A young adult who was hit by a car was fortunate because the level of his injury did not interrupt his respiratory function. The cord segment involved with maintaining respiratory function is?

1. A

   Thoracic level 5 and 6

2. B

   Thoracic level 2 and 4

3. C

   Cervical level 7 and 8

4. D

   Cervical level 3 and 4

Appeared in: PGIMER NO - 2020

Explanation

• The primary muscle responsible for breathing is the diaphragm.
• The diaphragm is controlled by the phrenic nerve, which provides its sole motor innervation.
• The phrenic nerve originates from the cervical spinal cord roots C3, C4, and C5.
• A well-known mnemonic in medicine is 'C3, 4, 5 keep the diaphragm alive,' highlighting the critical role of these spinal segments in maintaining life-sustaining respiration.
• Therefore, an injury above the C3 level results in respiratory arrest, while injuries below C5 spare the diaphragm.

Why Other Options Were Wrong

• Option A: The thoracic levels innervate the intercostal muscles, which are accessory (secondary) muscles for respiration, not the primary muscle.
• Option B: Similar to option A, these thoracic levels supply the intercostal muscles, which assist in breathing but are not the primary drivers of respiration.
• Option C: These lower cervical levels (C7-C8) primarily provide motor innervation to the triceps, wrist extensors, and finger muscles. They have no direct role in controlling the diaphragm.

Related Visual

Clinical Relevance

• Nursing practice connection: Knowing Spinal Cord Injury Levels and Respiratory Function helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• In any patient with a suspected cervical spine injury, the nurse's priority is to assess respiratory status immediately and continuously. An injury at or above C3-C5 can cause respiratory arrest.
• Signs of impending respiratory compromise in a spinal cord injury patient include a weak cough, paradoxical breathing (abdomen rises while chest falls on inspiration), and use of accessory neck muscles.
• Spinal immobilization (e.g., with a cervical collar and backboard) is crucial in trauma patients until a spinal injury is ruled out to prevent further damage to the cord.

How to Approach the Question

• First, identify the key physiological function in the question: 'respiratory function'.
• Second, recall the primary muscle responsible for this function. For respiration, this is the diaphragm.
• Third, connect the muscle to its nerve supply. The diaphragm is innervated by the phrenic nerve.
• Fourth, recall the spinal cord origin of the phrenic nerve. A helpful mnemonic is 'C3, 4, 5 keep the diaphragm alive.'
• Finally, scan the options to find the one that includes these critical cervical levels. Option D, 'Cervical level 3 and 4,' is the best fit.

Concept Tested & Keywords

• Concept Tested: Spinal Cord Injury Levels and Respiratory Function
• Stem keywords: spinal cord injury, respiratory function, cord segment
• Lead-in keywords: involved with
• Clinical cues: respiratory function not interrupted
• Negative lead-in flag: false

Question ID

QCs8hgdAUitiJtCySHe3qn

Copy ID

Reference Book

E6 Anatomy Grays 43e Vol 2 Part 2 p. 53-55

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 624-626

E6 Medicine Harrison 22e Part 2 p. 1464-1466