Dorsal column nuclei

Structure

Nerve pathways

The dorsal column nuclei each have an associated nerve tract in the spinal cord, the gracile fasciculus and the cuneate fasciculus, together forming the dorsal columns. Both dorsal column nuclei contain synapses from afferent nerve fibers that have travelled in the spinal cord. They then send on second-order neurons of the dorsal column–medial lemniscal pathway.

Neurons of the dorsal column nuclei eventually reach the midbrain and the thalamus. They send axons that form the internal arcuate fibers. These cross over at the sensory decussation to form the medial lemniscus. They then synapse with third-order neurons of the thalamus.

Nuclei

The major nuclei are the cuneate nucleus and gracile nucleus. These are present at the bottom of the medulla oblongata.

Gracile nucleus

The gracile nucleus is medial to the cuneate nucleus. Its neurons receive afferent input from dorsal root ganglia sensory neurons of the lower torso and the lower limbs. The gracile nucleus and gracile fasciculus carry epicritic, kinesthetic, and conscious proprioceptive information from the lower part of the body (below the level of T6 in the spinal cord). Because of the large population of neurons in the gracile nucleus they give rise to a raised area called the gracile tubercle on the posterior side of the closed medulla at the floor of the fourth ventricle.

Cuneate nucleus

The cuneate nucleus is lateral to the gracile nucleus. It carries the same type of information, but from the upper body and the upper limbs (except the face, which is carried by the principal sensory nucleus of trigeminal nerve). The cuneate nucleus is wedge-shaped and located in the closed part of the medulla. It lies lateral to the gracile nucleus and medial to the spinal trigeminal nucleus in the medulla. The large number of neurons found there give rise to the cuneate tubercle seen on viewing the posterior aspect of the medulla on the side of the brainstem.