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DESCENDING TRACTS OF
SPINAL CORD
DR SANA YASEEN
ANATOMY DEPARTMENT
KIMS
TRACTS
DESCENDING PATHWAYS
PYRAMIDAL TRACT
1. CORTICOSPINAL TRACT
• Lateral corticospinal tract
• Anterior corticospinal tract
2. CORTICOBULBAR TRACT
EXTRA PYRAMIDAL TRACT
1. RETICULOSPINAL TRACT
2. TECTOSPINAL TRACT
3. RUBROSPINAL TRACT
ANATOMICAL
ORGANIZATION
1. 1ST ORDER NEURON upper motor
neuron
(cell body in cerebral cortex)
1. 2ND ORDER NEURON internunical
neuron (situated in anterior gray column
of spinal cord & has short axon)
2. 3rd ORDER NEURON lower motor
neuron
Axon of 3rd -order neuron innervates skeletal
muscle through anterior root and spinal nerve
(situated in anterior gray column of spinal
cord)
CORTICOSPINAL TRACTS
Descending motor commands:
 FIRST ORDER NEURON : Upper motor neuron
 Cell body in primary motor cortex
 Premotor area ,supplementary motor area
 Axon descends through
 internal capsule
• Here, fibers are organized so that
those closest to genu are concerned
with cervical portions while those
situated posteriorly are concerned
with lower extremity.
• Stimulation of different part of precentral gyrus produces
movement of different part of opposite side of body it can
also be presented as HOMUNCULUS.
• HOMUNCULUS:
is distorted picture of body
with various part having a size
proportional to area of
cerebral cortex to their
control
Descending tracts of sc
In MID BRAIN: passes through in mid 3/5 of the
cruscerebri.
Pon: the tract broke down and forms many bundles. Few
fibers synapse here in pons while others continues going
down into medulla.
In medulla oblongata, the bundles become grouped
together anteriorly to form a swelling known as the
PYRAMID
(the alternative name, PYRAMIDAL TRACT)
• 80-90 % fibers crosses the midline (decussate) to form
the lateral corticospinal tract OR
• 10-20 % fibers doesn’t cross and form the anterior
corticospinal tract (probably cross right before
synapsing)
Descending tracts of sc
Descending tracts of sc
SECOND ORDER NEURON : Lower motor neuron
Cell body in anterior horn of spinal cord
• Anterior cortical spinal tract: seen in cervical and upper thoracic region
• Lateral corticospinal tract is seen along entire length of spinal cord
Descending tracts of sc
CORTICOBULBAR
TRACT/ corticonuclear
• The corticobulbar tracts arise from the
lateral aspect of the primary motor
cortex. They recieve the same inputs as
the corticospinal tracts. The fiber
converge and pass through the internal
capsule to the brain stem.
• The neurons terminate on the motor
nuclei of the cranial nerves. Here they
synapse with lower motor neurons,
which carry the motor signal to the
muscles of the face and neck
EXTRAPYRAMIDAL TRACTS
• The extrapyramidal tracts originate in the brain stem, carries motor fibers to the
spinal cord
• They are responsible for the in voluntary movement and autonomic control of all
the musculature , such as mucle tone, balance posture and locomotion.
• There are four tracts in total.
The vestibulospinal, reticulospinal : donot decussate and provide ipsilateral
innervation
Rubrospinal and tecto spinal: do decussate and provide contralateral innervation
Descending tracts of sc
OTHER DESCENDING PATHWAYS
Vestibulospinal tracts: concerned with balance.
Tectospinal pathway: provides postural responses to visual
stimuli
Rubrospinal and Olivospinal pathways modulate motor
activity
Corticobulbar pathways carry information from the cerebral
cortex to the motor cranial nerve nuclei.
Descending tracts of sc
Descending tracts of sc
Descending tracts of sc
Descending tracts of sc
AUTONOMIC FIBERS
• Higher centers of ANS are located in cerebral cortex, hypothalamus, amygdaloid
complex andd reticular formation.
• The fibers arising from these centers runs down and crosses in the brain stem.
• They run as lateral white column of spinal cord and terminate by synapsing in
the lateral grey horn of the spinal cord lovcated in thoracic and upper lumbar
spinal segments(sympathetic) And sacral segments (para sympathetic)
Clinical Considerations: UMN vs. LMN loss
• upper motor neurons (UMN) refers to the corticospinal tracts as
they descend (before synapse in anterior horn)
• lower motor neurons (LMN) refers to the neurons that have their
cell bodies in the anterior horn and send their axons out to the
muscles
• Loss of UMN vs. LMN gives very different clinical symptoms
Clinical Considerations: Upper motor neuron lesions
• Severe paralysis: no muscle atrophy
• Spasticity: an increase in muscle tone with an associated inability
to voluntarily control the muscle
• Hyper-reflexia: hyperactive reflexes
• Clonus: a sustained series of rhythmic jerks in a muscle
• Clasp Knife rigidity : Resistance due to spasticity of muscles
• Babinski Sign: stroking the bottom of the foot results in up-going
toe
• Limited and delayed muscle atrophy
• Unchanged conduction velocity in peripheral nerve
Clinical Considerations: Lower motor neuron lesions
• Flaccidity :
• Hypo-reflexia: diminished or absent reflexes
• Muscle atrophy (wasting) due to lack of innervation
• Conduction velocity in peripheral nerve reduced or absent
• Loss of reflexes : muscles supplied
• Muscle fasiculations : slow destruction of lower motor neuron
Descending tracts of sc
Spinal cord injury
 Spinal shock, which takes place for first 24 hours (can last longer) after injury, leads to:
 sensory impairment
 flaccid paralysis
 depressed spinal reflexes
 can cause severe hypotension (if lesion at high level)
 Transection: complete severing of spinal cord.
 Contusion: crushing of the spinal cord.
 Complete transection of the cord leads to:
 Bilateral loss of all sensation below the level of the lesion
 Bilateral loss of voluntary movement below the level of the lesion
 bilateral LMN (flaccid) paralysis in segment of the lesion
 bilateral spastic paralysis below lesion
 Bilateral Babinski sign
 loss of control of bladder and bowel function
Hemitransection: Brown-Sequard
Syndrome
• Loss of these 3 major pathways:
• ipsilateral lateral corticospinal tract
• loss of motor control; spasticity
ipsilateral below lesion
• ipsilateral flaccidity at level of lesion
• ipsilateral posterior column
• ipsilateral loss of discriminative touch,
vibration and proprioception
• spinothalamic tract carrying
information from contralateral side
• loss of pain and temperature sensation
from contralateral side below level of
lesion
• bilateral loss of pain and temperature
sensation at level of lesion
Spinal Cord Infections
• Poliomyelitis
• infection of cell bodies in
anterior horn (LMN loss)
• in severe polio, problems with
respiration due to paralysis of
diaphragm and intercostal
muscles
• Tabes dorsalis
• late stages of neurosyphilis
• posterior column damage
• also damage to spinal nerve
roots
Degenerative disorders of the spinal cord
 Amyotrophic Lateral Sclerosis
(ALS):
 Chronic progressive disease of corticospinal tracts and
neurons of anterior gray horn
 Multiple Sclerosis (MS):
 Demyelination of ascending and descending tracts
 Weakness of limbs
 Ataxia
 Syringomyelia :
 Tubel ike enlargement of central canal, expands and
destroys surrounding tissue
 most often affects cervical and upper thoracic levels
“
”

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Descending tracts of sc

  • 1. DESCENDING TRACTS OF SPINAL CORD DR SANA YASEEN ANATOMY DEPARTMENT KIMS
  • 3. DESCENDING PATHWAYS PYRAMIDAL TRACT 1. CORTICOSPINAL TRACT • Lateral corticospinal tract • Anterior corticospinal tract 2. CORTICOBULBAR TRACT EXTRA PYRAMIDAL TRACT 1. RETICULOSPINAL TRACT 2. TECTOSPINAL TRACT 3. RUBROSPINAL TRACT
  • 4. ANATOMICAL ORGANIZATION 1. 1ST ORDER NEURON upper motor neuron (cell body in cerebral cortex) 1. 2ND ORDER NEURON internunical neuron (situated in anterior gray column of spinal cord & has short axon) 2. 3rd ORDER NEURON lower motor neuron Axon of 3rd -order neuron innervates skeletal muscle through anterior root and spinal nerve (situated in anterior gray column of spinal cord)
  • 5. CORTICOSPINAL TRACTS Descending motor commands:  FIRST ORDER NEURON : Upper motor neuron  Cell body in primary motor cortex  Premotor area ,supplementary motor area  Axon descends through  internal capsule • Here, fibers are organized so that those closest to genu are concerned with cervical portions while those situated posteriorly are concerned with lower extremity.
  • 6. • Stimulation of different part of precentral gyrus produces movement of different part of opposite side of body it can also be presented as HOMUNCULUS. • HOMUNCULUS: is distorted picture of body with various part having a size proportional to area of cerebral cortex to their control
  • 8. In MID BRAIN: passes through in mid 3/5 of the cruscerebri. Pon: the tract broke down and forms many bundles. Few fibers synapse here in pons while others continues going down into medulla. In medulla oblongata, the bundles become grouped together anteriorly to form a swelling known as the PYRAMID (the alternative name, PYRAMIDAL TRACT) • 80-90 % fibers crosses the midline (decussate) to form the lateral corticospinal tract OR • 10-20 % fibers doesn’t cross and form the anterior corticospinal tract (probably cross right before synapsing)
  • 11. SECOND ORDER NEURON : Lower motor neuron Cell body in anterior horn of spinal cord • Anterior cortical spinal tract: seen in cervical and upper thoracic region • Lateral corticospinal tract is seen along entire length of spinal cord
  • 13. CORTICOBULBAR TRACT/ corticonuclear • The corticobulbar tracts arise from the lateral aspect of the primary motor cortex. They recieve the same inputs as the corticospinal tracts. The fiber converge and pass through the internal capsule to the brain stem. • The neurons terminate on the motor nuclei of the cranial nerves. Here they synapse with lower motor neurons, which carry the motor signal to the muscles of the face and neck
  • 14. EXTRAPYRAMIDAL TRACTS • The extrapyramidal tracts originate in the brain stem, carries motor fibers to the spinal cord • They are responsible for the in voluntary movement and autonomic control of all the musculature , such as mucle tone, balance posture and locomotion. • There are four tracts in total. The vestibulospinal, reticulospinal : donot decussate and provide ipsilateral innervation Rubrospinal and tecto spinal: do decussate and provide contralateral innervation
  • 16. OTHER DESCENDING PATHWAYS Vestibulospinal tracts: concerned with balance. Tectospinal pathway: provides postural responses to visual stimuli Rubrospinal and Olivospinal pathways modulate motor activity Corticobulbar pathways carry information from the cerebral cortex to the motor cranial nerve nuclei.
  • 21. AUTONOMIC FIBERS • Higher centers of ANS are located in cerebral cortex, hypothalamus, amygdaloid complex andd reticular formation. • The fibers arising from these centers runs down and crosses in the brain stem. • They run as lateral white column of spinal cord and terminate by synapsing in the lateral grey horn of the spinal cord lovcated in thoracic and upper lumbar spinal segments(sympathetic) And sacral segments (para sympathetic)
  • 22. Clinical Considerations: UMN vs. LMN loss • upper motor neurons (UMN) refers to the corticospinal tracts as they descend (before synapse in anterior horn) • lower motor neurons (LMN) refers to the neurons that have their cell bodies in the anterior horn and send their axons out to the muscles • Loss of UMN vs. LMN gives very different clinical symptoms
  • 23. Clinical Considerations: Upper motor neuron lesions • Severe paralysis: no muscle atrophy • Spasticity: an increase in muscle tone with an associated inability to voluntarily control the muscle • Hyper-reflexia: hyperactive reflexes • Clonus: a sustained series of rhythmic jerks in a muscle • Clasp Knife rigidity : Resistance due to spasticity of muscles • Babinski Sign: stroking the bottom of the foot results in up-going toe • Limited and delayed muscle atrophy • Unchanged conduction velocity in peripheral nerve
  • 24. Clinical Considerations: Lower motor neuron lesions • Flaccidity : • Hypo-reflexia: diminished or absent reflexes • Muscle atrophy (wasting) due to lack of innervation • Conduction velocity in peripheral nerve reduced or absent • Loss of reflexes : muscles supplied • Muscle fasiculations : slow destruction of lower motor neuron
  • 26. Spinal cord injury  Spinal shock, which takes place for first 24 hours (can last longer) after injury, leads to:  sensory impairment  flaccid paralysis  depressed spinal reflexes  can cause severe hypotension (if lesion at high level)  Transection: complete severing of spinal cord.  Contusion: crushing of the spinal cord.  Complete transection of the cord leads to:  Bilateral loss of all sensation below the level of the lesion  Bilateral loss of voluntary movement below the level of the lesion  bilateral LMN (flaccid) paralysis in segment of the lesion  bilateral spastic paralysis below lesion  Bilateral Babinski sign  loss of control of bladder and bowel function
  • 27. Hemitransection: Brown-Sequard Syndrome • Loss of these 3 major pathways: • ipsilateral lateral corticospinal tract • loss of motor control; spasticity ipsilateral below lesion • ipsilateral flaccidity at level of lesion • ipsilateral posterior column • ipsilateral loss of discriminative touch, vibration and proprioception • spinothalamic tract carrying information from contralateral side • loss of pain and temperature sensation from contralateral side below level of lesion • bilateral loss of pain and temperature sensation at level of lesion
  • 28. Spinal Cord Infections • Poliomyelitis • infection of cell bodies in anterior horn (LMN loss) • in severe polio, problems with respiration due to paralysis of diaphragm and intercostal muscles • Tabes dorsalis • late stages of neurosyphilis • posterior column damage • also damage to spinal nerve roots
  • 29. Degenerative disorders of the spinal cord  Amyotrophic Lateral Sclerosis (ALS):  Chronic progressive disease of corticospinal tracts and neurons of anterior gray horn  Multiple Sclerosis (MS):  Demyelination of ascending and descending tracts  Weakness of limbs  Ataxia  Syringomyelia :  Tubel ike enlargement of central canal, expands and destroys surrounding tissue  most often affects cervical and upper thoracic levels