Q.(i) Draw a labelled diagram of mechanism of inspiration and expiration.

The average resting breathing rate in a healthy human is roughly 12–16 breaths per minute.

Breathing rate (the number of complete breathing cycles — one inspiration plus one expiration — per minute) is one of the basic respiratory volumes/parameters discussed alongside tidal volume, vital capacity, and residual volume. For a healthy adult at rest, this rate averages about 12 to 16 times per minute. It rises during exercise, fever, high altitude, or emotional stress because the body's oxygen demand and CO₂ output i …

The normal breathing rate in a healthy adult is 12-16 breaths per minute, so the answer is (B).

The respiratory rate is the number of breaths (one inspiration + one expiration) taken per minute. In a healthy adult at rest, this is normally about 12 to 16 breaths per minute.

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During inspiration the diaphragm contracts and moves downwards, so the answer is (B).

Inspiration is an active process. The diaphragm (dome-shaped at rest) contracts and flattens, moving downwards, while the external intercostal muscles lift the ribs and sternum. Together these increase the volume of the thoracic cavity and lungs, lowering the intrapulmonary pressure below atmospheric pressure so air rushes in.

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The statement is False — contraction, not relaxation, of the diaphragm and inter-costal muscles drives inspiration.

Breathing in humans is driven by changes in the volume of the thoracic cavity. During inspiration, the diaphragm contracts and flattens (moving downward), and the external inter-costal muscles contract, lifting the ribs and sternum outward and upward. Together these actions increase the volume of the thoracic chamber, decreasing the pulmonary pressure below atmospheric pressure so air rushes into the lungs. During expiration, the diaphragm and inter-costal muscles rel …

Inspiration happens when the diaphragm and the external intercostal muscles both CONTRACT, enlarging the thoracic cavity and drawing air in — option (a).

Step 1 — Muscles involved in breathing.

Breathing (pulmonary ventilation) is achieved by rhythmic contraction and relaxation of the diaphragm (a dome-shaped muscle separating thorax from abdomen) and the intercostal muscles between the ribs.

Step 2 — What happens during inspiration.

• The diaphragm contracts, so its dome flattens and moves downward, increasing the vertical dimension of the thoracic cavity.
• The external intercostal muscles contract, pulling the ribs and sternum upward and outward, increasing the antero-posterior and lateral dimensions of the thoracic cavity. …

Inspiration begins when the diaphragm's muscle fibres contract, flattening its dome shape and enlarging the thoracic cavity so air is drawn in.

Breathing (pulmonary ventilation) works on pressure differences created by changing the volume of the thoracic chamber. The diaphragm is a dome-shaped muscular partition between the thoracic and abdominal cavities.

• During inspiration, the diaphragm contracts, which pulls it downward and flattens its dome shape; simultaneously the external intercostal muscles contract, lifting the ribs and sternum outward. Both actions increase the volume of the thoracic cavity, decreasing intra-pulmonary pressure below atmospheric pressure, so air flows into the lungs. …

Expiration (exhalation) is the breathing movement that pushes air out of the lungs into the atmosphere, occurring when the thoracic (chest) volume decreases.

During expiration:

• The diaphragm relaxes and domes upward, and the external intercostal muscles relax, allowing the ribcage to move down and inward.
• This decreases the volume of the thoracic cavity and lungs, which increases the pulmonary (intra-pulmonary) pressure above atmospheric pressure. …

The diaphragm's contraction and relaxation, together with the intercostal muscles, drive breathing: relaxation of the diaphragm assists expiration.

During inspiration, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and drawing air in. During expiration, the diaphragm relaxes and returns to its dome (upward-curved) shape, decreasing tho …