Which nerve supplies the diaphragm?

Appeared in: AIIMS Delhi NO - 2017

Explanation

The phrenic nerve provides the sole motor supply to the diaphragm, the main muscle of respiration.
It originates from the cervical plexus, specifically from the anterior rami of spinal nerves C3, C4, and C5.
The nerve's name comes from the Greek word 'phren', which means diaphragm.
It provides both motor fibers for muscle contraction and sensory fibers for the central part of the diaphragm, as well as surrounding pleura and peritoneum.

Option A: The gastric nerves are branches of the vagus nerve (cranial nerve X) that supply the stomach, not the diaphragm. They are involved in digestive functions like acid secretion and motility.
Option C: The ulnar nerve is a major nerve of the upper limb, originating from the brachial plexus. It supplies muscles in the forearm and hand, primarily responsible for finger movements and grip.
Option D: The radial nerve, also from the brachial plexus, is the primary nerve for the extensor muscles of the arm and forearm. It is responsible for extending the wrist and fingers.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Innervation of the diaphragm as background academic context rather than a clinical decision trigger.
Understanding the phrenic nerve's path is crucial during thoracic and cardiac surgeries to avoid iatrogenic injury, which can lead to diaphragmatic paralysis and respiratory compromise.
A nurse may assess for unilateral diaphragmatic paralysis by observing for paradoxical movement of the abdomen during breathing (the abdomen moves in on inspiration instead of out).
Phrenic nerve stimulation (diaphragm pacing) is a therapeutic option for patients with central hypoventilation syndrome or high spinal cord injuries who are ventilator-dependent.

How to Approach the Question

First, identify the key anatomical structure in the question, which is the 'diaphragm'.
Next, recall the primary function of the diaphragm, which is respiration.
Access your knowledge of the nervous system, specifically the innervation of major body structures. The question asks for the nerve that 'supplies' or innervates this muscle.
Evaluate the options provided. The phrenic nerve is specifically associated with the diaphragm. A common mnemonic is 'C3, 4, 5 keeps the diaphragm alive,' linking the nerve's spinal roots to its function.
Eliminate the other options by recalling their primary functions: Gastric (stomach), Ulnar (hand), and Radial (arm/wrist extensors). This confirms the phrenic nerve as the correct choice.

Concept Tested & Keywords

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E6 Anatomy BDChaurasia V2 10e Part 2 p. 116-118

E6 Anatomy Applied Ashalatha 4e p. 436-438

E6 Anatomy Grays 43e Vol 2 Part 2 p. 114-116

Practise the full AIIMS Delhi NO - 2017

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