The correct option is (c) 2 and 3 only.
Explanation
The diaphragm is the primary muscle of respiration in mammals. It serves as a structural partition separating the thoracic (chest) cavity from the abdominal cavity and plays a critical role in the mechanics of breathing through its contraction and relaxation.
Statement-wise Analysis
- Statement 1 is Incorrect. The diaphragm is not a rigid bony plate; it is a large, dome-shaped sheet of skeletal muscle and fibrous tissue. It is flexible and contractile, which allows it to change shape to facilitate breathing, unlike rigid bone structures.
- Statement 2 is Correct. Anatomically, the diaphragm forms the floor of the chest (thoracic) cavity and the roof of the abdominal cavity. This positioning allows it to effectively regulate the volume and pressure within the thoracic cavity.
- Statement 3 is Correct. During the process of inhalation (inspiration), the diaphragm contracts and flattens, moving downwards towards the abdominal cavity. This movement increases the volume of the thoracic cavity, thereby decreasing the intrathoracic pressure and drawing air into the lungs.
Key Takeaway
The diaphragm is a muscular partition, not a bone, that forms the floor of the thoracic cavity. Its downward movement (contraction) is the primary mechanism for increasing thoracic volume during inhalation.