Medial lemniscus
Ascending bundle of axons which cross in the brainstem
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Through Brainstem, Somatosensory system and Spinal cord
The medial lemniscus is part of the somatosensory dorsal column–medial lemniscus pathway, which ascends in the spinal cord to the thalamus. Lesions of the medial lemniscus cause an impairment of vibratory and touch-pressure sense.
Etymology
Lemniscus means "ribbon", reflecting the elongated tract of the medial lemniscus.
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Anatomy
Path
After neurons carrying somatosensory proprioceptive or fine touch information synapse at the gracile and cuneate nuclei, axons from second-order 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 pathway, which transmits touch, vibration sense, as well as the pathway for proprioception.
The medial lemniscus carries axons from most of the body and terminates by synapsing with third-order neurons 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 through the brainstem
The cuneate and gracile nuclei reside at the closed (lower) medulla, so the medial lemniscus is not formed at this level. Fibres from these nuclei will pass to the contralateral side of the brainstem, as the internal arcuate fibres. In the midbrain, it is situated dorsal to the substantia nigra, and medial to either red nucleus.