Somatosensory pathways: dorsal column and anterolateral !

Concept
Exam priority: high

Touch, vibration and position travel up the cord in one bundle, pain and temperature in another. Where each crosses explains cord injuries.

Updated 2026-11-01

Also called: Medial lemniscus, Spinothalamic tract

See it in 3D: Dorsal root ganglia · Spinal cord · Medulla oblongata · Thalamus · Sensory cortex

Key points

Dorsal column: the first neuron ascends on the same side to the gracile and cuneate nuclei of the medulla; the second neuron crosses (internal arcuate fibres) and rises as the medial lemniscus.
Spinothalamic: the first neuron synapses in the dorsal horn; the second crosses in the anterior white commissure within 1–2 segments and ascends on the opposite side.
Cord hemisection (Brown-Séquard): same-side loss of vibration, position and motor power below; opposite-side loss of pain and temperature from 1–2 segments below.
Third neuron: thalamus VPL (body) and VPM (face) → primary somatosensory cortex; leg on the medial surface, hand and face lateral.
Fasciculus gracilis carries the leg and lower trunk (medial); fasciculus cuneatus the arm, present only above about T6.
B12 deficiency and tabes dorsalis damage the dorsal columns: loss of vibration and a positive Romberg sign.

What it is

Two main systems carry body sensation to the cortex. The dorsal column–medial lemniscus system carries fine touch, vibration and conscious position sense in fast myelinated fibres and crosses in the medulla. The anterolateral (spinothalamic) system carries pain, temperature and crude touch; it synapses in the dorsal horn and crosses within one or two segments. Both relay in the thalamus and end in the postcentral gyrus, which holds a map of the body.

The two ascending systems compared

Feature	Dorsal column–medial lemniscus	Anterolateral
Modalities	Fine touch, vibration, position, two-point discrimination	Pain, temperature, crude touch, itch
Fibres	Aβ, large and myelinated	Aδ and C
Second neuron	Gracile and cuneate nuclei (medulla)	Dorsal horn (laminae I, II, V)
Crossing	Medulla (internal arcuate fibres)	Spinal cord, anterior white commissure, 1–2 segments up
Spatial and temporal precision	High	Low
Thalamic relay	VPL and VPM	VPL plus intralaminar and other nuclei

Clinical notes

Syringomyelia (a central cavity in the cervical cord) cuts the crossing spinothalamic fibres: cape-like loss of pain and temperature with touch preserved.
A stab wound that hemisects the cord produces the classic dissociated loss of Brown-Séquard syndrome.
Subacute combined degeneration (B12 deficiency) hits the dorsal columns and corticospinal tracts: lost vibration, positive Romberg, spasticity.
A thalamic (VPL) stroke removes all sensation on the opposite side; a burning central pain may appear weeks later.

Test yourself

Think of the answer, then tap the question to see it.

A right-sided cord hemisection at T10: which sensations are lost in the left leg, and why?

Pain and temperature, because fibres from the left leg crossed into the right cord just above entry. Vibration and position are lost in the right leg, since the dorsal columns ascend uncrossed to the medulla.

Why is the Romberg sign positive in dorsal column disease but not a key finding in cerebellar ataxia?

With dorsal column loss, vision replaces missing position sense, so balance fails when the eyes close. In cerebellar ataxia the patient is unsteady with eyes open too, so closing them adds little.

Why does a central cord cavity spare touch while abolishing pain and temperature over the shoulders?

It interrupts second-order spinothalamic fibres crossing in the anterior white commissure at those segments. The dorsal columns lie posteriorly and are spared until late.

Sensory loss mainly in the contralateral leg points to which part of the postcentral gyrus and which artery?

The medial (paracentral) surface, supplied by the anterior cerebral artery. Face and hand lie laterally in middle cerebral artery territory.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

In Biochemistry

Cobalamin (vitamin B12)

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Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 14.2 Central Processing (OpenStax (Rice University), 2022); 14.1 Sensory Perception (OpenStax (Rice University), 2022); Neuroanatomy, Postcentral Gyrus (StatPearls (NCBI Bookshelf), 2023); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 48). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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