Muscle contractions

myofibrils

long cylindrical organelle that makes up muscle fibres

sarcromeres

contractile units of a muscle

what type of myosin is present in muscles?

myosin II

what does actin pull on in a sarcromere?

the z plates

I band

only has thin filaments

H band

only has myosin filaments

A band

has both thin and thick filaments (2)

what area of the muscle shrinks during muscle contraction?

I band

cap z

Binds actin at the cell disk

mediates attachment at Z disk Tropomodulin proteins - end

bipolar thick filament

Multiple Myosin II molecules

nebulin

long rope protein that establishes the length of actin filaments

determines length of thin filaments when they are generated

tropomodulin

caps the end of the actin filaments to prevent them disasembling

titin

attaches z disks together to prevent them moving to far apart

is long and has elasticity Barrel domains near Z line accommodates flexible protein Prevents over extension (lose contact with myosin)

where is action potential triggered?

Action potential triggered at the plasma membrane of the neuromuscular junction

How does the Ca2+ signal get throughout the muscle fibers?

• Neuromuscular Junction receive impulse for secreting acetylcholine

• acetylcholine leads to depolarization

• voltage gated ca2+ channels are opened

• ca2+ bind troponin → expressing myosin binding sites

why does ca2+ need to bind troponin?

to expose myosin binding sites

transverse tubules

invaginate in other cell allowing action potentials to move into the muscle swiftly (depolarization)

sarcoplasmic reticulum

a form of the endoplasmic reticulum specialized to store Ca 2+

what causes the release of Ca2+ from the sarcoplamsic reticulum>

a voltage gated channel

why is smooth muscle activated after binding myosin receptors

phosphorylation of myosin heads

tropomyosin

a coil coil protein that covers the myosin binding sites

what strucutre binds the released Ca2+?

trpomyosin

taxal

depolarized microtubules so motors can't bind to them

sliding filament model in muscle contraction

• multiple myosin that are bound to the sarcomere in the muscle go under power stroke due to the ATP cycle

• sliding of actin and myosin: causes shortening of muscle fibre

• ca2+: regulates muscle contraction by binding troponin (initiator)