Muscle Architecture and Contraction Flashcards
Function of T-tubules:
transmit action potential into interior muscle cell
Function of sarcoplasmic reticulum:
calcium storage, release, and reuptake
Where are troponin and tropomyosin located?
on actin protein (thin filament)
H zone:
only thick filament
I band:
only thin filament with titin and Z discs
A band:
all thick filament
Function of titin:
molecular blueprint and spring
Function of nebulin:
regulates actin length
MHC isoforms contribute to what?
contraction velocity
-I, IIa, IIx/d
Function of tropomyosin during rest:
block myosin binding site
What is the steric block model?
troponin regulating position of tropomyosin relative to myosin binding site
Muscle fiber contraction sequence:
- AP propagated along sarcolemma into T-tubules
- Stimulates release of (Ca+) from SR
- Ca+ binds to Troponin C, resulting in a conformation change that pulls tropomyosin away from myosin binding site on actin filament
- Hydrolysis of ATP “cocks” myosin head
- “Cocked” myosin head binds to actin and contraction occurs
- Hydrolysis of ATP detaches myosin head from actin
- Sequence continues as long as Ca+ is available
- In absence of APs, SR resorbs Ca+ from sarcoplasm
- In absence of Ca+, troponin and tropomyosin return to resting states, blocking myosin/actin binding site
Type I muscle fibers are:
slow oxidative
Type IIa muscle fibers are:
fast oxidative-glycolytic
Type IIb muscle fibers are:
fast glycolytic
