CorpusHuman Anatomy
NervousNeural pathway

Dorsal column–medial lemniscus pathway

Also known as: DCML, posterior column pathway, dorsal columns, fasciculus gracilis, fasciculus cuneatus, medial lemniscus

The three-neuron pathway for fine (discriminative) touch, vibration, pressure and conscious proprioception. It ascends ipsilaterally in the dorsal columns and crosses in the medulla.

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Overview

First-order neurons are large pseudounipolar DRG cells with thick myelinated Aβ (and Aα) fibres. Their peripheral branches come from Meissner and Pacinian corpuscles, Merkel discs, Ruffini endings, muscle spindles and joint receptors. The central branches enter medially in the dorsal root and turn upward, without synapsing, in the ipsilateral dorsal column. Fibres from below T6 run in the medial fasciculus gracilis. Fibres from T6 and above are added laterally to form the fasciculus cuneatus.

Second-order neurons lie in the nucleus gracilis and nucleus cuneatus of the caudal medulla. Their axons sweep ventromedially as the internal arcuate fibres and cross the midline: this is the sensory decussation. They then ascend as the medial lemniscus through the medulla, pons and midbrain, rotating so that leg fibres come to lie laterally. They end in the ventral posterolateral (VPL) nucleus of the thalamus.

Third-order neurons project through the posterior limb of the internal capsule (thalamocortical radiation) to the primary somatosensory cortex (postcentral gyrus, areas 3, 1 and 2), mapped as the sensory homunculus. The face uses the equivalent trigeminal lemniscus to VPM.

The clinical rule follows from the anatomy. A lesion below the medullary decussation causes ipsilateral loss. A lesion in the brainstem above it, the thalamus or the cortex causes contralateral loss.

Parts & subdivisions

  1. Fasciculus gracilis
    The medial dorsal column, carrying lower-limb and lower-trunk input (T7 and below). It is present throughout the cord.
  2. Fasciculus cuneatus
    The lateral dorsal column, carrying upper-limb, upper-trunk and neck input (T6 and above). It is present only above T6.
  3. Nuclei gracilis and cuneatus
    Second-order relay nuclei forming the gracile and cuneate tubercles on the dorsal medulla.
  4. Medial lemniscus
    The crossed ribbon of second-order fibres ascending through the brainstem to VPL. In the medulla it lies paramedian, supplied by the anterior spinal artery, so it is involved in medial medullary syndrome.

Anatomy

Course

Receptor → DRG (1st neuron) → ipsilateral fasciculus gracilis or cuneatus → nucleus gracilis or cuneatus in the medulla (2nd neuron) → internal arcuate fibres cross (sensory decussation) → medial lemniscus → thalamic VPL (3rd neuron) → posterior limb of internal capsule → postcentral gyrus (areas 3, 1, 2).

Function

  • Fine discriminative touch and two-point discrimination.
  • Vibration sense (tested with a 128 Hz tuning fork).
  • Conscious proprioception: joint position and movement sense.
  • Stereognosis and graphaesthesia, together with the parietal cortex.
Physiology

It uses fast, large-diameter myelinated fibres (35–75 m/s) and has high spatial and temporal resolution, with little convergence. It is precisely somatotopic at every level. Lateral inhibition at the relay nuclei sharpens receptive fields.

Clinical significance

Romberg sign and sensory ataxia

With dorsal column disease (B12 deficiency, tabes dorsalis, Friedreich ataxia, large-fibre neuropathy) the patient can stand with eyes open, using vision to compensate, but sways or falls when the eyes are closed. That is a positive Romberg test. Cerebellar ataxia is present with eyes open as well.

Localising the lesion

Brown-Séquard hemisection causes ipsilateral loss of vibration and proprioception below the lesion. A thalamic (VPL) or postcentral lacunar stroke causes contralateral loss. Medial medullary syndrome causes contralateral loss with ipsilateral tongue weakness.

Mnemonics

Gracilis vs cuneatus

Gracilis = Ground (legs), medial; Cuneatus = Ceiling (arms), lateral. "Gracile ballerina's legs".

Test yourself

Fibres of the dorsal column–medial lemniscus pathway decussate in the:
  1. Anterior white commissure of the spinal cord
  2. Medulla (internal arcuate fibres)
  3. Pons
  4. Midbrain

Answer: Medulla (internal arcuate fibres)

First-order fibres ascend ipsilaterally to the gracile and cuneate nuclei of the medulla. Second-order axons cross as internal arcuate fibres to form the medial lemniscus. Spinothalamic fibres, by contrast, cross in the anterior white commissure of the cord.

More nervous system questions

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.