Peripheral nervous system disease or spinal cord injury is typically associated with which change in muscle tone?

• A. Increased tone
• B. Decreased tone
• C. Normal tone
• D. Fluctuating tone

Answer: (B)

Muscle tone is governed by a balance between brain-driven signals (upper motor neurons) and reflex activity in the spinal cord and peripheral nerves. When the motor input is damaged at the level of the peripheral nervous system or the spinal cord regions that directly supply the muscle (lower motor neuron involvement), the reflex arc is diminished and the muscle lacks steady, baseline activation. This leads to decreased resting resistance to movement, i.e., hypotonia. In peripheral nerve disease or spinal cord injury, this diminished tone is the typical pattern seen. Remember, injuries affecting the upper motor pathways tend to raise tone (spasticity), though acute spinal cord injury can briefly present with reduced tone due to spinal shock.