Muscle I Flashcards
What do you call the cytoplasm, smooth ER, and cell membrane in muscle cells?
Sarcoplasm, sarcoplasmic reticulum, sarcolemma
What are the two types of striated muscle?
Skeletal and cardiac
What is the non-striated muscle type?
Smooth muscle
Describe the general structure/contraction of skeletal muscle. Where is it usually found?
Long, multi-nucleated cells intended for quick, forceful contractions under voluntary control.
Axial, extremity, and cranial bones
Describe structure/contraction of cardiac muscle.
Elongated, branched cells connected to each other through intercalated discs. Rhythmic, forceful contractions that are involuntary.
Describe the general structure/contraction of smooth muscle. Where is it commonly found?
Simple, slow involuntary contractions.
Present in vessels, airways, GI, and GU tracts.
Where do muscle cells originate from? What is general structure of a muscle cell?
Originate from mesoderm.
Myoblasts fuse to form myotubes which differentiate into muscle fibers. Satellite cells sit on top of these muscle fibers and act as progenitor cells if muscle is damaged.
What other functions does muscle have besides contractions?
Protein storage and metabolic functions w/ other organs, esp liver
Which muscle type is predominant in our bodies?
Skeletal
Describe organization of skeletal muscle in terms of connective tissue.
- Endomysium - conn. tissue that bundles myofibers into fasicles
- Perimysium - conn. tissue that bundles fasicles
- Epimysium - dense conn. tissue that surrounds entire muscle
Describe cellular organization of striated muscle. What makes it striated?
Longitudinally arranged myofibers that contain contractile units called sarcomeres.
Striations due to alternating I-bands and A-bands.
What are the thick and thin filaments that make up the sarcomere.
Thick - myosin, thin - actin
What is actin anchored in?
Z-lin
What is myosin anchored in?
M-line
Where do myosin and actin overlap? (Dark region)
A-band
Where do myosin and actin NOT overlap? (Light region)
I-band
What is the H-zone?
Where myosin is attached to M-line, but does not overlap with actin (lighter zone of A-band)
What are the two regulatory proteins that act on actin?
Troponin and tropomyosin
What does titin do? Where is it located?
Connects myosin to Z-disc, present in the I-band
What does nebulin do?
It’s a spacer/linker protein between actin.
What is the source of emergency high energy phosphate in the muscle cell? Where is it located?
Creatine kinase - the H-zone
Describe the mechanism of muscle contraction.
- Bound ATP is hydrolyzed to ADP and Pi on the myosin head.
- Myosin extends and attaches to binding site on actin, forming a cross-bridge.
- Power stroke triggers, myosin pulls actin filament towards M line.
- Sarcomere shortens as Z line draws closer to M line and muscle contracts.
- ADP and Pi are released
- ATP binds to myosin, freeing myosin from actin
Describe mechanism of muscle contraction regulation.
- Tropomyosin blocks cross-bridge binding sites on actin in relaxed muscle state.
- When neurotransmitters bind to receptors on cell membrane, depolarizes muscle fiber membrane.
- Electrical impulse travels down T tubules and opens Ca2+ stores in SR.
- Ca2+ flows into myofibrils.
- When Ca2+ levels are high enough and there is ATP, Ca2+ binds troponin.
- Troponin displaces tropomyosin, exposing myosin binding sites on actin.
- Myosin can now bind actin and form cross bridge.
