What motor and sensory defects are caused by a unilateral spinal cord lesion, also known as Brown-Sequard syndrome?

Brown-Sequard syndrome refers to the neurological condition resulting from a unilateral lesion in the spinal cord, which leads to a distinct pattern of motor and sensory deficits. The correct answer reflects the nature of these deficits, where there is ipsilateral motor disturbance meaning that the muscle control on the same side as the lesion is affected. This occurs due to the disruption of the corticospinal tract, which descends from the brain to the motor neurons in the spinal cord.

Additionally, there is contralateral loss of pain and temperature sensation, which is attributed to the interruption of the spinothalamic tract. This tract decussates (crosses over) to the opposite side several levels above the site of sensory loss. Therefore, while the motor disturbance is observed on the same side as the injury, pain and temperature sensation are lost on the side opposite the injury.

In contrast, the other answer choices do not correctly represent the neurological deficits associated with Brown-Sequard syndrome. The first choice inaccurately implies that proprioception, which is typically mediated by the dorsal columns, is lost contralaterally rather than ipsilaterally. The third option describing complete bilateral loss of function does not apply to Brown-Sequard syndrome, as the syndrome results in