Decussation of medial lemniscus

The decussation of medial lemniscus refers to the crossing of second-order sensory neurons within the caudal medulla. This decussation is a key component of the dorsal column-medial lemniscal (DCML) pathway, which facilitates the transmission of fine touch, vibration, proprioception, and two-point discrimination sensations from the periphery to the brain.

After ascending through the spinal cord via the dorsal column, the first-order neurons of the fasciculus gracilis (lower body sensory input) and fasciculus cuneatus (upper body sensory input) terminate in the nucleus gracilis and nucleus cuneatus, respectively, located in the caudal medulla. Here, the second-order neurons emerge as internal arcuate fibers, which cross from the ipsilateral to the contralateral side of the medulla, forming the decussation of medial lemniscus. Once the fibers have crossed, they organize themselves into a vertical, ribbon-like structure known as the medial lemniscus. This medial lemniscus ascends through the brainstem, positioned dorsally to the pyramids, and carries sensory information to the thalamus.

The decussation ensures that sensory information from one side of the body is processed by the contralateral side of the brain, maintaining the pattern of sensory crossover observed in many neural pathways.