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NEET Questions / Zoology / Locomotion And Movement / Mechanism Of Muscle Contraction
A researcher is studying muscle contraction in vitro. They observe that even with sufficient ATP and $Ca^{2+}$$, contraction doesn't occur when they introduce a compound that specifically inhibits the binding of myosin heads to actin filaments. Which step of the cross-bridge cycle is directly affected by this compound?
Release of Pi from the myosin head
Attachment of myosin heads to actin
Hydrolysis of ATP
Power stroke
Rigor mortis, the stiffening of muscles after death, occurs because:
$Ca^{2+}$$ influx into the sarcoplasm ceases.
Troponin-tropomyosin complex permanently blocks myosin binding sites.
ATP depletion prevents detachment of myosin heads from actin.
Acetylcholine is no longer released at the neuromuscular junction.
A genetic mutation affects the $Ca^{2+}$$-ATPase pumps in the sarcoplasmic reticulum (SR). Which of the following would be the MOST likely direct consequence of this mutation in muscle fibers?
Inhibition of action potential propagation along the sarcolemma
Reduced release of acetylcholine at the neuromuscular junction
Prolonged muscle contraction due to impaired $Ca^{2+}$$ removal from the sarcoplasm
Inability of troponin to bind $Ca^{2+}$$
In a skeletal muscle fiber, during a single twitch, the amount of tension generated during the contraction phase is directly proportional to:
The concentration of ATP in the sarcoplasm
The duration of the action potential
The frequency of nerve stimulation
The number of cross-bridges formed between actin and myosin
Which of the following statements accurately describes the role of ATP in muscle contraction?
ATP hydrolysis provides energy for the power stroke, but not for detachment of myosin from actin.
ATP binding to myosin causes the power stroke.
ATP is only required for the detachment of myosin heads from actin.
ATP is required for both the attachment and detachment of myosin heads to actin.
In a research experiment, a muscle fiber is exposed to a drug that inhibits the activity of acetylcholinesterase. Which of the following is the MOST likely direct effect on muscle contraction?
Inhibition of action potential generation in the muscle fiber
Prevention of calcium release from the sarcoplasmic reticulum
Prolonged muscle contraction due to continuous stimulation at the neuromuscular junction
Increased rate of ATP hydrolysis
Which ion is directly responsible for initiating muscle contraction by binding to troponin?
Na+
K+
Ca2+
Mg2+
What is the role of ATP in muscle contraction?
Provides energy for the power stroke and detachment of myosin heads
Initiates the release of calcium ions from the sarcoplasmic reticulum
Causes the shortening of actin filaments
Transports calcium ions back into the sarcoplasmic reticulum
What protein filaments slide past each other during muscle contraction?
Actin and Myosin
Actin and Tropomyosin
Myosin and Troponin
Troponin and Tropomyosin
The functional unit of muscle contraction is called:
Sarcomere
Myofibril
Sarcolemma
Sarcoplasmic reticulum
