Mechanism of Breathing · NCERT Biology

Which muscles are primarily responsible for the relaxation phase during normal quiet expiration?

  1. Contraction of internal intercostal muscles
  2. Active contraction of abdominal muscles
  3. Passive recoil; no muscles actively contract
  4. Sustained diaphragm contraction
Show answer and explanation

Correct answer: Passive recoil; no muscles actively contract

Normal expiration is largely a passive process. It occurs when the diaphragm and external intercostal muscles relax, allowing the lungs and thoracic cage to recoil to their original positions.

Difficulty: Medium Question 5 of 20

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