An abnormal posture in a patient with traumatic brain injury most likely indicates dysfunction in which structure?

• A. Basal ganglia
• B. Cranial nerves
• C. Motor tracts of the spinal cord
• D. Cerebral cortex

Answer: (C)

An abnormal posture after brain injury usually stems from loss of control by the descending motor pathways that reach the spinal cord. These motor tracts—the pathways that carry commands from the brain to the spinal cord and modulate the activity of spinal motor neurons and interneurons—set muscle tone and coordinate posture. When these tracts are damaged, the spinal circuits can become overly active or poorly coordinated, leading to abnormal postures such as persistent extension or flexion patterns. This is why dysfunction of the motor tracts of the spinal cord best explains an abnormal posture in traumatic brain injury.

Basal ganglia involvement tends to produce patterns of involuntary movement and changes in tone rather than a straightforward postural abnormality after diffuse injury. Cranial nerves damage would cause specific cranial-nerve–related deficits rather than a generalized postural change. Damage to the cerebral cortex affects planning and voluntary movement but the observed posture in this context most directly reflects disruption of the spinal cord’s motor pathways.