Which condition is responsible for inspiration?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Explanation

Inspiration is an active process requiring the contraction of key respiratory muscles.
The diaphragm, the primary muscle of inspiration, contracts and flattens, increasing the vertical dimension of the chest cavity.
The external intercostal muscles also contract, elevating the ribs and sternum, which increases the front-to-back and side-to-side dimensions of the chest.
The combined action of both muscle groups expands the thoracic volume, creating a pressure gradient that draws air into the lungs.

Option A: The term 'dilatation' is incorrect for muscle action; muscles contract or relax. Furthermore, the intercostal muscles relax during passive expiration, they do not dilate.
Option B: While the contraction of the external intercostal muscles is a key component of inspiration, it is not the sole action. This answer is incomplete as it omits the primary role of the diaphragm.
Option C: While the contraction of the diaphragm is the main driver of quiet inspiration, it is not the only muscle involved. This answer is incomplete as it omits the action of the external intercostal muscles.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of Respiration: Muscles of Inspiration as background academic context rather than a clinical decision trigger.
Assessing the work of breathing is a fundamental nursing skill. Observing for the use of accessory muscles (like the sternocleidomastoid in the neck) can indicate respiratory distress, as the body struggles to get enough air.
Conditions like phrenic nerve damage (which controls the diaphragm) or muscular dystrophy can paralyze respiratory muscles, leading to significant breathing difficulty and reliance on accessory muscles.
What if? If a patient has a high spinal cord injury (at or above the C3-C5 vertebrae), the phrenic nerve can be severed or damaged. This results in paralysis of the diaphragm, leading to respiratory failure and the need for long-term mechanical ventilation.

How to Approach the Question

First, identify the core physiological process asked in the question: inspiration (inhalation).
Recall that normal inspiration is an active process, meaning it requires energy and muscle contraction.
Consider the primary muscles involved in breathing. The two main groups are the diaphragm and the intercostal muscles.
Evaluate each option. Options B and C describe correct individual actions that occur during inspiration.
Look for the most comprehensive answer. Since both the diaphragm and external intercostal muscles contract simultaneously to cause inspiration, the option that includes both actions is the best and most complete choice.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 2A pp. 46-48, 47-49