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Descending tract

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Descending tract

  1. 1. www.MedicalLecturenotes.com
  2. 2. Descending tracts have 3 neurons•1st order neurons (UMN) : Cell bodies are inthe cerebral cortex & other supra spinal areas•2nd order neurons : Short & situated inthe anterior grey column of the spinal cord•3rd order neuron (LMN) : Situated in theanterior grey column & innervate the skeletalmuscles through anterior roots of the spinalnerves www.medicallecturenotes.com
  3. 3. Cortico-spinal tract : Rapid, skilled & voluntary movements www.medicallecturenotes.com
  4. 4. Cortico-spinal tract : Rapid, skilled & voluntary movements1st order neuron 1)Axons arise from the pyramidal cells of the cerebral cortex (Situated in the 5th layer), 2/3 from the pre central gyrus & 1/3 from the post central gyrus 1.1/3 of fibers arise from the 1stry motor cortex (Area 4) 2.1/3 of fibers arise from the 2ndry motor cortex (Area 6) 3.1/3 of fibers arise from the parietal lobe (Area 1, 2 & 3) 2)Descending fibers converge in the corona radiata & pass though the posterior limb of the internal capsule; Organization of fibers within the internal capsule: 1.Close to genu (Medial) : Concerned with the cervical parts of the body 2.Away from the genu (lateral) : Concerned with the lower extremity 3)The tract then passes through the middle 3/5 of the basis pedunculi of the midbrain; Organization of fibers in the midbrain: 1.Medially : Cervical parts of the body 2.Laterally : Lower limbs www.medicallecturenotes.com
  5. 5. Cortico-spinal tract : Rapid, skilled & voluntary movements4. When the tract enters the pons, it’s broken into many bundles by thetransverse pontocerebellar fibers5.In the medulla oblongata, the bundles group together to form the pyramids6.At the junction of the MO & the spinal cord, most fibers cross the midline atthe decussation of the pyramids & enter the lateral white column of the spinalcord to form the lateral corticospinal tract (LCST)7.LCST descends length of the spinal cord; terminate in the anterior greycolumn of all the spinal segments8.The fibers which didn’t cross, descend in the anterior white column of thespinal cord as the anterior corticospinal tract (ACST)9.Fibers of the ACST eventually cross & terminate in the anterior grey columnof the spinal cord segments in the cervical & upper thoracic regions www.medicallecturenotes.com
  6. 6. Cortico-spinal tract : Rapid, skilled & voluntary movements2nd order neuron : it’s an internuncial neuron3rd order neuron : it’s a alpha or gamma motor neuron www.medicallecturenotes.com
  7. 7. "It will take only 2 sec to say thanks and will take only 10 sec to write a comment it will be a nice encouragement for us "Dr. Pulasthi Senaratna www.medicallecturenotes.com

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