Medial lemniscus
Lemniscus medialis
Definition
The medial leminiscus is a bundle of white matter tracts, or neurons, that ascends within the brainstem, located dorsally to the pyramids. It transmits sensory information related to conscious proprioception, vibration, fine touch, and two-point discrimination to the thalamus.
The above-mentioned sensory information originates from various parts of the body and is carried by a spinal tract found in the posterior part of the spinal cord, known as the dorsal column. More specifically, it involves the fasciculus gracilis and the fasciculus cuneatus, which represent the first-order neurons of the dorsal column medial leminiscus (DCML) sensory pathway. These first-order neurons terminate at the nucleus gracilis and nucleus cuneatus in the caudal medulla.
From here onwards, the second order neurons emerge, called the internal arcuate fibers, which decussate (cross over) at the caudal medulla, moving from the posterior to the anterior region. These fibers then ascend contralaterally through the brainstem, located dorsally to the pyramids. At this point, these vertically ascending fibers are called the medial leminiscus.
The medial lemniscus continues its ascent until it synapses at the ventral posterolateral nucleus of the thalamus. Here, the third-order neurons of the DCML pathway begin and extend to the primary somatosensory cortex.
References
Navarro-Orozco D, Bollu PC. Neuroanatomy, Medial Lemniscus (Reils Band, Reils Ribbon) [Updated 2023 Aug 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526040/
Snell, R.S. (2010). ‘Chapter 5: The Brainstem’, in Clinical Neuroanatomy. (7th ed.) Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, pp.205.