Contraction of skeletal muscle Flashcards
(10 cards)
How is energy used and needed in active muscles?
rapidly generating ATP anaerobically is also requires
- this is partly achieved using a chemical called phosphocreatine and partly by more glycolysis
- phosphocreatine cannot supply energy directly to the muscle, so instead it regenerates ATP, which can
- phosphocreatine is stored in muscle and acts as a reserve supply of phosphate, which is available immediately to combine with ADP and so re-form ATP
- the phosphocreatine store is replenished using phosphate from ATP when the muscle is relaxed
What is evidence for sliding filament mechanism?
- myofibrils appear darker in colour where the actin and myosin filaments overlap and lighter where they do not
- if the sliding filament mechanism is correct, the there will be more overlap of actin and myosin in a contracted muscle than in a relaxed one
What is tropomyosin?
-protein which blocks the actin binding site to prevent myosin heads from forming an actin myosin bridge
Which three main proteins are involved in the sliding filament mechanism?
- myosin is a globular (tail) and fibrous (head) protein
- actin is a globular protein
- tropomyosin protein
What is the energy produced by the hydrolysis of ATP to ADP needed for?
- the movement of the myosin heads
- the reabsorption of calcium ions into the endoplasmic reticulum by active transport
What is the process of the sliding filament mechanism of muscle contraction?
1-tropomyosin molecule prevents myosis head from attaching to the binding site on the actin molecule
2-calcium ions released from the endoplasmic reticulum cause the tropomyosin molecule to change shape and so pull away from the binding sites on the actin molecule
3-myosin head now attaches to the binding site on the actin filament
4-head of myosis changes angle, moving the actin filament along as it does, the ADP molecule is released
5-ATP molecule fixed to myosin head, causing it to detach from the actin filament
6-hydrolusis of ATP to ADP by ATPase provides the energy for the myosin head to resume its normal position
7-head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated
How do skeletal muscles bring about movement?
-skeletal muscles occur and act in pairs that pull in opposite directions and when one is contracted the other is relaxed as muscles can only pull different parts of the skeleton around joints
What is muscle relaxation?
- when the stimulation stops, calcium ions are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP
- this reabsorption of the calcium ions allows tropomyosin to block the actin filament again
- myosis heads are now unable to bind to actin filaments and contraction ceases, that is, the muscle relaxes
What is a weakness of the sliding filament theory?
- the width of the A band is determined by the length of myosin filaments, it follows that the myosin filaments have not become shorter
- this discounts the theory that muscle contraction is due to the filaments shortening
What is muscle stimulation?
- an action potential reaches many neuromuscular junctions simultaneously, causing calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob
- the calcium ions cause the synaptic vehicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
- acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle cells-surface membrane, causing it to depolarise
- triggers the sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction
- this causes muscle contraction
