The is the major muscle responsible for breathing in humans?

JODHPUR AIIMS SNO-2018

Applied Physiology

Easy

Appeared in: JODHPUR AIIMS SNO-2018

Explanation

The diaphragm is the principal muscle of inspiration, responsible for approximately 75% of the air movement during quiet breathing.
It is a large, dome-shaped muscle located at the base of the thoracic cavity, separating it from the abdominal cavity.
During inhalation, the diaphragm contracts and moves downward, increasing the vertical dimension of the chest cavity, which draws air into the lungs.
Normal exhalation is a passive process resulting from the elastic recoil of the lungs and chest wall as the diaphragm relaxes.

Option A: The trapezius is a large muscle of the upper back. Its primary role is to move the scapula and support the arm.
Option C: The rectus abdominis is the primary muscle for flexing the trunk. In respiration, it is involved in forceful expiration, not primary inspiration.
Option D: The sternocleidomastoid is a prominent neck muscle whose main function is to rotate and flex the head.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Primary vs. Accessory Muscles of Respiration as background academic context rather than a clinical decision trigger.
Nurses must recognize the use of accessory muscles (like the sternocleidomastoid) as a critical sign of respiratory distress. This indicates the patient's work of breathing is high and the diaphragm alone cannot meet oxygen demands.
Paralysis of the diaphragm, often resulting from phrenic nerve injury (e.g., from a spinal cord injury at the C3-C5 level), is a life-threatening emergency requiring immediate mechanical ventilation.
What if? - If a patient with a chronic lung disease like COPD is observed leaning forward with hands on their knees (tripod position) and has visible neck muscle contractions during breathing, it signifies severe respiratory distress. The tripod position helps the diaphragm move, and the neck muscle use shows accessory muscles are engaged to maximize air intake. This requires immediate nursing assessment and intervention.

How to Approach the Question

Identify the keyword in the question: "major muscle". This asks for the primary muscle, not just any muscle involved in breathing.
Recall the basic anatomy of the torso and neck.
Consider the primary function of each muscle listed in the options.
Differentiate between muscles used for normal, quiet breathing (primary) and those recruited only during forceful or labored breathing (accessory).
The diaphragm is uniquely responsible for the vast majority of work in quiet breathing, making it the correct answer.
Eliminate the other options by identifying them as accessory muscles with different primary functions (back/shoulder movement, abdominal flexion, head rotation).

Concept Tested & Keywords

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