Skeletal Muscle Structure and Function Flashcards
What are qualities of muscles with parallel arrangement?
Rapid shortening but with less tension
What are the qualities of muscles with fivers at an angle to the axis of shortening?
Slow shortening but with greater tension
What is the order of muscle arrangement from macro to micro?
Muscle-> Fascicle-> Muscle Fiber-> Myofibril-> Sarcomere-> Thick/Thin filaments
What does the epimyisium cover?
The whole muscle
What does perimysium cover?
The fascicle
What does the endomysium cover?
The muscle fiber
Where do all three muscle covering connect?
To the tendon
What occurs with a single motor unit?
One motor unit innervates all the muscle fibers
What occurs with two motor units?
Some of the muscle fibers are innervated by one motor unit and the rest are innervated by the other motor unit; motor units are all the same they can just affect different muscle fibers
For fine movements what is true of the motor units?
There are few motor units per muscle fibers
What are satellite cells?
Muscle stem cells found between the basement membrane and sarcolemma
When are satellite cells activated?
When a muscle is damaged (can be by multiple means)
The application of what stains myocyte nuclei blue?
Hemalum
What are the three biochemical systems that are the basis of muscle function?
Metabolic system
Calcium regulation
Contractile
Where is ATP expended when a myocyte is active?
1/3 to calcium regulation and 2/3 to cross-bridge cycling
Where is ATP expended when a myocyte is inactive?
Ion transport and protein synthesis
What is titin?
A protein that allows for passive tension (springy); needed for the left ventricle to fill with blood in between contractions
What is a main determinant of muscle function?
Myosin isoforms
What are Type I fibers?
Slow-oxidative fibers (slow twitch)
What are Type II A fibers?
Fast-oxidative fibers (intermediate)
What are Type II X fibers?
Fast-glycolytic fibers (fast twitch)
The recruitment of muscle motor units occurs in what predetermined sequence?
Type I-> Type IIA-> Type IIX
What are the three systems needed for a myocyte to function?
Metabolic
Calcium recycling
Cross-bridge cycling
What is the H band?
Zone across the center of the sarcomeres of skeletal muscle; contains only myosin filaments
What is the I band?
Light band on each side of Z line; contains only thin (actin) filaments
What is the M band?
Runs directly through the center of the A band
What is the A band?
Spans the myosin filaments; overlaps with some of the actin filaments
What defines one sarcomere?
The segment between two neighboring Z-lines
What is the ratio of actin to myosin filaments?
2:1
What happens to the bands when a muscle contracts?
H-band shortens
I-band is shortened
A-band is unchanged
What is titin?
A protein needed for passive tension giving muscles a spring-like property; it is important in the filling of blood into the left ventricle
What is the clinical association of titin mutations?
Associated with hereditary myopathy with early respiratory failure
What is a biomarker for acute MI?
Troponin: TnI and TnC
How are different muscle types differentiated in a muscle biopsies?
Myosin heavy chain isoforms
What MyHC isoform is found in Type-1 fibers?
MyHC I
What MyHC isoforms are found in IIX and IIA muscle forms?
MyHC IIx and MyHC IIa and MyHC IIb (have genes but not expressed in humans)
What is the main determinant of muscle function?
Myosin isoforms
Which muscle type has the highest and lowest amount of mitochondria respectively?
Type I
Type IIX
What implications does the order of motor unit recruitment have?
Rehabilitation
