Ascending Tracts of the Spinal
cord
Dr Rania Gabr
Objectives
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Define the meaning of a tract.
Distinguish between the different types of tracts.
Locate the position of each tract.
Describe the sensory pathway.
Describe gracile and cuneate tracts and pathways for
conscious proprioception, touch, pressure and vibration
from the limbs and trunk. Describe lateral spinothalamic
tract and pathways for pain and temperature from the
limbs and trunk.
• Describe ventral spinothalamic tract and pathways for
simple touch from the limbs and trunk.
• Describe dorsal and ventral spinocerebellar tracts and
pathways for unconscious proprioception from the limbs
and trunk.
• Describe Reticulothalamic and spinothalamic tracts for dull
aching pain
TRACTS
• Bundles or fasciculi of fibers that occupy more
or less definite positions in the white matter.
• They have the same Origin, Termination and
carry the same Function.
• They serve to join the brain to the spinal cord.
• They are classified into:
1-Ascending (sensory or afferent).
2-Descending (motor or efferent).
Ascending Tracts
• Carry impulses from pain, thermal, tactile, muscle and joint
receptors to the brain.
• Some of this information eventually reaches a conscious
level (the cerebral cortex),
• while some is destined for subconscious centers (e.g. the
cerebellum).
• Ascending sensory pathways between the peripheral
receptors and the cerebral cortex, are organized in a three
neuronal chain:
- First order neurone
- Second order neurone
- Third order neurone
• The first-order
neurone or
(primary afferent
neurone) :
• enters the spinal
cord through the
dorsal root of a
spinal nerve and its
cell body lies in the
dorsal root
ganglion.
• The main fibers remain on the ipsilateral side
of the cord and terminate by syapses with the
second neurone either in the spinal grey
matter or in the medulla oblongata of the
brain stem.
• The second order neurone
• Has its cell bodies in the cord or
medulla oblongata.
• Its axon cross over (decussates)
to the opposite side of the CNS
and ascend to the thalamus,
where it terminate upon the
third neurone.
• The third-order neurone
Has its cell bodies in the
thalamus.
• Its axons pass to the
somatosensory cortex of the
parietal lobe of the cerebral
hemisphere.
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VPL
SECOND ORDER NEURON
2nd
1st
• cross the mid line
• in front of central canal
Ascending Tracts
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Dorsal column tracts
Spinothalamic tracts( Ventral AND Lateral)
Posterior spinocerebellar
Anterior spinocerebellar
Cuneocerebellar
Spinotectal
Spinoreticular
Spino-olivary
Functions of Ascending Tracts
• Lateral spinothalamic
• Anterior spinothalamic
• Posterior column
• Anterior and posterior
spinocerebellar and
cuneocerebellar tracts
• Spinotectal
• Spinoreticular
• Painful and thermal sensations
• Crude touch and pressure
• Descriminative fine touch and
joint and muscle information
and vibration sense
• Muscle and joint unconscious
information
• Pain, thermal and tactile
information to superior
colliculus
• Muscle and joint information
to reticular formation
Ascending Or Sensory Tracts
1- Dorsal column tracts:
(Gracile & Cuneate)
Function: Transmit
a. Proprioceptive
(deep) sensations
(sense of movement,
position, vibration).
b. Fine touch sensations
(tactile localization,
tactile discrimination
& stereognosis).
These senses reach a
Conscious level
(cerebral cortex).
2- Spinothalmic tracts:
Function:
Transmit impulses concerned with specific sensory
modalities:
pain, temperature, touch, that reach a Conscious
level (cerebral cortex).
3- Spinocerebellar tracts:
Function:
Carries unconscious information from muscles,
joints, skin, subcutaneous tissues
Transmit impulses from tactile and stretch
receptors to Subconscious centers (cerebellum) for
1. Dorsal column Tracts
Fasciculus gracilis and fasciculus cuneatus
• Function: carry discriminative(fine) touch,
proprioception: vibratory sense and conscious
muscle joint sense
• Inputs from pacinian corpuscles, Messiner’s
corpuscles, joint receptors, muscle spindles
and Golgi tendon organs )
Axon of 1st order neuron enter the spinal cord
through the dorsal roots of the spinal nerves.
• passes directly to the posterior white column
of the same side ( without synapsing )
• Long ascending fibers travel upward in the
posterior column of the same side as fasciculus
gracilis and fasciculus cuneatus
• Fibers of Fasciculus Gracilis enter via the sacral,
lumbar and lower thoracic 6 levels; (lower
limbs).
• Fibers of Fasciculus Cuneatus enter via the
upper 6 thoracic and cervical levels; (upper
limbs).
• Synapse on the 2nd order neuron in the nucleus
gracilis and cuneatus of medulla oblongata of
the same side.
[ nucleus G & C ]
in medulla
fasciculus cuneatus
cervical segments
upper 6 thoracic segments
lower 6 thoracic segments
lumbar segments
sacral segments
G
C
fasciculus gracilis
• Axons of second-order
neurones :
• decussate in the medulla as
the internal arcuate
fibers(sensory decussation).
• Then it ascend in (opposite
side) through brain stem as
the Medial Lemniscus.
• The medial lemniscus
ASCENDS through medulla
oblongata, pons, and
midbrain terminates in the
ventral posterior (VP)
nucleus of the thalamus.
Prof. Makarem
18
• Third-order neurone:
• (thalamocortical, or sensory radiations- run in
the internal capsule,corona radiata to reach
the postcentral gyrus of cerebral cortex area
3, 1 and 2 ) : somatosensory cortex.
Clinical application
destruction of fasciculus gracilis
and cuneatus
• loss of muscle joint sense,
position sense, vibration sense
and tactile discrimination
• on the same side
• below the level of the lesion
(extremely rare to have a lesion of the spinal cord to
be localized as to affect one sensory tract only )
Spinothalamic tracts lie
lateral and ventral to the
ventral horn of the spinal grey
matter.
2- Spinothalamic tracts
• They carry pain and thermal (temperature) sensations and also nondiscriminative (crude) touch and pressure.
– The Lateral spinothalamic tracts carry pain and temperature
sensations.
– The ventral spinothalamic tracts carry crude touch and pressure.
• But fibers carrying these modalities are probably intermingled, at least
to some extent.
Prof. Makarem
21
A-Lateral Spinothalamic
Tract (pain & temperature)
 Function:
• Carries pain & Temperature to
thalamus and sensory area of
the cerebral cortex.
 Neurones: 3 Neurones
• Neurone I: Small cells in the
dorsal root ganglia.
• Neurone II: Cells of substantia
gelatinosa of Rolandi in the
posterior horn.
• Neurone III: Cells of (VPL)
nucleus of the thalamus.
• The spinothalamic tract contains
second-order neurones, the cell
bodies of which lie in the
Pain and thermal impulses
( input from free nerve endings,
thermal receptors )
• transmitted to spinal cord in
delta A and C fibres
• central process enters the
spinal cord through Dorsal
nerve root,
• the central process of 1st order
neuron
synapse with cell body of 2nd
order neuron
in substantia gelatinosa of
posterior gray column of the
• the axon of 2nd order neuron
cross to the opposite side
in the anterior white commissure and
ascend in contralateral white column
as lateral spinothalamic tract
• end by synapsing with 3rd order
neuron in the ventral posterolateral
nucleus (VPL )of thalamus
• axon of the 3rd order neuron passes
through the posterior limb of internal
capsule and corona radiata to reach
the postcentral gyrus of cerebral
cortex ( area 3, 1 and 2 )
Clinical application
destruction of LSTT
• loss of
– pain and thermal sensation
– on the contralateral side
– below the level of the lesion
patient will not
respond to pinprick
recognize hot and cold
Lesion:
•Syringomyelia, (widening of the central
canal) leads to Loss of pain & temperature
below the level of the lesion.
B- Ventral Spinothalamic
(Crude touch & Pressure)
Function:
• Carries crude touch &
pressure to thalamus and
sensory cortex.
• input from free nerve
endings, Merkel’s tactile
disks
 Neurones: 3 Neurones
• Neurone I:
Medium sized cells in the dorsal root ganglia.
• Neurone II:
Cells of main sensory nucleus or (nucleus proprius). cross
to the opposite side (decussate)
– ascend in the contralateral ventral column as ASTT
– Ends in the VPL nucleus of the thalamus.
• Neurone III:
Cells of VPL nucleus of thalamus project to cerebral cortex
( area 3, 1 and 2 )
 Effect of lesion:
Loss of crude touch sensation below the level of the
lesion. on the contralateral side of the body
• Axons carrying
pain and
temperature
decussate within
one segment of
their origin,
• while those
carrying touch
and pressure may
ascend for
several segments
before crossing.
• It is highly organised
somatotopically;
consequently, the origin of
sensory stimuli can be
accurately localised.
• It is thought to be the route
via which sharp, pricking pain
(sometimes called 'fast' pain)
is conducted
3- Spinocerebellar
tracts
• Ascending pathways that
carry impulses to a
subconscious level are
represented by the
spinocerebellar tracts.
• Fibres of spinocerebellar
tracts form dorsal and
ventral tracts that are
located at the dorsolateral
& ventrolateral surfaces of
the cord, respectively.
Prof. Makarem
30
• Both tracts carry information derived from
muscle spindles, Golgi tendon organs and
tactile receptors to the cerebellum for the
control of posture & coordination of
movement.
Prof. Makarem
• The spinocerebellar system
consists of a sequence of only
two neurones.
• Neurone I:Large cells of dorsal
root ganglia.
• Neurone II: cells of the nucleus
dorsalis Clark's nucleus.
• give rise to axons ascending to
the cerebellum of the same
side
• Both spinocerebellar tracts
contain second-order
neurones.
• The tract neurons terminate
directly in the cerebellar
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cortex. MOSTLY VERMIS
Dorsal (Direct)
Spinocerebellar tract
• Fibers of the dorsal
spinocerebellar tract
originate from the cells
of Clarke's column at
the base of the
posterior horn.
• The axons ascend
ipsilaterally to enter
the cerebellum
through the inferior
cerebellar peduncle.
Ventral (Indirect)
Spinocerebellar Tract
• Fibers of the ventral
spinocerebellar tract
decussate, ascend on
the contralateral side
of the cord and enter
the cerebellum via the
Superior cerebellar
peduncle.
• Some axons then
recross within the
cerebellar white
matter.
Spinoreticulothalamic
• The spinoreticulothalamic system
represents an additional route by
which sensory impulses ascend to
higher centers.
• Second-order neurons arising
from the dorsal horn ascend in the
ventrolateral region of the cord
• They terminate in the brain stem
reticular formation, particularly
within the medulla.
• Reticulothalamic fibres then
ascend to the intralaminar
thalamic nuclei, which in turn
activate the cerebral cortex.
• The spinoreticulothalamic
system is thought to be the
route via which dull, aching
pain (sometimes called 'slow'
pain) is transmitted to a
conscious level.
• Activation of spinothalamic
and spinoreticular fibers,
which may ultimately be
perceived as unpleasant or
painful, can be modulated by
descending pathways from
the brain.