Anatomy of ascending and descending tracts apresentacao hpsc canoas

1. Ascending& Descending tracts
Aluno: Juan Zambon, med Ulbra
Prof.: Dr. Luiz “Lakka” Brasiliano e
Dr. Humberto “Shifu” Muller
Tema de casa da Neurocirurgia

2. contents
• function of nervous system in general
• sensory system overview
• spinal cord and nerve tracts
• ascending tracts
• organization in general
• ascending tracts
• functional components

3. nervous system
communication
receive information
transform it into impulses ( transduction )
transmit impulses to the CNS
correlate / coordinate
transmit impulses to the effector organs
response / action

4. CENTRAL NERVOUS SYSTEM
integration / processing / modulating
stimulus
receptor neurone
motor / descending tracts
effector organ / response
PNS
transmission
lower motor neurone
sensory / ascending tracts

5. Sensory system
• sensory information
• three basic information
 Exteroceptive information
 Interoceptive information
 Proprioceptive information

6. sensory information
are received and carried by ascending tracts
• exteroceptive sensation
origin:- outside the body
e.g. temp, touch, light, sound, chemicals, mechanical
receptors:- surface layer of skin, mucosa
• proprioceptive sensation
origin:- within the body
e.g. muscles, joints, tendons
receptors – deeper layer of skin, tendons, joints, GTO, muscle
spindles, ligaments

7. information
• conscious sensation
• reach the cerebral cortex
• unconscious sensation
• reach to the areas other than cortex

11. Dura mater
• Dense, strong fibrous membrane
• Encloses the spinal cord & cauda equina
• Continuous above with meningeal layer of dura covering the brain
• Ends at the level of S2
• Separated from wall of vertebral canal by the extradural space
• Contains loose areolar tissue & internal vertebral venous space

13. Arachnoid mater
• Delicate impermeable membrane
• Lies between pia and dura mater
• Separated from pia mater by subarachnoid space
• Continuous above with arachnoid mater covering the brain
• Ends on filum terminale at level of S2

14. Pia mater
• Vascular membrane
• Closely covers spinal cord
• Thickened on either side between nerve roots to form the
ligamentum denticulatum

15. Blood supply
Arteries of the spinal cord
• Anterior spinal artery
• Posterior spinal artery
• Segmental spinal arteries

17. Anterior spinal artery
• Formed by the union of 2 arteries
• From vertebral artery
• Supply anterior ⅔ of spinal cord
Posterior spinal arteries
• Arise from vertebral artery or posterior inferior cerebellar arteries
(PICA)
• Descend close to the posterior roots
• Supply posterior ⅓ of spinal cord
• The area between C1-T2 and T9 are well supplied.
• The area between T3-T8 is poorly irrigated, wich makes this place
prone to ischaemia

20. Segmental spinal arteries
• Branches of arteries outside the vertebral column
• Gives off the anterior & posterior radicular arteries
• Great anterior medullary artery of Adamkiewicz
• Arise from lateral intercostal artery or lumbar artery at any level
from T8 – L3

25. nerve fibres
• enter the spinal cord through posterior nerve root
• after entering the spinal cord
sorted out and segregated into nerve bundles, tracts
( origin, function, termination )

26. ascending tracts
bundles of nerve fibres
linking
spinal cord with higher centres of the brain
convey information
from
soma / viscera to higher level of neuraxis

27. ascendingsensorypathway are
organizedin
three neuronalchain
-Firstorderneurone
-Secondorderneurone
-Thirdorderneurone

28. First order neurone
• cell body in posterior root ganglion
• peripheral process connects with sensory receptor
ending
• central process enter the spinal cord through the
posterior root
• synapse with second order neuron in spinal gray
matter

29. dorsal root
dorsal root
ganglion
spinal
nervedorsal
horn
FIRST ORDER NEURON

30. Second order neurone
• cell body in posterior gray column of spinal cord
• axon crosses the midline ( decussate )
• ascend & synapse with third order neuron in VPL
nucleus of thalamus

31. SECOND ORDER NEURON
• cross the mid line
• in front of central canal
VPL
1st
2nd

32. Third order neurone
• cell body in the thalamus
• give rise to projection fibres to the cerebral cortex,
postcentral gyrus ( sensory area )

33. ascending sensory pathway
( in general form )
from sensory endings
to
cerebral cortex
( note the three neurons chain )

35. Tracts & their functional components
• lateral spinothalamic tract
• pain, temperature
• anterior spinothalamic tract
• touch, pressure

36. • posterior white column
• conscious proprioceptive sense, discriminative touch, vibratory
sense
• spinocerebellar tract / cuneocerebellar tract
• unconscious information from muscle, joints, skin, subcutaneous
tissues

37. sensation receptors pathways destination
Pain and temperature Free nerve endings Lateral STT
Spinal lemniscus
Postcentral
gyrus
Light touch and pressure Free nerve endings Anterior STT
Spinal lemniscus
Postcentral
gyrus
Discriminative touch,
vibratory sense,
conscious muscle joint sense
Meissner’s corpuscle,
pacinian corpuscles,
muscle spindles,
tendon organs
Fasciculus gracilis and cuneatus
Medial lemniscus
Postcentral
gyrus
Main somatosensory pathways

38. Lateral spinothalamic tract
pain and thermal impulses
( input from free nerve endings, thermal receptors )
• transmitted to spinal cord in delta A and C fibres
• central process enters the spinal cord through posterior
nerve root, proceed to the tip of the dorsal gray column

39. • the central process of 1st order neuron
synapse with cell body of 2nd order neuron
in substantia gelatinosa of posterior gray column of
the spinal cord

40. • the axon of 2nd order neuron
cross to the opposite side
in the anterior gray and white commissure and
ascend in contralateral white column as lateral
spinothalamic tract
• end by synapsing with 3rd order neuron in the
ventral posterolateral nucleus of thalamus

41. • axon of the 3rd order neuron passes through the
posterior limb of internal capsule and corona
radiata to reach the postcentral gyrus of cerebral
cortex ( area 3, 1 and 2 )

42. pain and temperature pathways

43. Clinical application
destruction of LSTT
• loss of
• pain and thermal sensation
• on the contralateral side
• below the level of the lesion
patient will not
respond to pinprick
recognize hot and cold

44. Anterior spinothalamic tract
light touch and pressure impulses
( input from free nerve endings, Merkel’s tactile disks )
• First order neuron
• dorsal root ganglion( all level )
• Second order neuron
• in the dorsal horn, cross to the opposite side (decussate)
• ascend in the contralateral ventral column as ASTT
• end in VPL nucleus of thalamus
• Third order neuron
• in the VPL nucleus of thalamus
• project to cerebral cortex ( area 3, 1 and 2 )

45. touch and pressure pathways

46. Clinical application
destruction of ASTT
loss of touch and pressure sense
• below the level of lesion
• on the contralateral side of the body

47. Fasciculus gracilis and fasciculus cuneatus
discriminative touch, vibratory sense and conscious
muscle joint sense
( inputs from pacinian corpuscles, Messiner’s corpuscles,
joint receptors, muscle spindles and Golgi tendon organs )
• axon of 1st order neuron enter the spinal cord
• passes directly to the posterior white column of the
same side ( without synapsing )

48. • long ascending fibres travel upward in the posterior
column of the same side as fasciculus gracilis and
fasciculus cuneatus
• ( FG – carrying fibres from lower thoracic, lumbar and sacral regions /
including lower limbs )
• ( FC - only in thoracic and cervical segments / including upper limb fibres )
• synapse on the 2nd order neuron in the nucleus
gracilis and cuneatus of medulla oblongata of the
same side.

49. lower 6 thoracic segments
lumbar segments
sacral segments
cervical segments
upper 6 thoracic segments
fasciculus gracilis
fasciculus cuneatus
[ nucleus G & C ]
in medulla
G
C

50. • axons of 2nd order neuron
“ internal arcuate fibres ” cross the
median plane
( sensory decussation )
• ascend as medial lemniscus
through medulla oblongata, pons, and
midbrain
• synapse on the 3rd order neuron in
ventral posteriolateral nucleus of
thalamus
• axon of 3rd order neuron leaves and
passes through the internal capsule,
corona radiata to reach the postcentral
gyrus of cerebral cortex area 3, 1 and 2 )

51. pathways for
conscious proprioception
discriminative touch
vibratory sense

52. Clinical application
destruction of
fasciculus gracilia and cuneatus
• loss of muscle joint sense,
position sense, vibration sense
and tactile discrimination
• on the same side
• below the level of the lesion
(extremely rare to have a lesion of the spinal cord to
be localized as to affect one sensory tract only )

53. Posterior & anterior spinocerebellar tract
• transmit unconscious proprioceptive information to
the cerebellum
• receive input from muscle spindles, GTOs and
pressure receptors
• involved in coordination of posture and movement of
individual muscles of the lower limb

54. First order neuron
• in dorsal root ganglion
• axons end in nucleus dorsalis of Clarke
Second order neuron
• cell body in nucleus dorsalis of Clarke
• give rise to axons ascending to the cerebellum of the same
side
( anterior – crossed & uncrossed fibres / posterior – uncrossed fibres)

55. muscle joint sense pathways to cerebellum

56. • Spinotectal tract
• passes pain, thermal, tactile information to superior colliculus for
spinovisual reflexes
• cross the median plane
• synapse in the superior colliculus
• integrate visual and somatic sensory information ( it
brings about the movement of eye and head towards the
source of information )
• Spinoreticular tract
• uncrossed fibres, synapse with neurones of reticular formation
(important role in influencing level
of consciousness)
• Spino-olivary tract

57. spinotectal tract
spinoreticular tract
spino-oloivary tract

58. clinical application
• relief of pain
posterior rhizotomy (posterior root)
cordotomy (lateral STT)
• Injury
hemisection of spinal cord
• diseases
tabes dorsalis / syringomyelia / vascular

59. Hemisection of the spinal cord
( Brown Sequard’s syndrome )
• Dorsal column damage
• Lateral column damage
• Anterolateral column damage
• Damage to local cord segment and nerve roots

60. spinal cord hemisection

61. below the level of lesion
on the side of lesion
lateral column damage
• UMNL
dorsal column damage
• loss of position sense
• loss of vibratory sense
• loss of tactile discrimination
anterolateral system damage
• loss of sensation of pain and
temperature on the side opposite
the lesion
local segment
side of lesion
Dorsal Root
• irritate
• destruction
Ventral root
• flaccid paralysis

62. Lesions of central gray matter
• seen in syringomyelia ( progressive cavitation around or near the
central canal of spinal cord especially in cervical segments )
• interrupt fibres of lateral spinothalamic tract that passes in
front of the central canal
• loss of pain and temperature sensibility on both sides (
proprioception and light touch is spared )
sensory dissociation

64. Posterior root lesions
seen in tabes dorsalis ( neurosyphilis )
• bilateral degeneration of posterior root and posterior
funiculus ( particularly in lower segments of spinal cord )
Clinically
Initial stage
• Irritation - paraesthesia
• Intermittant of attack of sharp pain
Later
• decreased sensitivity to pain
• loss of muscle stretch reflexes
• loss of position sense, posture senses
• positive Romberg sign ( visual compensation )
• walk with legs apart, high stepping gait

65. blood supply of spinal cord
 Anterior spinal artery
 Posterior spinal arteries
 Segmental spinal arteries
- radicular arteries
 Feeder arteries
- Adamkiewicz

66. posterior 3rd of spinal cord
dorsal column
penetrating branches
• anterior and part of gray matter
circumferential branches
• anterior white matter

67. dorsal 1/3rd resulting from occlusion of the posterior spinal artery
ventral 2/3rd resulting from occlusion of the anterior spinal artery

68. Descending tracts
• define the tract
• enumerate the tracts according to their
functional components
• apply their knowledge of anatomy to correlate
with the clinical condition in relation to the injury
to these tracts

69. Motor system
areas of the nervous system that are responsible for
controlling movements

70. cerebellum
premotor cortex motor cortex
motor unit
muscle spindle
pyramidal tract
sp cd internreurons &
central pattern generator
extrapyramidal tracts
premotor cortex SMA PMC basal ganglia
cortical
sensory area
MOTOR SYSTEM
I
II
III
IV
V

71. Level I
• initiation, planning, programming of movements
• in response to desire to move
( probably originate in the limbic system and posterior parietal cortex )
• desire is translated into movements
( basal ganglia and their cortical projections in the frontal lobe-SMA, PMC )
Level II
• coordination of movements
• cerebellum
( compare the intended movement / actual movement )

72. Level III
• descending pathways
• pyramidal tract - CoSt
• originates in the motor, premotor and somatosensory corticies
• synapse direclty on MN , IN
• extrapyramidal tract – VeSt, ReSt, TeSt, RuSt
• originate from subcortical structures
• receive inputs from motor cortex
• complex distribution, synapse on MN, IN

73. Level IV
• motor organization in spinal cord
• alpha & gamma neurons
• Renshaw’s cells
• interneurons / CPGs
• descending tracts
• CoSt, RuSt
distal musculature – fine skilled movement
• VeSt- ReSt- TeSt
axial, proximal musculature – balance, posture
Level V
• final common pathway

74. primary structure
responsible for translating
desire into a movement is
the basal ganglia

75. Introduction
• brain exerts powerful and subtle influences upon the
activity of the voluntary musculature (
modulate, regulate, bias the activities of LMN )
• through the descending pathways

76. descending tracts
• segregated bundles of nerve fibres in the white
matter of the spinal cord descending from the
supraspinal centres
referred to as upper motor neurons ( UMN )
• are concerned with somatic and visceral motor
activity
• cells of origin lie in cerebral cortex and brain stem
• regulate the LMN activity

77. motor homunculus
cerebral cortex

78. lower motor neurons ( LMN )
motor neurons that innervate the voluntary muscles
• in anterior gray column of spinal cord /
• motor nuclei of brainstem
• innervate skeletal muscles
form final common pathway
LMN

79. LMN
constantly bombarded by
• nerve impulses( excitatory or inhibitory )
that descend from cerebral cortex,
pons,
midbrain and
medulla
• sensory inputs from the posterior root

80. upper motor neurons ( UMN )
• the descending supraspinal pathways that influence
the activity of the LMN
e.g. CoSt, CoBt, RuSt, TeSt, ReSt, VeSt

81. UMN
• control voluntary motor activity
• maintenance of posture & equilibrium
• control of muscle tone and reflex activity
generally exerts their effect
• on groups of muscles ( not on one specific muscle )
• reciprocally on agonist and antagonist muscle group

82. cerebral cortex – midbrain - pons - medulla oblongata
descending tracts
LMN
sensory inputs

84. Corticospinal tract
• arises from the pyramidal cells of cerebral cortex
• fibres travel through
• corona radiata
• posterior limb of the internal capsule
• cerebral peduncle ( middle 3/ 5th )
• pons
• medulla oblongata ( passed through the pyramids )

85. • at the caudal part of medulla oblongata
• most of the fibres 90 % cross the mid line (motor
decussation)
• descend in the lateral column as LCST
• terminate on LMN of anterior gray column at all spinal level
• remaining uncrossed fibres descend as ACST
• eventually fibres cross the mid line and terminate on LMN
of anterior gray column of respective spinal cord segments

86. motor decussation
medulla oblongata

87. corticospinal tract
for fine skilled movements

88. Rubrospinal tract
• nerve cells in red nucleus
( tegmentum of midbrain at the level of superior colliculus )
• nerve fibres / axons
• cross the mid line
• descend as rubrospinal tract
• through pons and medulla oblongata
• terminate anterior gray column of spinal cord
( facilitate the activity of flexor muscles )

90. Tectospinal tract
• nerve cells in superior colliculus of the
midbrain
• nerve fibres/ axons
• cross the mid line
• descend close to medial longitudinal
fasciculus
• terminate in the anterior gray column
of upper cervical segments of spinal
cord
( responsible for reflex movement of
head & neck in response to visual stimuli )

92. Vestibulospinal tract
• nerve cells in vestibular nucleus (in
the pons and medulla oblongata
• received afferents from inner ear and
cerebellum
• axons descend uncrossed
• through medulla and through the
length of spinal cord
• synapse with neuron in the anterior gray
column of the spinal cord
( balance by facilitate the activity of the
extensor muscles )

94. Reticulospinal tract
• nerve cells in reticular formation
• fibres pass through
• midbrain, pons, and medulla oblongata
• end at the anterior gray column of spinal cord
• control activity of motor neurons
(influence voluntary movement and reflex activity )

95. reticulospinal tract

96. clinical application
• pyramidal tract
refer to corticospinal tracts
• extrapyramidal tract
other than corticospinal tract
( VeSt, ReSt, TeSt, RuSt )

97. upper motor neuron lesion
• Babinski sign ( extensor plantar response )
• Superficial abdominal reflexes ( absent )
• Cremasteric reflex ( absent )
• Loss of performance of fine skilled voluntary movement

98. lower motor neuron lesion
• flaccid paralysis
• atrophy of muscles
• loss of reflexes
• muscular fasciculation
• muscular contracture

99. extrapyramidal tract lesions
• severe paralysis with little or no atrophy
• spasticity or hypertonicity
• exaggeration of deep muscular reflexes and clonus
• clasp-knife reaction

100. These motor pathways are complex and
multisynaptic, and regulate:
• Axial muscles that maintain balance and
posture
• Muscles controlling coarse movements of
the proximal portions of limbs
• Head, neck, and eye movement

101. dorsal column
lateral STT
anterior STT
pyramidal tracts
extrapyramidal tracts
nerve roots

102. spinal cord hemisection

103. Próximo tema
•Aspectos anatômicos das
Mielopatias

104. Obrigado!

105. Biblio
• Ascending& Descending tracts Lecture. Dr. Israa M. Sulaiman,
Department of Anatomy, IMS/MSU
• Neurologia de Netter, 2º ed. H.Royden Jones, Jr
• Clinical Neuroanatomy by Richard S. Snell
• Neuroanatomia Funcional. Leão Henrique Záquia. Canoas,
2012
• Gray's Anatomy, 40th Edition. Susan Standring. ISBN-
9780443066849, Printbook , Release Date: 2008