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What are the three kinds of muscle?
- 1) Skeletal Muscle
- 2) Smooth Muscle
- 3) Cardiac Muscle
Which muscle type is not striated?
Name three functions of skeletal muscle.
- body movement (locomotion)
- maintainance of posture
- respiration (diaphragm and intercostal contractions)
Name two functions of smooth muscle.
- Constriction of viscera (peristalsis of gastrointestinal tract)
- Constriction of blood vessels
What is a fascicle?
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
Describe the organization of sketal muscle.
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.
Define and describe the myotendinous junction.
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.
How does the basal lamina bind to the skeletal myofiber?
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)
Describe the structure of a myofiber.
- long, cylindrical and striated
- multinucleated with nuclei located at the periphery
Describe the structure of a myofibril.
- alligned in parallel
- separated by mitochondria and the sarcoplasmic reticulum
- composed of filaments called myofilaments
What is a T-tubule?
- 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
Describe the structure of the sarcoplasmic reticulum.
- 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
Name two functions of the sarcoplasmic reticulum.
- Stores Ca2+ when muscle is at rest
- Releases Ca2+ in the sarcoplasm when muscle is stimulated (leads to contraction)
Fill in the blanks.
- 1. Actin filament
- 2. Myosin filament
- 3. Z-line
- 4. H-zone
- 5. A-band
- 6. I-band
- 7. Cross-bridges
Describe the structure of thick filaments.
Hundreds of myosin molecules twist around one another to form a myosin filament.
Describe the structure of thin filaments.
- 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
What is the function of tropomyosin?
- 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.
Explain the steps that must be taken in order for myosin to bind 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
What are the four steps in the skeletal muscle contraction cycle?
- 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.