Muscles of inspiration include all except

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2023

Explanation

The internal intercostal muscles are primarily muscles of forced expiration, not inspiration.
When the internal intercostals contract, they pull the rib cage downward and inward, decreasing the volume of the thoracic cavity.
This action actively pushes air out of the lungs, which is the opposite of inspiration (drawing air in).

Option A: The diaphragm is the main muscle responsible for normal, quiet inspiration.
Option B: The external intercostal muscles work with the diaphragm during normal inspiration to elevate the ribs and expand the chest cavity.
Option C: The sternocleidomastoid is an accessory muscle of inspiration, used during deep or labored breathing to further elevate the sternum.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Muscles of Respiration as background academic context rather than a clinical decision trigger.
Nurses assess for the use of accessory muscles of inspiration, such as the sternocleidomastoid, as a key sign of respiratory distress. This finding indicates increased work of breathing and may signal impending respiratory failure.
Understanding the muscles of respiration is vital when caring for patients with neuromuscular disorders like Guillain-Barré syndrome or myasthenia gravis, as progressive muscle weakness can lead to respiratory compromise.
What if? If a patient has a high spinal cord injury at the C3 level, the phrenic nerve (which innervates the diaphragm) would likely be damaged. This would result in paralysis of the diaphragm, leading to respiratory arrest and the need for immediate mechanical ventilation, as the primary muscle of inspiration is no longer functional.

How to Approach the Question

First, identify the negative framing of the question by spotting the word 'except'. This means you must find the option that is NOT a muscle of inspiration.
Next, recall the main muscles involved in the process of breathing.
Categorize each option based on its primary function: inspiration or expiration.
The diaphragm and external intercostals are the primary muscles for normal, quiet inspiration.
The sternocleidomastoid is an accessory muscle used for deep, forced inspiration.
The internal intercostals are primarily used for active, forced expiration.

Concept Tested & Keywords

Concept Tested: Muscles of Respiration
Stem keywords: Muscles of inspiration
Lead-in keywords: except
Negative lead-in flag: The question asks to identify the option that is NOT a muscle of inspiration.

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E6 Physiology Guyton 4SAE Part 2A p. 45-47

Practise the full RUHS, Jaipur, M.Sc Nursing Entrance Exam-2023

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