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•They are located in the white matter


• Conduct afferent information (May or may not reach
consciousness)
                                        www.medicallecturenotes.com
www.medicallecturenotes.com


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
1st order neuron

Peripheral process extends to skin or other
tissues & ends as free nerve endings
(Receptors)
•Cell body is situated in the posterior root
ganglion
•Central process extends into the posterior
grey column & synapses with the 2nd order
neuron


                   www.medicallecturenotes.com
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 lateral
spinothalamic tract (LSTT)
•As the LSTT 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)
•The fibers carrying pain are situated anterior to those conducting
temperature


                                              www.medicallecturenotes.com
2nd order neuron

•As the LSTT ascends through the medulla oblongata, it’s
joined by the anterior spinothalamic tract & the
spinotectal tract and forms the spinal lemniscus
•Spinal lemniscus ascends through the pons & the mid
brain
•Fibers of the LSTT end by synapsing with the 3rd order
neurons in the ventral posterolateral nucleus of the
thalamus (Here crude pain & temperature sensations are
appreciated)
                                    www.medicallecturenotes.com
3rd order neuron

•Axons pass through the posterior limb of the internal
capsule & corona radiata to reach the somesthetic area in
the post central gyrus of the cerebral cortex
•From here information is transmitted to other regions of
the cerebral cortex to be used by motor areas
•The role of the cerebral cortex is interpreting the quality
of the sensory information at the level of the
consciousness

                                      www.medicallecturenotes.com
1st order neuron : It is similar to the pain &
temperature pathway




                                   www.medicallecturenotes.com
2nd order neuron

•The axon crosses obliquely to the opposite side in the anterior grey & white
commissures 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 lateral
spinothalamic 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 ventral
posterolateral nucleus of the thalamus (Here crude awareness of touch & pressure
sensations are appreciated)

                                                    www.medicallecturenotes.com
3rd order neuron

•Axons pass through the posterior limb of the internal capsule &
corona radiata to reach the somesthetic area in the post central
gyrus of the cerebral cortex
•The sensations can be crudely localized
•Very little discrimination is possible




                                           www.medicallecturenotes.com
"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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Ascending tracts

  • 2. •They are located in the white matter • Conduct afferent information (May or may not reach consciousness) www.medicallecturenotes.com
  • 3. www.medicallecturenotes.com 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
  • 4. 1st order neuron Peripheral process extends to skin or other tissues & ends as free nerve endings (Receptors) •Cell body is situated in the posterior root ganglion •Central process extends into the posterior grey column & synapses with the 2nd order neuron www.medicallecturenotes.com
  • 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 lateral spinothalamic tract (LSTT) •As the LSTT 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) •The fibers carrying pain are situated anterior to those conducting temperature www.medicallecturenotes.com
  • 6. 2nd order neuron •As the LSTT ascends through the medulla oblongata, it’s joined by the anterior spinothalamic tract & the spinotectal tract and forms the spinal lemniscus •Spinal lemniscus ascends through the pons & the mid brain •Fibers of the LSTT end by synapsing with the 3rd order neurons in the ventral posterolateral nucleus of the thalamus (Here crude pain & temperature sensations are appreciated) www.medicallecturenotes.com
  • 7. 3rd order neuron •Axons pass through the posterior limb of the internal capsule & corona radiata to reach the somesthetic area in the post central gyrus of the cerebral cortex •From here information is transmitted to other regions of the cerebral cortex to be used by motor areas •The role of the cerebral cortex is interpreting the quality of the sensory information at the level of the consciousness www.medicallecturenotes.com
  • 8. 1st order neuron : It is similar to the pain & temperature pathway www.medicallecturenotes.com
  • 9. 2nd order neuron •The axon crosses obliquely to the opposite side in the anterior grey & white commissures 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 lateral spinothalamic 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 ventral posterolateral nucleus of the thalamus (Here crude awareness of touch & pressure sensations are appreciated) www.medicallecturenotes.com
  • 10. 3rd order neuron •Axons pass through the posterior limb of the internal capsule & corona radiata to reach the somesthetic area in the post central gyrus of the cerebral cortex •The sensations can be crudely localized •Very little discrimination is possible www.medicallecturenotes.com
  • 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