Gracile tubercle

Gracile tubercle is part of the dorsal column medial leminiscal sensory neuronal pathway. It is visible as an elevation or as a bump in the dorsal medulla, in the floor of the fourth ventricle. This bump is created by the underlying gracile nucleus. The gracile tubercle is quite distinct from the cuneate tubercle (or cuneate nucleus). The latter is also part of the dorsal column medial leminiscal pathway. However, the gracile tubercle (or gracile nucleus) is situated closer to the midline compared to the more laterally placed cuneate tubercle (or cuneate nucleus).

The first order neurons of the dorsal column medial leminiscal pathway–that carry sensory information of vibration, conscious proprioception, and 2-point discrimination and ascend in the dorsal spinal cord and medulla–are called dorsal fasciculi. In this context, the gracile fasciculus represents those first order neurons of the dorsal column pathway, that transmit this sensory information from the lower extremities. Hence, it can be found throughout the length of the spinal cord. It ascends in the dorsal spinal cord and medulla to terminate by synapsing with the gracile nuclei (in the gracile tubercle). On the contrary, the cuneate fasciculus, which also forms part of the dorsal column pathway, transmits the same sensory information from the upper extremities (sparing the head). Thus, it is situated at spinal segment level T6 and above only (being absent in the lower spinal cord). It ascends in dorsal medulla–staying lateral to gracile fasciculus–and ends up by synapsing with the cuneate nuclei (in the cuneate tubercle).