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
What is myoplasticity?
changes in use and environment can alter structural and enzymatic protein content in muscles
Are type II to I conversions possible?
little evidence to suggest they are
What are adaptations to endurance training?
- inc oxidative capacity
- inc mito density
- inc type I expression
- delayed onset of m. acidosis
- inc fatigue resistance
- inc O2 consumption
What are adaptations to resistance training?
- inc CSA all fiber types
- inc cells/nuclei
- dec mito density
- inc IIa fibers
- inc contractility
- inc elasticity
- inc neuromotor recruitment
Deconditioning results in what muscle fiber shift?
from IIa to IIb
-slow to fast
How does aging affect muscle?
- loss of mass
- preferential atrophy of type II
- larger proportion of type I
- motor unit reorganization from fast to slow
