Ascending tracts and general sensory neuro stuff
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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

Ascending tracts and general sensory neuro stuff 

Asfand Baig


Ascending tracts and general sensory neuro stuff

  • 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 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


What are the general senses

What are the general senses?


There are different types of mechanoreceptors in the skin

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


The 3 ascending tracts are

The 3 ascending tracts are...

  • Dorsal Columns

  • Vibration,

  • FineTouch,

  • Proprioception

  • Lateral Spinothalamic

  • Pain,

  • Temperature

  • Anterior Spinothalamic

  • Crude touch,

  • Pressure


And there s one more

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?


How many sets of neurons are the main ascending tracts split into

How many sets of neurons are the main ascending tracts split into?

  • 3

  • 1st order, 2nd order and 3rd order


The spinal cord

The spinal cord

Proprioception

Vibration

Fine Touch

P+T

Pressure


Ascending tracts and general sensory neuro stuff

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


Anterior spinothalamic tract

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


Lateral spinothalamic tract

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


Spinocerebellar tracts

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


Spinocerebellar tracts remember these 2 diagrams

Spinocerebellar tracts. Remember these 2 diagrams?

rostral

Cuneocerebellar

Upper limb

Upper limb

dorsal

ventral

Lower limb

Lower limb


Why doesn t the spinocerebellar tract have a 3 rd neuron

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


Ascending tracts and general sensory neuro stuff

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


Trigeminal nerve cn v

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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