Locomotion and Movement MCQs

Choose the correct statements about the masking mechanism and troponin in resting muscles:

I. In the resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments.
II. Troponin is a monomeric simple protein that binds to calcium during relaxation.
III. Tropomyosin acts to mask the active site for actin on the myosin head.
IV. Removal of the troponin mask is a prerequisite for cross-bridge formation.

Which of the following statements regarding the thick filament (myosin) are correct?

I. Myosin is a polymerised protein composed of monomeric units called meromyosins.
II. Each meromyosin has two parts: a globular head with a short arm (HMM) and a tail (LMM).
III. The LMM component projects outwards at a regular distance and angle, forming the cross arm.
IV. The globular head of meromyosin is an active ATPase enzyme.

Consider the following statements about the binding sites on the myosin monomer:

I. The globular head of meromyosin has active binding sites for ATP.
II. The globular head of meromyosin has active binding sites for actin.
III. The short arm of HMM contains the primary calcium-binding sites that trigger contraction.
IV. The tail of LMM contains the active ATPase enzyme domain.

Read the statements regarding the initiation of muscle contraction:

I. Muscle contraction is initiated by a signal from the central nervous system (CNS) via a sensory neuron.
II. A motor neuron along with the muscle fibres connected to it constitute a motor unit.
III. The junction between a motor neuron and the sarcolemma of a muscle fibre is called the neuromuscular junction.
IV. A neural signal reaching the neuromuscular junction releases acetylcholine, generating an action potential in the sarcolemma.

Analyze these statements about the role of calcium ions in muscle contraction:

I. An action potential in the sarcolemma spreads through the muscle fibre and triggers calcium release into the sarcoplasm.
II. Calcium ions are stored in high concentrations within the sarcoplasmic reticulum.
III. Ca++ binds to a subunit of tropomyosin, causing it to undergo a conformational shift that unmasks actin.
IV. Increase in sarcoplasmic Ca++ levels removes the masking of active sites for myosin on thin filaments.

Identify the correct sequence of events during cross-bridge formation and rotation:

I. The myosin head binds to the exposed active sites on actin utilizing energy from ATP hydrolysis.
II. Formation of the cross-bridge pulls the attached actin filaments towards the center of the 'A' band.
III. The 'Z' lines attached to these actins are pulled outwards, elongating the sarcomere.
IV. During contraction, the 'I' bands get reduced, whereas the 'A' bands retain their original length.

Which of the following statements about the cross-bridge cycle and relaxation are true?

I. Myosin releases ADP and inorganic phosphate (Pi) to return to its relaxed state.
II. Binding of a new ATP molecule to the myosin head breaks the established cross-bridge.
III. The cross-bridge cycle continues indefinitely even after Ca++ is completely pumped back into the sarcoplasmic cisternae.
IV. Relaxation occurs when Ca++ is active in the sarcoplasm, keeping the troponin subunits fully bound.

Read the following statements regarding muscle fatigue and red muscle fibres:

I. Repeated activation of muscles leads to the accumulation of lactic acid due to the anaerobic breakdown of glycogen.
II. Red muscle fibres contain a high concentration of the oxygen-storing pigment myoglobin.
III. Red muscle fibres have very few mitochondria, making them depend strictly on anaerobic respiration.
IV. Because of their high capacity to utilize oxygen for ATP production, red fibres are also called aerobic muscles.

Compare red muscle fibres and white muscle fibres using the following statements:

I. White muscle fibres possess a very high quantity of myoglobin compared to red fibres.
II. The number of mitochondria is significantly fewer in white fibres than in red fibres.
III. White fibres contain a highly developed and abundant sarcoplasmic reticulum.
IV. White muscle fibres depend primarily on anaerobic processes for energy production.

Consider the statements regarding the human skeletal system matrix composition:

I. The skeletal system consists of a framework of bones and a few cartilages.
II. Bone has a very hard matrix due to the deposition of calcium salts.
III. Cartilage has a slightly pliable matrix due to the presence of chondroitin salts.
IV. In an adult human, the skeletal system is made up of 300 bones and numerous cartilages.