This document summarizes several major sensory pathways in the human body. It describes the first, second, and third order neurons involved in pathways for fine touch sensation, proprioception, and vibration which travel from the dorsal root ganglion up the spinal cord and terminate in the thalamus and somatosensory cortex. It also outlines pathways for pain sensation, proprioceptive information to the cerebellum, and pathways connecting the spinal cord to brainstem structures like the reticular formation and superior colliculus.

1. Sensory Pathways
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

4. Introduction
Ascending tracts conduct afferent information which may or may
not reach consciousness
Series of neurons involved
First-order neuron
Second-order neuron
Third order neuron

8. Fine touch pathway
Posterior white column
Dorsal white column
Fasciculus Gracilis and Fasciculus Cuneatus
Tract of gall and Burdach
Medial lemniscal pathway

9. Fine touch pathway
The axons entering the spinal cord from the dorsal root ganglion
Pass directly to the posterior white column on the same side
Here, the fibers divide into long ascending and short descending
branches
The short descending branches involves in the inter segmental
reflexes

11. Fine touch pathway
Long ascending fibers travel upward in the posterior white
column as fasciculus gracilis and fasciculus cuneatus
Fasciculus gracilis is present throughout the length of spinal
cord
It contains long ascending fibers from sacral, lumbar and
lower six thoracic spinal nerves

12. Fine touch pathway
The fasciculus cuneatus is situated laterally in the upper
thoracic and cervical segments of spinal cord
It is separated from fasciculus gracilis by a septum
It contains long ascending fibers from the upper six thoracic
and all the cervical spinal nerves

13. Fine touch pathway
 The fibers of fasciculus gracilis and cuneatus ascend ipsilaterally
 terminate by synapsing on the second-order neurons in the nucleus of
gracilis and cuneatus of medulla oblongata
 The axons of second order neurons called internal arcuate fibers
 Crosses the midline decussating with corresponding fibers from opposite
side ( sensory decussation)
 The fibers then ascend as a bundle – medial lemniscus

15. Fine touch pathway
 The fibers pass through the medulla, pons and midbrain
 The fibers terminate by synapsing on the third order neurons in the
ventral posterolateral nucleus of thalamus
 The axons of third order neuron leave and pass through the posterior
limb of the internal capsule, corona radiata to reach the somaesthetic
area of post central gyrus of cerebral cortex ( area 3,1,2)

17. Fine touch pathway
 Fine touch
 Pressure
 Proprioception
 Steriognosis
 Tactile localization
 Tactile discrimination
 Vibration

18. Cuneo cerebellar tract
Fibers in the fasciculus cuneatus from cervical and upper
thoracic segments
Terminated on the second order neuron on nucleus cuneatus
Travel and enter the cerebellum on the same side
These fibers are called as posterior external arcuate fibers
Conveys muscle, joint sense to cerebellum

20. Trigeminal pathway
 All sensations from face are carried by this pathway
 Fibers carrying sensations from the receptors belong to 5th cranial nerve
 Reach Gasserian ganglion
 From ganglion, fibers enter pons to synapse in the chief sensory nucleus
and spinal sensory nucleus
 From these nucleus, second order neuron takes origin and crosses
midline to reach opposite side

22. Trigeminal pathway
These fibers ascend upward as trigeminal lemniscus
They synapse in the venteroposteromedial nucleus of thalamus
Third order neurons from thalamus originate and end in the lateral
most area of cerebral cortex area number 3,1,2 ( face area)

25. Anterior spinothalamic pathway
 Crude touch and pressure pathway
 The axons enter the spinal cord from DRG and proceed to the tip of the
posterior gray column
 Here they divide into ascending and descending branches
 Contributes to posterolateral tract of Lissauer
 Terminates by synapsing with cells in the substansia gelatinosa group in
the posterior gray column

27. Anterior spinothalamic pathway
 Axons of second order neuron now cross very obliquelyto the opposite
side in the anterior gray and white commissures
 Ascends in the opposite anterolateral white column as anterior
spinothalamic tract
 As this tract ascends through medulla, it accompanies lateral
spinothalamic tract and spinotectal tract, all of which form spinal
lemniscus

29. Anterior spinothalamic pathway
Spinal lemniscus continues to ascend through posterior part of
pons, tegmentum of midbrain
Terminates on the third order neurons in the VPLN of thalamus
The axons of third order neurons pass through the posterior limb
of internal capsule, corona radiata to reach the somesthetic area
in the post central gyrus of the cerebral cortex

31. Lateral spinothalamic pathway
Pain pathway
Dual pathway
Fast pain- Neo-spinothalamic pathway
Slow pain- Paleo-spinothalamic pathwaty

32. Neo- spinothalamic pathway
Fast type A delta fibers transmit mainly mechanical and acute
thermal pain
They terminate in the lamina I ( lamina marginalis) of the dorsal
horns
The second order neurons originates and cross immediately to
the opposite side of the spinal cord through anterior commissure

34. Neo- spinothalamic pathway
Second order neurons ascends via medulla, pons, midbrain
Few fibers terminates in the reticular areas of brain stem
Most of the fibers pass to the VPLN of thalamus
Third order neurons arises and pass through the posterior limb of
internal capsule and corona radiata and terminates in the post
central gyrus of cerebral cortex area 3,1,2.

36. Paleo- spinothalamic pathway
Much older system
Transmits slow-chronic pain
Type C fibers
Substance P is neuro transmitter
First order neurons terminates in the lamina 2 and lamina 3 (
together called as substansia gelatinosa)

37. Paleo- spinothalamic pathway
 From there short axons arises and terminates in the lamina 5
 Second order neurons arises from lamina 5 and crosses the midline
immediately to opposite side in anterior commissure
 Ascends through medulla, pons, midbrain
 Most of the fibers terminates in the brain stem at reticular nuclei, tectal
area and periaqueductal gray region
 Only one tenth fibers reach thalamus

40. Posterior spinocerebellar pathway
 Muscle joint sense
 From trunk and lower limbs
 The axons entering the spinal cord from DRG terminates in the base of
the posterior gray column
 These neurons are called as Clarke’s column
 The second order neurons enter posterolateral part of the lateral white
column on same side and asced to medulla

42. Posterior spinocerebellar pathway
Second order neurons enters cerebellum via inferior
cerebellar peduncle
Terminates in the cerebellar cortex
This pathway do not ascends top cerebral cortex

44. Anterior spinocerebellar pathway
 Muscle joint sense
 From trunk, upper limbs and lower limbs
 The axons entering the spinal cord from DRG terminate in nucleus
dorsalis at the base of posterior gray column
 Majority of second order neurons cross the midline and ascends on
opposite side in contralateral white column
 Very few fibers ascend on same side in lateral white column

46. Anterior spinocerebellar pathway
Fibers enters the cerebellum via superior peduncle and
terminates in the cerebellar cortex
It is believed that those fibers that crossed over to opposite
side in the spinal cord cross back in the cerebellum

48. Spinotectal pathway
 The axons enter the spinal cord from the posterior root ganglion and
travel to the gray matter
 where they synapse on unknown second order neurons
 The axons of second order neurons cross the midline and ascend in the
anterolateral white matter
 After passing through the medulla and pons, the neurons terminate by
synapsing in the superior colliculus of the midbrain

49. Spinotectal pathway
Provides afferent information for spinovisual reflexes
Brings about movement of eyes and head toward the source
of the stimulation

52. Spinoreticular pathway
 The axons enter the spinal cord from the posterior root ganglion and
terminate on unknown second order neurons in the gray matter
 The axons from these second order neurons ascend the spinal cord in
the lateral white column
 Most of the fibers are uncrossed
 Terminates by synapsing with neurons of reticular formation in medulla,
pons and midbrain

53. Spinoreticular pathway
Afferent pathway for the reticular formation
Plays important role in influencing level of conciousness

56. Spino-olivary pathway
 The axons enter the spinal cord from the posterior root ganglion and terminate
on unknown second order neurons in the gray matter
 The axons from these second order neurons cross midlineand ascend in white
matter at the junction of anterior and lateral columns
 The axons terminates on the third order neurons in the inferior olivary nucleus
in medulla
 Third order neurons cross midline and enter cerebellum through inferior
cerebellar peduncle

57. Spino-olivary pathway
Conveys information to the cerebellum from cutaneous and
proprioceptive organs

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