Question

John has an injury to the lower thoracic spinal cord experienced a loss of pain sensation on the right side of the lower body following the injury since ________?

a. the left side of the spinal cord contains neuronal bodies that transmit painful stimuli from both sides of the body.

b. thalamocortical neurons send collaterals that cross over the midline of the brain, innervating the somatosensory cortex on the contralateral side of the body from the lesion.

c. the nucleus gracilis receives input from the contralateral nociceptive DRG neurons

d. DRG neurons transmitting ascending nociceptive information cross over the midline of the spinal cord at the spinal segment receiving the input.

e. the right side is primarily innervated by TrkC-expressing neurons in left DRGs

Answer 1

d DRG neurons transmitting ascending nociceptive information cross over the midline of the spinal cord at the spinal segment receiving the input

Within the pain pathway there are 3 orders of neurons which carry action potentials signalling pain:

First order neurons – These are pseudounipolar neurons which have cells bodies within the dorsal root ganglion. They have one axon which splits into two branches, a peripheral branch (which extends towards the peripheries) and a central branch (which extends centrally into spinal cord/brainstem).

Second order neurons – The cell bodies of these neurons are found in the Rexed laminae of the spinal cord, or in the nuclei of the cranial nerves within the brain stem. These neurons then decussate in the anterior white commissure and ascend cranially in the spinothalamic tract to the ventral posterolateral (VPL) nucleus of the thalamus.

Third order neurons – The cell bodies of third order neurons lie within the VPL of the thalamus. They project via the posterior limb of the internal capsule to terminate in the ipsilateral postcentral gyrus (primary somatosensory cortex). The postcentral gyrus is somatotopically organised. Therefore, pain signals initiated in the hand will terminate in the area of the cortex dedicated to represent sensations of the hand.