The phrenic nerve normally originates from:

Appeared in: DSSSB 6 September 2024

Explanation

The phrenic nerve originates from the anterior rami of the cervical spinal nerves C3, C4, and C5.
A widely used mnemonic to remember this anatomical fact is: 'C3, 4, and 5 keep the diaphragm alive.'.
This nerve provides the sole motor innervation to the diaphragm, which is the primary muscle responsible for inspiration.
It also carries sensory fibers from the central diaphragm, pericardium, and mediastinal pleura.

Option B: These are thoracic spinal nerves. The T1 root is a major contributor to the brachial plexus, which innervates the upper limb, while T1 and T2 also form intercostal nerves for the chest wall.
Option C: These are typical thoracic spinal nerves that form intercostal nerves, providing motor supply to the intercostal muscles and sensory supply to the skin of the chest wall.
Option D: These upper cervical nerves supply the suboccipital muscles and skin of the upper neck and back of the head. They also contribute to the ansa cervicalis, which innervates infrahyoid muscles, but not the phrenic nerve.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy and origin of the phrenic nerve as background academic context rather than a clinical decision trigger.
A spinal cord injury at or above the C3 level is catastrophic because it severs the brain's connection to the phrenic nerve, leading to diaphragmatic paralysis and the inability to breathe independently.
Nurses must be aware that patients undergoing thoracic or cardiac surgery are at risk for iatrogenic (inadvertent) phrenic nerve injury, which can cause significant postoperative respiratory compromise.
What if? If a patient has a spinal cord injury at the C6 level, their diaphragm function would remain intact because the phrenic nerve originates higher (C3-C5). However, they would have paralysis of the intercostal and abdominal muscles, impairing their ability to cough and clear secretions, increasing the risk of pneumonia.

How to Approach the Question

This is a factual recall question testing knowledge of basic neuroanatomy.
Identify the key anatomical structure in the question: 'phrenic nerve'.
Recall the primary function of this nerve, which is to control the diaphragm for breathing.
Access the common medical mnemonic associated with this nerve: 'C3, 4, and 5 keep the diaphragm alive.'
This mnemonic directly links the nerve to its spinal cord origins.
Compare this information (C3-C5) with the given options and select the matching choice.

Concept Tested & Keywords

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E6 Anatomy Grays 43e Vol 2 Part 1 p. 37-39

Practise the full DSSSB 6 September 2024

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