The nerve which supplies the diaphragm?

Appeared in: SCTIMST Staff Nurse - 2015 (Set-B)

Explanation

The phrenic nerve is the primary motor nerve that supplies the diaphragm, which is the main muscle of respiration.
It originates from the cervical spinal nerves C3, C4, and C5 in the neck.
A common mnemonic to remember its origin is "C3, 4, 5 keep the diaphragm alive," highlighting its critical role in breathing.

Option B: The sciatic nerve is the largest nerve in the body and innervates the muscles and skin of the posterior thigh, leg, and foot.
Option C: The trigeminal nerve (Cranial Nerve V) is primarily responsible for sensory information from the face and motor control of the muscles of mastication (chewing).
Option D: The accessory nerve (Cranial Nerve XI) controls the sternocleidomastoid and trapezius muscles, which are involved in turning the head and shrugging the shoulders.

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.
A crucial nursing assessment for patients with high cervical spine injuries (at or above C5) is monitoring respiratory status, as phrenic nerve function may be compromised, leading to respiratory arrest.
Irritation of the phrenic nerve, for example, from a subphrenic abscess or fluid collection after abdominal surgery, can cause persistent hiccups or referred pain to the shoulder (Kehr's sign), which are important diagnostic clues.
What if? If a patient has unilateral phrenic nerve palsy (paralysis on one side), they might be asymptomatic at rest, but on an X-ray, the affected side of the diaphragm will appear elevated. The patient would likely experience significant shortness of breath (dyspnea) with exertion.

How to Approach the Question

First, identify the core of the question: it asks for the specific nerve that controls the diaphragm.
This is a factual recall question based on knowledge of human anatomy and the peripheral nervous system.
Systematically review the options provided.
Recall the primary function of each nerve: Phrenic nerve is linked to the diaphragm and breathing. Sciatic nerve to the leg. Trigeminal nerve to the face. Accessory nerve to the neck and shoulder muscles.
Eliminate the distractors whose functions do not involve the diaphragm.
Select the option that correctly matches the nerve to the diaphragm, which is the phrenic nerve.

Concept Tested & Keywords

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E6 Anatomy Applied Ashalatha 4e p. 433-435

Practise the full SCTIMST Staff Nurse - 2015 (Set-B)

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