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Ascending & Descending Tracts Of The Spinal Cord
1. Ascending & Descending Tracts
Of The Spinal Cord
By
Dr.Faris Al-Haddad
M.B.Ch.B, PhD Anatomy
College of Medicine,
Hawler Medical University
Arbil, Iraq
e-mail: farisurgeon@gmail.com
2. White matter of the spinal cord
As in other regions of the CNS, white matter of
the spinal cord consists of a mixture of:
1. Nerve fibers,
2. Neuroglia,
3. Blood vessels.
It surrounds the gray matter, and its white
color is due to the high proportion of
myelinated nerve fibers.
3. The white matter, for purposes of description,
may be divided into:
1. Anterior white column (or funiculus)
2. Lateral white column (or funiculi) ,
3. posterior white column (or funiculus),
4. Anterior white commisure.
4. 1.1. Posterior columnPosterior column
• Located between the
dorsal median
sulcus& dorsal
lateral sulcus
• Subdivided into two:
A. Fasciculi Gracilis:
B. Fasciculus
Cunatus:
5. 2.2. Lateral Column:Lateral Column:
• Located between
dorsal lateral &
ventral lateral sulci
3. Anterior Column:3. Anterior Column:
• Located between the
ventral median
fissure& ventral
lateral sulcus
11. Destination Posterior central gyrus
3rd
Order
Neuron
Ventral posterolateral
nucleus of Thalamus
Pathways
Lateral spinothalamic,
Spinal lemniscus
2nd
Order
Neuron
Substantia
gelatinosa
1st
Order
Neuron
Posterior root
ganglion
Receptor
Free nerve
endings
12.
13. Notes on Lateral
spinothalamic tracts
:
• Posterolateral tract ofPosterolateral tract of
Lissauer :Lissauer :
1st
order neuron enters
posterior horn & divides
into ascending and
descending branchesthat
travel for 1-2 segments,
then terminatesynapsing
with 2nd
order neuronsin
substantiagelatinosa.
14. • L. Spinoth.T. in cervical segmentL. Spinoth.T. in cervical segment
shows:shows:
1.1.Sacral fibersSacral fibersarelateral, while
Cervical fibersCervical fibersaremedial.
2.2.Pain fibersPain fibersareanterior, while
TemperaturefibersTemperaturefibersareposterior.
15. • AstheLST ascendsat
medullaoblangata, is
accompanied by :
a. anterior spino-
thalamic tract,
b.
spinotectal tract.
Together they form :
SpinalSpinal
Lemniscus(SL).Lemniscus(SL).
19. Notes on Anterior
spinothalamic tracts :
• Posterolateral tract ofPosterolateral tract of
Lissauer :Lissauer :
1st
order neuron enters
posterior horn & divides
into ascending & descend-
ing branchesthat travel for
1-2 segments, then term-
inatesynapsing with 2nd
order neuronsin substan-tia
gelatinosa.
20. • A. Spinoth.T. in cervical segment shows:A. Spinoth.T. in cervical segment shows:
Sacral fibersSacral fibersarelateral, while
Cervical fibersCervical fibersaremedial.
21. • AstheAST ascendsat
medullaoblangata, is
accompanied by :
a. lateral spino-
thalamic tract,
b.
spinotectal tract.
Together they form :
Spinal LemniscusSpinal Lemniscus
(SL).(SL).
23. Destination Posterior central gyrus
Third-Order Neuron Ventral posterolateral nucleus of
Thalamusof oppositeside
Site of cross over Internal arcuatefibers
Second-Order Neuron Nuclei gracilisand cuneatusin
medullaoblagata
Pathways Ipsilateral Fasciculi gracilis&
cuneatus& medial lemniscus
First-Order Neuron Posterior root ganglion
Receptor
Meissner'scorpuscles, pacinian
corpuscles, musclespindles&
tendon organs
24.
25. Notes on FG and FC:
• Fibersdivideinto :
a. long ascending branches
(FG & FC)
b. short descending branches.
• Both of (a& b) synapsewith
cellsin the:
a. Posterior gray horn,
b. Internuncial neurons,
c. Anterior horn cells
• Thesesynapsesareinvolved with
intersegmental reflexes.
28. • Theaxonsof thesecond-order neurons, called the
internal arcuatefibersinternal arcuatefibers, crossthemedian plane,
decussating with thecorresponding fibersof the
oppositesidein themedullaas :
sensory Decussation
• Thefibersthen ascend asasinglecompact bundle
called meDial lemniscus through the
brainstem.
29. Cuneocerebellar tract:
• Also called posterior externalposterior external
arcuatefibersarcuatefibers
• 2nd
order neuron axonsof the
nucleuscuneatustravel asto enter
thecerebellum through theinferior
cerebellar peduncleof thesame
side.
• Thefunction of thesefibersisto
convey information of musclejoint
senseto thecerebellum.
30. unconcious muscle joint sense
Pathways to the cerebellum
(Anterior Spinocerebellar Tract)
(Posterior Spinocerebellar Tract)
31. Destination Cerebellar
cortex
Pathways
Through Superior & inferior
cerebellar peduncles
respectively
Anterior and posterior
spinocerebellar
Second-Order Neuron Nucleusdorsalis
First-Order Neuron Posterior root ganglion
Receptor Musclespindles, tendon
organs, joint receptors
39. Origin
Primary motor cortex (area4),
secondary motor cortex (area6), parietal
lobe(areas3, 1, and 2)
Pathway Corticospinal tracts
Pass
through
Coronaradiata, posterior limb of internal
capsule& middle3/5 of basispedunculi of
midbrain
Site of
crossover
in pyramids
of medulla
• 75-90% of fiberscrossto contralateral side
and descend in spinal cord aslateral
corticospinal tracts.
• 10-25% of fibersdescend uncrossed in
spinal cord asanterior corticospinal tracts
and cross over at level of destination
Destination Internuncial neuronsor motor neurons
40.
41. Notes about corticospinal tract:
• 2/3 of thefibersarisefrom theprecentral gyrus
( area4 & 6),
• 1/3 of thefibersarisefrom thepostcentral gyrus (
areas3, 1 and 2).
• In themedullaoblongata,In themedullaoblongata, thebundlesbecome
grouped together along theanterior border to form a
swelling known asthepyramid (hencethe
alternativename, pyramidal tractpyramidal tract).
42. • Thepyramidal tract controls rapid, skilled,
voluntary movements, especially distal endsof
limbs
• Thepyramidal tract givesbranchesto cerebral
cortex, basal nuclei, red nucleus, olivary nuclei,
reticular formation. Thesebrancheskeep the
subcortical regionsinformed about thecortical
motor activity.
44. Origin Reticular formation
Pathway Reticulospinal tracts
Site of
crossover Somecrossat variouslevels
Destination Motor neurons
Function
Inhibit or facilitatevoluntary move-ment,
reflex activity, assist hypothala-mus
controlssympathetic, parasympa-thetic
outflows.
45.
46. Notes about reticulospinal tract:
• From the pons, reticulospinal fibersaremostly
descending uncrossed into thespinal cord and form
thepontinereticulospinal tract.
• From the medulla, similar neuronssend
axons, which arecrossed and uncrossed, to the
spinal cord and form themedullary reticulospinal
tract.
48. Origin Superior colliculusof midbrain
Pathway Tectospinal tract
Site of
crossover
Immediately decussatesat posterior
Midbrain tegmentum
Destination Motor neurons
Function Reflex postural movementsconcerning
sight
49.
50. Notes about tectospinal tract:
• Descendsthrough spinal cord closeto :
anterior median fissure.
• Themajority of thefibersterminatein anterior gray
column in theC1-C4 of thespinal cord by
synapsing with internuncial neurons. Thesefibers
arebelieved to beconcerned with :
turning of head to contralateral
side in response to visual
stimulations
52. Origin Red nucleusof midbrain
Pathway Rubrospinal tract
Site of
crossover Immediately in midbrain
Destination Motor neuronsin C1-C3
Function
Facilitatesactivity of flexor musclesand
inhibitsactivity of extensor musclesin the
upper limb
53.
54. Notes about rubrospinal tract:
• Theneuronsof thered nucleusreceiveafferent
impulsesthrough connectionswith the:
1. cerebral cortex
2. cerebellum.
Thisisbelieved to bean important indirect
pathway by which thecerebral cortex and the
cerebellum can influencetheactivity of motor
neuronsof thespinal cord.
60. Origin Cerebral cortex, hypothalamus, amygdaloid
complex, reticular formation
Pathway
Descending autonomic fibers
Probably through reticulospinal tract ?
Site of
crossover crossthemidlinein thebrainstem ?
Destination Sympathetic and parasympathetic outflows
Function Control sympathetic and parasympathetic
systems
61. Notes about Descending autonomic
tract:
• distinct tractshavenot been recognized,
• investigation of spinal cord lesionshasdemonstr-
ated that descending autonomic tractsdo exist.
• probably form part of thereticulospinal tract.
62. Reflex Arc
Itsan involuntary responseto astimulus, consistsof the
following anatomical structures:
(1) areceptor organ,
(2) an afferent neuron,
(3) an efferent neuron,
(4) an effector organ.
A reflex arc involving only
onesynapseisreferred to asamonosynaptic reflex arc.
64. Injury to the AscendIng
trActs WIthIn the spInAl
cord
• Lateral Spinothalamic Tract :
injury resultsin :
1. contralateral lossof pain sensationsbelow the
level of thelesion,
2. contralateral lossof thermal sensationsbelow the
level of thelesion,
Thepatient will, therefore, not respond to pinprick
& cant recognizehot and cold objectsplaced in
contact with theskin.
65. • Anterior Spinothalamic Tract
injury of thistract produces
• contralateral lossof light touch sensationsbelow the
level of thelesion
• contralateral lossof pressuresensationsbelow the
level of thelesion
• Thepatient will not feel thelight touch of apieceof
cotton placed against theskin and cant feel pressure
from ablunt object placed against theskin.
66. • Fasciculus Gracilis and Fasciculus
Cuneatus
Injury resultsin:
• Ipsilateral lossof position and movements
sensationsof limbsbelow thelevel of thelesion.
• Ipsilateral lossof vibration sensebelow thelevel of
thelesion
• Ipsilateral lossof two point discrimination below the
level of thelesion.
67. • Tabes Dorsalis :
• iscaused by syphilis.
• aselectivedestruction of nervefibersat thepoint of
entranceof theposterior root into thespinal cord,
• specially in thelower thoracic and lumbosacral
regions.
• Resultsin lossof somesensation & hypersensitivity
others.
68. Descending tracts lesions
A. Upper Motor Neuron (UMN) Lesions:
include:
1. Lesionsof corticospinal tracts(Pyramidal Tracts)
2. Lesionsof descending tractsother than the
Corticospinal Tracts(Extrapyramidal Tracts)
69. 1. Lesions of corticospinal tracts (Pyramidal
Tracts)
signsinclude
• TheBabinski sign ispresent. .
• Thesuperficial abdominal reflexesareabsent.
• Thecremasteric reflex isabsent.
• Thereislossof performanceof fine-skilled
voluntary movements, especially at thedistal end
of thelimbs.
70. 2. Extrapyramidal Tracts lesions:
• Spastic paralysis,Spastic paralysis,
(lower limb extended, and theupper limb flexed),
• Exaggerated deep musclereflexesin someflexors,Exaggerated deep musclereflexesin someflexors,
• Clasp-knifereactionClasp-knifereaction. Themuscles, after resistance
on stretching, suddenly giveway.
71. 2. Lower Motor Neuron (LMN) Lesions:
• Caused by any lesion ( ex. Poliomyelitis)
destroying neuronsin theanterior gray column or
itsaxon in theanterior root or spinal nerve.
• Hasthefollowing clinical signs:
1. Flaccid paralysisof musclessupplied.
2. Atrophy of musclessupplied.
3. Lossof reflexesof musclessupplied.
72. 4. Muscular fasciculation (visibleuseless
muscletwitching )
5. Muscular contracture(shortening of the
paralyzed muscles).
6. Reaction of degeneration, amusclewill no
longer respond to interrupted electrical
stimulation
73. Spinal Shock syndromeSpinal Shock syndrome
Following aspinal cord injury therewill be:
• ashort term lossof all neurological activity below
thelevel of injury. Thislossof neurological
activity includelossof motor, sensory reflex &
autonomic function.
• dueto temporary physiologic disorganisation of
spinal cord function, may last 30-60 minutesor up
to 6 weeks.
74. Complete Cord Transection
Syndrome
• It can becaused by fracturedislocation of the
vertebral column,
• Thefollowing clinical features:
1. Bilateral lower motor neuron paralysis
2. Bilateral spastic paralysisbelow thelevel of the
lesion (dueto extrapyramidal tract injury)
3. Bilateral lossof all sensationsbelow thelevel of
thelesion.
4. Bladder and bowel functionsareno longer under
voluntary control (injury to descending autono-
mic fibershavebeen destroyed).
75. Anteriorcord syndrome
Resultsin :
1. Bilateral LMN paralysisin thesegment of lesion,
2. Bilateral spastic paralysisbelow level of the
lesion,
3. Bilateral lossof pain, temprature& light touch
below thelevel of thelesion,
4. Two point discrimination & vibratory and
proprioception sensationsarepreserved.
76. Central cord syndrome
Resultsin :
1. Bilateral LMN paralysisin thesegment of
lesion,
2. Bilateral spastic paralysisbelow thelevel of the
lesion with characteristic sacral sparing,
3. Bilateral lossof pain, temprature& light touch
and pressuresensationsbelow thelevel of the
lesion with characteristic sacral sparing.
77. Brown-sequard syndrome
(hemisection of the spinal cord)
Resultsin :
1. Ipsilateral LMN paralysisin segment of lesion
2. Ipsilateral spastic paralysisbelow thelevel of the
lesion,
3. Ipsilateral band of cutaneousanasthesiain the
segment of thelesion
4. Ipsilateral lossof two point didcrimination &
vibratory and proprioceptivesensebelow thelevel
of lesion.
78. 4. Contralteral lossof pain & tempraturesensebelow
thelevel of thelesion,
5. Contralateral partial lossof two point discrim-
ination sensebelow thelevel of thelesion.
79.
80. Funicli ( Columns)Funicli ( Columns)
1.1. Dorsal FuniculusDorsal Funiculus
• Located between the
dorsal median sulcus
& dorsal lateral sulcus
• Subdivided into two:
A. Fasci cul i Graci l i s:
• Located between dorsal
median sulcus & dorsal
intermediate sulcus
• Found at all levels
B. Fasci cul us Cunat us:
• Between dorsal intermed-
iate sulcus & septum & the
dorsal lateral sulcus
• Found at C1-T6
2 1
81. 2. Lateral Funiculus:2. Lateral Funiculus:
• Located between
dorsolateral &
ventrolateral sulci
3. Ventral Funiculus:3. Ventral Funiculus:
• Located between
the ventral median
fissure & ventral
lateral sulcus
