|Brain: Medial lemniscus|
The sensory tract. (Medial lemniscus labeled at center right.)
After neurons carrying proprioceptive or touch information synapse at the gracile and cuneate nuclei, axons from secondary neurons decussate at the level of the medulla and travel up the brainstem as the medial lemniscus on the contralateral (opposite) side. It is part of the posterior column-medial lemniscus system, which transmits touch, vibration sense, as well as the pathway for proprioception.
The medial lemniscus carries axons from most of the body and synapses in the ventral posterolateral nucleus of the thalamus, at the level of the mamillary bodies. Sensory axons transmitting information from the head and neck via the trigeminal nerve synapse at the ventral posteromedial nucleus of the thalamus.
Location of the medial lemniscus through the brainstem
- The cuneate and gracile nuclei reside at the closed (lower) medulla, so the lemniscus isn't formed at this level. Fibres from these nuclei will pass to the contralateral side of the brainstem, as the internal arcuate fibres.
- At the open medulla (further up the brainstem), the medial lemniscus contains axons from the trigeminal nerve (which supplies the head region), as well as the arms and legs. It sits very close to the midline, at the same orientation of the midline, with head fibres more dorsal (closer to the back), towards the fourth ventricle.
- By mid-pons, the medial lemniscus has rotated. Fibres from the head are medial, fibres from the leg are lateral.
- The orientation in the midbrain is similar to that in the pons.
- Illustration and text: 04NGNC at the University of Wisconsin–Madison Medical school
- Stained brain slice images which include the "medial lemniscus" at the BrainMaps project
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