L4.1 Muscle Cells Flashcards
what are the three kinds of muscle tissue?
skeletal, cardiac and smooth
describe the skeletal muscle
- skeletal muscle tissue is striated and subject to voluntary control
- the skeletal muscles make up the muscular system
- the skeletal muscles are innervated by the somatic nervous system
thin filament = ?
thick filament = ?
thin filament = actin
thick filament = myosin
describe the sliding filament mechanism
the myosin cross bridges can bind to the actin, pulling these thin filaments toward the centre if the sarcomere.
(actin molecules is arranged in a string and the troponin tropomyosin complex cover the active sides on actin)
describe how the myosin cross bridges go from ‘detachment’ stage to ‘power stroke’
- relaxed stage (detachment): none of the cross bridges have bound onto active sides of actin= muscle relaxed
- energized: ATP energises myosin at cross bridge (load spring). When the muscle is still relaxed, all these myosin heads/cross bridge are being loaded
- resting: when no calcium is available it means the muscle is resting because all the active sides on actin are covered by troponin tropomyosin complex
- binding: calcium is being released from the sarcoplasmic reticulum. During excitation the active sides on actin are being covered and the myosin heads can bind onto the active sides on actin. Once bind spring is released and pulls the actin in one direction, which gives a…..
- powerstroke: need another ATP to get a detachment from the active sides then back to stage one (detachment) where another ATP loads the spring again
(see diagram)
describe the whole process of excitation contraction coupling
- motor nerve action potential travels down the motor nerve towards the neuromuscular junction (the motor nerve itself has a terminal butt)
- the action potential will depolarise the terminal butt and therefore voltage gated calcium channel will open and calcium will enter the terminal butt
- just like in a synapse, we have vesicles with neurotransmitters. when the calcium enters the terminal butt the vesicles bind with the membrane and ACH (acetylcholinesterase) is released, diffuses across a cleft and on the muscle membrane we find receptors for ACH
- these receptors open, sodium will enter the cell and potassium will leave but more sodium ion will enter the cell than potassium leaving which means we get a local depolarisation of the muscle membrane = greater potential
- the greater potential (depends) may be enough for the muscle membrane to reach threshold = voltage gated sodium channel will open in the muscle membrane and we get an action potential
- the action potential travels along the muscle membrane and then into the T-tubule
- in close proximity of the t-tubule we have calcium storage facilities called sarcoplasmic reticulum
- when an action potential travels along a muscle membrane reaching the t-tubule it will travel down the t-tubule. once inside it will make the sarcoplasmic reticulum release calcium ions. this results in the calcium ions being released from the sarcoplasmic reticulum with the muscle (intracellular)
- actin have active sides and this is where the the myosin cross bridges bind to it. when the muscle is relaxed these active sides are covered up by a lid-> tropomyosin complex allowing the cross bridges not to bind to it
- if you want to activate a muscle you send an action potential via the motor nerve which turns into a muscle action potential which travels down the t-tubule and releases calcium. these calcium ions now bind onto the troponin of the tropomyosin complex and once calcium has been bound onto the tropomyosin complex the whole complex shift its orientation away, exposing the active side of actin = once exposed, the cross bridges can bind onto the active sides of actin and they get power stroke which means actin and myosin slides together and muscle shortens
describe a nerve action potential to a muscle contraction
(see diagrams)
- once the nerve action potential has crossed the neuromuscular junction we get a muscle action potential in the muscle membrane which travels along the muscle membrane reaching the T-tubule = calcium is released from the sarcoplasmic reticulum = binds onto the troponin tropomyosin complex = calcium is released = exposes active side of action and get cross bridge building and the muscles start to contract
- after 1 action potential you get one muscle twitch (contraction). the muscle contraction itself is much longer than one action potential
by which mechanism does our body control muscle tone/force of contraction?
two mechanisms:
- motor unit recruitment (choose which muscle fibres in each of the muscle bellies are being activated)
- frequency
describe motor unit frequency
single nerve fibre and all nerve fibres that the single nerve fibres innervates
small + large (small = a single nerve fibre which innovates 1 or 2 fibres; large= a single nerve fibre which innovates 10 or more fibres)
small motor unit: small muscle contraction
large motor unit: few muscle fibres will contract = strong contraction
describe frequency
increase force by increasing frequency of stimulation (see diagram)
describe the effects of muscles resting length, stretched muscle and shortened muscle
rest length: actin and myosin at rest is at optimum overlap = muscle fibres slightly stretch = optimum number of cross bridge building = muscle can develop maximum force at that figuration
stretch muscle: above resting length while the muscle is not contracted, you physically pull actin and myosin apart = less overlap = if you then activate the muscle it can’t develop as much force anymore because you get fewer cross bridge building
below resting length (shortened muscle): optimum overlap of actin and myosin but myosin heads might not find the actin because it’s too loose or if they do find the active side of actin and get a power stroke all the looseness means the action and myosin have to slide a long way before the physical pull on the tendon and develop force
see notes for anaerobic vs aerobic & effects of anabolic steroids
see notes for anaerobic vs aerobic & effects of anabolic steroids
