The dorsal column–medial lemniscus pathway

Why it matters

Knowing where your feet are without looking, feeling a vibration or telling two touches apart all depend on this pathway ^[1]. The dorsal column system and the spinothalamic tract are the two major pathways that bring sensory information from below the neck to the brain ^[2].

What it is

The dorsal column system, sometimes called the dorsal column–medial lemniscus, is primarily responsible for touch sensations and proprioception ^[2]. In the cord it runs in the dorsal column, which is divided into two tracts ^[2]:

• the fasciculus gracilis, with axons from the legs and lower body ^[2];
• the fasciculus cuneatus, with axons from the upper body and arms ^[2].

How it works

The pathway is a chain of three neurons ^[2]:

1. A dorsal root ganglion neuron sends its axon through the dorsal root into the dorsal column white matter of the cord, on the same side ^[2].
2. The axon ends in the nucleus gracilis or nucleus cuneatus of the medulla, where it synapses with the second neuron; that neuron's axon crosses the midline of the medulla and ascends the brainstem as the medial lemniscus ^[2].
3. In the thalamus the second neuron synapses with the third, which projects to the postcentral gyrus, where the stimulus is first processed and consciously perceived ^[2].

Dorsal column–medial lemniscusTouch and position signals from the right side of the body climb the right dorsal column, synapse in the medulla, cross, and travel as the left medial lemniscus to the left thalamus and sensory cortex.

Step through

• Excitatory synapse (filled arrowhead)
• Inhibitory synapse (bar)
• Modulatory (open circle)
• Signal or data flow, not a synapse (dashed)
• Midline crossing (decussation)

• The fasciculus gracilis carries axons from the legs and lower body, the fasciculus cuneatus from the upper body and arms.^[2]

Simplified: Synapses are marked on the edges as places, without claiming their sign.

Text description of this diagram

1. Touch and position signals from the right side of the body climb the right dorsal column, synapse in the medulla, cross, and travel as the left medial lemniscus to the left thalamus and sensory cortex.
2. Touch receptor (right side, Skin and joints) to Dorsal column (right side, Spinal cord); signal or data flow (not a synapse); dorsal root, same side.
3. Dorsal column (right side, Spinal cord) to Gracile or cuneate (right side, Medulla); signal or data flow (not a synapse); synapse in the medulla.
4. Gracile or cuneate (right side, Medulla) to Medial lemniscus (left side, Brainstem); signal or data flow (not a synapse); crosses the midline at the medulla.
5. Medial lemniscus (left side, Brainstem) to Thalamus (left side, Thalamus); signal or data flow (not a synapse); synapse in the thalamus.
6. Thalamus (left side, Thalamus) to Primary sensory cortex (left side, Cerebral cortex); signal or data flow (not a synapse).

When it does not behave

Because this pathway climbs the cord on the same side as the stimulus and crosses only in the medulla, damage to one half of the cord removes fine touch below the damage on that same side; pain is still felt there, because pain fibres cross in the cord ^[1].

How we see and measure it

The neurological examination tests it with a tuning fork for vibration, by moving a finger or toe to test position sense, and with two-point discrimination; failing to recognise two points may indicate a dorsal column deficit ^[1]. The Romberg test, standing with the feet together, can show deficits in dorsal column proprioception ^[1].

Common misconceptions

Check yourself

Where does the dorsal column pathway cross the midline?

In the medulla, after the synapse in the nucleus gracilis or cuneatus ^[2].

Which tract carries axons from the legs?

The fasciculus gracilis ^[2].

Read next

• The pathway in 3D.
• The spinothalamic tract.