Tracts – Applied Physiology

Dr.Jeena Aslam BHMS,MD(Hom)

Definition : – A tract may be defined as a bundle of fiber carrying one or a group of fiber of motor or sensory impulses in the central nervous system.

Functionally grouped in to 1) Ascending (sensory)
2) Descending (Motor) 3) Intr-segmental fibre.

Ascending tracts:
1) Tract of Goll ( Fasciculus gracillis )
2) Tract of Burdach ( Fasciculus cuneatus)
3) Comma tract of Schultze (Tractus inter fascicularis )
4) Dorsal spinothalamic tract ( lateral spinothalamic tract)
5) Spinotectal tract
6) Dorsal spinocerebellar tract( Fleschig’s tract )
7) Ventral spinocerebellar tract ( Gower’s tract )
8) Spino-olivery tract
9) Spinoreticular tract
10) Spino vestibular tract
11) Spino pontine
12) Spino cortical
13) Ventral spinothalamic tract (anterior spinothalamic tract)

 Descending Tract:
1) Pyramidal tract
a) Crossed pyramidal tract (large lateral cortico spinal tract)
b) Direct pyramidal tract (uncrossed anterior cortico spinal tract)
c) Uncrossed small lateral pyramidal tract
2) Cortico bulbar tract
3) Extra pyramidal tract
a) Rubrospinal tract
b) Tectospinal & tectobulbar
c) Reticulospinal
d) Dorsal vestibulo spinal
e) Ventral vestibulospinal
f) Olivospinal (bulbospinal)
g) descending medial longitudinal fasciculus

Inter segmental fibers
1) ground bundle of anterior column
2) ground bundle of lateral column
3) posterior column

Ascending tracts

•  Form periphery to center there are 3 neurons and 2 relays
•  For cerebral tracts crossing takes place in the second neuron
•  For cerebellar tract no crossing

 Sensory tract in Posterior column:
1) Tract of Goll
2) Tract of Burdach
3) Tractus inter fascicularis

 Sensory Tract In Lateral Column
1) Lateral spinothalamic tract
2) Spinotectal tract
3) Fleschig’s tract
4) Gower’s tract
5) Spino olivery tract
6) Spino reticular tract
7) Spino vestibular tract
8) Spino pontine tract
9) Spino cortical tract

Sensory Tract In Anterior Column
1) Ventral spinothalamic tract.

Posterior column tracts:
I) Tract of Goll (Fasciculus Gracillis):
Origin: – made up of axons of the bipolar cells of the posterior root ganglion receiving afferents from the lower half of  the body

Situation & extent:-
After entering the spinal cord, fibers run in the posterior column and extend through out the column .Below mid thoracic region it occupies the whole breadth of posterior column, above this level fibers are pushed medially by the tract of Burdach

Neuron, crossing & termination:-
First order neuron ends in 4 ways
1) Some make regular connections at different segments.
2) Some fibers end round the posterior horn cell and then cross and join ventral spino thalamic tract of opposite side.
3) Some fibers give descending tract which make up the Comma tract of Schultze.

Majority of fibers ends in the medulla in nucleolus Gracillis Õ first relay Õ second order neuron arise.
The axons of the neuron are divided in to 2 groups, external and internal arcuate fibers.
External dorsal
ventral
Dorsal external group pass through inferior cerebellar peduncle of the same side and ends in the cerebellum.
Ventral external group ê crosses opposite side passes through inferior cerebellar peduncle and ends in cerebellum of opposite side.
Internal arcuate fibers ê crosses to the opposite side and enter medial lemniscuses and pass through mid brain and ends in ventral posterolateral nucleus of the thalamus, second relay Õ third order neuron Õ axons pass through the posterior limb of internal capsule and ends in post central gyrus .

Functions:-
From the lower half of the body
1) Fine touch ,tactile localization and discrimination
2) Kinesthetic sensation
3) Vibration sense
4) some unconscious impulses (probably kinesthetic) passing to the cerebellum through the external arcuate fibers.
5) May constitute the sensory pathway for some superficial reflexes.

II) Fasciculus cuneatus (Tract of Burdach):
Similar to Goll with some difference
1) It is made up of fibers from the upper half of the body
2) Situated laterally in the posterior column in the upper thoracic and cervical region
3) Ends in medulla at nucleus cuneatus

III) Comma tract of Schultz ( Tractus inter fascicularis):
Made up of short discending tracts derived from tract of Goll & Burdach .
Situated in posterior column between these two tract and looks like a comma in transverse section .
Function:
a) To establish intersegmental communication
b) To form short reflex arc
Although sensory in function ascending in course.

Lateral column
1) Lateral spinothalamic tract :-
*Origin :-
Some posterior root fibers of all segments after entering the spinal cord end around the cells of Substantia gelatinosa of Rolando These unmyalinated fiber of the posterior root are known as the tract of Leissor .The second order neurone start from these cell. Most axons of the second order neurone cross in the anterior white commissure obliquely to the opposite side of the same segment and ascends in the lateral column of the cord .Some fiber of the second order neurone before crossing may ascend up one segment and then cross in the anterior white commisure to reach the lateral column of the opposite side of the cord This tract togather with anterior spinothalamic tract constitute the spinal leminiscus in the medulla oblongata.
Spinal leminiscus then ascends up to join the medial leminiscus in the upper part of medulla oblongata and finally terminate in the ventral posterolateral nucleus of the thalamus .
The lateral spinothalamic tract at higher brain stem level sends several collateral in to the reticular formation and tegmentum before ending in the thalamus .
Third order neurone starts at thalamus and axons of these terminate in the post central gyrus of cerebral cortex through the posterior limb of internal capsule.
Function :
1) Pain impulse
2) Temperature impulse

Spinotectal tract:

• Fibers arise from the posterior horn cell of opposite side
• Situated in lateral column ventral to lateral spinothalamic tract
• Most prominant in cervical region
• Pass through medial leminiscus and end in superior colliculus .

Function :-
1) Subserve spinovisual reflex

Fleschig’s tract (Dorsal spinocerebellar tract):
Some fibers of the posterior root end around Clark’s column of cell on the same side .Second order neurone arise and constitute the tract .

Becouse the tract is destined for cerebellum the second order neurone do not cross .The fibers bend laterally ,enter the lateral white column occupy the most peripheral part lateral to the spinothalamic tract and dorsal to the Gower’s tract .It extend through the upper lumbar ,thoracic and cervical region .In the medulla ,it enters the inferior cerebellar peduncle of the same side and ends in vermis .Here third order neuron arise and passes to the cerebellar cortex.

Gower’s tract (Ventral spinocerebellar tract ):
Origin:
Made up of fibers arising from Clark’s column of both side .It is composed mainly of crosed and partly of uncrossed fibres.
Situation: first appear in L-3 and remains in the lateral white column first ventral to Fleschig’s tract
Course: Passes through the cord and medula ,enters mid brain, goes up to red nucleus.Here the fibres turn sharply backwards and downwards and enters the superior cerebellar peduncle of the same side and end in the vermis .From here third order neuron arise and goes to the cerebellar cortex.

Function
1) Carries unconscious kinaesthetic sensation.

Spino-olivery tract :
Origin : from the dorasl horn of grey matter of all levels of spinal cord runs in parellal with olivospinal tract and ends mostly in the inferior olivery nucleus of the opposite side .More than half of the fibres cross in the medulla .
Function
1) Transmit proprioceptive impulse to cerebellum via the inferior olivery nucleus.

Spino reticular tract:
From posterior horn cell ascends in the antrerolateral funiculus and terminate chiefly in the nucleous reticularis gigantocellularis and partly in the lateral reticular nucleus in the medulla .In the pons,certain fibers terminte in the nucleus retuiculartis pontis caudalis .
Function:-
Maintanance of consciousnes and awareness.

Spinovestibular tract :
Originate form the spinal fibres projecting largely upon the dorsal part of the lateral vestibular nucleus .Ascends in the ipsilateral column of the spinal cord from the level as far as lumbar segments

Function
Concerned with postural reflex

Spinopontine tract :
These are largely collarelal from spinocortical fibres and ascend along with the spinocortical fibres and lastly terminate in the pontine nucleus.
Function:-
Concerned with certain exteroceptive impulses to the cerebellum

Spinocortical tract:
Ascends in parellal with corticospinal tract
Function : -not clear

Anterior column
Anterior spinothalamic tract .:
Origin : originate form the large cells of nucleus centerodorsalis of the posteior horn and second order neurone start from here .Axons of the second order ascend in the posterior column for 2-3 segment and then cross obliquelly in the anterior white commissure and this ascends in the anterior or anterolateral column of the opposite side as anterior spinothalamic tract. Most of the fibres are crossed and a small number of uncrossed fibre may ascend homolaterally as anterior spinothalamic tract.
While ascending upward anterior spinothaamic tract runs in parellal with the lateral spinothalamic tract in the spinal leminiscus.
The tract gives collaterals to the dorsolateral part of the brain stem reticular formation and also to the reticular formation.
At the upper border of pons and mid brain this tract along with lateral spinothalamic tract and internal arcuate fibres run in the medial leminiscus and terminate in the ventral posterolateral nucleus of the thalamus .
The thalamus is known as subcortical center for the spinothalamic tract here second relay takes place ,and third order neuron arise and pass through posterior limb of internal capsule to terminate in the post central gyrus .
Function:-
Fine touch and tactile localisation

Pathways of various sensation
Touch :
Tactile corpuscles Õ thick (A) medullated fibres in the sensory nerveÕ
posterir root Õ spinal cord   epicritic part Õ passes to the tract of
Goll and Burdach
protopathic partÕ passes to the
anterior spinothalamic tract

Pain and temperature:
Free nerve ending ( Pain) ,end organ of krausse (cold) ,organ of Ruffini and Golgi massoni bodies (heat) Õ Pain -C fibes; Temerature –medium sized (B) fibres Õ posterior root Õ Leissaur’s tract Õ posterior horn cell Õ

Lateral spinothalamic tract    Crude pain & temperatureÕ thalamus
nbsp;            Fine Õ sensory cortex

Kinaesthetic:
Muscle spindle, Golgi bodies ,Pacinian corpuscles Õ sensory nerve Õ posterior root Õ

Spinal cord      Conscious kinaesthetic     Õ Tract of Goll and Burdach
Unconscious kinaesthetic Õ Fleschigs and Gowers tract