anat12.txt

• 1) Skeletal Muscle
• 2) Smooth Muscle
• 3) Cardiac Muscle

Smooth muscle

• body movement (locomotion)
• maintainance of posture
• respiration (diaphragm and intercostal contractions)

• Constriction of viscera (peristalsis of gastrointestinal tract)
• Constriction of blood vessels

A bundle of muscle fibers

dense collagenous connective tissue that surrounds the entire muscle

Collagenous connective tissue that surrounds bundles of muscle fibers called fascicles

Fine sheath of connective tissue composed of reticular fibers that surrounds individual muscle fibers

Skeletal muscle is formed from groups of fascicles that are held together by the epimysium.  Each fascicle is made up many muscle fibers and is covered by the perimysium.  Each muscle fiber contains hundreds of myofibrils and is covered by the endomysium.  The myofibrils are made of repeating sarcomere units.

The myotendinous junction is the location where skeletal muscle is attached to a tendon.  Finger-like extennsions of the muscle fibers insert into the connective tissue of the tendon.

The basal lamina binds to the myofiber via the dystroglycan-containing complex.  This complex allows for the continuous cross-talk between the basal lamina and the cytoskeleton of the myofiber (actin)

• long, cylindrical and striated
• multinucleated with nuclei located at the periphery

• alligned in parallel
• separated by mitochondria and the sarcoplasmic reticulum
• composed of filaments called myofilaments

• deep invaginations of the sarcolemma (PM of a muscle cell) 
• run perpendicular to the length of the myofiber
• a single T-tubule and two terminal cisternae of the sarcoplasmic reticulum form a triad

• smooth endoplasmic reticulum
• forms an interconnected network of tubules
• runs longitudinally to the myofibril
• surrounds each myofibril
• form chambers called terminal cisternae on either side of the T-tubules

• Stores Ca2+ when muscle is at rest
• Releases Ca2+ in the sarcoplasm when muscle is stimulated (leads to contraction)

• 1.  Actin filament
• 2.  Myosin filament
• 3. Z-line
• 4.  H-zone 
• 5.  A-band
• 6.  I-band
• 7.  Cross-bridges

Hundreds of myosin molecules twist around one another to form a myosin filament.

• 2 filaments of F-actin interact with one another to form a double helix.  
• Tropomyosin winds around the double helix
• Troponin complexes are found periodically along the filaments

• At low Ca2+ concentrations, the myosin binding sites on actin are masked by tropomyosin.
• The troponin complex interacts with tropomyosin to prevent myosin binding to actin.

• Upon stimulation, the sarcoplasmic reticulum releases Ca2+ into the sarcoplasm.
• Ca2+ binds troponin causing a change in its conformation
• Shift in the position of tropomyosin
• Unmasking of myosin binding sites
• Myosin binding to actin- leads to contraction

• 1)  As ATP is split into ADP and Pi, cocking of the myosin head occurs.
• 2)  Myosin cross bridge attaches to the actin myofilament.
• 3)  ADP and Pi are released.  Power stoke occurs- the myosin head bends as it pulls on the actin filament, dragging it towards the centre of the sarcomere
• 4) As new ATP attaches to the myosin head, the cross bridge detaches.