Dorsal Column / Medial Lemniscus Flashcards
(35 cards)
What kind of sensations do the dorsal columns transmit?
- Light touch
- 2-point discrimination
- Stereognosis
- Graphesthesia
- Pressure
- Vibration
- Proprioception
What is stereognosis?
- Ability to identify an object by feeling it
What is graphesthesia?
- Ability to distinguish numbers or letters traced on the palm of the hand
What is proprioception?
- Limb position
- Motion sense
What are the basic components of the DC/ML system?
- Three Neurons:
- 1st neuron
- 2nd neuron
- 3rd neuron
Where are each of the three neurons found?
- 1st neuron – in sensory ganglion
- 2nd neuron – in spinal cord and/or brainstem
- 3rd neuron – in thalamus
Describe the basic processing pathway of the 1st neuron:
- Peripheral process transmits information from mechanoreceptor
- Cell body in DRG
- Central process transmits information via dorsal root and ascends within ipsilateral dorsal columns*
- Terminates in dorsal column nuclei
Describe the basic processing pathway of the 2nd neuron:
- Cell body in nucleus gracilis or nucleus cuneatus
- Axon decussates to contralateral side and ascends as medial lemniscus
- Terminates in ventral posterior lateral nucleus of thalamus
Describe the basic processing pathway of the 3rd neuron:
- Cell body in VPL of thalamus
- Axons pass through posterior limb of internal capsule
- Terminates in SI cortex (postcentral gyrus, primary somatosensory cortex)
What are the two dorsal columns?
- Fasciculus gracilis
- Fasciculus cuneatus
Where is fasciculus gracilis located and where does it carry information from?
- Located medially
- Axons from below T7
- Carries information from the lower limbs
Where is fasciculus cuneatus located and where does it carry information from?
- Located laterally
- Axons from above T7
- Carries information from the upper limbs
What is the somatotopy of the 1st neuron?
- Sacral dermatomes located medially.
- lumbar, thoracic and cervical dermatomes are located progressively more laterally.
- helps preserve information about location and nature of stimulus
What are the consequences a unilateral spinal cord lesion?
1st Neuron:
- Loss of light touch, pressure, vibration and proprioception on the SAME SIDE of the lesion from dermatomes JUST BELOW the level of the lesion
- Loss of other sensory and motor functions
What are the consequences a bilateral spinal cord lesion?
1st Neuron:
- Loss of light touch, pressure, vibration and proprioception from dermatomes JUST BELOW the level of the lesion
- Loss of other sensory and motor functions
In what neuron does Posterior Cord Syndrome occur? What are the symptoms?
1st Neuron:
- Loss of light touch, pressure, vibration and proprioception from dermatomes BELOW the level of the lesion
- Other sensory and motor functions intact
Large Central Cord Lesion:
1st Neuron:
- Loss of light touch, pressure, vibration and proprioception from dermatomes below the level of the lesion –
- Sacral region is spared
- Loss of other sensory and motor functions
Where are the cell bodies for the 2nd neuron?
- Cell bodies located in caudal medulla:
- Nucleus gracilis
- Nucleus cuneatus
What do the axons from the 2nd neuron form?
Axons form medial lemniscus through rostral medulla, pons and midbrain.
Where does the 2nd neuron terminate?
VPL of thalamus
What is the somatotopy of the 2nd neuron?
- Rostral medulla
- At level of pons, fibers from face are added via trigeminal nerve
Mnemonic for rostral medulla:
“Headless hemi-man standing on the pyramids”
Lesion of medial lemniscus
- Loss of light touch, pressure, vibration and proprioception from dermatomes below the level of the lesion on the contralateral side of the body
- e,g, medial medullary syndrome
Why does sensation to the face remain intact of the medial meniscus is lesioned?
The face is coordinated at the level of the pons
