Year 13 - Muscles Flashcards
(11 cards)
Describe events at a synapse that allow for transmission of nerve impulse at a neuromuscular junction
Depolarisation of presynaptic membrane at presynaptic knob of a motor neuron causes Ca2+ channels to open
Influx of Ca2+ by facilitated diffusion into synaptic knob.
Cause synaptic vesicles to move to and fuse with presynaptic membrane
Releasing acetylcholine (ACh) neurotransmitter that diffuses across synaptic cleft.
Binds to complementary ACh receptors on sarcolemmea
Sarcolemma is folded to increase surface area for more receptors
Opens Na+ channels on sarcolemma so Na+ enters by facilitated diffusion
Causing depolarisation of sarcolemma
Action potential (impulse) travels down T tubule
Ca2+ channels open on sarcoplasmic reticulum (which surround sarcomere)
Ca2+ is released and diffuses out (see Ca2+ role in muscle contraction)
Role of ATP/ATPase in the sliding filament model of muscle contraction
Binds to myosin head breaking the actinomyosin crossbridge so detaches myosin from actin
ATPase, on myosin heads, hydrolyses ATP releasing energy to recock myosin head so moves to original position (recovery stroke)
Releases the energy to drive power stroke = hydrolysis of ATP causes myosin head to bend pulling actin molecules over it self so shortening sarcomeres as Z lines come closer together)
Used in active transport of Ca2+ into the sarcoplasmic reticulum
What is the consequence of an oxidative phosphorylation inhibitor on the sliding filament model of muscle contraction?
Less aerobic respiration so less ATP produced
Less force generated as fewer actin and myosin interactions in myofibril
Less ATP available to detach myosin head from actin
Fatigue caused by lactate from anaerobic respiration
Role of Ca2+ in the sliding filament model of muscle contraction
Ca2+ diffuse into myofibrils from sarcoplasmic reticulum
Causes movement of tropomyosin so reveals myosin head binding sites on the actin
Allowing myosin heads to attach to exposed binding sites forming an actinomyosin bridge
Ca2+ activate ATPase on myosin head allowing for hydrolysis of ATP to release energy
What is the consequence of blocking sarcoplasmic reticulum Ca2+ channels to the sliding filament model of muscle contraction?
No Ca2+ so no interaction with and no movement of tropomyosin from binding sites on actin.
Myosin heads do not bind to actin as no binding site exposed so no actinomyosin bridges formed.
No activation of ATPase so no release of energy from ATP
Role of glycogen in the sliding filament model of muscle contraction
A polymer of glucose that can be hydrolysed to release glucose
For glycolysis within respiration
To provide ATP
Role of tropomyosin in the sliding filament model of muscle contraction
Blocks myosin head binding site on actin
Moves from binding site on actin due to Ca2+
Allowing myosin to bind to actin forming actinomyosin crossbridge
How can creatine help athletes in terms of the sliding filament model?
Creatine used to form phosphocreatine
This stores phosphate so can provide phosphate to combine with ADP to form ATP (ADP + CP -> ATP + C)
see ATP role in sliding filament model of muscle contraction
How can carbohydrate loading help athletes in terms of the sliding filament model?
Carbohydrate loading converted and stored as glycogen (glycogenesis)
Glycogen hydrolysed to glucose (glycogenolysis)
Glucose used in glycolysis in respiration (both anaerobic and aerobic) to produce ATP.
see ATP role in sliding filament model of muscle contraction
Describe and explain the general properties of fast twitch fibres
Used during short-term intense exercises with rapid contractions (eg sprinting)
Anaerobically respires
Contains high concentration of phosphocreatine that can be rapidly used up during contraction to make ATP.
More ATPases to allow rapid hydrolysis of ATP
A high glycogen content so it can be hydrolysed to give glucose for glycolysis/anaerobic respiration yielding a quick source of 2 ATP per glucose.
Fast rate of fatigue due to production of lactic acid.
Describe and explain the general properties of slow twitch fibres
Used during longer-term exercise with sustained contractions as can avoid fatigue (marathon/posture)
Aerobically respires
Have lots of mitochondria
Contains large number of named given krebs cycle enzyme (likely to be succinate dehydrogenase).
More capillaries to deliver high concentration of oxygen (and glucose) for more aerobic respiration and prevention of build up of lactic acid by anaerobic respiration
Slow rate of fatigue
Higher concentration of myoglobin which has a higher affinity to oxygen so loads oxygen from haemoglobin at same pp02.
