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Ascending tracts and general sensory neuro stuff 

Ascending tracts and general sensory neuro stuff . Asfand Baig. The ascending tracts carry sensory information from the peripheries to the primary somatosensory cortex in the post-central gyrus of the cerebral cortex. Sensory lesions and examination. Sensory symptoms can be either:

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Ascending tracts and general sensory neuro stuff 

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  1. Ascending tracts and general sensory neuro stuff 

    Asfand Baig
  2. The ascending tracts carry sensory information from the peripheries to the primary somatosensory cortex in the post-central gyrus of the cerebral cortex
  3. Sensory lesions and examination Sensory symptoms can be either: Positive symptoms: pins & needles Negative symptoms: numbness Abnormalities on examination: Hypaesthesia: reduce pressure, light touch or temperature sensation Anaesthesia: absent pressure, light touch or temperature sensation Hypalgesia: reduced pain sensation Hyperaesthesia: pain in response to touch Hyperalgesia: severe pain in response to mildly noxious stimulus Allodynia: perception of non-painful stimulus as painful
  4. What are the general senses?
  5. There are different types of mechanoreceptors in the skin: Rapidly adapting (Phasic) receptors Turn on and off quickly unless there is a wound Signal “dynamic repsosnes” Most receptors are like this E.g. hair follicle receptors in hairy skin, meisseners corpuscles in glabrous skin, pacinian corpuscles in subcutaneous tissue Slowly adapting (Tonic) receptors Signal “static” responses that give overall information E.g. merkell cell endings, ruffiniendings
  6. The 3 ascending tracts are... Dorsal Columns Vibration, FineTouch, Proprioception Lateral Spinothalamic Pain, Temperature Anterior Spinothalamic Crude touch, Pressure
  7. And there’s one more THE SPINOCEREBELLAR Why is the spinocerebellar important? Unconscious proprioception But then is that the same thing as the proprioception done by the dorsal columns?
  8. How many sets of neurons are the main ascending tracts split into? 3 1st order, 2nd order and 3rd order
  9. The spinal cord Proprioception Vibration Fine Touch P+T Pressure
  10. Dorsal Columns Cross at Medulla 3rd order neurone: From VP nucleus in thalamusthough posterior limb of internal capsule cortex 2nd order neurone: From nuclei gracilis and cuneatus in medulla decussate in medulla become internal arcuatefibres ascend brainstem as the medial lemniscusVPLnucleus of thalamus 1st order neurone: From receptors in peripheryfasciculusgracilis and cuneatusascend to nucleuigracilis and cuneatus in medulla
  11. Anterior Spinothalamic Tract 3rd order neurone: From VP nucleus in thalamusthough posterior limb of internal capsule cortex 2nd order neurone: From substantiagelatinosadecussates over several spinal segments and ascends in ant. Spinothalamictractbecomes lateral then spinal lemniscus in brainstemventralposterolateral (VP) nucleus in thalamus 1st order neurone: From various receptors in periphery substantiagelatinosa in dorsal horn
  12. Lateral Spinothalamic Tract 3rd order neurone: From VP nucleus in thalamusthough posterior limb of internal capsule cortex 2nd order neurone: From substantiagelatinosadecussates within 1 spinal segment and ascends in lat. Spinothalamictractbecomes lateral then spinal lemniscus in brainstemventralposterolateral (VP) nucleus in thalamus 1st order neurone: From receptors in periphery (fast (Aδ) or slow (C) fibres) substantiagelatinosa in dorsal horn
  13. Spinocerebellar Tracts 2nd order neurone: Ventral TRACT Some fibres decussate as soon as enter spinal cordascend in anterior spinocerebellar tract to superior cerebellar peduncle in cerebellumrecross back over to side it entered in Other fibres remain uncrossedascend to sup. cerebellar peduncle in ipsilateral ant. Spinocerebellar tract 2nd order neurone: Dorsal TRACT Remains uncrossed ascend in post. Spinocerebellartractinferior cerebellar peduncle in cerebellum 1st order neurone: From receptors in periphery nucleus dorsalis
  14. Spinocerebellar tracts. Remember these 2 diagrams? rostral Cuneocerebellar Upper limb Upper limb dorsal ventral Lower limb Lower limb
  15. Why doesn’t the spinocerebellar tract have a 3rd neuron? There is no 3rd order neurone as it is doesn’t reach consciousness i.e the cortex
  16. What sensory modality does each branch of the spinocerebellar tractconvey?Therefore what receptors does each branch use? Dorsal spinocerebellar tract monitors muscle length, speed of contraction and tension from lower body and lower limb Muscle spindles A few Golgi tendon organs Cuneocerebellar for upper Ventral spinocerebellar tract monitors stretch of the tendon at the muscle-tendon interface of the lower limb     - Golgi tendon organs Rostral for upper
  17. Trigeminal Nerve (CN V) 3rd order neurons pass to primary sensory cortex 2nd order neurons ascend in trigeminal lemniscus to ventral posterior medial nucleus of the thalamus Ventral Posterior n. 1st order trigeminal nerve sensory neurons synapse in CN V nucleus Ventral Posterior Lateral n. (Body) Ventral Posterior Medial n. (Face – CN V)
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