Which statement about third-order neurons is false?

Which statement about third-order neurons is false?

• A. They reside in the thalamus
• B. They project to the primary somatosensory cortex
• C. They are involved in conscious sensation
• D. They originate in the dorsal root ganglion

Answer: (D)

The main idea is that the somatosensory pathway is a three-neuron relay: first-order neurons begin in the dorsal root ganglion, second-order neurons relay in the spinal cord or brainstem and then cross, and third-order neurons reside in the thalamus and send signals to the primary somatosensory cortex to produce conscious sensation. Because of this arrangement, the statement that third-order neurons originate in the dorsal root ganglion is incorrect. The dorsal root ganglion houses the first-order neurons, not the third-order ones. The other statements are consistent with this pathway: third-order neurons are located in the thalamus, they project to the primary somatosensory cortex, and their activity underlies conscious perception of touch, proprioception, and related modalities.

The main idea is that the somatosensory pathway is a three-neuron relay: first-order neurons begin in the dorsal root ganglion, second-order neurons relay in the spinal cord or brainstem and then cross, and third-order neurons reside in the thalamus and send signals to the primary somatosensory cortex to produce conscious sensation. Because of this arrangement, the statement that third-order neurons originate in the dorsal root ganglion is incorrect. The dorsal root ganglion houses the first-order neurons, not the third-order ones. The other statements are consistent with this pathway: third-order neurons are located in the thalamus, they project to the primary somatosensory cortex, and their activity underlies conscious perception of touch, proprioception, and related modalities.