Skeletal Muscle Physiology Flashcards
What transcription factors determine if cells become myogenic?
MyoD and myf-5 early
Myogenin and MRF-4/herculin/myf-6 later
Overlapping functions
How are myotubes formed?
Single cell myoblasts fuse to form multinucleated myotubes
What is the bHLH region of the muscle transcription factors?
Basic helix-loop-helix region that is responsible for binding DNA
What is the E-box?
Region on DNA that binds to these transcription factors
Need at least two to bind the TFs
How are these TFs most effective?
When they form heterodimers with E2 family TFs
The HLH region is required for dimerization
What is myostatin?
Member of TGFB family of signaling proteins
Negative regulator of muscle growth (prevents it)
Inhibits myoblast proliferation and progression from G1 to S
What is the result of GoF and LoF of myostatin?
GoF = fewer muscle cells (hypotrophy)
LoF = more muscle cells (hypertrophy)
What is the function of satellite cells?
Located on surface of muscle fiber, beneath basal lamina
Recruited to supply myoblasts for repair and regeneration
How are satellite cells activated?
Immune response to injury
Start dividing, form new muscle fibers, reconstitute pool of SCs
Migrate to site of injury
How do Satellite cells increase muscle mass after exercise?
Repair damage done, which increases thickness and size of muscle fiber
GFs and hormones increase protein synthesis and glucose uptake in satellite cells (e.g. effect of testosterone)
What are the components of muscle sarcomere?
Actin and mysoin
What is the structure of myosin?
2 heavy chains with a globular head and filamentous tail
2 light chains which are essential and regulatory
What are cross bridges?
Composed of the head filament and project laterally
Serve as the link between thick and thin myofilaments
Acts as ATPase, binds to actin
What is tropomyosin?
Lies in the groove between actin strands
Regulates binding sites of actin and provides structural rigidity
What is troponin?
Complex of three proteins: TT, TC, TI
TC - contains two high and two low affinity sites for Ca
TT - binds troponin to tropomyosin
TI - inhibits interaction between actin and myosin
What is the function of titin?
Acts as a spring to keep myosin filaments centered in sarcomere and maintain resting tension
What is the function of nebulin?
Associated with actin
Regulates assembly of actin filaments
What is the role of Ca in muscle contraction?
Binds to troponin C to change conformation of complex
Increase intracellular concentration when stimulated
Dissociates from regulatory proteins when concentration decreases
What is the function of the T-tubule system of the sarcolemma?
Contains voltage-gated Ca channels
When depolarized due to stimulation from motor nerve, causes release of Ca
What is the function of dihydropyridine calcium channels?
Act as a voltage sensor in the T-tubules, causes the opening of ryanodine receptor calcium channels
Ca does not travel through these
What is the function of RyR1 calcium channels?
Release calcium in response to conformational changes in DHP channel proteins
What is SERCA?
Sarcoendoplasmic reticulum calcium ATPase
Pumps calcium from cytoplasm back to the SR
Describe the sliding filament model.
Describe in four steps, study separately
What is the function of chloride channel CIC-1?
Creates a large resting chloride conductance of skeletal muscle
Stabilizes resting membrane potential to prevent false action potentials
Also important in repolarizing membrane