Somatosensory Pathways

Question 1

Pyramidal Tracts

Answer 1

• Lateral Corticospinal Tract
• Anterior Corticospinal Tract

Question 2

Extrapyramidal Tracts

Answer 2

• Rubrospinal Tract
• Reticulospinal Tract
• Vestibulospinal Tract
• Olivospinal Tract

Question 3

Dorsal Column Medial Lemniscus: Functions

Answer 3

• Light discriminative touch
• Conscious proprioception
• Vibration
• Two Point Discrimination

Question 4

Anterolateral (Spinothalamic) System: Functions

Answer 4

• Pain
• Temperature
• Non-discriminative touch

Question 5

Spinocerebellar Tract: Functions

Answer 5

Unconscious proprioception

Question 6

Dorsal Column Medial Lemniscus Pathway: Level of Decussation

Answer 6

Decussation occurs as Internal Arcuate Fibers at the level of the Dorsal Medulla

Question 7

Dorsal Column Medial Lemniscus Pathway: Location in Internal Capsule

Answer 7

Posterior 1/3

Question 8

Dorsal Column Medial Lemniscus Pathway: Location of Synapse in Thalamus

Answer 8

Ventroposterior Lateral Nucleus (VLN)

Question 9

Dorsal Column Medial Lemniscus Pathway: Name for fibers after they decussate and ascend towards the Thalamus

Answer 9

Medial Lemniscus

Question 10

Anterolateral Spinothalamic Tract: Organization of Nerve Fibers in Spinal Cord

Answer 10

Medial –> Lateral
- Cervical
- Thoracic
- Lumbar
- Sacral

Question 11

Fasciculi Gracile and Cuneatus Lesions in the spinal cord result in:

Answer 11

Ipsilateral loss of sense of touch, proprioception, and vibration at and below the level of injury

Question 12

Dorsal Column Medial Lemniscus Pathway: Medial Lemniscus

Answer 12

• 2nd order neuron
• Heavily myelinated ascending axons in the brainstem
• What the neurons ascend as in the contralateral brainstem

Question 13

Ventral Posterolateral Nucleus (VPL) of the Thalamus

Answer 13

• Receives sensory input from medial lemniscus (discriminative touch) and spinothalamic (nociceptive) tracts
• Fibers from the contralateral nucleus cuneatus terminate medial to those of the nuclease gracile
• Output is primary somatosensensory cotex (Brodmann areas 3, 1 and 2) of the parietal lobe

Question 14

Anterolateral Spinothalamic Tract: 1st Order Neurons

Answer 14

Do not synapse when entering SC, and instead ascend up 1-3 levels in the Tract of Lissuer, then enter SC and synapse on Dorsal Horn

Question 15

Anterolateral Spinothalamic Tract: 2nd Order Neurons

Answer 15

Neurons in Dorsal Horn decussate at the Anterior Spinal Commissure then ascend on contralateral side

Question 16

Anterolateral Spinothalamic Tract: Location of Synapse in Thalamus

Answer 16

VPL

Question 17

When the central canal is swelled by a syrinx, the medial pain and temperature fibers from the ___ ___ take the first hit, and ____ and ___ ___ sensation may be spared, giving rise to a ‘cape-like distribution’ of sensory loss and paresthesia

Answer 17

• Upper limbs
• Sacral and Lower Limbs

Question 18

Syringomyelia

Answer 18

• Fluid-filled cyst (syrinx) forms within the spinal cord, typically the central canal
• Compress the SC
• If located in central canal then can push upon the anterior white commissure damaging the crossing fibers of the spinothalamic tract; usually affects the cervical level and results in a cape-like bilateral, symmetrical loss of pain and temperature sense at the level of damage
• As the syrinx grows it can lead to further damage of the ventral horns

Question 19

Thalamic Pain Syndrome

Answer 19

• Affects the Ventral Nuclear group
• Patients present with burning, aching pain in contralateral limbs of body
• Involvement of DCML part of the VPL increases the sensitivity to pain and presents as contralateral loss of vibratory sense and gait ataxia
• Resistant to analgetic meds

Question 20

Brown-Sequard Syndrome

Answer 20

• Hemisection of spinal cord
• 3 main neural systems are affected
• Hallmark of a lesion is 2 ipsilateral signs and 1 contralateral sign
• Loss of pain and temp sensation on opposite side with loss of voluntary motor control on ipsilateral side of cord damage

Question 21

Tracts that are frequently involved in Brown-Sequard Syndrome

Answer 21

• DCML: one or both fasciculi of dorsal columns damaged –> ipsilateral loss of joint position sense, discriminative touch, and vibration below site of lesion
• Spinothalamic Tract: Damage to tract –> contralateral loss of pain and temperature sensation 1 or 2 segments below lesion
• Main Upper Motorneuron Pathway: Damage to pathway –> ipsilateral spastic paresis below lesion
• Ipsilateral flaccid paralysis in muscles supplied by the injured SC segments

Question 22

Anterior Cord Syndrome

Answer 22

Loss of motor power, pain and temperature sensation with preservation of positon, vibration and touch sense