Somatosensory Pathways Flashcards
Pyramidal Tracts
- Lateral Corticospinal Tract
- Anterior Corticospinal Tract
Extrapyramidal Tracts
- Rubrospinal Tract
- Reticulospinal Tract
- Vestibulospinal Tract
- Olivospinal Tract
Dorsal Column Medial Lemniscus: Functions
- Light discriminative touch
- Conscious proprioception
- Vibration
- Two Point Discrimination
Anterolateral (Spinothalamic) System: Functions
- Pain
- Temperature
- Non-discriminative touch
Spinocerebellar Tract: Functions
Unconscious proprioception
Dorsal Column Medial Lemniscus Pathway: Level of Decussation
Decussation occurs as Internal Arcuate Fibers at the level of the Dorsal Medulla
Dorsal Column Medial Lemniscus Pathway: Location in Internal Capsule
Posterior 1/3
Dorsal Column Medial Lemniscus Pathway: Location of Synapse in Thalamus
Ventroposterior Lateral Nucleus (VLN)
Dorsal Column Medial Lemniscus Pathway: Name for fibers after they decussate and ascend towards the Thalamus
Medial Lemniscus
Anterolateral Spinothalamic Tract: Organization of Nerve Fibers in Spinal Cord
Medial –> Lateral
- Cervical
- Thoracic
- Lumbar
- Sacral
Fasciculi Gracile and Cuneatus Lesions in the spinal cord result in:
Ipsilateral loss of sense of touch, proprioception, and vibration at and below the level of injury
Dorsal Column Medial Lemniscus Pathway: Medial Lemniscus
- 2nd order neuron
- Heavily myelinated ascending axons in the brainstem
- What the neurons ascend as in the contralateral brainstem
Ventral Posterolateral Nucleus (VPL) of the Thalamus
- 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
Anterolateral Spinothalamic Tract: 1st Order Neurons
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
Anterolateral Spinothalamic Tract: 2nd Order Neurons
Neurons in Dorsal Horn decussate at the Anterior Spinal Commissure then ascend on contralateral side
Anterolateral Spinothalamic Tract: Location of Synapse in Thalamus
VPL
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
- Upper limbs
- Sacral and Lower Limbs
Syringomyelia
- 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
Thalamic Pain Syndrome
- 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
Brown-Sequard Syndrome
- 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
Tracts that are frequently involved in Brown-Sequard Syndrome
- 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
Anterior Cord Syndrome
Loss of motor power, pain and temperature sensation with preservation of positon, vibration and touch sense
