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Ascending Pathways: Dorsal Column Medial Lemniscal (DCML) System

by Craig Canby, PhD
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    00:00 Now, I want you to understand an example of an ascending pathway. Ascending pathways are relaying sensory information up to the brain, to the primary somatosensory cortex. One of the ascending pathways is the dorsal column – medial meniscal system. That is shown here in blue on this side of the cord and then the opposite one would be in through here that’s unshaded. The dorsal column - medial meniscal system is composed of two fasciculi. One lies medial as you see here. This is going to be the fasciculus gracilis.

    00:51 This is conveying sensory information from the lower extremity. It will enter the most inferior part of the spinal cord and then ascend through the spinal cord in this medial location. The one lateral to the fasciculus gracilis is known as the fasciculus cuneatus. This is conveying sensory information from the upper extremity.

    01:20 So information will come in to this fasciculus at the level of T6 and then all the way up through C2.

    01:33 When this information comes in, it can’t go medial. That’s occupied by the fasciculus gracilis. So these more superior points of entry have to stay on the lateral side of the dorsal columns. Another way to perhaps distinguish which one’s lower and which one’s upper is that the gracilis, the G is found in leg. So the cuneatus has to be the upper portion of the body relaying sensory information superiorly. What are the functions of these ascending components that make up the dorsal column – medial meniscal system? First, these fasciculi are conveying conscious proprioception to the primary somatosensory area.

    02:35 Fine touch is also conveyed in this system as is two-point discrimination. In addition, vibration as well as pressure are also being conveyed in this important pathway. The dorsal column – medial lemniscal system is composed of three neurons, so a first order neuron, a second order neuron, and a third order neuron.

    03:10 The pathway is going to involve the spinal cord, medulla, ventral posterolateral nucleus of the thalamus.

    03:21 Then our destination is going to be the primary somatosensory cortex. Now, I want you to understand the travels of these three neurons as they begin and then ultimately end at the primary somatosensory cortex.

    03:39 The first order neuron that we see here is coming in from the right. Here’s a receptor that has stimulated the first order neuron coming in to the right side of the dorsal column – medial lemniscal system. It’s going to ascend one or two levels in the Lissauer's tract before actually entering the ipsilateral fasciculus gracilis or cuneatus. If this is coming in from the lower extremity, this first order neuron is going to ascend in the fasciculus gracilis. We see it continuing up to the medulla. Within the medulla, you have the nucleus gracilis and the nucleus cuneatus. Since this is coming from the lower limb, this first order neuron will synapse ipsilaterally in the nucleus gracilis. The second order neuron now, if we follow it, will cross over.

    04:45 It decussates. It’s decussating to the left side of the medulla and entering the contralateral medial lemniscus that we see up in through here. That’s a part of the brainstem. The second order neuron will continue its ascent and then will synapse with the ventral posterolateral nucleus of the thalamus.

    05:15 It synapses with the third order neuron that will then reach the primary somatosensory cortex.


    About the Lecture

    The lecture Ascending Pathways: Dorsal Column Medial Lemniscal (DCML) System by Craig Canby, PhD is from the course Spinal Cord.


    Included Quiz Questions

    1. It is located on the lateral side in dorsal column from level CII—TVI.
    2. It is present throughout the spinal cord and receives sensory information from visceral organs.
    3. It is located on the medial side in the dorsal column and receives sensory information from upper extremities.
    4. It is located on the lateral side in dorsal column and receives sensory input from lower extremities.
    5. It is located on the medial side in dorsal column from level TII—TVI.
    1. Thalamus
    2. Somatosensory cortex
    3. Spinal Cord
    4. Midbrain
    5. Medulla
    1. Left fasciculus gracilis
    2. Right fasciculus graciis
    3. Left dorsal horn
    4. Right fasciculus cuneatus
    5. Left fasciculus cuneatus
    1. 2nd order neuron resides in medulla and decussates at the same level.
    2. Fasciculus gracilis ascends ipsilateral and decussates at the level of spinal cord.
    3. Cerebellar nuclei are the main relay center for sensory information carried by the dorsal column.
    4. Pain and temperature are the main sensations perceived by dorsal column.
    5. Fasciculus cuneatus provides motor innervation to the upper extremities.

    Author of lecture Ascending Pathways: Dorsal Column Medial Lemniscal (DCML) System

     Craig Canby, PhD

    Craig Canby, PhD


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