A spinal injury at C4 most directly affects which function?

• A. Diaphragm and breathing
• B. Urinary continence
• C. Lower limb sensation
• D. Facial expression

Answer: (A)

The question tests how a cervical spinal injury affects breathing through the diaphragm. The diaphragm is the main muscle for inspiration and is innervated by the phrenic nerve, which fibers originate from the spinal segments C3–C5. If an injury occurs at C4, the neural signals to the diaphragm can be disrupted, leading to impaired diaphragmatic contraction and reduced ventilation. That direct impact on the diaphragm explains why breathing is the function most affected.

Urinary continence depends on nerves that originate lower in the spinal cord (and pelvic nerves), so it isn’t directly disrupted by a cervical injury. Lower limb sensation comes from nerve pathways that begin lower down the spinal cord, so while extensive cervical injury can affect overall motor and sensory function, the most immediate and direct consequence of a C4 injury is compromised diaphragmatic breathing. Facial expression is controlled by cranial nerves in the brainstem, not the spinal cord, so it’s not directly impacted by cervical spinal injury.