Final answer:
The spinothalamic tract is responsible for transmitting pain and temperature sensations in the ascending spinal cord pathways.
Step-by-step explanation:
The ascending spinal cord tract responsible for transmitting pain and temperature sensations is the spinothalamic tract. Unlike the dorsal column-medial lemniscus pathway, which conveys fine touch, vibration, and proprioceptive information, the spinothalamic tract specializes in carrying pain and temperature signals to the brain. After entering the spinal cord, these signals cross over to the opposite side (decussate) and travel up to the brain contralaterally.