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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
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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
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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
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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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