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Tracts (ascending and descending)
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Tracts (ascending and descending)

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  • 1. Ascending and Descending Tracts SMS 1084 Dr. Mohanad R. Alwan
  • 2.
    • Contents
      • function of nervous system in general
      • sensory system overview
      • spinal cord and nerve tracts
        • ascending tracts
          • organization in general
          • ascending tracts
          • functional components
  • 3.
    • Nervous System
    • Communication
    • receive information
    • transform it into impulses ( transduction )
    • transmit impulses to the CNS
    • correlate / coordinate
    • transmit impulses to the effector organs
    • response / action
  • 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.
    • Ascending Tracts
    • bundles of nerve fibres
    • linking
        • spinal cord with higher centres of the brain
    • convey information
    • from
    • soma / viscera to higher level of neuraxis (CNS)
  • 6. Ascending Sensory Pathway are organized in three neuronal chain - First order neurone - Second order neurone - Third order neurone
  • 7.
    • First order neurone
    • cell body in posterior root ganglion
    • peripheral process connects with sensory receptor ending
    • central process enter the spinal cord through the posterior root
    • synapse with second order neuron in spinal gray matter
  • 8. dorsal root dorsal root ganglion spinal nerve dorsal horn FIRST ORDER NEURON
  • 9.
    • Second order neurone
    • cell body in posterior gray column of spinal cord
    • axon crosses the midline ( decussate )
    • ascend & synapse with third order neuron in VPL nucleus of thalamus
  • 10. SECOND ORDER NEURON
    • cross the mid line
    • in front of central canal
    VPL 1 st 2 nd
  • 11.
    • Third order neurone
    • cell body in the thalamus
    • give rise to projection fibres to the cerebral cortex, postcentral gyrus ( sensory area )
  • 12. ascending sensory pathway ( in general form ) from sensory endings to cerebral cortex ( note the three neurons chain )
  • 13. ascending tracts in spinal cord
  • 14.
    • lateral spinothalamic tract
      • pain, temperature
    • anterior spinothalamic tract
      • touch, pressure
    Tracts & Their Functional Components
  • 15.
    • posterior white column
      • conscious proprioceptive sense, discriminative touch, vibratory sense
    • spinocerebellar tract / cuneocerebellar tract
      • unconscious information from muscle, joints, skin, subcutaneous tissues
  • 16.
    • Lateral spinothalamic tract
    • pain and thermal impulses
    • ( input from free nerve endings, thermal receptors )
    • transmitted to spinal cord in delta A and C fibres
    • central process enters the spinal cord through posterior nerve root , proceed to the tip of the dorsal gray column
  • 17. pain and temperature pathways
  • 18.
    • Anterior spinothalamic tract
    • light touch and pressure impulses
    • ( input from free nerve endings, Merkel’s tactile disks )
    • First order neuron
      • dorsal root ganglion( all level )
    • Second order neuron
      • in the dorsal horn, cross to the opposite side (decussate)
      • ascend in the contralateral ventral column
      • end in VPL nucleus of thalamus
    • Third order neuron
      • in the VPL nucleus of thalamus
      • project to cerebral cortex ( area 3, 1 and 2 )
  • 19. Touch and pressure pathways
  • 20.
    • Posterior & anterior spinocerebellar tract
    • Transmit unconscious proprioceptive information to the cerebellum
    • receive input from muscle spindles, and pressure receptors
    • involved in coordination of posture and movement of individual muscles of the lower limb
  • 21. muscle joint sense pathways to cerebellum
  • 22.
    • Spinotectal tract
      • passes pain, thermal, tactile information to superior colliculus for spinovisual reflexes
        • cross the median plane
        • synapse in the superior colliculus
        • integrate visual and somatic sensory information ( it brings about the movement of eye and head towards the source of information )
    • Spinoreticular tract
      • uncrossed fibres, synapse with neurones of reticular formation (important role in influencing level of consciousness )
    • Spino-olivary tract
  • 23. Spinotectal tract Spinoreticular tract Spino-oloivary tract
  • 24.
    • Descending Tracts
    • Segregated bundles of nerve fibres in the white matter of the spinal cord descending from the supraspinal centres
      • referred to as upper motor neurons ( UMN )
    • are concerned with somatic and visceral motor activity
    • cells of origin lie in cerebral cortex and brain stem
    • regulate the LMN activity
  • 25. motor homunculus cerebral cortex
  • 26.
    • lower motor neurons ( LMN )
    • motor neurons that innervate the voluntary muscles
    • in anterior gray column of spinal cord /
    • motor nuclei of brainstem
      • innervate skeletal muscles
    • form final common pathway
    LMN
  • 27.
    • LMN
    • constantly bombarded by
    • nerve impulses( excitatory or inhibitory )
      • that descend from cerebral cortex,
      • pons,
      • midbrain and
      • medulla
    • sensory inputs from the posterior root
  • 28.
    • Upper motor neurons ( UMN )
    • The descending supraspinal pathways that influence the activity of the LMN
  • 29.
    • UMN
    • control voluntary motor activity
    • maintenance of posture & equilibrium
    • control of muscle tone and reflex activity
    • generally exerts their effect
    • on groups of muscles ( not on one specific muscle )
    • reciprocally on agonist and antagonist muscle group
  • 30. cerebral cortex – midbrain - pons - medulla oblongata descending tracts LMN sensory inputs
  • 31.  
  • 32.
    • Corticospinal tract
    • arises from the pyramidal cells of cerebral cortex
      • fibres travel through
        • corona radiata
        • posterior limb of the internal capsule
        • cerebral peduncle ( middle 3/ 5 th )
        • pons
        • medulla oblongata ( passed through the pyramids )
      • eventually fibres cross the mid line and terminate on LMN of anterior gray column of respective spinal cord segments
  • 33. motor decussation medulla oblongata
  • 34. Corticospinal Tract for fine skilled movements
  • 35.
    • Rubrospinal tract
    • nerve cells in red nucleus
    • ( tegmentum of midbrain at the level of superior colliculus )
    • nerve fibres / axons
      • cross the mid line
      • descend as rubrospinal tract
        • through pons and medulla oblongata
    • terminate anterior gray column of spinal cord
    • ( facilitate the activity of flexor muscles )
  • 36.  
  • 37.
    • Tectospinal tract
    • nerve cells in superior colliculus of the midbrain
    • nerve fibres/ axons
      • cross the mid line
      • descend close to medial longitudinal fasciculus
    • terminate in the anterior gray column of upper cervical segments of spinal cord
    • ( responsible for reflex movement of
    • head & neck in response to visual stimuli )
  • 38.  
  • 39.
    • Vestibulospinal tract
    • nerve cells in vestibular nucleus (in the pons and medulla oblongata
      • received afferents from inner ear and cerebellum
    • axons descend uncrossed
      • through medulla and through the length of spinal cord
    • synapse with neuron in the anterior gray column of the spinal cord
    • ( balance by facilitate the activity of the extensor muscles )
  • 40.  
  • 41.
    • Reticulospinal tract
    • nerve cells in reticular formation
    • fibres pass through
      • midbrain, pons, and medulla oblongata
    • end at the anterior gray column of spinal cord
      • control activity of motor neurons
    • (influence voluntary movement and reflex activity )
  • 42. Reticulospinal Tract
  • 43. Thank You