1.
www.MedicalLecturenotes.com

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