Ascending spinal tract

8/16/2019 Ascending spinal tract

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Ascending & Descending tracts of spinal cord

General overview

Ascending tracts - SensoryDescending tracts – Motor

General arrangement of both tracts “ pathway “

1st order neron

!nd order neron

"rd order neron

#he only di$erence is the di$erent locations where each order of neron ends%

Decssation is the cross-over of the tract from one side to the other% #herefore

there are instances where the left side of the body is controlled by the right brain

hemisphere% Decssation occrs at di$erent locations for each tract%

'linical anatomy(

)esion of one half of the spinal cord may lead to

*pposite side of body

loss of pain temperatre light toch pressre sensations

Same side of body

loss of the other sensations

Sensory corte+ of the cerebral hemisphere controls the opposite side of the body

contralateral

)esion above the sensory decssation

all the sensations of the *,,*S#. side of the body are lost

)esion below the sensory decssation

sensations of the SAM. side of the body are lost

'ortical lesionsa$ected areas are sally limited


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paralysis/parasthesia is locali0ed

nternal capsle lesions

all ascending & descending tracts are a$ected

hemiplegia/hemiparasthesiaSame homncls arrangement

more sensitive areas in the body have a greater representation

Descending tracts Motor2


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General arrangement of descending tracts

1st order neron

3irst-order nerons condct implses from receptors of the s4in and from

proprioceptors receptors located in a 5oin mscle or tendon2 to the spinal cord

or brain stem where they synapse with second-order nerons% 3irst-order

neron6s cell bodes reside in ganglion dorsal root or cranial2%

starts at the cerebral corte+ in the somatomotor area

!nd order neron

!nd neron to carry an order% #he order cold be a sensory stimls or a motor

stimls%

a+on of the 1st order neron will synapse with the !nd order neron at the level

of the brain stem which commonly decssate crosses over2 to the opposite

side%

"rd order neron

#he "rd order neron is located in the ventral horn of the spinal cord which will

e+it with the spinal nerve to spply the mscle%


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#ypes of descending tracts(

)ateral corticospinal tract

Anterior corticospinal tract #herefore the descending tract is also 4nown as corticospinal tract%

3low of arrangement of the corticospinal tract(

'orticospinal tract arise from

long a+ons of the pyramidal cells e+trapyramidal layer2 of the precentral gyrs

primary motor centre of the cerebral corte+2

lies in front of the central slcs

7omncls arrangement


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arranged pside down

the 8ner the movement the more the cortical representation

8ngers face tonge – more

trn4 lower limbs – lessmedial srface( lower limbs

sperolateral srface( everything else

12 1st order neron

3ibres of the 1st order neron arise from the precentral gyrs

#hese 8bres converge and enter a small area

internal capsle

li4e a bnch of 9owers with a ribbon tied arond it

A)) the 8bers from ascending & descending tracts2 converge here

3nction( separates the cadate ncles and the thalams from the lenticlar

ncles

:es( location of internal capsle

bonded medially by the thalams and cadate ncles

bonded laterally by the lenticlar ncles


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,arts of internal capsle not homncls arrangement normal head to toe2

anterior limb

head & nec4 8bres most anterior

posterior limblower limb 8bres most posterior

#he descending 8bres passes throgh the

)A#.;A) half of the posterior limb of internal capsle

After the internal capsle the 8bres enter the brain stem

midbrain

pons

medlla

!2 !nd order neron

3ibres of the 1st order neron ends when it enters the brain stem and synapse

with the !nd order neron

#he 8bres pass throgh the brainstem

1st – throgh the mid


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Motor decssation

ncrossed 8bres

.nters the spinal cord

"2 "rd order neron

!nd order neron 8bres in the medlla oblongata enters the spinal cord and

synapse with the "rd order neron

Motor decssation

in the spinal tract the crossed tract descend as the lateral corticospinal tract

#herefore the motor corte+ of the cerebral hemisphere controls the opposite

side of the body ) – ; ; – )2


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contra-lateral side

n pper motor neron lesions(

above the motor decssation above medlla2

opposite side of body a$ectedbelow the motor decssation

same side of body a$ected

ipsilateral side

@ncrossed 8bres

in the spinal tract the ncrossed tract descent as the anterior corticospinal tract

its 8bres cross at spinal level

AS'.BDBG #;A'#S S.BS*;C2


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#ypes of ascending tracts(

Spinothalamic tracts

)ateral - pain & temperatre

Anterior - light toch & pressre

,osterior/Dorsal colmn tract - soft toch & pressre proprioception vibration

sensation

Spinocerebellar tract - postre & coordination

3low of arrangement of Spinothalamic tracts(

1st order neuron:

Arise from sensory receptors of the body #he 8bres enter the spinal cord via

dorsal root and ends at the sbstantia gelatinosa tip of posterior gray horn


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2nd order neuron:

#he 8bres of 1st order neron synapse with the !nd order neron at the

sbstantia gelatinosa #hese 8bres then cross to the opposite side

,ain & temperatre 8bres - enters the lateral spinothalamic tract

)ight toch & crde toch/ pressre 8bres - enters the anterior spinothalamic

tract

#hese tracts ascend to brainstem in brainstem these 8bres ascend to medlla

oblongata pons and midbrain via tracts 9attened in the brainstem spinal

lemniscs ;eaches and terminates at the ventral posterolateral E,)2 ncles

of the thalams

3rd order neuron:

#he "rd order nerons arise from the E,) ncles of thalams and pass throgh

the internal capsle thalamocortical 8bres enters the postcentral gyrsprimary sensory corte+ Area no "1!2 of the cerebrm behind the central slcs

3low of arrangement of the dorsal colmn tracts(


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1st order neuron:

3ascicls Gracilis originate from the receptors from the lower half of the body

3ascicls cneats originate from the receptors from the pper half of the body

3ibres enter the dorsal colmn of the SAM. side posterior colmn of spinal cord2

ascends throgh the spinal cord and enters medlla oblongata does not synapse

and end here li4e spinothalamic tract2 and 3asicls Gracilis terminates

ipsilaterally on Bces Gracilis whereas 3asicls 'neats terminates

ipsilaterally on Bces 'neats%

2nd order neuron:


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Starts at the gracile & cneate ncles of the medlla oblongata #hese 8bres

crosses/ decssate to the opposite side of the medlla oblongata Ascends

throgh the brain stem via medial lemniscs .nds in the ventral posterolateral

ncles E,)2 of the thalams

3rd order of nucleus:

Arise from the E,) of thalams ,ass throgh the internal capsle medial

aspect of the posterior limb of internal capsle2 ;eaches the postcentral gyrs

Area no "1!2 & somatosensory areas at the wall of the lateral slcs


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Flow of arrangement of Spinocerebellar

tract:

1st order neurons:

Arise from the sensory receptors of the body proprioceptors of mscles and 5oints2 .nters the spinal cord and ends in the 'lar4e6s 'olmn of the posterior

grey horn synapse with !nd order nerons at the dorsal horn of spinal cord%

* Proprioceptive information is obtained by Golgi tendon organs andmuscle spindles.

2nd order neuron:

Secondary nerons stay ipsilateral and ascends throgh the lateral colmn of

spinal cord via spinocerebellar tracts to the brain stem

Dorsal spinocerebellar tract enters cerebellm throgh inferior cerebellar

pedncle


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Eentral spinocerebellar tract enters cerebellm throgh sperior cerebellar

pedncle

* interior and superior cerebellar peduncles are te only tract tatenters te cerebellum

#hese tracts decssate ! times therefore cerebellm controls same side of bodyright spinocerebellar tract controls the right side and vice versa2

Actal decssation of these tracts( Fdoble-crosser%F

Ascending spinal tract

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