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Neuro > Descending Tracts > Flashcards

Descending Tracts Flashcards

1
Q

What are the types of descending pathways

A

Pyramidal:
Corticospinal
Corticobulbar

Extra-pyramidal: 
Tectospinal
Reticulospinal
Vestibulospinal 
Rubrospinal
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2
Q

What is the pyramidal pathway

A

Descending motor pathway from cortex to spinal cord

Involved in voluntary control of muscles of face and body

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3
Q

What is corona radiata

A

White matter region containing ascending and descending axons travelling to/from cortex

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4
Q

What is internal capsule

A

White matter region located between 2 areas of grey matter, Thalamus and lentiform nucleus

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5
Q

Describe the structure of internal capsule

A

It is divided into genu, anterior limb and posterior limb
Genu contains corticobulbar axons to the face
Posterior limb contains corticospinal axons to body; UL, Trunk, LL fibres as you go posteriorly

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6
Q

Why are corticospinal and corticobulbar tracts called “pyramidal” tracts

A

Axons pass through medullary pyramids

Medullary pyramids are paired ventral swellings in medulla, between anterior median fissure and Ventrolateral sulcus

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7
Q

Describe the corticospinal pathway

A
  1. UMN arises from primary motor cortex in pre-central gyrus
  2. Fibres descend from cortex to internal capsule through corona radiata
  3. Fibres pass through internal capsule: CST fibres in posterior limb, CBT fibres in genu
  4. Fibres enter cerebral peduncles of midbrain
  5. Fibres descend into medullary pyramids
  6. 90% Fibres decussate at pyramids: ventral to lateral to form lateral CST. 10% fibres do not decussate to form ventral CST.
  7. Fibres descend in spinal cord
  8. LCST terminate at ipsilateral lamina IX by synapsing with LMN.
    VCST decussate at spinal level then synapse with LMN at contralateral lamina IX
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8
Q

What is the role of corticospinal tract

A

Voluntary control of muscles of body
Lateral cst: precise control of distal limb musculature
Ventral cst: coarse control of trunk musculature

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9
Q

Describe the corticobulbar tract

A
  1. UMNs arise from PMC of pre-central gyrus
  2. UMNs descend from cortex to internal capsule through corona radiata
  3. UMNs enter genu of internal capsule
  4. UMNs enter cerebral peduncles of midbrain
  5. UMNs descend into medullary pyramids
  6. UMNs decussate at brainstem
  7. UMNs terminate at cranial nerve motor nuclei to synapse with LMN. UMNs synapse bilaterally: synapse with contralateral and ipsilateral CN motor nuclei.
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10
Q

How might UMNL of facial nerve present

How does this differ from LMNL of facial nerve

A

Facial paralysis on contralateral side
With forehead sparing

You do not get forehead sparing in LMNL of facial nerve

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11
Q

Why do you get forehead sparing in UMNL of facial nerve

A

CN VII motor nuclei is divided into upper and lower parts, supplying upper and lower facial muscles
Upper half receives bilateral UMN innervation
Lower half receives contralateral UMN innervation only
UMNL will lead to complete de-innervation of lower half of contralateral nuclei, while sparing of upper half by ipsilateral UMN

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12
Q

What type of stroke can cause UMNL of facial nerve

A

Lacunar infarct of genu

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13
Q

What is a lacunar infarct

A

Ischaemic stroke due to occlusion of lenticulostriate arteries

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14
Q

What structures do lenticulostriate arteries supply

A

Internal capsule

Putamen

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15
Q

How might a lacunar infarct present

A

If posterior limb affected: pure motor stroke/hemiparaesis

If genu affected: dysarthria, Contralateral facial paralysis with forehead sparing

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16
Q

What are extra pyramidal tracts

A

Descending tracts that arise from brainstem

Involved in involuntary and automatic control of musculature: tone, posture, balance, locomotion

17
Q

Which extrapyramidal tracts decussate and which do not

A

Decussate:
Rubrospinal
Tectospinal

Do not decussate:
Vestibulospinal
Reticulospinal

18
Q

Describe the tectospinal tract

A

UMNs arise from tectum of midbrain:
Superior colliculi (receives input from optic nerves)
Inferior colliculi (receives auditory input)
UMNs descend into spinal cord
Synapse with LMNs in ventral horn of cervical and thoracic levels

19
Q

What is the role of tectospinal tract

A

Involuntary automatic movement of head in response to visual/auditory stimulus

20
Q

Describe the vestibulospinal tract

A
  1. UMNs arise from vestibular nuclei in medulla (input from organs of balance)
  2. UMNs descend ipsilaterally in spinal cord
  3. UMNs synapse with LMNs innervating anti-gravity muscles (arm flexors, leg extensors)
21
Q

What is the role of vestibulospinal tract

A

Automatic control of balance: increase tone of appropriate anti-gravity muscles to maintain centre of gravity between feet

22
Q

Describe the reticulospinal tract

A
  1. UMNs arise from reticular formation in pons and medulla
  2. Pontine reticulospinal tract descends in anterior funiculus, medullary reticulospinal tract in lateral funiculus
  3. UMNs synapse with LMNs of trunk and proximal limb musculature
23
Q

What is the role of reticulospinal tract

A

Locomotion: coordinating rhythmic movements of all four limbs on walking
Posture: position held between movements

24
Q

Describe the rubrospinal tract

A
  1. UMNs arise from red nuclei in midbrain
  2. Descend in spinal cord
  3. Synapse with LMNs in cervical level
25
Q

What is the role of rubrospinal tract

A

Large and fine movement of upper limb musculature

Rudimentary in humans

Neuro (18 decks)

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