1.
Ascending & Descending Tracts
Of The Spinal Cord
By
Dr,Meher Moin Khan
Mehermk83@gmail.com

2.
W h i t e m a t t e r o f t h e s p i n a l c o r d
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.
Funicli ( Columns)
1. Dorsal 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

5.
2. Lateral Funiculus:
• Located between
dorsolateral &
ventrolateral sulci
3. Ventral Funiculus:
• Located between
the ventral median
fissure & ventral
lateral sulcus

6.
Relationship Between
Vertebrae No. Sp.Cord Segment
C1-C7
T1-T6
T7-T9
T10
T11
T12
L1
Add 1
Add 2
Add 3
L1-L2
L3-L4
L5
Sacral &
Coccygeal

7.
1. Posterior column
•
• Located between
the dorsal median
sulcus & dorsal
lateral sulcus
Subdivided into two:
A. Fasciculi Gracilis:
B. Fasciculus
Cunatus:

8.
2. Lateral Column:
• Located between
dorsal lateral &
ventral lateral
sulci
3. Anterior Column:
• Located between
the ventral median
fissure & ventral
lateral sulcus

9.
4. Anterior White
commissure
is a bundle of nerve
fibers which cross the
midline of the spinal
cord just anterior to
the gray commisure

10.
Ascending and
descending tracts of
the Spinal Cord

11.
a sc en d i n g
t r a c t s
d esc en d i n g
t r a c t s
Lat. spinothalamic
Ant. spinothalamic
Fasciculi gracilis &
cuneatus
Ant. & Post.
Spinocerebellar
Spinotectal
spinoreticular
Spino-olivary
corticospinal
reticulospinal
tectospinal
Rubrospinal
Vestibulospinal
Descending autonomic
-

12.
p a i n a n d t e m p r a t u r e s e n s a t i o n s :
Lateral spinothalamic tract (LST)

13.
Destination Posterior central gyrus
3rd Order
Neuron
Ventral posterolateral
nucleus of Thalamus
Pathways
Lateral spinothalamic,
Spinal lemniscus
Substantia
gelatinosa
2nd Order
Neuron
1st Order
Neuron
Posterior root
ganglion
Receptor
Free nerve
endings

14.
Notes on Lateral
spinothalamic tracts
:
• Posterolateral tract of
Lissauer :
1st order neuron enters posterior
horn & divides into ascending
and descending branches that
travel for 1-2 segments, then
terminate synapsing with 2nd
order neurons in substantia
gelatinosa.

15.
• L. Spinoth.T. in cervical segment
shows:
1.Sacral fibers are lateral, while
Cervical fibers are medial.
2.Pain fibers are anterior, while
Temperature fibers are posterior.

16.
• As the LST ascends at
medulla oblangata, is
accompanied by :
a. anterior spino-
thalamic tract,
b.spinotectal tract.
Together they form :
Spinal
Lemniscus(SL).

17.
INJURY TO THE ASCENDING TRACTS
WITHIN THE SPINAL
CORD
• Lateral Spinothalamic Tract :
injury results in :
1. contralateral loss of pain sensations below
the level of the lesion,
2. contralateral loss of thermal sensations below
the level of the lesion,
The patient will, therefore, not respond to
pinprick & cant recognize hot and cold objects
placed in contact with the skin.

18.
l i g h t t o u c h a n d p r e s s u r e
Anterior spinothalamic tract (AST)

19.
Posterior central gyrus
Ventral posterolateral
nucleus of Thalamus
Anterior
spinothalamic, Spinal
lemniscus
Substantia gelatinosa of
the contralateral dorsal
horn
Posterior root ganglion
Destination
Third-Order Neuron
Pathways
Second-Order Neuron
First-Order Neuron
Receptor Free nerve endings

20.
Notes on Anterior
spinothalamic tracts:
• Posterolateral tract of
Lissauer :
1st order neuron enters
posterior horn & divides
into ascending & descend-
ing branches that travel for
1-2 segments, then term-
inate synapsing with 2nd
order neurons in substan-
tia gelatinosa.

21.
• A. Spinoth.T. in cervical segment shows:
Sacral fibers are lateral, while
Cervical fibers are medial.

22.
• As the AST ascends at
medulla oblangata, is
accompanied by :
a. lateral spino-
thalamic
tract,
b.spinotectal
tract.
Together they form :
Spinal Lemniscus
(SL).

23.
• Anterior Spinothalamic Tract
injury of this tract produces
• contralateral loss of light touch sensations below
the level of the lesion
• contralateral loss of pressure sensations below
the level of the lesion
• The patient will not feel the light touch of a piece
of cotton placed against the skin and cant feel
pressure from a blunt object placed against the
skin.

24.
D i s c r i m i n a t i v e t o u c h , v i b r a t o r y
sense, c o n s c i o u s m u s c l e j o i n t
sense
Fasciculi gracilis and cuneatus ( FG
FC)

25.
Notes on FGandFC:
• Fibers divide into :
a. long ascending
branches (FG & FC)
b. short descending branches.
• Both of (a & b) synapse with
cells in the :
a. Posterior gray horn,
b. Internuncial neurons,
c. Anterior horn cells
• These synapses are involved with
intersegmental reflexes.

26.
• The axons of the second-order neurons, called
the internal arcuate fibers, cross the median
plane, decussating with the corresponding fibers
of the opposite side in the medulla as :
sensory Decussation
• The fibers then ascend as a single compact
bundle called medial lemniscus through the
brainstem.

27.
Posterior central gyrus
Ventral posterolateral nucleus of
Destination
Third-Order Neuron
Site of crossover
Second-Order Neuron
Pathways
First-Order Neuron
Receptor
Thalamus of opposite side
Internal arcuate fibers
Nuclei gracilis and cuneatus in
medulla oblagata
Ipsilateral Fasciculi gracilis &
cuneatus & medial lemniscus
Posterior root ganglion
Meissner's corpuscles,
pacinian corpuscles, muscle
spindles & tendon organs

28.
f a s c i c u l u s g r a c i l i s (fg)
• present throughout the length of the spinal
cord
• contains the long ascending fibers from the:
1. Sacral spinal nerves
2. Lumbar spinal nerves
3. lower 6 thoracic spinal nerves

29.
fasciculus cuneatus (f.c) :
• contains the long ascending fibers from the:
1. upper six thoracic spinal nerves,
2. all the cervical spinal nerves.

30.
• Fasciculus Gracilis and Fasciculus
Cuneatus
Injury results in:
• Ipsilateral loss of position and movements
sensations of limbs below the level of the
lesion.
• Ipsilateral loss of vibration sense below the level
of the lesion
• Ipsilateral loss of two point discrimination below the
level of the lesion.

31.
• Tabes Dorsalis :
• is caused by syphilis.
• a selective destruction of nerve fibers at the point
of entrance of the posterior root into the spinal
cord,
• specially in the lower thoracic and
lumbosacral regions.
• Results in loss of some sensation & hypersensitivity
others.

32.
Cuneocerebellar tract:
• Also called posterior
external arcuate fibers
• 2nd order neuron axons of the
nucleus cuneatus travel as to
enter the cerebellum through the
inferior cerebellar peduncle of
the same side.
• The function of these fibers is to
convey information of muscle joint
sense to the cerebellum.

33.
u n c o n c i o u s m u s c l e j o i n t sense
P a t h w a y s t o t h e c e r e b e l l u m
(Anterior Spinocerebellar Tract)
( Posterior Spinocerebellar Tract)

34.
Destination
Pathways
Second-Order Neuron
First-Order Neuron
Receptor
Cerebellar
cortex
Through Superior & inferior
cerebellar peduncles
respectively
Anterior and posterior
spinocerebellar
Nucleus dorsalis
Posterior root ganglion
Muscle spindles, tendon
organs, joint receptors

35.
AST

36.
OTHER ASCENDING TRACTS :
1. Spinotectal Tract
2. Spinoreticular Tract
3. Spino-olivary Tract

37.
1. Spinotectal Tract :
• This pathway provides afferent information
for spinovisual reflexes and brings about
movements of the eyes & head in response
to the source of the stimulation.

38.
2. Spinoreticular Tract :
The spinoreticular tract provides an
afferent pathway for the reticular
formation, which plays an important role
in influencing levels of consciousness.

39.
3. Spino-olivary Tract:
conveys information to cerebellum
from cutaneous proprioceptive organs.

40.
t h e D e s c e n D i n g t r a c t s
o f t h e s P i n a l c o r D
(Corticospinal Tracts)

41.
Origin parietal
Primary motor cortex (area 4),
secondary motor cortex (area 6),
lobe (areas 3, 1, and 2)
Pathway Corticospinal tracts
Pass
through
Corona radiata, posterior limb of internal
capsule & middle 3/5 of basis pedunculi
of midbrain
Site of
crossover
of medulla
•75-90% of fibers cross to contralateral side
and descend in spinal cord as
lateral corticospinal tracts .
in pyramids • 10-25% of fibers descend uncrossed in
spinal cord as anterior corticospinal
tracts and cross over at level of
destination
Destination Internuncial neurons or motor
neurons

42.
Notes about corticospinal tract:
• 2/3 of the fibers arise from the precentral
gyrus ( area 4 & 6),
• 1/3 of the fibers arise from the postcentral gyrus (
areas 3, 1 and 2).
• In the medulla oblongata, the bundles become
grouped together along the anterior border to form
a swelling known as the pyramid (hence the
alternative name, pyramidal tract).

43.
• The pyramidal tract controls rapid, skilled,
voluntary movements, especially distal ends
of limbs
• The pyramidal tract gives branches to cerebral
cortex, basal nuclei, red nucleus, olivary nuclei,
reticular formation. These branches keep the
subcortical regions informed about the cortical
motor activity.

44.
Reticulospinal tracts

45.
Origin Reticular formation
Pathway Reticulospinal tracts
Site of
crossover Some cross at various levels
Destination Motor
neurons
Function
Inhibit or facilitate voluntary move-
ment, reflex activity, assist hypothala-
mus controls sympathetic, parasympa-
thetic outflows.

46.
Notes about reticulospinal tract:
• From the pons , reticulospinal fibers are mostly
descending uncrossed into the spinal cord and
form the pontine reticulospinal tract.
• From the medulla , similar neurons send
axons, which are crossed and uncrossed, to the
spinal cord and form the medullary
reticulospinal tract.

47.
Tectospinal tract

48.
Origin Superior colliculus of midbrain
Pathway Tectospinal tract
Immediately decussates at
posterior Midbrain tegmentum
Site of
crossover
Destination Motor neurons
Reflex postural movements
concerning sightFunction

49.
Notes about tectospinal tract:
• Descends through spinal cord close to
: anterior median fissure.
• The majority of the fibers terminate in anterior gray
column in the C1-C4 of the spinal cord by
synapsing with internuncial neurons. These fibers
are believed to be concerned with :
Turning of head to contralateral side in response to visual
stimulations

50.
Rubrospinal tracts

51.
Origin Red nucleus of midbrain
Pathway Rubrospinal
tract
Site of
crossover Immediately in midbrain
Destination
Function
Motor neurons in C1-C3
Facilitates activity of flexor muscles and
inhibits activity of extensor muscles in the
upper limb

52.
Notes about rubrospinal tract:
• The neurons of the red nucleus receive
afferent impulses through connections with
the :
1. cerebral cortex
2. cerebellum.
This is believed to be an important indirect
pathway by which the cerebral cortex and the
cerebellum can influence the activity of
motor neurons of the spinal cord.

53.
Vestibulospinal tract

54.
Origin 1. Medial vestibular nucleus ( medulla)
2. Lateral vestibular nucleus ( pons )
Pathway
Site of
crossover
1. Medial vestibulospinal tract from MVN
2. Lateral vestibulospinal tract from LVN
3. Contain crossed & uncrossed fibers
4. Contains uncrossed fibers
Destination
1.Dose not extend below T6 motor
neurons
2. Motor neurons of all spinal levels
Function Facilitates activity of extensor & inhibits
flexor muscles

55.
MLF= Medial Longitudenal
Fasciculous

56.
Notes about vestibulospinal tract:
• Lateral vestibulospinal tract is involved in:
1. maintenance of upright posture and balance;
2. mediates head & neck movements in response
to vestibular sensory input
• Medial vestibulospinal tract mediates head
movement while maintaining gaze fixation on an
object

57.
Descending autonomic
fibers

58.
Origin Cerebral cortex, hypothalamus, amygdaloid
complex, reticular formation
Pathway
Descending autonomic fibers
Probably through reticulospinal tract
?
Site of
crossover cross the midline in the brainstem
?
Destination Sympathetic and parasympathetic outflows
Control sympathetic and
parasympathetic systemsFunction

59.
Notes about Descending autonomic
tract:
• distinct tracts have not been recognized,
• investigation of spinal cord lesions has
demonstr- ated that descending autonomic
tracts do exist.
• probably form part of the reticulospinal tract.

60.
Reflex Arc
Its an involuntary response to a stimulus, consists of
the following anatomical structures:
(1) a receptor organ,
(2) an afferent neuron,
(3) an efferent neuron,
(4) an effector organ.
A reflex arc involving only
one synapse is referred to as a monosynaptic reflex
arc.

61.
l e s i o n o f s p i n a l c o r d

62.
INJURY TO THE ASCENDING TRACTS
WITHIN THE SPINAL
CORD
• Lateral Spinothalamic Tract :
injury results in :
1. contralateral loss of pain sensations below
the level of the lesion,
2. contralateral loss of thermal sensations below
the level of the lesion,
The patient will, therefore, not respond to
pinprick & cant recognize hot and cold objects
placed in contact with the skin.

63.
• Anterior Spinothalamic Tract
injury of this tract produces
• contralateral loss of light touch sensations below
the level of the lesion
• contralateral loss of pressure sensations below
the level of the lesion
• The patient will not feel the light touch of a piece
of cotton placed against the skin and cant feel
pressure from a blunt object placed against the
skin.

64.
• Fasciculus Gracilis and Fasciculus
Cuneatus
Injury results in:
• Ipsilateral loss of position and movements
sensations of limbs below the level of the
lesion.
• Ipsilateral loss of vibration sense below the level
of the lesion
• Ipsilateral loss of two point discrimination below the
level of the lesion.

65.
• Tabes Dorsalis :
• is caused by syphilis.
• a selective destruction of nerve fibers at the point
of entrance of the posterior root into the spinal
cord,
• specially in the lower thoracic and
lumbosacral regions.
• Results in loss of some sensation & hypersensitivity
others.

66.
Descending tracts lesions
A. Upper Motor Neuron (UMN) Lesions:
include:
1. Lesions of corticospinal tracts (Pyramidal
Tracts)
2. Lesions of descending tracts other than the
Corticospinal Tracts (Extrapyramidal Tracts)

67.
1. Lesions of corticospinal tracts ( Pyramidal
Tracts)
signs include
• The Babinski sign is present. .
• The superficial abdominal reflexes are absent.
• The cremasteric reflex is absent.
• There is loss of performance of fine-skilled
voluntary movements, especially at the distal
end of the limbs.

68.
2. Extrapyramidal Tracts lesions:
• Spastic paralysis,
(lower limb extended, and the upper limb flexed),
• Exaggerated deep muscle reflexes in some flexors,
• Clasp-knife reaction. The muscles, after resistance
on stretching, suddenly give way.

69.
2. Lower Motor Neuron (LMN) Lesions :
• Caused by any lesion ( ex. Poliomyelitis)
destroying neurons in the anterior gray column
or its axon in the anterior root or spinal nerve.
• Has the following clinical signs:
1. Flaccid paralysis of muscles supplied.
2. Atrophy of muscles supplied.
3. Loss of reflexes of muscles supplied.

70.
4. Muscular fasciculation (visible useless
muscle twitching )
5. Muscular contracture (shortening of
the paralyzed muscles).
6. Reaction of degeneration, a muscle will no
longer respond to interrupted electrical
stimulation

71.
Spinal Shock syndrome
Following a spinal cord injury there will be :
• a short term loss of all neurological activity below
the level of injury. This loss of neurological
activity include loss of motor, sensory reflex &
autonomic function.
• due to temporary physiologic disorganisation of
spinal cord function, may last 30-60 minutes or
up to 6 weeks.

72.
Complete Cord Transection
Syndrome
• It can be caused by fracture dislocation of
the vertebral column,
• The following clinical features :
1. Bilateral lower motor neuron paralysis
2. Bilateral spastic paralysis below the level of the
lesion (due to extrapyramidal tract injury)
3. Bilateral loss of all sensations below the level of
the lesion.
4. Bladder and bowel functions are no longer
under voluntary control (injury to descending
autono- mic fibers have been destroyed).

73.
Anterior cord syndrome
Results in :
1. Bilateral LMN paralysis in the segment of lesion,
2. Bilateral spastic paralysis below level of the
lesion,
3. Bilateral loss of pain, temprature & light touch
below the level of the lesion,
4. Two point discrimination & vibratory and
proprioception sensations are preserved.

74.
Central cord syndrome
Results in :
1. Bilateral LMN paralysis in the segment of
lesion,
2. Bilateral spastic paralysis below the level of the
lesion with characteristic sacral sparing,
3. Bilateral loss of pain, temprature & light touch
and pressure sensations below the level of the
lesion with characteristic sacral sparing.

75.
Brown-sequard syndrome
( hemisection of the spinal cord)
Results in :
1. Ipsilateral LMN paralysis in segment of lesion
2. Ipsilateral spastic paralysis below the level of the
lesion,
3. Ipsilateral band of cutaneous anasthesia in
the segment of the lesion
4. Ipsilateral loss of two point didcrimination &
vibratory and proprioceptive sense below the
level of lesion.

76.
4. Contralteral loss of pain & temprature sense
below the level of the lesion,
5. Contralateral partial loss of two point
discrim- ination sense below the level of the
lesion.