calmodulin complex binds to myosin light chain kinase (MLCKÆ 'activates' myosin which then binds to actin & contraction begins ½ The calcium-calmodulin complex may also bind with

caldesmon regulate its phosphorylation and releases from F-actin ½ Cells do not have t-tubules & have very little sarcoplasmic reticulum ½ Cells do not contain sarcomeres (so are not striatedÆ. ø
 

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arrangement ,myosin II molecules are oriented in one direction on one side of the filament band in an opposite direction on the other side of the filament. ½ No central bare zone but instead has asymmetrically tapered bare end. "ø

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Structural features

Long elongated cell diameter(›0-›00umÆ Length up to ›00cm

Short narrow cell D =›0-›5um L=80-›00um

short elongated ,fusiform .D=2-2um, L=20-200um

Location

Muscles of skeleton Visceral striated

Heart, SVC, IVC, pulmonary vein

Vessels, organs,& viscera

Connective tissue components

pimysium, perimysium, endomysium

ndomysium (sub endocardial & subpericardial,CTÆ

ndomysium. sheaths &bundles

fibre

Single skeletal muscle cell

Linear. branched arrangement of several CM

single smooth muscle cell

striation

Present

Present

None

nucleus

Many peripheral

Single central, juxtanuclear region

Single central

T-tubules

Present at  ȂI junction, triad;

Present at line Diad. one T-

2 T-tubules/sarcomere

tubule/sarcomere

None ,well developed sR many invaginations

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Cell to cell junction

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Intercalated disks

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Gap junctions Fasciae adherentes (nexusÆ Macula adherents Gap junctions

Special features

Well-developed sR & T-tubules

Intercalated disks

Dense bodies, caveolae & Cytomlasmic vesicles

Functions Type of innervation

Voluntary

Involuntary

Involuntary

fferent innervation

Somatic

utonomic

utonomic

Type of contraction

ll or none

ll or none

Slow, partial,rhythmic

Regulation of contraction

By binding Ca to TnC causes trypomysin movement &exposes myosin binding site on actin filament

By binding Ca to TnC causes trypomysin movement &exposes myosin binding site on actin filament

By phosphorylation of myosin light chain by myosin light chain kinase in the presence of Cacalmodin complex

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Growth and generation Mitosis

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