Posterior intermediate sulcus of spinal cord

The posterior intermediate sulcus of spinal cord is an additional sulcus which is situated on the dorsal (or posterior) surface of the spinal cord, between the posterior midline fissure and the posterolateral sulcus.

The posterior intermediate sulcus of spinal cord divides the dorsal sensory ascending column into two halves–separating the gracile fasciculus medially, from the cuneate fasciculus laterally.

The gracile fasciculus represents the first order neurons of the dorsal column medial leminiscal pathway, that carry sensory information of vibration, proprioception, and 2-point discrimination from lower extremities (spinal segment level T6 and below) and ascend in the dorsal spinal cord and medulla to synapse with gracile nuclei. On the contrary, the cuneate fasciculus, which also forms part of the dorsal column pathway, transmits the same sensory information from upper extremities (spinal segment level T6 and above) and ascends in dorsal medulla–lateral to gracile fasciculus–to end up synapsing with the cuneate nuclei.

Please note that since, there is no fasciculus cuneatus from T6 below, therefore the posterior intermediate sulcus of spinal cord cannot be seen in the lower half of the spinal cord.