Final answer:
Fast pain sensations are transmitted via the spinothalamic tract, with signals relayed in the thalamus before reaching the primary somatosensory cortex in the cerebrum.
Step-by-step explanation:
Fast pain is carried by the spinothalamic tract (anterolateral system), relayed in the thalamus, and conducted to the primary somatosensory cortex of the cerebrum.
The two major tracts in the spinal cord, originating from sensory neurons in the dorsal root ganglia, are the dorsal column system and the spinothalamic tract. The spinothalamic tract is primarily responsible for transmitting pain and temperature sensations and crosses the midline right at the level where it enters the spinal cord, which differs from the dorsal column system that crosses in the medulla. Additionally, the trigeminal nerve contributes sensation information from the head to these pathways, with pain and temperature sensations being processed similarly to the spinothalamic tract.