1.
ASCENDING TRACTS
(SENSORY PATHWAY)
Submitted under the guidance of : Dr. Sachin Shris, MBBS, MS
Submitted by : Nibedita Ayan

2.
PATHWAY:
• There is a continuous flow of information between the brain,
spinal cord, and peripheral nerves.
• A group of neurons connecting two masses of grey matter is called a
tract.
• Generally the pathways:
 Consists of a chain of tracts, associated nuclei and varying number of
relays (synapses)
 Consist of two or three neurons
 Exhibit somatotopy (precise spatial relationships)
 Decussate
 Involve both the brain and spinal cord
 Are paired (bilaterally and symmetrically)

3.
SOMATOSENSORY PATHWAY:
When a tract relays sensory information from the receptors (peripheral nerve endings) to the brain ,
the tract is the Ascending (somatosensory) tract .
• Monitor conditions both inside the body and in the external
environment
• Sensation-stimulated receptor passes information to the CNS via
afferent (sensory) fibers
• Most sensory information is processed in the spinal cord , thalamus,
or brain stem. Only 1% reaches the cerebral cortex and our
conscious awareness
• Processing in the spinal cord can produce a rapid motor response
(stretch reflex)
• Processing within the brain stem may result in complex motor
activities (positional changes in the eye, head, trunk)

4.
ASCENDING TRACTS:
• LATERAL SPINOTHALAMIC TRACT
• ANTERIOR SPINOTHALAMIC TRACT
• FASCICULUS GRACIALIS
• FASCICULUS CUNEATUS
• DORSAL (post.) SPINOCEREBELLAR TRACT
• VENTRAL (ant.) SPINOCEREBELLAR TRACT
• SPINO-OLIVARY TRACT
• SPINOTECTAL TRACT

5.
• Three major pathways
carry sensory information
Posterior/Dorsal
column pathway
(gracile & cuneate
fasciculi)
Anterolateral pathway
(spinothalamic)
Spinocerebellar
pathway

6.
All these three pathways involve a sequence of three neurons each.
>> 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

7.
Based on the perception
• For conscious perception:
Spinothalamic system
• For unconscious perception:
Spinocerebellar
Spino-olivary
Spinotectal
Spinoreticular

8.
DorsalColumn
•Containstwotracts,Fasciculusgracilis
(FG)&fasciculuscuneatus(FC)
•Carryimpulsesconcernedwith
proprioceptionanddiscriminativetouch
fromipsilateralsideofbody
•Containtheaxonsofprimaryafferent
neuronsthathaveenteredcordthrough
dorsalrootsofspinalnerves
FG contains fibers received at sacral, lumbar and lower thoracic levels,
FC contains fibers received at upper thoracic and cervical levels.

9.
Fibers ascend without interruption where they
terminate upon 2nd order neurons in nucleus
gracilis and nucleus cuneatus
The axons of the 2nd order neurons decussate in
the medulla as internal arcuate fibers and ascend
through the brain stem as medial lemniscus.
The medial lemniscus terminates in the ventral
posterior nucleus of the thalamus upon 3rd order
neurons, which project to the somatosensory
cortex (thalamocortical fibers)

10.
Spino-thalamicTracts
• Located lateral and ventral to
the ventral horn
• Carry impulses concerned
with pain and thermal
sensations (lateral tract) and
also non- discriminative touch
and pressure (medial tract)
• Fibers of the two tracts are
intermingled to some extent
• Fibers are highly somato-
topically arranged, with those
for the lower limb lying most
superficially and those for the
upper limb lying deeply
Information is sent to the
primary sensory cortex on
the opposite side of the body

11.
SpinocerebellarTracts
• The spinocerebellar system
consists of a sequence of
only two neurons
• Two tracts: Posterior &
Anterior
• Located near the dorsolateral
and ventrolateral surfaces of
the cord
• Contain axons of the second
order neurons
• Carry information derived
from muscle spindles, Golgi
tendon organs and tectile
receptors to the cerebellum
for the control of posture and
coordination of movements

12.
SpinotectalTract
• Ascends in the anterolateral
part in close association with
spinothalamic system
• Primary afferents reach dorsal
horn through dorsal roots and
terminate on 2nd order neurons
• The cell bodies of 2nd order
neuron lie in base of the dorsal
horn
• Axons of 2nd order neuron
cross to opposite side, and
project to the superior colliculus
in the midbrain

13.
Spino-olivaryTract
• Indirect spinocerebellar pathway (spino-olivo-
cerebellar)
• Impulses from the spinal cord are relayed to
the cerebellum via inferior olivary nucleus
• Conveys sensory information to the
cerebellum
• Fibers arise at all level of the spinal cord

14.
TRACT SENSATION FIRST
ORDER
SECOND ORDER THIRD ORDER FINAL DESTINATION CROSS-OVER
SITE
POSTERIOR COLUMNS
FASCICULUS GRACIALIS Proprioception; inferior to T6 Dorsal root
ganglia
Nucleus Gracialis Posteriolateral ventral
nucleus of thalamus
Primary Sensory Cortex on
opposite side (contralateral)
Uncrossed
FASCICULUS CUNEATUS Proprioception; superior to
T6
Dorsal root
ganglia
Nucleus Cuneatus Posteriolateral ventral
nucleus of thalamus
Primary Sensory Cortex on
opposite side (contralateral)
Uncrossed
SPINOTHALAMIC TRACTS
LATERAL SPINOTHALAMIC Pain and temperature Dorsal root
ganglia
Substantia
Gelatinosa
Posteriolateral ventral
nucleus of thalamus
Primary sensory cortex
;contralaterally
Crosses in the
same segment
ANTERIOR SPINOTHALAMIC Crude touch and pressure Dorsal root
ganglia
Nucleus Proprius Posteriolateral ventral
nucleus of thalamus
Primary sensory cortex
;contralaterally
Ascends 2-3
segments and
then crosses
SPINOCEREBELLAR TRACTS
POSTERIOR SPINOCEREBELLAR Proprioception Dorsal root
ganglia
Clark’s Column NIL Cerebellar cortex ;
ipsilaterally
Uncrossed
ANTERIOR SPINOCEREBELLAR Proprioception Dorsal root
ganglia
Neurons of
Posterior Horn
NIL Cerebellar cortex ;
ipsilaterally
Crosses twice;
-spinal cord
-midbrain
NON SPECIFIC
SPINO-OLIVARY Proprioception - - - Olivary nuclei Uncrossed
SPINOTECTAL Afferent limb of reflex
movement of eyes and head
- - - Tectum or superior colliculus Crossed

15.
CLINICAL CO-RELATES
TRACT CLIINICAL TEST RELATED DISORDERS
LATERAL
SPINOTHALAMIC
 Pain with pin prick
 Temperature test Brown Sequard’s
Syndrome (due to
hemisection of spinal
cord)
Syringomyelia
ANTERIOR
SPINOTHALAMIC
 Joint sense
 Vibration
 Tactile localization
 Romberg's test
 Stereognosis
 Crude touch
 Crude pressure
FASCICULUS GRACIALIS
FASCICULUS CUNEATUS
DORSAL
SPINOCEREBELLAR  Cerebellar tests (finger ,nose, heel-
knee tests)VENTRAL
SPINOCEREBELLAR
SPINO-OLIVARY
 Visual and proprioception testsSPINOTECTAL

16.
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