Microscopic Muscular Anatomy Flashcards
What is a sarcomere?
- region between two successive Z discs
- contractile unit (functional unit) of muscle fibers
- composed of myofilaments made of contractile proteins
What are the three types of contractile myofilaments?
Thick (myosin), thin (actin) and elastic (titin)
What is myosin made of?
- 4 light and 2 heavy polypeptide chains
- 2 heavy helically intertwined polypeptide chains make up the tail
- The tail is attached to 2 globular head by a flexible hinge region
- Two light chains make up the globular heads
What are the 2 binding sites on the 2 globular heads of a myosin molecule?
ATP-binding site and actin-binding site
What do the globular heads do during contraction?
Link the thick and thin myofilaments together by forming cross-bridges
What are thin filaments comprised of?
Actin molecules and regulatory proteins tropomyosin and troponin
What forms the backbone of each thin filament?
Intertwined actin filaments
What active site does Globular actin (G actin) have?
Active sites to which myosin heads attach during contraction
What is the function of tropomyosin?
- Stiffen and stabilize actin core
- Block the active sites of actin subunits so that globular heads of myosin cannot bind to thick filaments(during relaxation)
What is troponin and its function?
- Globular 3 polypeptide complex
- TnI is an inhibitory subunit that binds to actin
- TnC binds to calcium ions
- TnT binds to tropomyosin and helps position it on actin
What are elastic filaments and their functions?
- extend from Z discs, running through thick filaments (forming the core) and attach to M line
- holds thick filament in place
- maintain organization of A band
- helps muscle spring into shape after stretching
What is the microscopic organization of muscles?
From largest to smallest a in size:
Muscle tissue, fascicles, muscle fiber, myofibril, sarcomere, myofilaments
