Cardiac Muscle Contraction 1

Question 1

Thin filaments are composed of which of the following?

A. Actin filaments
B. Titin
C. Light chains
D. Myosin-binding proteins
E. Desmin

Answer 1

A. Actin

Question 2

Thick filaments are composed of which of the following?

A. Myosin
B. Tropomyosin
C. Connexin
D. Troponin complex
E. Nebulin

Answer 2

A. Myosin

Question 3

Cardiomyocyte ion channels include which of the following?

A. The ryanodine receptor
B. The beta adrenoceptor
C. Calcium activated channels
D. ADP-sensitive potassium channels

Answer 3

A & C.

A. The ryanodine receptor is a cardiomyocyte calcium ion channel, which releases calcium ions from the sarcoplasmic reticulum to be used for contraction.
C. Calcium activated channels are cardiomyocyte ion channels.

B. Incorrect. The beta adrenoceptor is a not cardiomyocyte ion channel. Beta receptors are G protein-coupled enzymatic receptors.

D. Incorrect. Cardiomyocytes possess ATP-sensitive, i.e. not ADP-sensitive, potassium channels.

Question 4

In contrast to skeletal muscle, cardiac muscle has which of the following?

A. Greater capillary density
B. T-tubules corresponding to A-band and I-band overlap
C. Longer and thinner transverse tubules
D. More mitochondria by volume
E. Cytoplasm joined by connexons

Answer 4

A., D. & E.

In contrast to skeletal muscle, cardiac muscle has:

Greater capillary density
Cytoplasm joined by connexons
More mitochondria (up to 25% by volume, compared to 2% in skeletal muscle cells)
However, cardiac muscle does not have:

T-tubules corresponding to A-and I-band overlap
Longer and thinner transverse tubules