Cardiac Muscle Flashcards
what gives the cardiac muscle its striated appearance?
regularly repeating sarcomeres
what are the thick and thin filaments made of?
thick: myosin
thin: actin, tropomyosin and troponin
how are adjacent cardiac muscles attached to each other?
intercalated discs
what do the microfibrils (thick and thin filaments) attach to?
desmosomes in intercalated discs
what does one sarcomere comprise of? (in terms of lines and bands)
2 half I bands, 1 A band, 1 H zone, 1 M-line, 2 Z lines
what is myosin composed of? how are these elements arranged?
myosin: 2 heavy polypeptide chains + 4 light chains
long tail: 2 intertwining heavy chains that lie along the axis of thick filament
2 globular heads: made of heavy and light chains; extend out to the sides
what are the two binding sites on myosin’s globular heads?
- actin binding site
2. ATP binding site
what does the ATP-binding site on myosin’s globular head double up as?
as enzyme ATPase –> hydrolyses bound ATP and harnesses energy released for contraction
what is the thin filament composed of? how are these elements arranged in the cardiac muscle?
actin: globular protein made of a single polypeptide –> polymerises with other actin monomers –> 2 intertwined helical chains make up the core of the thin filament
each actin molecule also contains a binding site for myosin
describe tropomyosin + where tropomyosin lies
tropomyosin is an elongated molecule that fills the grooves between 2 actin strands. It overlies the myosin binding sites on actin.
describe troponin + its purpose in muscle contraction
troponin is a protein that changes shape when ca2+ binds to it, pushing tropomyosin and exposing myosin binding site on actin –> enables muscle contraction to occur
describe the A-band, I-band, Z-lines, H-zone and M-line
A band: region of sarcomere occupied by thick and few overlapping thin filaments (2x as many thin filaments as thick filaments in A band)
I band: occupied by only thin filaments that extend to centre of sarcomere from Z line
H zone: contains only thick filaments
M line: centre of H zone; corresponds to protein that link thick filaments together at central region
what is titin? what is its purpose?
titin: elastic protein filaments that extend from z line to m line; linked to both m line proteins and thick filaments
what is the sarcoplasmic reticulum?
it is the membrane network that surrounds the contractile proteins
how does the sarcoplasmic reticulum release Ca2+?
sarcoplasmic reticulum: rich Ca2+ store
sarcolemma: has frequent invaginations known as T-tubules
L-type Ca2+ gated channels are coupled with ryanodine receptors (found in sarcoplamsic reticulum)
action potential travelling down sarcolemma leads to opening of L-type channels –> Ca2+ diffuse into cytosol of the cell
