Tracts (ascending and descending)

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Tracts (ascending and descending)

  1. 1. Ascending and Descending Tracts SMS 1084 Dr. Mohanad R. Alwan
  2. 2. <ul><li>Contents </li></ul><ul><ul><li>function of nervous system in general </li></ul></ul><ul><ul><li>sensory system overview </li></ul></ul><ul><ul><li>spinal cord and nerve tracts </li></ul></ul><ul><ul><ul><li>ascending tracts </li></ul></ul></ul><ul><ul><ul><ul><li>organization in general </li></ul></ul></ul></ul><ul><ul><ul><ul><li>ascending tracts </li></ul></ul></ul></ul><ul><ul><ul><ul><li>functional components </li></ul></ul></ul></ul>
  3. 3. <ul><li>Nervous System </li></ul><ul><li>Communication </li></ul><ul><li>receive information </li></ul><ul><li>transform it into impulses ( transduction ) </li></ul><ul><li>transmit impulses to the CNS </li></ul><ul><li>correlate / coordinate </li></ul><ul><li>transmit impulses to the effector organs </li></ul><ul><li>response / action </li></ul>
  4. 4. CENTRAL NERVOUS SYSTEM integration / processing / modulating stimulus receptor neurone motor / descending tracts effector organ / response PNS transmission lower motor neurone sensory / ascending tracts
  5. 5. <ul><li>Ascending Tracts </li></ul><ul><li>bundles of nerve fibres </li></ul><ul><li>linking </li></ul><ul><ul><ul><li>spinal cord with higher centres of the brain </li></ul></ul></ul><ul><li>convey information </li></ul><ul><li>from </li></ul><ul><li>soma / viscera to higher level of neuraxis (CNS) </li></ul>
  6. 6. Ascending Sensory Pathway are organized in three neuronal chain - First order neurone - Second order neurone - Third order neurone
  7. 7. <ul><li>First order neurone </li></ul><ul><li>cell body in posterior root ganglion </li></ul><ul><li>peripheral process connects with sensory receptor ending </li></ul><ul><li>central process enter the spinal cord through the posterior root </li></ul><ul><li>synapse with second order neuron in spinal gray matter </li></ul>
  8. 8. dorsal root dorsal root ganglion spinal nerve dorsal horn FIRST ORDER NEURON
  9. 9. <ul><li>Second order neurone </li></ul><ul><li>cell body in posterior gray column of spinal cord </li></ul><ul><li>axon crosses the midline ( decussate ) </li></ul><ul><li>ascend & synapse with third order neuron in VPL nucleus of thalamus </li></ul>
  10. 10. SECOND ORDER NEURON <ul><li>cross the mid line </li></ul><ul><li>in front of central canal </li></ul>VPL 1 st 2 nd
  11. 11. <ul><li>Third order neurone </li></ul><ul><li>cell body in the thalamus </li></ul><ul><li>give rise to projection fibres to the cerebral cortex, postcentral gyrus ( sensory area ) </li></ul>
  12. 12. ascending sensory pathway ( in general form ) from sensory endings to cerebral cortex ( note the three neurons chain )
  13. 13. ascending tracts in spinal cord
  14. 14. <ul><li>lateral spinothalamic tract </li></ul><ul><ul><li>pain, temperature </li></ul></ul><ul><li>anterior spinothalamic tract </li></ul><ul><ul><li>touch, pressure </li></ul></ul>Tracts & Their Functional Components
  15. 15. <ul><li>posterior white column </li></ul><ul><ul><li>conscious proprioceptive sense, discriminative touch, vibratory sense </li></ul></ul><ul><li>spinocerebellar tract / cuneocerebellar tract </li></ul><ul><ul><li>unconscious information from muscle, joints, skin, subcutaneous tissues </li></ul></ul>
  16. 16. <ul><li>Lateral spinothalamic tract </li></ul><ul><li>pain and thermal impulses </li></ul><ul><li>( input from free nerve endings, thermal receptors ) </li></ul><ul><li>transmitted to spinal cord in delta A and C fibres </li></ul><ul><li>central process enters the spinal cord through posterior nerve root , proceed to the tip of the dorsal gray column </li></ul>
  17. 17. pain and temperature pathways
  18. 18. <ul><li>Anterior spinothalamic tract </li></ul><ul><li>light touch and pressure impulses </li></ul><ul><li>( input from free nerve endings, Merkel’s tactile disks ) </li></ul><ul><li>First order neuron </li></ul><ul><ul><li>dorsal root ganglion( all level ) </li></ul></ul><ul><li>Second order neuron </li></ul><ul><ul><li>in the dorsal horn, cross to the opposite side (decussate) </li></ul></ul><ul><ul><li>ascend in the contralateral ventral column </li></ul></ul><ul><ul><li>end in VPL nucleus of thalamus </li></ul></ul><ul><li>Third order neuron </li></ul><ul><ul><li>in the VPL nucleus of thalamus </li></ul></ul><ul><ul><li>project to cerebral cortex ( area 3, 1 and 2 ) </li></ul></ul>
  19. 19. Touch and pressure pathways
  20. 20. <ul><li>Posterior & anterior spinocerebellar tract </li></ul><ul><li>Transmit unconscious proprioceptive information to the cerebellum </li></ul><ul><li>receive input from muscle spindles, and pressure receptors </li></ul><ul><li>involved in coordination of posture and movement of individual muscles of the lower limb </li></ul>
  21. 21. muscle joint sense pathways to cerebellum
  22. 22. <ul><li>Spinotectal tract </li></ul><ul><ul><li>passes pain, thermal, tactile information to superior colliculus for spinovisual reflexes </li></ul></ul><ul><ul><ul><li>cross the median plane </li></ul></ul></ul><ul><ul><ul><li>synapse in the superior colliculus </li></ul></ul></ul><ul><ul><ul><li>integrate visual and somatic sensory information ( it brings about the movement of eye and head towards the source of information ) </li></ul></ul></ul><ul><li>Spinoreticular tract </li></ul><ul><ul><li>uncrossed fibres, synapse with neurones of reticular formation (important role in influencing level of consciousness ) </li></ul></ul><ul><li>Spino-olivary tract </li></ul>
  23. 23. Spinotectal tract Spinoreticular tract Spino-oloivary tract
  24. 24. <ul><li>Descending Tracts </li></ul><ul><li>Segregated bundles of nerve fibres in the white matter of the spinal cord descending from the supraspinal centres </li></ul><ul><ul><li>referred to as upper motor neurons ( UMN ) </li></ul></ul><ul><li>are concerned with somatic and visceral motor activity </li></ul><ul><li>cells of origin lie in cerebral cortex and brain stem </li></ul><ul><li>regulate the LMN activity </li></ul>
  25. 25. motor homunculus cerebral cortex
  26. 26. <ul><li>lower motor neurons ( LMN ) </li></ul><ul><li>motor neurons that innervate the voluntary muscles </li></ul><ul><li>in anterior gray column of spinal cord / </li></ul><ul><li>motor nuclei of brainstem </li></ul><ul><ul><li>innervate skeletal muscles </li></ul></ul><ul><li>form final common pathway </li></ul>LMN
  27. 27. <ul><li>LMN </li></ul><ul><li>constantly bombarded by </li></ul><ul><li>nerve impulses( excitatory or inhibitory ) </li></ul><ul><ul><li>that descend from cerebral cortex, </li></ul></ul><ul><ul><li>pons, </li></ul></ul><ul><ul><li>midbrain and </li></ul></ul><ul><ul><li>medulla </li></ul></ul><ul><li>sensory inputs from the posterior root </li></ul>
  28. 28. <ul><li>Upper motor neurons ( UMN ) </li></ul><ul><li>The descending supraspinal pathways that influence the activity of the LMN </li></ul>
  29. 29. <ul><li>UMN </li></ul><ul><li>control voluntary motor activity </li></ul><ul><li>maintenance of posture & equilibrium </li></ul><ul><li>control of muscle tone and reflex activity </li></ul><ul><li>generally exerts their effect </li></ul><ul><li>on groups of muscles ( not on one specific muscle ) </li></ul><ul><li>reciprocally on agonist and antagonist muscle group </li></ul>
  30. 30. cerebral cortex – midbrain - pons - medulla oblongata descending tracts LMN sensory inputs
  31. 32. <ul><li>Corticospinal tract </li></ul><ul><li>arises from the pyramidal cells of cerebral cortex </li></ul><ul><ul><li>fibres travel through </li></ul></ul><ul><ul><ul><li>corona radiata </li></ul></ul></ul><ul><ul><ul><li>posterior limb of the internal capsule </li></ul></ul></ul><ul><ul><ul><li>cerebral peduncle ( middle 3/ 5 th ) </li></ul></ul></ul><ul><ul><ul><li>pons </li></ul></ul></ul><ul><ul><ul><li>medulla oblongata ( passed through the pyramids ) </li></ul></ul></ul><ul><ul><li>eventually fibres cross the mid line and terminate on LMN of anterior gray column of respective spinal cord segments </li></ul></ul>
  32. 33. motor decussation medulla oblongata
  33. 34. Corticospinal Tract for fine skilled movements
  34. 35. <ul><li>Rubrospinal tract </li></ul><ul><li>nerve cells in red nucleus </li></ul><ul><li>( tegmentum of midbrain at the level of superior colliculus ) </li></ul><ul><li>nerve fibres / axons </li></ul><ul><ul><li>cross the mid line </li></ul></ul><ul><ul><li>descend as rubrospinal tract </li></ul></ul><ul><ul><ul><li>through pons and medulla oblongata </li></ul></ul></ul><ul><li>terminate anterior gray column of spinal cord </li></ul><ul><li>( facilitate the activity of flexor muscles ) </li></ul>
  35. 37. <ul><li>Tectospinal tract </li></ul><ul><li>nerve cells in superior colliculus of the midbrain </li></ul><ul><li>nerve fibres/ axons </li></ul><ul><ul><li>cross the mid line </li></ul></ul><ul><ul><li>descend close to medial longitudinal fasciculus </li></ul></ul><ul><li>terminate in the anterior gray column of upper cervical segments of spinal cord </li></ul><ul><li>( responsible for reflex movement of </li></ul><ul><li>head & neck in response to visual stimuli ) </li></ul>
  36. 39. <ul><li>Vestibulospinal tract </li></ul><ul><li>nerve cells in vestibular nucleus (in the pons and medulla oblongata </li></ul><ul><ul><li>received afferents from inner ear and cerebellum </li></ul></ul><ul><li>axons descend uncrossed </li></ul><ul><ul><li>through medulla and through the length of spinal cord </li></ul></ul><ul><li>synapse with neuron in the anterior gray column of the spinal cord </li></ul><ul><li>( balance by facilitate the activity of the extensor muscles ) </li></ul>
  37. 41. <ul><li>Reticulospinal tract </li></ul><ul><li>nerve cells in reticular formation </li></ul><ul><li>fibres pass through </li></ul><ul><ul><li>midbrain, pons, and medulla oblongata </li></ul></ul><ul><li>end at the anterior gray column of spinal cord </li></ul><ul><ul><li>control activity of motor neurons </li></ul></ul><ul><li>(influence voluntary movement and reflex activity ) </li></ul>
  38. 42. Reticulospinal Tract
  39. 43. Thank You

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