Muscle Quiz

The curare blocks the Acetyl choline receptors on muscle tissue. This would result in:

• Increased stimulation of the muscle fiber

• Increased contractile strength of the muscle fiber

• Opening of ligand gated Na+ channels on the motor end plate

• Inability of muscle to respond to the motor neuron stimulus

Synaptic transmission at the neuromuscular junction is:

• Increased by high levels of cholinesterase

• Caused by an influx of potassium ions into the muscle membrane

• Increased by abnormally high levels of magnesium

• Produced by the release of acetylcholine from synaptic vesicles in the axon terminal

Neuromuscular transmission is

• Bi-directional (In both directions)

• Does not show fatigue

• Inhibited by calcium ions

• Increased by neostigmine

Which of the following statements concerning cross bridges is NOT correct?

• Bind to actin during muscle contraction.

• Bend during muscle contraction.

• Are formed by the globular heads of the myosin molecules.

• Consist of troponin and tropomyosin protruding from the actin helix.

The function of tropomyosin in skeletal muscle includes:

• Sliding on actin to produce shortening

• Binding to myosin during contraction

• Binding to Ca2+ at start of contraction

• Acting as a relaxing protein at rest by covering the active site on actin

The function of troponin is:

• Binding with Ca2+

• Forming cross bridges to bind with actin to initiate contraction

• Binding with myosin

• Covering active sites of actin

The propagation of AP along the membrane of the T-tubules causes:

• Closure of Ca2+channels on the terminal cisternae of the sarcoplasmic reticulum

• Contraction of the T-tubules

• The release of Acetyl choline from the terminal cisternae

• The release of Ca2+ from the terminal cisternae.

Which of the following about excitation contraction coupling of skeletal muscle fibers is correct?

• Excitation of the T-tubules results in the release of calcium from the sarcoplasmic reticulum

• Calcium binds to myosin to start cross-bridge cycling

• Calcium is pumped into sarcoplasmic reticulum to initiate contraction

• Sliding of myosin over actin to generate tension

Relaxation of skeletal muscles:

• Occurs in absence of ATP

• Caused by decrease of cytosolic Ca2+

• Results from simple diffusion of Ca2+ to extracellular fluid

• Tropomyosin is removed away to uncover active sites of actin during relaxation

During muscle contraction

• Generation of tension occurs by cross - bridge cycling

• It is a passive process does not need ATP

• Actin cross-bridges bind to myosin to help actin sliding over myosin

• Cross-bridge cycling continues after pumping of Ca2+ back to sarcoplasmic reticulum