Notes

• The ascending branches of Aβ axons (conveying discriminative touch information, i.e., carrying mechanoreceptive information) ascend in the dorsal columns (the gracile and cuneate fasciculi), and synapse on cells in the dorsal column nuclei (DCN) in the medulla (the gracile and cuneate nuclei, respectively).
• The axons of DCN cells cross the midline and ascend in the medial lemniscus to the lateral division of the ventro-posterior nucleus (VPL) of the thalamus.
• VPL cells in turn project to the primary somatosensory cortex (SI).

The Dorsal Column System

Things to Note About Dorsal Column -- Medial Lemniscal Pathway

• The Gracile Fasciculus extends the entire length of the spinal cord; it and the Gracile Nucleus contain a representation of the feet, legs, and lower trunk.
• The Cuneate Fasciculus begins at the cervical level; it and the Cuneate Nucleus contain a representation of the hands, arms, and upper trunk.
• The entire system is topographically organized (i.e., adjacent parts of the body surface are represented by adjacent neurons - Somatotopy).
• The decussation (crossing over) of the medial lemnisci results in a representation of the contralateral body surface on each side of the brain at levels above the DCN.