Muscles Flashcards
2 protein filaments in myofibrils
Actin and myosin
I band
Light bands where actin is and does not cross over with myosin
A band
Dark region where actin and myosin overlap
H zone
Light coloured region in the middle of the A band (myosin)
Sarcomere
Distance between adjacent Z lines
Properties of slow twitch
Adapted for aerobic.
Large store of myoglobin
Rich supply of blood vessels and numerous mitochondria
Properties of fast twitch
Thicker and more numerous myosin filaments.
Higher conc of glycogen.
High conc of enzymes involved in anaerobic for rapid ATP.
Phosphocreatine store (can rapidly generate ATP from ADP in anaerobic conditions)
Motor unit
All the muscle fibres supplied by the same motor neurone
Neuromuscular junction
When nerve impulse arrives calcium ion protein channels open and diffuse into knob, synaptic vesicle fuses with presynaptic membrane and releases acetylcholine. Diffuses to postsynaptic membrane and increases permeability to Na+ which enter and depolarise membrane, creating impulse. Acetylcholinesterase breaks it down to avoid overstimulation.
Similarities between neuromuscular junction and synapse
Both neurotransmitters transported by diffusion.
Both have receptors that cause influx of Na+ when binded to.
Use Na+-K+ pump to repolarise axon.
Use enzymes to break down neurotransmitter
Differences between neuromuscular junction and synapse
NMJ only links motor neurone to muscle
End of action potential.
What happens to I band during muscle contraction
Becomes narrower
What happens to Z lines during muscle contraction
Go closer together, sarcomere shortens
What happens to H zone during muscle contraction
Narrower
What happens to A band during muscle contraction
Same length as it is determined by length of myosin
How does the action potential cause muscle contraction
Action potential travels into muscle fibre via T-tubules (extension of cell-surface membrane that branch into cytoplasm).
Tubules in contact with endoplasmic reticulum which actively transports Ca2+ into it from cytoplasm.
Action potential opens Ca2+ protein channels on ER causing Ca2+ to diffuse into cytoplasm down conc gradient.
How does influx of Ca2+ into cytoplasm cause muscle contraction
Bind to troponin and cause tropomyosin molecules blocking binding sites on actin to move away.
ADP molecules on myosin head allow them to bind actin filament and form cross bridge.
Myosin heads bend and change their angle to perform a power stroke and release ADP.
The ATP binds to myosin heads which causes them to release from actin filament.
ATP hydrolase hydrolyses ATP which causes the myosin heads to move back to original position.
Repeats until full contraction
Role of ATP in muscle contraction
Return movement of myosin heads to cause actin filament to slide.
Return of calcium ions to sarcoplasmic reticulum via active transport.
Phosphocreatine
Molecule stored by muscles for rapid production of ATP as phosphate ion from phosphocreatine transferred to ADP to form ATP and creatine.
