Spinal Tracts

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Author:
kjschult
ID:
128187
Filename:
Spinal Tracts
Updated:
2012-01-16 14:40:01
Tags:
tracts
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Description:
Motor and sensory tracts
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  1. Dorsal Columns-Medial Lemniscus Tract
    Function, Area of decussation, 1st Neuron, 1st Synapse, 2nd Neuron, 2nd Synapse, 3rd Neuron
    • Function: Proprioception, fine/active touch, and vibratory sense
    • 1st neuron: Spinal nerve endings that enter the posterior horn from the dorsal root ganglia (DRG); fibers from below T6 ascend is gracilis fasciculus medially, fibers above T6 ascend in cuneatus fasciculus near the dorsal horn
    • 1st Synapse: Occurs in the gracilis/cuneatus nuclei located in the caudal pons
    • 2nd Neurons:Decussate in the medulla just superior to the foramen magnum to the ventral medulla and forms the Medial Lemniscus (ML); fibers ascend contralaterally now with sacral fibers more anterior than thoracic fibers
    • 2nd Synapse: Venteroposterolateral nucleus of thalamus (VPL)
    • 3rd Neuron: Ascend in posterior limb of internal capsule and terminate in the somatosensory cortex
  2. Spinothalamic Tract
    Function, Area of decussation, 1st Neuron, 1st Synapse, 2nd Neuron, 2nd Synapse, 3rd Neuron
    • Function: Pain, temperature, and crude/fine touch
    • Area of decussation: At the level of entrace to spinal cord
    • 1st Neuron: Sensory nerve endings (A-delta and C fibers) enter the dorsal root from the DRG
    • 1st Synapse: Fibers synapse on neurons in the posterior horn at level of entry
    • 2nd Neuron: These neurons then decussate via the anterior white commisssure and ascend contralaterally in the lateral funiculus (leg fibers are more superficial than trunk than head)
    • 2nd Synapse: VPL of thalamus (leg fibers are more lateral)
    • 3rd Neuron: Ascend in posterior limb of internal capsule to end in the post central gyrus
  3. Dorsal Spinocerebellar Tract
    Function, Area of decussation, 1st Neuron, 1st Synapse, 2nd Neuron, 2nd Synapse, 3rd Neuron
    • Function: Unconscious proprioception
    • Area of decussation: Does NOT decussate
    • 1st Neuron: Large motor dorsal root axons ascend in posterior columns either to T1/L2 or to C2
    • 1st Synapse: T1/L2 fibers synapse on the dorsal nucleus (Clarke's nucleus) and give rise to the Dorsal Spinocerebellar tract; C2 fibers synapse in the lateral cuneat nuclease and form cuneocerbellar axons
    • 2nd Neuron: Cuneocerebellar axons join the Dorsal spinocerebellar tract and ascend ipsilaterally via the inferior cerebellar peduncle (restiform body)
    • 2nd Synapse: Terminate in the vermian and paramedian cerebellar cortex as mossy fibers
  4. Lateral Corticospinal Tract
    Function, Area of decussation, 1st Neuron, 1st Synapse, 2nd Neuron, 2nd Synapse, 3rd Neuron
    • Function:
    • Area of decussation: In the caudal medulla
    • 1st Neuron: Axons (upper motor neurons; UMN) from precentral, prefrontal, and postcentral gyri course through corona radiata and converge in the posterior limb of the internal capsule; they then descend, enter the poss, and emerge from the pontomedullary junction as pyramids; 60-90% decussate in the caudal medulla and join the opposite Lateral Funiculus of the spinal cord (cervical fibers lie more medially)
    • 1st Synapse: On alpha-motor neurons and interneurons in the ventral horn of the spinal cord
    • 2nd Neuron: Leaves the cord ventrally as lower motor neurons (LMN)
    • 2nd Synapse: NMJ

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