After ascending two segments, where do A-delta and C fibers synapse?

After ascending two segments, where do A-delta and C fibers synapse?

• A. The reticular formation.
• B. The ventral horn.
• C. The dorsal horn.
• D. The gracile nucleus.

Answer: (C)

Pain and temperature signals carried by A-delta and C fibers enter the spinal cord through the dorsal root and travel a short distance in Lissauer's tract, ascending or descending about one to two segments before they synapse. The first synapse occurs in the dorsal horn, particularly in the superficial laminae (I–II, with substantia gelatinosa). From there, second-order neurons cross to the opposite side via the ventral white commissure and ascend in the spinothalamic tract to thalamic nuclei. This dorsal-horn synaptic location distinguishes it from the other options, which relate to different pathways or functions (reticular formation for pain modulation/arousal; ventral horn for motor neurons; gracile nucleus for fine touch/proprioception in the dorsal column).

Pain and temperature signals carried by A-delta and C fibers enter the spinal cord through the dorsal root and travel a short distance in Lissauer's tract, ascending or descending about one to two segments before they synapse. The first synapse occurs in the dorsal horn, particularly in the superficial laminae (I–II, with substantia gelatinosa). From there, second-order neurons cross to the opposite side via the ventral white commissure and ascend in the spinothalamic tract to thalamic nuclei. This dorsal-horn synaptic location distinguishes it from the other options, which relate to different pathways or functions (reticular formation for pain modulation/arousal; ventral horn for motor neurons; gracile nucleus for fine touch/proprioception in the dorsal column).