The dorsal column–medial lemniscus pathway

The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway, PCML) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception(position) from the skin and joints. It transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain.

 The pathway receives information from sensory receptors (missner’s corpuscle, pacinian corpuscle etc.) throughout the body, and carries this in nerve tracts in the white matter of the dorsal columns of the spinal cord to the medulla, where it is continued in the medial lemniscuses, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex.

The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

There are three groupings of neurons that are involved in the pathway: first-order neurons, second-order neurons, and third-order neurons.

 The first-order neurons are sensory neurons located in the dorsal root ganglia, that send their afferent fibers through the two dorsal columns – the gracile fasciculus, or gracile tract, and the cuneate fasciculus, or cuneate tract. The first-order axons make contact with second-order neurons of the dorsal column nuclei (the gracile nucleus and the cuneate nucleus) in the lower medulla.

The second-order neurons send their axons to the thalamus.

The third-order neurons are in the ventral nuclear group in the thalamus and fibres from these ascend to the postcentral gyrus.

Sensory information from the upper half of the body is received at the cervical level of the spinal cord and carried in the cuneate tract, and information from the lower body is received at the lumbar level and carried in the gracile tract. The gracile tract is medial to the more lateral cuneate tract.

The axons of second-order neurons of the gracile and cuneate nuclei are known as the internal arcuate fibers and when they cross over the midline, at the sensory decussation in the medulla, they form the medial lemniscus which connects with thalamus; the axons synapse on neurons in the ventral nuclear group which then send axons to the postcentral gyrus in the parietal lobe. All of the axons in the DCML pathway are rapidly conducting, large, myelinated fibers.