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10 Cards in this Set

  • Front
  • Back

Explain why a position on a sarcomere may appear darker at diff period of time?

Movement of actin betwen myosin


Contraction of muscle

Describe the role of calcium ions in the contraction of a myofibril

Calcium ions bind to troponin/Move tropomyosin


Expose myosin binding sites on actin filament


Allow cross-bridges to form/myosin to bind to actin


activates ATPase for hydrolysis of ATP

Explain what causes the cross bridges between actin and myosin to remain firmly bound after death

No respiration


No ATP produced


ATP used for separation of actin and myosin/cross-bridged

Describe what causes the different bands seen in the muscle myofibril

A-band; mainly myosin filaments


I-band; actin filaments


darker band; both filaments


H-zone; just myosin

Describe how the banding pattern of a sarcomere is different during contraction

H-zone and I-band narrower


A-band same size/dark band wider

Explain the importance of ATPase during muscle contraction.

Hydrolysis of ATP into ADP and P releasing energy


Energy used to break actin-myosin bridges

Describe the role of ATP and phosphocreatine in producing contraction of a muscle fibre

ATP allows myosin to detach from actin


're-cocks' myosin cross-bridge


phosphocreatine allows regeneration of ATP


in anaerobic conditions


Releases Pi to join with ADP

Endurance athletes have a high proportion of slow twitch fibres. Explain the benefit

Endurance athletes excercise for extended period of time


Respire aerobically


Lactate does not accumulate


Many mitochondria


Site of Krebs cycle


And ETC


Produce a lot of ATP


High resistance to fatigue


Myoglobin + rich supply of blood vessels

Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction result in shortening of sarcomeres. Describe how.

Opening of Ca channels, enters synaptic knob


Vesicles with acetylcholine fuse with membrane


Acetylcholine diffuses across cleft


Binds to specific receptors on sarcolemma


Causes depolarisation (changes permeability to Na+)


Action potential travels through T-tubules to cause Ca ions to diffuse out of sarcoplasmic reticulum


Ca binds to troponin and moves tropomyosin


exposes binding sites


allows cross-bridges to form


change in angle causes sliding filament

Explain why no force is generated when the sarcomere length is at its max?

No overlap


No cross-bridges form


No contraction