1. The document describes the ascending tracts of the spinal cord which transmit sensory information to the brain. It discusses tracts like the lateral and anterior spinothalamic tracts that carry pain, temperature and touch sensations and the posterior white columns that carry proprioceptive information. 2. It provides details on the neurons involved in transmitting sensory information from the receptors via the spinal cord to the thalamus and sensory cortex. It includes a diagram of the sensory homunculus map in the cortex. 3. The tracts transmit different sensory modalities and project to different areas of the brain like the thalamus, cerebellum and reticular formation to process sensory information and maintain consciousness.

1. SPINAL CORD & ITS TRACTS – I
(ASCENDING TRACTS)
Dr. Abdul Qadeer
MBBS;(MRCS);FCPS;FICS
Assistant Prof. of Surgery
LCMD, Karachi.

3. Spinal cord
• Continuation of medulla oblongata from
foramen magnum up to lower border of L1
vertebra
• Ends conus medularis and here give rise cauda
equina & filum terminale
• Covered in all three meninges; dura,
arachnoid & pia
• Has CSF within subarachnoid space

4. Spinal cord
• Lies within vertebral foramina
• Gives rise 31 pairs of spinal nerves which
emerge out of intervertebral foramina

5. Structure of the spinal cord
• Inner core of gray matter and outer covering
of white matter

6. SPINAL NERVE

7. Gray matter of spinal cord
• In transverse section of spinal cord, gray
matter gives appearance of an H
• Gives rise anterior & posterior gray columns or
horns
• Lateral horns in thoraco-lumbar & sacral areas
• A central canal
• Both sides united by gray commissure which
may be anterior and posterior with respect to
the central canal

10. Gray matter of spinal cord
• The amount of gray matter present at any
given level of spinal cord is related to the
amount of muscle innervated at that level
• Hence its size is big within cervical & lumbo-
sacral areas which innervate the muscles of
upper & lower limbs respectively

11. NERVE CELL GROUPS IN ANTERIOR
GRAY COLUMNS
• Three basic groups or columns i.e. medial,
central and lateral
• Axons are multipolar which pass through
anterior (motor) roots of the spinal nerves
• Αn α-efferent type of fibers innervate skeletal
muscles
• While γ-efferent type of fibers innervate
intrafusal fibers of neuromuscular spindle

12. Medial group of anterior horn
• Mostly innervates the skeletal muscles of neck
& trunk

13. Central group of anterior horn
• Smallest group
• Present in some cervical & lumbo-sacral
segments & known as:
1. Phrenic nucleus: present in C3-5 segments of
spinal cord and innervates the diaphragm
2. Accessory nucleus: innervates to
sternocleido-mastoid & trapezius muscles
3. Lumbo-sacral nucleus: present from L2 to S1
segments having unknown distribution

14. Lateral group of anterior horn
• Present in cervical and lumbo-sacral segments
of spinal cord
• Innervates the skeletal muscles of the limbs

16. NERVE CELL GROUPS IN POSTERIOR
GRAY COLUMNS
• Four nerve cell groups out of which, two
extend throughout the length of spinal cord
and two are restricted to thoracic and lumbar
segments
• These groups are:
1. Substantia gelatinosa group
2. Nucleus proprius group
3. Nucleus dorsalis (Clarke’s column) group
4. Visceral afferent nucleus

17. 1. Substantia gelatinosa group
• Situated in the apex of posterior horn
throughout the spinal cord length
• Receives afferent fibers from posterior root
concerned with:
1. Pain
2. Temperature &
3. Touch

18. 2. Nucleus proprius group
• Situated anterior to the substantia gelatinosa
throughout the length of spinal cord
• Receives fibers from posterior white column
that are associated with the senses of:
1. position and movement (proprioception)
2. Two-point discrimination
3. vibration

19. 3. Nucleus dorsalis (Clarke’s) group
• Situated at the base of posterior gray horn
• Extends from C8 to L3 or 4 segments of Spinal
cord
• Take sensation from neuromuscular & neuro-
tendinous spindles

20. 4. Visceral afferent nucleus
• Situated lateral to the nucleus dorsalis
• Extends from T1 to L3 segments of the spinal
cord
• Receives visceral afferent information

21. NERVE CELL GROUPS IN LATERAL
GRAY COLUMNS
• Extends from T1 to L2-3 segments of the spinal
cord
• Give rise to pre-ganglionic sympathetic fibers
• A similar group of cells is found in S2-4
segments of the spinal cord
• This group gives rise to pre-ganglionic
parasympathetic fibers

22. GRAY COMMISSURE & CENTRAL
CANAL
• Posterior gray commissure is situated behind
the central canal
• Anterior gray commissure is situated in front
of central canal

23. Laminar organization in spinal cord
(Laminae of Rexed)
• Gray matter of spinal cord is arranged in layers
• These are given numbers by Roman numerals
• There are ten layers starting from dorsal horn
and moving ventrally into ventral horn

24. Laminar organization in spinal cord
(Laminae of Rexed)
Laminar organization in spinal cord (Laminae
of Rexed)

25. Laminar organization in spinal cord
(Laminae of Rexed)
• Lamina I: corresponds to posteromarginal
nucleus
• Lamina II: corresponds to the substantia
gelatinosa
• Laminae III & IV: correspond to nucleus
proprius
• Laminae V & VI: correspond to base of dorsal
column

26. Laminar organization in spinal cord
(Laminae of Rexed)
• Lamina VII: between dorsal & ventral horns
i.e. the area of interneurons. This lamina
consists of 3 columns
1. Intermediolateral
2. Intermediomedial
3. Nucleus dorsalis (Clarke’s column)

27. Laminar organization in spinal cord
(Laminae of Rexed)
• Lamina VIII: lies on the medial aspect of
anterior horn
• Lamina IX: includes the lateral group of ventral
horn
• Lamina X: surrounds the central canal. It is
composed of decussating axons

28. Laminar organization in spinal cord
(Laminae of Rexed)

29. Laminar organization in spinal cord
(Laminae of Rexed)

30. WHITE MATTER
• The white matter is divided into following
columns (funiculi)
1. Anterior column: on each side lies between
the midline & the point of exit of the anterior
nerve roots
2. Lateral column: lies between the exit of
anterior nerve roots & the entry of posterior
nerve roots
3. Posterior column: lies between the entry of
posterior nerve roots & midline

31. Tracts within spinal cord
1. Ascending tracts
2. Descending tracts
3. Intersegmental tracts

32. Ascending tracts of spinal cord
1. Lateral spino-thalamic tract
2. Anterior spino-thalamic tract
3. Fasciculus gracilis
4. Fasciculus cuneatus
5. Posterior spino-cerebellar tract
6. Anterior spino-cerebellar tract
7. Spino-olivary tract
8. Spino-tectal tract

33. Descending tracts of spinal cord
A. Pyramidal (cortico-spinal)
tracts
1. Lateral cortico-
spinal tract
2. Anterior cortico-
spinal tract
B. Extra-pyramidal tracts
1. Rubro-spinal tract
2. Medial reticulo-
spinal tract
3. Lateral reticulo-
spinal tract
4. Olivo-spinal tract
5. Vestibulo-spinal
tract
6. Tecto-spinal tract

34. Intersegmental tracts
• These are short ascending & descending tracts
that originate and end within spinal cord
• These tracts exist in the anterior, lateral &
posterior white columns
• Their function is to interconnect the neurons
of different segmental levels
• These are important in intersegmental spinal
reflexes

35. Ascending tracts of spinal cord
• These tracts conduct afferent information to
the higher centers
• The information may be divided into two main
groups
1. Exteroceptive: the information that
originates from outside the body e.g. pain,
temperature, touch etc.
2. Proprioceptive: the information which
originates from inside the body e.g. muscles
& joints

36. Anatomical organization of ascending
tracts (three neuron chain)
1. Sensory nerve endings (receptors)
2. First-order neuron: its cell body is located in
the posterior root ganglion of the spinal
nerve
3. Second-order neuron: gives rise to an axon
that decussates & ascends to a higher levels
of CNS
4. Third-order neuron: usually located in
thalamus which gives rise to a projection
fiber that passes into sensory region of the
cerebral cortex

37. • The three neuron chain may give branches to
the reticular formation, which activates the
cerebral cortex and maintains wakefulness
• These may also give branches to motor
neurons and participate in reflex muscular
activity

39. Functions of the ascending tracts
• Pain & temperature (thermal) sensation:
Lateral spinothalamic tract
• Light (crude) touch & pressure sensation:
Anterior spinothalamic tract

40. Functions of the ascending tracts
(Posterior white columns)
• Discriminative touch including two-point
discrimination: Posterior white columns
• Muscle & joint position & movements:
Posterior white columns
• Vibratory sensation: Posterior white columns

41. Functions of the ascending tracts
• Unconscious information from muscles, joints,
skin & subcutaneous tissues: Anterior +
Posterior spino-cerebellar tracts & Cuneo-
cerebellar tract

42. Functions of the ascending tracts
• Pain, thermal & tactile information for
spinovisual reflexes: Spinotectal tract
• Wakefulness (level of consciousness):
spinoreticular tract
• Proprioceptive sensation: Spino-olivary tract

43. Lateral spino-thalamic tract
(Pain & temperature pathways)
• RECEPTORS for pain & temperature = Free
nerve endings in the skin & other tissues
Nerve fibers through the posterior root
ganglion enter the spinal cord (first-
order neuron) Tip of the posterior gray
horn Divide into small ascending &
descending branches. These branches travel
for a distance of one or two segments of
spinal cord and form the Postero-lateral tract
of Lissauer.

44. Lateral spino-thalamic tract
(Pain & temperature pathways)
• The fibers (axons) of the first-order neuron
terminate by synapsing with the cells in
posterior horn & substantia gelatinosa
(Substance P is a neurotransmitter here)
• Axons of second-order neuron cross obliquely
to the opposite side in the anterior gray & white
commissures within one spinal segment of the
cord Ascend in the contra-lateral
white column as the lateral spinothalamic tract

46. Lateral spino-thalamic tract
(Pain & temperature pathways)
• Lateral spino-thalamic tract lies medial to the
anterior spino-cerebellar tract
• As the lateral spino-thalamic tract ascends
through the spinal cord, new fibers are added
to the anteromedial aspect of the tract
• Thus, in the upper cervical segments of the
cord, the sacral fibers are lateral & the cervical
fibers are medial
• The pain fibers are situated slightly anterior to
the temperature fibers

49. Lateral spino-thalamic tract
(Pain & temperature pathways)
• In the medulla oblongata, the lateral spino-
thalamic tract is accompanied by the anterior
spino-thalamic tract and the spino-tectal tract
• All the three tracts together form spinal
lemniscus

50. Lateral spino-thalamic tract
(Pain & temperature pathways)
• Spinal lemniscus Pons Midbrain
Thalamus (here, crude pain & temperature
sensations are appreciated & emotional
reactions are initiated) From thalamus,
third-order neurons pass through the internal
capsule and the corona radiata to the
somesthetic area in the post-central gyrus of the
cerebral cortex

58. Sensory homunculus
• Contralateral half of the body is represented
in the cerebral cortex as inverted
• Hand & mouth situated inferiorly
• Leg situated superiorly
• Foot and anogenital region on the medial
surface of cerebral hemisphere

60. Homunculus
• The homunculus is a distorted picture of body,
with the various parts having a size
proportional to the area of cerebral cortex
devoted to their control

62. Anterior spinothalamic tract
(Light/Crude touch & pressure sensations)
• Receptors Axons (dorsal root
ganglion) Tip of the posterior gray
horn (Substantia gelatinosa) Divide
into ascending & descending branches (Tract
of Lissauer) Second-order neuron
cross obliquely to the opposite side in the
anterior gray & white commissures within
several spinal segments Ascend as
anterior spino-thalamic tract

63. Anterior spinothalamic tract
(Light/Crude touch & pressure sensations)
• Anterior spinothalamic tract (situated in the
opposite white antero-lateral column of the
spinal cord) Medulla oblongata (spinal
lemniscus) Pons Midbrain
Thalamus Third-order neuron from
thalamus through internal capsule & corona
radiata to the somesthetic area in the post-
central gyrus of the cerebral cortex (see sensory
homunculus)

65. Posterior white columns i.e. Fasciculus
Gracilis & Fasciculus Cuneatus
• These tracts are concerned with:
1. Discriminative touch i.e. for location & two-
point discrimination
2. Vibratory sense
3. Conscious muscle joint sense

66. Posterior white columns i.e. Fasciculus
Gracilis & Fasciculus Cuneatus
• Receptors Posterior root ganglion
Spinal cord Pass directly to the
posterior white column of the same side
Here, fibers divide to long ascending &
short descending branches Long
ascending fibers travel upward in the fasciculus
gracilis & fasciculus cuneatus

67. Fasciculi Gracilis & Cuneatus
• Fasciculus gracilis is present throughout the
length of spinal cord & contains the long
ascending fibers of the sacral, lumbar & lower
6 thoracic spinal nerves
• Fasciculus cuneatus is situated laterally in
upper thoracic & cervical segments of the
spinal cord. It contains the long ascending
fibers from upper six thoracic and all the
cervical spinal nerves

68. Fasciculi Gracilis & Cuneatus
• The fibers of both the fasciculi ascend
ipsilaterally terminate by synapsing on
the second-order neurons in the nuclei gracilis
& cuneatus of the medulla oblongata
• The axons of second-order neurons, called
internal arcuate fibers, cross the median
plane around the central gray matter,
decussating with the corresponding fibers of
the opposite side in the sensory decussation

69. Fasciculi Gracilis & Cuneatus
• From sensory decussation fibers
ascend as a single compact bundle, the medial
lemniscus, through the medulla oblongata,
pons and the midbrain Thalamus
Third-order neurons from thalamus to the
Internal capsule & Corona radiata
the somesthetic area of the post-central
gyrus of the cerebral cortex (see the sensory
homunculus)

70. Cuneo-cerebellar tract
• Many fibers of fasciculus cuneatus relay at
cuneate nucleus and and continue as second-
order neurons to enter the cerebellum
through inferior cerebellar peduncle
• This pathway is called cuneo-cerebellar tract
and the fibers are known as posterior external
arcuate fibers
• Their function is to convey information of
muscle joint sense to the cerebellum

71. Posterior spino-cerebellar tract
• This tract is the pathway of muscle joint sense to
the cerebellum
• First-order neuron Dorsal root ganglion
the spinal cord Enter the base of
posterior gray column Second-order
neurons, collectively known as nucleus dorsalis
(Clarke’s column) enter the lateral white column
on the same side and ascend as posterior spino-
cerebellar tract to the medulla oblongata
Inf. Cerebellar peduncle Cerebellar cortex

72. Nucleus dorsalis (Clarke’s column)
• Nucleus dorsalis (Clarke’s column) extends
only from C8 to L3-4 spinal segments
• Axons of lower lumbar & sacral segments
ascend in the posterior white column until
they reach the L3-4 segment, where they enter
the nucleus dorsalis

73. Posterior spino-cerebellar tract
• Posterior spino-cerebellar fibers receive the
muscle joint information from the:
1. Muscle spindles of the
2. Tendon organs trunk and
3. Joint receptors lower limbs
• This information of movement of muscles
and joints is used by the cerebellum in the
coordination of limb movements & the
maintenance of posture

74. Anterior spino-cerebellar tract
• First-order neurons Dorsal root ganglion Nucleus
dorsalis
i. (majority) cross to
the opposite side, ascend as
anterior spino-cerebellar tract
in the contralateral white column,
SECOND-ORDER enter the cerebellar cortex through sup.
NEURONS Cerebellar peduncle
ii. (minority) ascend as anterior
spino-cerebellar tract in the
lateral white column of the
same side, enter the cerebellar
cortex through sup. Cerebellar
peduncle

76. Spinotectal tract
• First-order neuron Dorsal root ganglion
Enter to the gray matter
Second-order neuron Cross the
median plane Ascend as spinotectal
tract in the antero-lateral white column
Medulla oblongata Pons
Midbrain (Superior colliculus)
• Provides afferent information for spino-visual
reflexes & brings about movements of the
eyes & head toward the source of stimulation

77. Spinoreticular tract
• First-order neuron Dorsal root ganglion
Enter to the gray matter Second-
order neuron Ascend as spinoreticular
tract in the lateral white column (Most of the
fibers are uncrossed) Terminate in the
reticular formation of medulla oblongata, pons &
midbrain
• This tract influences in the level of consciousness

78. Spino-olivary tract
• First-order neuron Dorsal root ganglion
Enter to the gray matter
Second-order neuron (cross the midline)
Ascend as spino-olivary tract in the antero-
lateral white column Terminate in the
inferior olivary nuclei of medulla oblongata
Third-order neurons cross the midline
Enter the cerebellum through inferior
cerebellar peduncle
• This tract conveys information to the cerebellum
from cutaneous & proprioceptive organs

79. Visceral sensory tracts
• Sensations arise in the viscera of thorax &
abdomen First-order neurons enter
the spinal cord through the posterior root (cell
bodies located in dorsal root ganglia)
Relay with second-order neurons in lateral
horn Join the spinothalamic tracts
Relay with third-order neurons in thalamus
Finally end at post-central gyrus
• Carry pain & stretch sensations

80. THE END