Internal arcuate fibers

The internal arcuate fibers refer to that part of the second-order sensory neurons of the dorsal column-medial lemniscal (DCML) pathway that link the gracile and cuneate nuclei to the medial lemniscus.

• These fibers originate in the caudal medulla from the nucleus gracilis and nucleus cuneatus, which are the sites where first-order sensory neurons (carrying signals from the fasciculus gracilis and fasciculus cuneatus) synapse.

• Once the internal arcuate fibers emerge from the respective nuclei, they proceed to cross the midline of the medulla in a process known as decussation (also sometimes called the decussation of medial lemniscus). This crossing occurs in a sweeping arc-like fashion from the posterior medulla toward the anterior, forming a characteristic pattern as they migrate to the contralateral side.

• After the decussation, these fibers ascend the brainstem as part of the medial lemniscus, which transmits sensory information, including fine touch, proprioception, vibration, and two-point discrimination, to the thalamus.

• The critical role of the internal arcuate fibers is to ensure that sensory information from one side of the body is processed contralaterally in higher brain centers.