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Ascending tracts and general sensory neuro stuff Asfand Baig.

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Presentation on theme: "Ascending tracts and general sensory neuro stuff Asfand Baig."— Presentation transcript:

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? General SenseReceptor Temp and painFree nerve ending Discriminative TouchMeissner corpuscle Light TouchMerkel cells & disk TouchRuffini ending Deep pressurePacinian corpuscle

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, ruffini endings

6 The 3 ascending tracts are... Anterior Spinothalamic Crude touch, Pressure Lateral Spinothalamic Pain, Temperature Dorsal Columns Vibration, Fine Touch, Proprioception

7 And theres 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 1 st order, 2 nd order and 3 rd order

9 The spinal cord Proprioception Vibration Fine Touch Pressure P+ T

10 Dorsal Columns Cross at Medulla 1 st order neurone: From receptors in periphery fasciculus gracilis and cuneatus ascend to nucleui gracilis and cuneatus in medulla 1 st order neurone: From receptors in periphery fasciculus gracilis and cuneatus ascend to nucleui gracilis and cuneatus in medulla 2 nd order neurone: From nuclei gracilis and cuneatus in medulla decussate in medulla become internal arcuate fibres ascend brainstem as the medial lemniscus VPL nucleus of thalamus 2 nd order neurone: From nuclei gracilis and cuneatus in medulla decussate in medulla become internal arcuate fibres ascend brainstem as the medial lemniscus VPL nucleus of thalamus 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex

11 Anterior Spinothalamic Tract 1 st order neurone: From various receptors in periphery substantia gelatinosa in dorsal horn 1 st order neurone: From various receptors in periphery substantia gelatinosa in dorsal horn 2 nd order neurone: From substantia gelatinosa decussates over several spinal segments and ascends in ant. Spinothalamic tract becomes lateral then spinal lemniscus in brainstem ventral posterolateral (VP) nucleus in thalamus 2 nd order neurone: From substantia gelatinosa decussates over several spinal segments and ascends in ant. Spinothalamic tract becomes lateral then spinal lemniscus in brainstem ventral posterolateral (VP) nucleus in thalamus 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex

12 Lateral Spinothalamic Tract 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex 3 rd order neurone: From VP nucleus in thalamus though posterior limb of internal capsule cortex 2 nd order neurone: From substantia gelatinosa decussates within 1 spinal segment and ascends in lat. Spinothalamic tract becomes lateral then spinal lemniscus in brainstem ventral posterolateral (VP) nucleus in thalamus 2 nd order neurone: From substantia gelatinosa decussates within 1 spinal segment and ascends in lat. Spinothalamic tract becomes lateral then spinal lemniscus in brainstem ventral posterolateral (VP) nucleus in thalamus 1 st order neurone: From receptors in periphery (fast (Aδ) or slow (C) fibres) substantia gelatinosa in dorsal horn 1 st order neurone: From receptors in periphery (fast (Aδ) or slow (C) fibres) substantia gelatinosa in dorsal horn

13 Spinocerebellar Tracts 1 st order neurone: From receptors in periphery nucleus dorsalis 1 st order neurone: From receptors in periphery nucleus dorsalis 2 nd order neurone: Dorsal TRACT Remains uncrossed ascend in post. Spinocerebellar tract inferior cerebellar peduncle in cerebellum 2 nd order neurone: Dorsal TRACT Remains uncrossed ascend in post. Spinocerebellar tract inferior cerebellar peduncle in cerebellum 2 nd 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 2 nd 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

14 Spinocerebellar tracts. Remember these 2 diagrams? Lower limb Upper limb Lower limb Upper limb Cuneocerebellar dorsal ventral rostral

15 Why doesnt the spinocerebellar tract have a 3 rd neuron? There is no 3 rd order neurone as it is doesnt reach consciousness i.e the cortex

16 What sensory modality does each branch of the spinocerebellar tract convey? 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) Ventral Posterior n. Ventral Posterior Lateral n. (Body) Ventral Posterior Medial n. (Face – CN V) 1 st order trigeminal nerve sensory neurons synapse in CN V nucleus 3 rd order neurons pass to primary sensory cortex 2 nd order neurons ascend in trigeminal lemniscus to ventral posterior medial nucleus of the thalamus


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