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Med Neuro Block 2 > Dorsal Column / Medial Lemniscus > Flashcards

Dorsal Column / Medial Lemniscus Flashcards

1
Q

What kind of sensations do the dorsal columns transmit?

A
  • Light touch
    • 2-point discrimination
    • Stereognosis
    • Graphesthesia
    • Pressure
  • Vibration
  • Proprioception
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2
Q

What is stereognosis?

A
  • Ability to identify an object by feeling it
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3
Q

What is graphesthesia?

A
  • Ability to distinguish numbers or letters traced on the palm of the hand
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4
Q

What is proprioception?

A
  • Limb position
  • Motion sense
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5
Q

What are the basic components of the DC/ML system?

A
  • Three Neurons:
    • 1st neuron
    • 2nd neuron
    • 3rd neuron
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6
Q

Where are each of the three neurons found?

A
  • 1st neuron – in sensory ganglion
  • 2nd neuron – in spinal cord and/or brainstem
  • 3rd neuron – in thalamus
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7
Q

Describe the basic processing pathway of the 1st neuron:

A
  • 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
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8
Q

Describe the basic processing pathway of the 2nd neuron:

A
  • 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
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9
Q

Describe the basic processing pathway of the 3rd neuron:

A
  • Cell body in VPL of thalamus
  • Axons pass through posterior limb of internal capsule
  • Terminates in SI cortex (postcentral gyrus, primary somatosensory cortex)
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10
Q

What are the two dorsal columns?

A
  • Fasciculus gracilis
  • Fasciculus cuneatus
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11
Q

Where is fasciculus gracilis located and where does it carry information from?

A
  • Located medially
  • Axons from below T7
  • Carries information from the lower limbs
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12
Q

Where is fasciculus cuneatus located and where does it carry information from?

A
  • Located laterally
  • Axons from above T7
  • Carries information from the upper limbs
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13
Q

What is the somatotopy of the 1st neuron?

A
  • Sacral dermatomes located medially.
  • lumbar, thoracic and cervical dermatomes are located progressively more laterally.
  • helps preserve information about location and nature of stimulus
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14
Q

What are the consequences a unilateral spinal cord lesion?

A

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
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15
Q

What are the consequences a bilateral spinal cord lesion?

A

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
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16
Q

In what neuron does Posterior Cord Syndrome occur? What are the symptoms?

A

1st Neuron:

  • Loss of light touch, pressure, vibration and proprioception from dermatomes BELOW the level of the lesion
  • Other sensory and motor functions intact
17
Q

Large Central Cord Lesion:

A

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
18
Q

Where are the cell bodies for the 2nd neuron?

A
  • Cell bodies located in caudal medulla:
    • Nucleus gracilis
    • Nucleus cuneatus
19
Q

What do the axons from the 2nd neuron form?

A

Axons form medial lemniscus through rostral medulla, pons and midbrain.

20
Q

Where does the 2nd neuron terminate?

A

VPL of thalamus

21
Q

What is the somatotopy of the 2nd neuron?

A
  • Rostral medulla
  • At level of pons, fibers from face are added via trigeminal nerve
22
Q

Mnemonic for rostral medulla:

A

“Headless hemi-man standing on the pyramids”

23
Q

Lesion of medial lemniscus

A
  • 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
24
Q

Why does sensation to the face remain intact of the medial meniscus is lesioned?

A

The face is coordinated at the level of the pons

25
Q

Where are the cell bodies for the 3rd Neuron?

A

Cell body in VPL of thalamus

26
Q

What do the axons of the 3rd neuron pass through?

A

Axons pass through posterior limb of internal capsule

27
Q

Where does the 3rd neuron terminate?

A

Terminates in SI cortex (postcentral gyrus, primary somatosensory cortex)

28
Q

Areas of the Thalamus:

A
  • VPL – sensation from body
  • VPM – sensation from face
29
Q

What is the course of 3rd neuron axons?

A
  • Axons pass through posterior limb of internal capsule
  • Axons from thalamus fan out as corona radiata
  • Fibers from VPL and VPM pass to SI cortex
30
Q

Lesion of Thalamus or SI Cortex

A
  • Loss of sensation from contralateral half of body
31
Q

What Brodmann areas correspond with the SI cortex?

A
  • 3a
  • 3b
  • 1
  • 2
32
Q

What do the Brodmann areas of the SI cortex correspond to?

A
  • Area 3a – limb movement
  • Area 3b – basic tactile info. (edges, texture)
  • Area 1 – motion and direction of movement of objects
  • Area 2 – limb position, shapes of objects
33
Q

Somatosensory Cortical Projections:

A
  • SI neurons project to SII cortex
    • Located along upper border of Sylvian fissure and insular cortex
  • Parietal Association Cortices
    • Located along intraparietal sulcus
    • Receive sensory info. and project to motor cortex
34
Q

What is the unimodal and multimodal functions of the parietal associastion cortices? What will happen if lesioned?

A
  • Unimodal
    • e.g. visual, auditory, somatosensory
    • Lesions ⇒ agnosias (inability to recognize an object or a property of an object)
  • Multimodal
    • e.g. combine sensation with motivation, attention, relevance
    • Lesions ⇒ contralateral neglect
35
Q

What is contralateral neglect?

A

Multimodal lesions of the parietal association cortices

Med Neuro Block 2 (13 decks)

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