2001A02 Briefly describe the effect of resting muscle length and load conditions on the
tension generated by a skeletal muscle. How do these factors affect velocity of shortening?

 

List:

·         Skeletal muscle physiology

·         Length-tension graph and mechanism

·         Tension-velocity graph and mechanism

 

Skeletal muscle physiology:

 

·         Excitation: action potential at motor nerve terminal -> depolarise post-junctional membrane

·         Contraction: muscle depolarisation -> ↑Ca²⁺ -> cross-bridge cycling

 

Length-tension relationship:

 

·         Total tension = active + passive

·         Active tension:

o   Actin-myosin cross bridge cycling

o   Usual sarcomere length 1.8μm

o   Optimal sarcomere length 2.2μm sarcomere. Ideal balance between

§  a)↓Length -> ↑actin-myosin overlap

§  b)↑Length -> ↑TnC affinity for Ca²⁺ -> ↑actin exposure by tropomyosin

·         Passive tension:

o   Stretch of muscle and connective tissue (some elasticity)

 

Tension-velocity relationship:

 

·         Energy spent on either shortening or force production

·         Hence reciprocal