Question

The extension of arm is brought about by muscles shown in the diagram. The movement takes place when

• A. Muscle 1 relaxes while muscle 2 contracts
• B. Muscle 1 contracts while muscle 2 relaxes
• C. Muscle 1 contracts and then both muscles relax
• D. Muscle 1 and muscle 2 both relax the same time
• E. Muscle 1 and muscle 2 both contract at the same time

Answer 1

Answer: (A)

Muscle 1 relaxes while muscle 2 contracts

Biceps brachii (1) and triceps brachii (2) are the antagonistic pair of the forearm and work opposite to one another to move the forearm in opposite direction. Contraction of biceps brachii flexes the lower arm while the contraction of triceps brachii extends it. So, when biceps brachii relaxes, triceps brachii contracts. Thus, the correct answer is option A.