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DESCENDING TRACTS

DESCENDING TRACTS. Dr. Ahmed Fathalla Ibrahim. CORTICOSPINAL TRACTS. Concerned with voluntary discrete & skilled movement, especially of distal parts of limbs Formed of one neurone Cells of origin: Large Betz cells in precentral gyrus (primary motor cortex). CORTICOSPINAL TRACTS.

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DESCENDING TRACTS

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  1. DESCENDING TRACTS Dr. Ahmed Fathalla Ibrahim

  2. CORTICOSPINAL TRACTS • Concerned with voluntary discrete & skilled movement, especially of distal parts of limbs • Formed of one neurone • Cells of origin: Large Betz cells in precentral gyrus(primary motor cortex)

  3. CORTICOSPINAL TRACTS PATHWAY • Axons descend in : • Corona radiata • Posterior limb of internal capsule • Crus cerebri (middle 3/5) • Basis pontis • Pyramid of medulla

  4. CORTICOSPINAL TRACTS LATERAL CORTICOSPINAL TRACT • Formed of 75 – 90% of fibers • Fibers decussate in the medulla(motor decussation) • Fibers descends in lateral white column of spinal cord • Fibers terminate in contralateral ventral horn cells of spinal cord

  5. CORTICOSPINAL TRACTS VENTRAL CORTICOSPINAL TRACT • Formed of 10 – 25% of fibers • Fibers descend uncrossed in medulla • Fibers descends in ventral white column of spinal cord • Fibers decussate near to their termination in the spinal cord • Fibers terminate in contralateralventral horn cells of spinal cord

  6. CORTICOSPINAL TRACTS

  7. RUBROSPINAL TRACTS • Cells of origin:red nucleus in midbrain • Receives afferents from motor cortex & cerebellum • Represents a route through which cerebral cortex & cerebellum can influence motor activity • Axons cross in ventral tegmental decussation

  8. RUBROSPINAL TRACTS • Axons descend in lateral white column of spinal cord (Tract is ventrolateral & partly mixed with lateral corticospinal tract) • Axons terminate in contralateral ventral horn cells of spinal cord • The tract carries excitatory fibers to motor neurones of limb flexor muscles

  9. RUBROSPINAL TRACTS

  10. TECTOSPINAL TRACT • Cells of origin:superior colliculus in midbrain • Axons cross in dorsal tegmental decussation • Axons descend in ventral white column of spinal cord • Axons terminate in contralateral ventral horn cells of spinal cord • The tract mediates reflex movement in response to visual stimuli

  11. VESTIBULOSPINAL TRACTS LATERAL VESTIBULOSPINAL TRACT • Cells of origin:lateral vestibular nucleus • Axons desend in ventralwhite column of spinal cord • Axons terminate in ipsilateralventral horn cells of spinal cord • The tract mediates excitatory influences upon extensor motor neurones to maintain posture

  12. VESTIBULOSPINAL TRACTS MEDIAL VESTIBULOSPINAL TRACT • Cells of origin:medial vestibular nucleus • Axons desend in ventral white column of spinal cord(as a part of medial longitudinal fasciculus) • Axons terminate in ipsilateralventral horn cells of spinal cord • The medial longitudinal fasciculus consists of both ascending & descending fibers that link vestibular nuclei to nuclei supplying the extraocular muscles for coordination of head and eye movements

  13. RETICULOSPINAL TRACTS MEDIAL RETICULOSPINAL TRACT • Cells of origin:pontine reticular formation • Axons descend in ventral white column of spinal cord • Axons terminate in ipsilateral ventral horn cells of spinal cord

  14. RETICULOSPINAL TRACTS LATERAL RETICULOSPINAL TRACT • Cells of origin:medullary reticular formation • Axons descend in ventral white column of spinal cord on both sides(both crossed & uncrossed) • Axons terminate in ipsilateral& contralateral ventral horn cells of spinal cord

  15. RETICULOSPINAL TRACTS • Concerned with control of reflex activity & muscle tone

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