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?
Receptor
Temp and pain
Free nerve ending
Discriminative Touch
Meissner corpuscle
Light Touch
Merkel cells & disk
Touch
Ruffini ending
Deep pressure
Pacinian 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...
Dorsal Columns
Vibration,
Fine Touch,
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?
Both. Muscle spindles sensory fibres carry information that feeds into the dorsal columns: conscious and  spinocerebellar: unconscious.

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
 Where is the anterior white commisure
LATERAL SPINOTHALAMIC TRACT
Enters substantia gelatinosa
Decussates into lateral spinothalamic tract
ANTERIOR SPINOTHALAMIC TRACT
Decussates into anterior spinothalamic tract
DORSAL COLUMNS
Enters fasciculus gracilis (medially) or fasciculus cuneatus (laterally)
Ascends to medulla and decussates there
SPINCEREBELLAR TRACTS
Enters nucleus dorsalis (“Clark’s column)
Posterior tracts stay uncrossed and ascend via posterior spinocerebellar tract
Anterior tracts mainly decussate into anterior spinocerebellar tracts
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 arcuate fibres ascend brainstem as the medial lemniscusVPL nucleus of thalamus
T6?
1st order neurone:
From receptors in peripheryfasciculus gracilis and cuneatusascend to nucleui gracilis 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 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
1st order neurone:
From various receptors in periphery substantia gelatinosa 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 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
1st order neurone:
From receptors in periphery (fast (Aδ) or slow (C) fibres) substantia gelatinosa 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. Spinocerebellar tractinferior cerebellar peduncle in cerebellum
1st order neurone:
From receptors in periphery nucleus dorsalis

14. Spinocerebellar tracts. Remember these 2 diagrams?
Cuneocerebellar
rostral
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. A few Golgi tendon organs Cuneocerebellar for upper
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)
1st order trigeminal nerve sensory neurons synapse in CN V nucleus
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.
Ventral Posterior Lateral n.
(Body)
Ventral Posterior Medial n.
(Face – CN V)