Muscle contraction Flashcards
(15 cards)
which muscle is striated
skeletal and cardiac
parts of a sarcomere
- A band = thick and thin overlap
- I band = thin filaments not overlapping
- M line = proteins holding thick together
- H zone = middle of a band thin don’t reach
Structure of thick filaments
- made of myosin
- have tails and heads
- head is where myosin binds to actin to cause cross bridges
Structure of thin filaments
- made of actin
- multiple sites for myosin to bind to
- the binding sites are covered with tropomyosin
- troponin bins to the tropomyosin
Calciums role in cross bridging
- Ca is able to bind to troponin to move the tropomyosin away from binding sites and allow myosin to bind and form bridges
Steps in cross-bridge cycle
- myosin heads bind to actin
- myosin flexes head to form power stroke
- power stroke moves thin filament relative to thick
- myosin head detaches + unflexes
- myosin head binds further along thin filament
this causes muscle contraction
what controls muscle contractions
somatic motor neurons
where are muscles innervated
neuromuscular junction
- motoneuron connects to muscle fibre
- these trigger the muscle contractions
steps at neuromuscular junction
- AP travels down motoneuron
- depolarisation opens Ca+ channels
- triggers release of ACh from vesicles
- ACh diffuses across gap and binds to nicotinic receptors (always to N receptors)
- allows Na influx
- causes depolarisation of muscle fibre
- sodium channels open on muscle fibre and triggers and AP
what are T tubules
- extensions of surface of membrane that extend into muscle fibres
- AP travels through these to muscle fibres
what is excitation contraction coupling
- AP comes down motoneuron
- triggers ACh release
- ACh binds and opens nicotinic receptors
- membrane depolarises = AP
- AP goes down T tubules
- triggers release of Ca into sarcoplasmic reticulum
- calcium binds to troponin
- tropomyosin moves
- myosin heads bind to actin
- power stroke
- Ca returned to reticulum
how does ATP help cross bridge cycle
- energy from reaction is required to detach myosin heads from actin after contraction > if there is no ATP it cannot detach for the next power stroke and is stuck contracted
where does ATP come from
- phosphate or creatine phosphate
- break down of fatty acids
- breakdown of glucose via glycolysis
what is the muscle length tension relationship
amt muscle can contract depends on length
- max contraction happens at optimal length
- when muscle is too long > less filaments accessible for binding
- when muscle too short, overlap so myosin can’t bind and too short to contract even further
How do we generate greater contractile activity
- multiple action potentials in close succession
when lots of AP come down close together the twitch hasn’t finished before the next one is evoked > if enough come down very close together it can cause tetanus - motor unit recruitment
recruit more motor units so more muscle fibres are contracting
