PHYSIOLOGY
SYNAPTIC PHYSIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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All motor units act together
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Muscle contraction continues for long periods after nervous stimulation ceases
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The crossbridges bind to the actin and shorten the sarcomeres
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Troponin is not needed to strengthen the contracting muscle cell.
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Detailed explanation-1: -During muscle contractions, actin filaments slide over myosin filaments resulting in shortening of a sarcomere. So the correct answer is ‘Length of A− band remains constant’.
Detailed explanation-2: -The globular heads of myosin bind actin, forming cross-bridges between the thick and thin filaments. It is important to note that the orientation of myosin molecules in the thick filaments reverses at the M line of the sarcomere.
Detailed explanation-3: -This process is known as myosin-actin cycling. As the myosin S1 segment binds and releases actin, it forms what are called cross bridges, which extend from the thick myosin filaments to the thin actin filaments. The contraction of myosin’s S1 region is called the power stroke (Figure 3).
Detailed explanation-4: -Once the myosin forms a cross-bridge with actin, the Pi disassociates and the myosin undergoes the power stroke, reaching a lower energy state when the sarcomere shortens. ATP must bind to myosin to break the cross-bridge and enable the myosin to rebind to actin at the next muscle contraction.