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Neuro Part 2 (Sensory Systems and Lesions)

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kdw750's version from 2015-07-26 21:46

Describe the dorsal column – medial lemniscus pathway

Question Answer
dorsal column – medial lemniscus pathwaythis is an ascending tract with 3 order neurons. The function is to relay discriminative touch, vibrating and conscious propioception to the brain.
1st order neuronsare pseudounipolar neurons in the dorsal root ganglia (DRG) that enters the fasciculus gracilis (sensory from foot, leg, thigh, gluteal, lower trunk) or fasciculus cuneatus( sensory from upper trunk, upper extremity, shoulder and neck) of the spinal cord. The tract continues upward toward the second order neurons.
2nd order neuronsthese neurons are located in the nucleus gracilis and nucleus cuneates in the caudal medulla. they synapse with their respected tract name. axons from both nuclueus decussate as internal arcuate fibers and form the medial leminscus. It courses through the pons and midbrain to the thalmus.
3rd order neuronsare located in the ventral posterolateral (VPL) of the thalmus. Axons in the VPL nucleus course through the coronal radiata to synapse in the region of the primary somatosensory cortex
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Describe the spinothalamic tracts

Question Answer
anterolateral systemis made up of 3 different ascending tracts: spinothalamic, spinocerbellar and spinomesencephalic tract. The function for all three is to send afferent signals of pain, temp and crude touch to the brain and course in the lateral and anterior white columns of the spinal cord. the spinothalamic tract has 3 order neurons.
1st order neuronsare pseudunipolar neurons in the dorsal rood ganglia. The central process goes into the lateral bundle of the dorsal rootlet and then enters the dorsolateral tract where it divides into a main ascending and descending branch. the main branch enters the dorsal horn and termiates on the tract neuron located in lamina 1 and 5. It also terminates on interneurons located in lamina 2.
2nd order neuronsare located in the dorsal horn of lamina 1 and 5. Their axons decussate in the ventral white comissure over 1-2 segments and then ascend in the lateral and ventral white columns as the spinothalmic tract. It courses through the spinal cord, medulla, pons and midbrain to the thalmus.
3rd order neuronsare also located in the VLP nucleus of the thalmus, where the axons they follow the same path as the dorsal column-medial leminisucs pathway
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Describe the dorsal spinocerebellar tract and cuneocerebellar tract

Question Answer
dorsal spinocerebellar tracthas its first order neuron the same as spinothalamic, second order neurons in the dorsal horn of lamina 5,6,8. their axons decussate and go to the reticular formation. the reticular formation projects to the intralaminar and other nuclei of the thalmus, hypothalmus, and periaqueductal gray. and the thalmic ncuclei project to the limbic cortex, orbitofrontal cortex and other regions of the cerebral cortex
cuneocerebellar tractcarries propeoception to the trunk and upper extremity. The first order neurons from C8 and above are pseudounipolar in the dorsal root gangli. They are A-alpha that enter the spinal cord through the medial bundle and ascend in the fasiculus cuneateus to synapse with its respected nucleus. Second order neurons are located in the lateral cuneate nucleus in the medulla and the axons course through the inferior cerebellar peduncle to synapse in the cortex of the spinocerebellum.
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Describe the ventral spinocerebellar tract

Question Answer
ventral spinocerebellar tractThis tract carries nonconcous propioception from the lower trunk and lower extremity. It also just has 2 order neurons.
1st order neuronsare pseudounipolar neurons in the dorsal root ganglia. They are a-alpha fibers that enter the spinal cord through the medial bundle and synapse with the neuron near the base of the dorsal horn.
2nd order neuronsare from neurons near the base of the dorsal horn (lamina 4,5,7 decussate and ascend in the ventral spinocerebellar tract in the lateral column). this tract courses through the superior cerebellar peduncle to synapse in the cortex of the spinocerebellum
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