Anatomy and Cell Biology 3319 Lecture Notes - Lecture 9: Dorsal Root Ganglion, Medial Lemniscus, Posterior Grey Column
1 May 2018
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Lecture 009: Ascending Sensory Pathways
What we want to know
● Origin and where they enter/ascend/terminate in the spinal cord and brain
● Where the pathways cross in the midline
● What kind of deficit is expected in the sensory system if there is injury to the spinal
cord/brain
Three main Ascending Pathways
1. Dorsal Column/Medial Lemniscus Sensory System
○ Main
○ Conscious tactile perception
2. Spinothalamic and Spinoreticular Pathways
○ Pain
3. Spinocerebellar Pathways
○ Information from spinal cord -> cerebellum
Dorsal Column of the medial Lemniscus System
● Discriminative touch
○ You know what you are touching
○ Where the touch is, how firm the touch, etc
● Pressure and vibration sensation
● Conscious join position
○CONSCIOUS proprioception
● Main pathway from the body
In the cervical spinal cord
● information from the upper body enters the dorsal root ganglia -> dorsal horn -> ascends
to the brain
● This information does not synapse in the spinal cord
In the lumbar spinal cord
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● Sensory information is received from the mixed spinal nerve
● The sensory axons split from the motor axons
● Those unipolar neurons have their cell bodies located in the dorsal root ganglia
● The proximal part of that axon goes into the dorsal horn
● Some of the information “stays” within the spinal cord (collaterals)
○Synapses on other neurons in the spinal cord (dorsal/ventral horns)
○ Ex. Stretch reflexes
● Other information is sent to the primary somatosensory cortex (cerebral cortex)
○ This is the major pathway
○ Information ascends ipsilaterally through the dorsal funiculus
Recall:
● Parts of the brain are “mapped” to specific areas of the body
● Same thing with the spinal cord
○ Body is “mapped” to different areas of the spinal cord
● Lower body is represented more medial than the upper body in the dorsal funiculus
○ Gracile fasciculus: lower body
■ Map exist within this level too!
○ Cuneate fasciculus: upper body
○ Mid-torso separate the lower/upper body
○ Most medial = most caudal
○This only applies for information that have not crossed the midline
In the medulla, the cuneate and gracile fasciculate (first order neuron) terminate in the
cuneate and gracile nucleus
● First synapses with 2nd order neurons takes place here
○ 2nd afferent nuclei
●Leaving the cuneate and gracile nucleus, the information crosses the midline
○ “Decussation of the medial lemniscus”
○Decussation = crossing
○medial lemniscus is the fiber pathway in the brain stem carrying the ascending
sensory information of the secondary neurons
● The secondary neuron ascends through the pons and midbrain
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find more resources at oneclass.com
Document Summary
Origin and where they enter/ascend/terminate in the spinal cord and brain. Where the pathways cross in the midline. What kind of deficit is expected in the sensory system if there is injury to the spinal cord/brain. Three main ascending pathways: dorsal column/medial lemniscus sensory system. Conscious tactile perception: spinothalamic and spinoreticular pathways. Where the touch is, how firm the touch, etc. Information from the upper body enters the dorsal root ganglia -> dorsal horn -> ascends to the brain. This information does not synapse in the spinal cord. Sensory information is received from the mixed spinal nerve. The sensory axons split from the motor axons. Those unipolar neurons have their cell bodies located in the dorsal root ganglia. The proximal part of that axon goes into the dorsal horn. Some of the information stays within the spinal cord (collaterals) Synapses on other neurons in the spinal cord (dorsal/ventral horns) Other information is sent to the primary somatosensory cortex (cerebral cortex)
