dorsal columns medial lemniscus

Question 1

Components of the DC/ML system

Answer 1

1st neuron: in sensory ganglia
2nd neuron: in brainstem nuclei/sp cd
3rd neuron: in thalamus

Question 2

1st neuron

Answer 2

peripheral process transmits information from mechanoreceptor, cell body in DRG, the central process transmits information via dorsal root and ascends within ipsilateral dorsal columns, termination in dorsal column nuclei

Question 3

2nd neuron

Answer 3

Cell body in nucleus gracilis or nucleus cuneatus (medulla)

The axon decussates to contralateral side in the cord and ascends as medial lemniscus, termination in ventral posterior lateral nucleus of thalamus (VPL)

Question 4

3rd neuron

Answer 4

cell body in VPL of thalamus, axons pass thru posterior limb of internal capsule terminates in S1 cortex, postcentral gyrus

Question 5

1st neuron central axon projection

Answer 5

Fasiculus gracilis (located medially, Axons from sp cd levels caudal to T6)- graceful dancing legs

Fasiculus cuneatus (located laterally, axons from T6 and rostral)- cunning hands

Somatotopy- lower levels of body located medially and the torso and neck laterally, preserves info about location and nature of stimulus

Unilateral sp cd lesion: loss of light touch, pressure, vibration, proprioception on same side of lesion and below, (will lose other sensory and motor function)
Bilateral sp cd lesion: loss of ight touch, pressure, vibration, proprioception on both sides of lesion below it

post cd lesion: youll only lose the tracts that convey light touch, pressure, vibration, proprioception from below, BUT NO motor function loss

large central cd lesion: because fas gracilis gets pushed to the lateral posterior cd the sacral region gets spared, but lose mechanoreceptors, and motor functions

Question 6

2nd neuron cell bodies and axons

Answer 6

located in caudal medulla
nucleus gracilis, nucleus cuneatus
Axons decussate as internal arcuate fibers, form medial leminiscus thru rostral medulla, pons, and midbrain, terminate in VPL

Somatotopy- rostral medulla, headless hemi man (contralateral) standing on the medullary pyramids. At the level of the pons, fibers from face are added via trigeminal nerve

Lesion of medial leminuscus- loss of light touch, vibration, pressure, proprioception below the lesion on the contralateral leminiscus: medial medullary syndrome

Question 7

3rd neuron cell bodies and axons

Answer 7

cell bodies in the VPL (ventral, posterior, lateral) nucleus of the thalamus- pass thru posterior limb of internal capsule terminates in S1

Somatotopy: VPL is sensation from body, VPM sensation from face

Axons from the thalamus fan out as corona radiata and pass to S1

Lesion of the thalamus or S1 cortex: loss of sensation from contralateral half of body

Question 8

S1 cortex

Answer 8

3a, 3b, 1, 2; each have a complete map of the skin

3a: limb movement
3b: basic tactile info (edges, texture)
1: motion and direction of movement of object
2: limb position, shapes of objects

project to S2 cortex, located along upper border of sylvian fissure

Parietal association: located along intraparietal sulcus, receive sensory info and project to motor cortex

Question 9

Association corices

Answer 9

Parital lobe: S association lesion–> astereognosis
Occipital lobe: Visual
Temporal: auditory

Multimodal: combines everything (an onion is not an apple) contralateral neglect due to lesion