Gracile nucleus

The gracile nucleus (a.k.a. nucleus gracilis), is a gray matter nucleus located in the dorsal medulla oblongata. Positioned near the midline, it marks the lower margin of fourth ventricle's floor and lies medial to the cuneate nucleus. It's location is externally indicated by a tubercle or a bump on the dorsal medulla, called the gracile tubercle.

Functionally, the gracile nucleus is part of the dorsal column-medial lemniscus pathway, processing sensory modalities such as vibration, proprioception, and two-point discrimination. This pathway is a three-order neuron system. Originating from the ipsilateral or same side of the body below the T6 level, first-order neurons transmit this sensory information via the gracile fasciculus to synapse in the gracile nucleus.

Next, the second-order neurons arising from the gracile nucleus project as internal arcuate fibers, crossing (decussating) to form the medial lemniscus. These fibers subsequently ascend to the Ventral Posterolateral (VPL) nucleus of the thalamus for further processing.

Lesions affecting the gracile nucleus or its fasciculus can result in sensory deficits, particularly affecting the trunk and legs, indicative of damage below the T6 level.