What is the correct sequence for transmitting a pain signal from receptor to cortex?

What is the correct sequence for transmitting a pain signal from receptor to cortex?

• A. Receptor -> First Order Neuron -> Spinal Cord/Brainstem -> Second Order -> Thalamus -> Third Order -> Cortex
• B. Receptor -> First Order Neuron -> Thalamus -> Cortex
• C. Receptor -> Second Order Neuron -> Third Order Neuron -> Spinal Cord
• D. Receptor -> First Order Neuron -> Spinal Cord -> Second Order Neuron -> Thalamus -> Third Order Neuron -> Cortex

Answer: (D)

Pain signals travel through a three-neuron relay: the first-order neuron carries the signal from the receptor to the dorsal root ganglion, then to the spinal cord where it synapses on a second-order neuron in the dorsal horn (for body) or brainstem nuclei (for face). The second-order neuron crosses to the opposite side and ascends to the thalamus, and a third-order neuron then relays the signal from the thalamus to the somatosensory cortex. This makes the correct sequence receptor -> first-order -> spinal cord -> second-order -> thalamus -> third-order -> cortex. The other options skip or rearrange one of these relays, which misplaces how the signal is transmitted from periphery to cortex.

Pain signals travel through a three-neuron relay: the first-order neuron carries the signal from the receptor to the dorsal root ganglion, then to the spinal cord where it synapses on a second-order neuron in the dorsal horn (for body) or brainstem nuclei (for face). The second-order neuron crosses to the opposite side and ascends to the thalamus, and a third-order neuron then relays the signal from the thalamus to the somatosensory cortex. This makes the correct sequence receptor -> first-order -> spinal cord -> second-order -> thalamus -> third-order -> cortex. The other options skip or rearrange one of these relays, which misplaces how the signal is transmitted from periphery to cortex.