Posterior external arcuate fibres are uncrossed fibers from the lateral part of the arcuate nucleus to the inferior cerebellar peduncle. Above the level of C8 they replace the posterior spinocerebellar tract. The dorsal nucleus is absent here.

a fiber bundle that extends across the midline of the medulla. Many of the fibers consist of axons traveling from the nucleus gracilis and nucleus cuneatus to the contralateral side of the medulla where they will begin traveling up to the cortex as part of the medial lemniscus.

The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

Brainstem. The neurons in these two nuclei (the dorsal column nuclei) are second-order neurons. Their axons cross over to the other side of the medulla and are now named as the internal arcuate fibers, that form the medial lemniscus on each side. This crossing over is known as the sensory decussation.

The medial lemniscus, also known as Reil’s band or Reil’s ribbon, is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus.

The internal arcuate fibers are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the posterior grey column in the spinal cord.

Fasciculus gracilis carries sensory information associated with the DCML pathway from the lower extremities and terminates and synapses at the nucleus gracilis in the caudal medulla. It is located medial relative to the fasciculus cuneatus and travels all along the spinal cord.

The medial longitudinal fasciculus (MLF) is one of a pair of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are made up of both ascending and descending fibers that arise from a number of sources and terminate in different areas.

the first neuron in a chain or tract of neurons. For example, in the somatosensory system, a first-order neuron receives peripheral input (e.g., sensations from the skin) and transmits it to the spinal cord.

Spinal lemniscus. – the anterolateral system (anterior and lateral spinothalamic tracts). In older terminology, the anterior and lateral spinothalamic tracts remained discrete while ascending in the spinal cord.

The accessory cuneate nucleus is located lateral to the cuneate nucleus in the medulla oblongata at the level of the sensory decussation. It receives input from cervical spinal nerves and transmits that information to the cerebellum.

Gracile and cuneate nuclei are second-order sensory neurons which receive peripheral input from the first-order neurons in the gracile fasciculus and the cuneate fasciculus of the dorsal columns. These nuclei send out axons called the internal arcuate fibers, which become the medial lemniscus after they decussate in the medulla oblongata 1,2.

(Arcuate fibers labeled at center right.) The internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the gracile and cuneate nuclei in the medulla.

The fibers of fasciculus gracilis reach the ipsilateral cuneatus nucleus in the caudal medulla, where they synapse with second-order neurons. These second-order neurons then cross over as internal arcuate fibers and form the medial lemniscus on the contralateral side.

Section of the medulla oblongata at about the middle of the olive. (Arcuate fibers labeled at center right.) The internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata.