Ascending tracts

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Ascending tracts

They are located in the white matter
Conduct afferent information (May or may not reach consciousness)
There are 2 types of information

Exteroceptive : Originates from outside the body (Pain, temperature & touch)
Proprioceptive : Originates from inside the body (From muscles & joints)


Normally there are 3 neurons in an ascending pathway

1st order neuron : Cell body is in the posterior root ganglion
2nd order neuron : Decussates (Crosses to the opposite side) & ascends to a higher level of the CNS
3rd neuron : Located in the thalamus & passes to a sensory region of the cortex

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Ascending tracts

  1. 1. www.MedicalLecturenotes.com
  2. 2. •They are located in the white matter• Conduct afferent information (May or may not reachconsciousness) www.medicallecturenotes.com
  3. 3. www.medicallecturenotes.comThere are 2 types of information• Exteroceptive : Originates from outside the body (Pain,temperature & touch)• Proprioceptive : Originates from inside the body (Frommuscles & joints)Normally there are 3 neurons in an ascending pathway• 1st order neuron : Cell body is in the posterior root ganglion•2nd order neuron : Decussates (Crosses to the opposite side)& ascends to a higher level of the CNS • 3rd neuron : Located in the thalamus & passes to a sensory region of the cortex
  4. 4. 1st order neuronPeripheral process extends to skin or othertissues & ends as free nerve endings(Receptors)•Cell body is situated in the posterior rootganglion•Central process extends into the posteriorgrey column & synapses with the 2nd orderneuron www.medicallecturenotes.com
  5. 5. 2nd order neuron•The axon crosses obliquely to the opposite side in the anterior grey& white commissures within one spinal segment of the cord•It ascends in the contra – lateral white column as the lateralspinothalamic tract (LSTT)•As the LSTT ascends through the spinal cord new fibers are addedto the antero – medial aspect of the tract (Sacral fibers are lateral &cervical fibers are medial)•The fibers carrying pain are situated anterior to those conductingtemperature www.medicallecturenotes.com
  6. 6. 2nd order neuron•As the LSTT ascends through the medulla oblongata, it’sjoined by the anterior spinothalamic tract & thespinotectal tract and forms the spinal lemniscus•Spinal lemniscus ascends through the pons & the midbrain•Fibers of the LSTT end by synapsing with the 3rd orderneurons in the ventral posterolateral nucleus of thethalamus (Here crude pain & temperature sensations areappreciated) www.medicallecturenotes.com
  7. 7. 3rd order neuron•Axons pass through the posterior limb of the internalcapsule & corona radiata to reach the somesthetic area inthe post central gyrus of the cerebral cortex•From here information is transmitted to other regions ofthe cerebral cortex to be used by motor areas•The role of the cerebral cortex is interpreting the qualityof the sensory information at the level of theconsciousness www.medicallecturenotes.com
  8. 8. 1st order neuron : It is similar to the pain &temperature pathway www.medicallecturenotes.com
  9. 9. 2nd order neuron•The axon crosses obliquely to the opposite side in the anterior grey & whitecommissures within several spinal segments•It ascends in the contra – lateral white column as the anterior spinothalamic tract(ASTT)•As the ASTT ascends through the spinal cord new fibers are added to the antero –medial aspect of the tract (Sacral fibers are lateral & cervical fibers are medial)•As the ASTT ascends through the medulla oblongata, it’s joined by the lateralspinothalamic tract & the spinotectal tract and forms the spinal lemniscus•Spinal lemniscus ascends through the pons & the mid brain•Fibers of the ASTT end by synapsing with the 3rd order neurons in the ventralposterolateral nucleus of the thalamus (Here crude awareness of touch & pressuresensations are appreciated) www.medicallecturenotes.com
  10. 10. 3rd order neuron•Axons pass through the posterior limb of the internal capsule &corona radiata to reach the somesthetic area in the post centralgyrus of the cerebral cortex•The sensations can be crudely localized•Very little discrimination is possible www.medicallecturenotes.com
  11. 11. "It will take only 2 sec to say thanks and will take only 10 sec to write a comment it will be a nice encouragement for us "Dr. Pulasthi Senartna www.medicallecturenotes.com

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