Muscle of inspiration is?

Appeared in: ESIC Nursing Officer 2016 (Shift -2)

Explanation

The diaphragm is the principal muscle of inspiration (inhalation).
During quiet breathing, the diaphragm contracts and flattens, moving downward.
This movement increases the vertical volume of the thoracic cavity, which decreases the pressure within the lungs.
The resulting negative pressure gradient draws air into the lungs from the atmosphere.

Option B: The sternum (breastbone) is a bone, not a muscle. It serves as an attachment point for ribs and some chest muscles but does not actively contract.
Option C: Ribs are the bony framework of the chest. They are moved by muscles (like the intercostals) but are not muscles themselves.
Option D: Abdominal muscles are the primary muscles of active or forced expiration, not inspiration. They contract to push the diaphragm up, expelling air.

Visual 1: Diagram: Anatomy of the respiratory system, highlighting the location and dome shape of the diaphragm below the lungs.
Visual 2: Animation: Illustrating the movement of the diaphragm and rib cage during the cycles of inspiration and expiration.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of Respiration as background academic context rather than a clinical decision trigger.
Nurses teach patients with conditions like COPD diaphragmatic ('belly') breathing exercises. This technique strengthens the diaphragm, reduces the work of breathing, and improves gas exchange.
Assessment of respiratory muscle strength is vital in patients with neuromuscular diseases (e.g., Guillain-Barré syndrome, myasthenia gravis) or spinal cord injuries, as diaphragm weakness can lead to respiratory failure.
What if? If a patient sustains a high spinal cord injury above the C3-C5 vertebrae, the phrenic nerve that innervates the diaphragm is severed. This results in paralysis of the diaphragm, leading to an inability to breathe independently and the need for mechanical ventilation.

How to Approach the Question

First, identify the keywords in the question: 'Muscle' and 'inspiration'. This tells you the question is asking for a specific muscle involved in the act of breathing in.
Next, evaluate each option based on its anatomical classification. 'Sternum' and 'Ribs' are bones, not muscles, so they can be immediately eliminated.
You are left with two muscle groups: 'Diaphragm' and 'Abdominal muscles'.
Recall the primary function of each in respiration. The diaphragm is the main driver of inspiration. The abdominal muscles are primarily used for forced expiration.
Based on this differentiation, select the option that correctly matches the function asked for in the question (inspiration).

Concept Tested & Keywords

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Practise the full ESIC Nursing Officer 2016 (Shift -2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.