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