Dorsal Column (Medial Lemniscus)

Summary

The dorsal column medial lemniscus pathway (DC-ML), also known simply as the dorsal column pathway, is a neural pathway that carries sensory information from the body upwards to the brain. The primary senses carried by the dorsal column pathway include proprioception or joint position sense, fine touch including 2 point discrimination, vibration sense, and pressure. Problems with any part of the dorsal column pathway can lead to loss of these 4 senses.

The anatomical path of the dorsal column pathway starts in the nerve endings in peripheral tissues. These nerve endings are actually nerve projections of the dorsal root ganglia, which is the first order neuron of this pathway. Sensory information in these neurons actually bypasses the pseudounipolar cell body in the dorsal root to enter the spinal cord, where it ascends ipsilaterally as the dorsal column.

The dorsal column then runs upwards in the spinal cord to eventually reach the brainstem, where it ends by synapsing with the nucleus gracilis and nucleus cuneatus. These nuclei form the 2nd order neurons of this sensory pathway. Nerve projections from these nuclei then notably decussate or cross over in the medulla, before traveling upwards in the brainstem as the medial lemniscus.

The medial lemniscus in turn terminates in the thalamus where it synapses with the ventral posterolateral or VPL nucleus. Therefore, the VPL nucleus of the thalamus is the 3rd order neuron of this sensory pathway. Nerve projections from this VPL nucleus eventually reach the primary somatosensory cortex to complete the pathway.

Key Points

• Dorsal Column
  • Ascending sensory tract
    • Nerve tract carries sensory information from periphery to brain
  • Functions
    • Fine touch (conscious)
    • Vibration
    • Proprioception
    • Pressure
  • Pathway
    • 1st order neuron: Pseudounipolar cell body in dorsal root ganglion
      • Sensory nerve ending → bypasses cell body in dorsal root ganglion → enters spinal cord → ascends ipsilaterally in dorsal columns
      • Synapses with 2nd order neuron
    • 2nd order neuron: Nucleus gracilis + Nucleus cuneatus in ipsilateral medulla
      • Decussates in medulla
      • Ascends contralaterally as medial lemniscus
      • Synapses with Ventral posterolateral nucleus of thalamus
    • 3rd order neuron: Ventral posterolateral nucleus of thalamus
      • Runs to primary somatosensory cortex
  • Clinical Context
    • Tabes dorsalis (neurosyphilis) can result in degeneration of the dorsal column and loss of vibration and proprioception
    • Vitamin B12 deficiency leads to subacute combined degeneration of both the dorsal column and the lateral corticospinal tracts.
    • Vitamin E deficiency can lead to degeneration of dorsal column and spinocerebellar tracts