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Ch 10: Muscle Tissue

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Muscle Tissue
Over 700 named skeletal muscle form the muscular system
Distributed almost everywhere in the body
Responsible for the movement of materials within and throughout the body
Excitability
Responsiveness to stimulation
Contractility
fibers shortening pulls on bone and/or moves specific body parts
Elasticity
The mnuscles ability to return to its original length
Extensibilty
Capability of extending in length in response to the contractino of opposing muscle fibers
Functions of Muscle tissue
Body movement
Maintenance of posture
Temperature regulation
Storage and movement of material
Muscle Tissue Types
Smooth, Cardiac, Skeletal
Smooth Muscle: Appearance
Spindle shaped and may be up to 600mm long
Single nucleus centrally located
Nonstraited and involuntary (ANS)
Located in the walls of blood vessels, gastroihtential, lower respitory tract, lower epopnagus, glands
Cardiac Muscle: Appearance
Main cylinder and collteral branches
Normally a single, centrally locasted nucleus
Intercalated discs
Gap junctions for electrical cintinuity between adjacent cells
Involuntary - Containd pacemaker cells that are autorjymic innervated by autonomic nervous system
Skeletal muscle: Appearance
Elongated cylinders up to 30cm long: most common tissue in body
Straited due to orgainzation of filaments within cells
Multiple nuclei lie peripherally just deep to cell membrane
Voluntary (CNS/PNS)
Movements initated by the cerebral cortex
Epimysium
Most external skeletal muscle
Dense irregular connective tissue fascia that envelops entore muscle belly
Perimysium
Deep to epimysium
Connective tissue septa that divides belly into compartments containing fiber bundles called fasoicles
Endomysium
Last skeletal muscle layer, internal
Fine connnective tissue extension of perimysium that envelop individual fibers
Organization of Skeletal muscle
muscle --> fascicle --> Fibers(cells) --> myofibrils --> myofilaments
Muscle fibers
muscle cells
Sarcolemma
cell membrane of muscle fibers
T-Tubules
Transverse tubules continuous with sarcolemma passing around microfibrals
Sacroplasmic reticulum
Specilized ER, Calcium stroage (improant for movement)
Terminal cisternae
enlarged ends of SR
Triad
Paired terminal cisternae and t-tubule
Sacromere
Each myofibril is divded into repeated segments
Borded by adjacent z-disc
This is the basic unit of muscle contraction
Z-disc
Dense strucural protien discs
Titin
Single protien
Linked to z-disc to thick filaments
I band (light band)
Area either side of the z-line composed of only thin filaments
A band (dark band)
Both thick and thin filaments
H zone
Contains only thick filaments
M line
Fine line marking center of sacromere
Actin (F actin/ Filamentous Actin)
Thin Filament
Anchored to the z disc
Composed of individual G-actin protiens arranged as an alpha helix
Tropomyosin
Protien strands lying in groove between actin filaments
Serve as regulatory protien by 'blocking' binding sites on actin from myosin
Troponin
Interspersed along tropomyosin strands; regulatory protien
Three subunits that bind to: tropomyosin, to G-actin, to calcium
Myosin
Shaft (tail, linear region)
Head (globular end; aka crossbridge)
Motor unit
One motor neuron and all the muscle fibers that it innervates
muscles include a number of motor units
means for regulating the strength of contraction
Stimulation is all-or-nothing; the motor neuron transmitting the impulsive stimulaton to all fibers it innervates
Fast skeletal muscle
Majority of skeletal muscle fiber in human body
Large diameter, densely packed myofibrils with few mitochiondria
called white fibers due to lack of myoglobin
Inertmediate Skeletal Muscle
Resemble fast fibers but have a greater resistance to fatigue
Slow Skeletal muscle
Smaller diameter fibers that contract more slowly
called red fibers because of myoglobin
Contraction of the Sacromere: sliding filaments
Calcium sites exposed to thin filaments by troponin/tropomyosin movement
Myosin needs a cross-bridge
Pivoting myosin pulls filaments towards m-line
ATP binds with myosin; breaks the cross bridge, myosin returns ro pre-pivot postion
freed myosin head in, now able to cross bridge, again further along the thin filament