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

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