Medial lemniscus pathway > projected onto sagittally sectioned brain

Medial lemniscus pathway > projected onto sagittally sectioned brain

• This is a pathway carrying discriminative touch, conscious proprioception and vibration sense from the periphery to the somatosensory cortex.


• This is a 3-neuron pathway. The first neuron in the sequence is a primary sensory neuron whose sensory terminals are in the periphery and cell body is located in a dorsal root ganglion. Its axon enters the spinal cord through the dorsal root, then swings rostrally into the dorsal column of the cord, passing up to the medulla oblongata before synapsing there. However, some small side branches also synapse with neurons in the grey matter of the spinal cord dorsal horn of the spinal cord close to the dorsal root entry point, where they can modify other incoming sensory messages including pain.


• On each side of the cord, the dorsal column contains two tracts serving different parts of the body:- the gracile tract carrying information from the lower limbs and lower trunk, and the cuneate tract supplying the upper limb, upper trunk, neck and posterior part of the head. The division between the two territories is approximately at T6 (sixth thoracic spinal nerve). Above T6 the gracile tract is medial to the cuneate, In the medulla, the dorsal column axons synapse dorsally in the gracile and cuneate nuclei.
  


• Second neuron: axons from the gracile and cuneate nuclei cross the midline and arch ventrally (arcuate fibres) in a major decussation, then enter a ribbon-like tract, the medial lemniscus. This passes up to the thalamus where they synapse in the lateral part of the ventro-posterior nucleus (VPL – latin: nucleus ventroposterioris pars lateralis).


• Third neuron: axons of VPL neurons ascend to the somatosensory cortex via the internal capsule (via the thalamocortical tract).
  

Medial lemniscus pathway > projected onto sagittally sectioned brain

Click/tap on the image 7 times to advance the animation. Wait for each action potential to reach its destination at the end of the neuron before clicking/tapping again. Click/tap again to re-start the animation.