Tractology

 

Image result for horizontal cross section of brain

 

2

 

3

 

Ascending pathways

  • 1st, 2nd and 3rd order
  • Lesions before decussation – ipsilateral paralysis
  • Lesions after decussation – contralateral paralysis

 

(I) Pain and temperatureLateral spinothalamic

  • Receptors:
  1. Free nerve endings – pain
  2. Krause end bulb
  3. Ruffini’s corpsules
  • 1st order neuron
  • Dorsal root ganglion
  • Spinal cord dorsal horn
  • Synapse with 2nd order neuron in substantia gelatinosa
  • Decussate in anterior white commisure
  • Ascend as lateral spinothalamic tract
  • And then as spinal lemniscus in medulla
  • To VPLN of thalamus
  • Synapse with 3rd order neuron
  • Posterior limb internal capsule and corona radiata
  • Posterior central gyrus

 

(II) Crude touch and pressure – Ventral spinothalamic

  • Receptors:
  1. Paccinian corpuscle – pressure
  2. Merkel’s disc – mechanoreceptor
  • 1st order neuron
  • Dorsal root ganglion
  • Spinal cord dorsal horn
  • Synapse with 2nd order neuron in nucleus proprius
  • Axons rise a few segments
  • Decussate in anterior white commisure
  • Ascend as anterior spinothalamic tract
  • And then as spinal lemniscus in medulla
  • To VPLN of thalamus
  • Synapse with 3rd order neuron
  • Posterior limb internal capsule and corona radiata
  • Posterior central gyrus

 

(III) Concious proprioception, vibration and fine touch Fasciculus gracilis and cuneatus

  • Receptors:
  1. Paccinian corpuscle
  2. Muscle spindle
  3. Golgi tendon organ
  4. Meissner’s corpuscle – light touch
  • 1st order neuron
  • Dorsal root ganglion
  • Ascend in ipsilateral fascicle
  • Synapse with 2nd order neuron in medulla in nucleus gracilis/cuneatus
  • Pyramidal decussation
  • Ascend in medial lemniscus
  • To VPLN of thalamus
  • Synapse with 3rd order neuron
  • Posterior limb internal capsule and corona radiata
  • Posterior central gyrus

 

(IV) Unconcious proprioception/ reflex – From muscles to cerebellum

Ventral spinocerebeller

  • Receptors:
  1. Muscle spindle
  2. Golgi tendon
  • 1st order neuron
  • Dorsal root ganglion
  • Spinal cord dorsal horn
  • Synapse with 2nd order neuron in dorsal horn
  • Decussate in anterior white commisure
  • Ascend as ventral spinocerebeller tract
  • Enter cerebellum in superior cerebeller peduncle
  • Decussate in cerebeller white mater
  • Terminate in vermis

NB: No 3rd order neuron, 2 decussations

 

Dorsal spinocerebeller

  • Receptors:
  1. Muscle spindle
  2. Golgi tendon
  • 1st order neuron
  • Dorsal root ganglion
  • Spinal cord dorsal horn
  • Synapse with 2nd order neuron in  Clarke’s nucleus/ nucleus dorsalis
  • Ascend ipsilateral in dorsal spinocerebeller tract
  • Enter cerebellum in inferior cerebeller peduncle
  • Terminate in vermis

NB: No 3rd order neuron, no decussations, ipsilateral tract


 

(V) Gustatory pathway – Taste

10


 

Descending pathways

  • Upper motor and lower motor

Voluntary and fine movements

11


 

These are summarized notes from various sources, mainly TeachMeAnatomy and Wikipedia

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