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Spinal cord
ascending tracts
Naming the tracts
•If the tract name begins with “spino” (as in spinocerebellar), the tract is a
sensory tract delivering information from the spinal cord to the cerebellum (in
this case)
•If the tract name ends with “spinal” (as in vestibulospinal), the tract is a motor
tract that delivers information from the vestibular apparatus (in this case) to the
spinal cord
•The three major sensory tracts involve chains of neurons
•First-order neuron
•Delivers sensations to the CNS
•The cell body is in the dorsal or cranial root ganglion
•Second-order neuron
•An interneuron with the cell body in the spinal cord or brain
•Third-order neuron
•Transmits information from the thalamus to the cerebral cortex
Neurons in the sensory tracts are arranged according to three anatomical principles
•Sensory modality
•Somatotopic
•Medial-lateral rule
Sensory modality
•Fine touch sensations are carried in one sensory tract
•Somatotopic
•Ascending tracts are arranged according to the site of origin
•Medial-lateral rule
•Sensory neurons that enter a low level of the spinal cord are more medial
within the spinal cord
•Sensory neurons that enter at a higher level of the spinal cord are more lateral
within the spinal cord
The cell bodies of the 1st order neurons are located
In the posterior root ganglion
lateral spinothalamic tract
- pain, temperature
-The pain impulses are transmitted to SC in fast-conducting delta A–type and slow
conducting C-type fibers
-The fibers of 1st order neurons terminate by synapsing with cells in the posterior
gray column (substantia gelatinosa)
-The axons of 2nd order neurons cross obliquely to the opposite side in the
anterior gray and white commissures , ascending in the contralateral white
column as the lateral spinothalamic tract
-The lateral spinothalamic tract lies medial to the anterior spinocerebellar tract
-Sacral fibers are lateral, cervical are medial
-Pain fibers are slightly anterior to temperature
-Ascends in medulla oblongata, pons, midbrain
- ant spinothalamic tract + spinotectal + lateral spinothalamic = spinal leminiscus
-The fibers of the tract end by synapsing with the 3rd- order neurons in VPL
nucleus of thalamus
-The axons of 3rd order neurons pass through internal capsule and corona
radiata to reach the Post central gyrus of cerebral cortex
lateral spinothalamic tract
Ventral nuclei in thalamus
Midbrain
Lateral spinothalamic tract
Pain and temperature sensations
from right side of body
1st order neuron
Second-order neuron
Third-order neuron
The cell bodies of the 1st order neurons are located
In the posterior root ganglion
Anterior spinothalamic tract
- crude touch and pressure
-The fibers of 1st order neurons terminate by synapsing with cells in the posterior
gray column (substantia gelatinosa)
-The axons of 2nd order neurons cross obliquely to the opposite side in the
anterior gray and white commissures , ascending in the contralateral white
column as the anterior spinothalamic tract
-Sacral fibers are lateral, cervical are medial
-Ascends in medulla oblongata, pons, midbrain
- ant spinothalamic tract + spinotectal + lateral spinothalamic = spinal leminiscus
-The fibers of the tract end by synapsing with the 3rd- order neurons in VPL nucleus of
thalamus
-The axons of 3rd order neurons pass through internal capsule and corona radiata to
reach the Postcentral gyrus of cerebral cortex
Anterior spinothalamic tract
Anterior spinothalamic tract
Crude touch and pressure sensations
from right side of body
Posterior white Column (Fasciculus gracilis, Fasciculus cuneatus )
Discriminative touch, vibratory sense, and conscious muscle-joint
sense
•Posterior Column tract consists of:
•Fasciculus gracilis
•Transmits information coming from areas inferior to T6
•Fasciculus cuneatus
•Transmits information coming from areas superior to T6
The cell bodies of the 1st order neurons are located
In the posterior root ganglion
 The axons of 1st order neurons pass directly to the posterior white column
As Fasciculus gracilis and Fasciculus cuneatus
• Fasciculus gracilis is present throughout the length of SC
• Contains ascending fibers from sacral ,lumbar and lower six thoracic nerves
• Fasciculus cuneatus is situated laterally in the upper thoracic and cervical segments
• Is separated from Fasciculus gracilis by a septum
• Contains ascending fibers from upper six thoracic nerves and all cervical nerves
The fibers of Fasciculus gracilis and Fasciculus cuneatus ascend ipsilaterally and terminate by
Synapsing on 2nd order neurons in nuclei gracilis and cuneatus of medulla oblongata
The axons of 2nd order neurons (internal arcuate fibers) cross the median plane
(sensory decussation)
Fibers then ascend as a single bundle (medial leminiscus) through medulla oblongata,
pons, midbrain
-The fibers of the tract end by synapsing with the 3rd- order neurons in
VPL nucleus of thalamus
-The axons of 3rd order neurons pass through internal capsule and
corona radiata to reach the Postcentral gyrus of cerebral cortex
Posterior Columns
Midbrain
Nucleus gracilis and nucleus cuneatus
Medial lemniscus
Medulla oblongata
Fasciculus cuneatus and fasciculus gracilis
Fine-touch, vibration, pressure, and proprioception
sensations from right side of body
The cell bodies of the 1st order neurons are located
In the posterior root ganglion
Posterior spinocerebellar tract
• muscle and joint sensation
• 1st order neuron axons terminate at the base of post gray column (nucleus dorsalis)
• the axons of 2nd order neurons enter posterolateral part of the lateral white matter
on the same side
• ascend as the posterior spinocerebellar tract to medulla oblongata
•Terminates in cerebellar cortex (through inferior cerebellar peduncle)
 note: axons of lower lumbar and sacral spinal nerves ascend in the posterior white
column until they reach L3 or L4 segments where they synapse with nucleus dorsalis
The cell bodies of the 1st order neurons are located
In the posterior root ganglion
Anterior spinocerebellar tract
• muscle and joint sensation
• 1st order neuron axons terminate at the base of post gray column (nucleus dorsalis)
• the majority of axons of 2nd order neurons cross to opposite side and ascend as
anterior spinocerebellar tract in the contralateral white column
 the minority of axons ascend as anterior spinocerebellar tract in the lateral white column
Of the same side
• ascend as anterior spinocerebellar tract to medulla oblongata and pons
•Terminates in cerebellar cortex (through superior cerebellar peduncle)
 the fibers that crossed over in spinal cord cross back within cerebellum
Spinocerebellar Tracts
PONS
Cerebellum
Medulla
oblongata
Anterior spinocerebellar tract
Spinal
cord
Proprioceptive input from Golgi tendon organs,
muscle spindles, and joint capsules
Posterior spinocerebellar tract
The term dorsolateral fasciculus of the spinal cord refers to a
bundle of nerve fibers located between the posterior white
column and the lateral white column and bounded
ventromedially by the posterior gray column of the spinal cord
A longitudinal bundle of thin, unmyelinated and poorly myelinated
fibers capping the apex of the posterior horn of the spinal gray matter,
composed of posterior root fibers and short association fibers that
interconnect neighboring segments of the posterior horn
Regional variation of spinal cord
structure
cross sections taken from the
cervical enlargement ( A ),
midthoracic cord ( B ), and
lumbosacral enlargement ( C )
cervical segment
 an oval shape with large white matter funiculi
 prominent, broad anterior gray horns that contain the motor neurons that innervate the
upper extremities
thoracic segment
 have a more rounded profile
 exhibit small, slender, peglike anterior gray horns
 lateral horns are unique to thoracic segments
lumbosacral segment
 has very large anterior gray horns (motor supply to the lower extremities)
 only a very small surrounding mantle of white matter
Cervical segment
Posterior white column
Fasciculus gracilis
Fasciculus cuneatus
Substantia gelatinosa
Nucleus proprius
Lateral white column
Lateral group (UL)
Accessory nucleus
Anterior white column
Medial group (neck)
Anterior median fissure
Thoracic segment
Fasciculus gracilis
Fasciculus cuneatus
Substantia gelatinosa
Nucleus proprius
Nucleus dorsalis
Lateral horn
(PREGANGLIONIC
SYMPATHETIC)
Motor neurons
(trunk muscles)
Lumbosacral segment
Fasciculus gracilis
Substantia gelatinosa
Nucleus proprius
Lateral horn
(PREGANGLIONIC
PARASYMPATHETIC
(S2-S3-S4)
Motor neurons
(LL muscles)
Motor neurons
(trunk muscles)