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CM - Control > L12 - descending motor pathways > Flashcards

L12 - descending motor pathways Flashcards

1
Q

what is the function of a upper motor neuron?

A

• Influence LMN activity
• Modify local reflex activity
• Superimpose more complex patterns of
movement

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2
Q

where does a upper motor neuron originate?

A

• Originate in the cerebrum & subcortical

structures

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3
Q

what is the function of a lower motor neuron?

A
  • axons supply a specific muscle
  • Peripheral nerves to motor end
    plates/neuromuscular junctions
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4
Q

where does a lower motor neuron originate?

A

Originate from the brain stem & spinal cord (

Ventral grey horn)

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5
Q

where in the spinal cord does a lower motor neuron originate?

A

ventral grey horn

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6
Q

what are the 3 descending motor pathways?

A

corticospinal

corticonuclear

extrapyramidal

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7
Q

which descending motor pathway can modify but not initiate movement?

A

extrapyramidal

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8
Q

which descending pathway does not start in the cortex?

A

extrapyramidal

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9
Q

which descending pathway plans and executes movement?

A

corticospinal (controls muscles of the body)

corticonuclear (controls movements of the head and neck)

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10
Q

which descending pathway controls movements of the head and neck?

A

corticonuclear

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11
Q

which descending pathway controls movements of the body?

A

corticospinal

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12
Q

briefly describe a descending motor pathway

A
  1. cerebral cortex (pre-central gyrus)
  2. posterior limb of
    the internal capsule
  3. brainstem (corticonuclea) or spinal cord (corticospinal)

( Fibres descend through cerebral peduncle of midbrain, ventral pons
and pyramids of medulla)

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13
Q

descending motor pathways are somatotopically organised, if you were to move your leg where would this project in the cortex?

A

more medially

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14
Q

descending motor pathways are somatotopically organised, if you were to move your face where would this project in the cortex?

A

more laterally

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15
Q

how are the descending fibers somatotopically organised as they pass through the internal capsule?

A

anterior

  • face
  • arm
  • trunk
  • leg

posterior

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16
Q

where will you find descending motor fibres in the brainstem?

A
  • cerebral peduncles
  • ventral pons
  • pyramids of medulla
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17
Q

corticonuclear fibres decussate at the pyramids of the medulla true or false?

A

false

  • only corticospinal tract
  • corticonuclear tract already ended further up the brainstem
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18
Q

do corticospinal tracts descend down the spinal cord ipsilaterally or contralaterally?

A

15% of UMNs descend Closed cord ipsilaterally ( Medulla
anterior corticospinal tract)
- bilateral innervation

Approx. 85% fibres cross at decussation of pyramids, then enter lateral corticospinal tract - Contralateral innervation

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19
Q

Where do all UMNs contact cell bodies of LMNs?

A

in contralateral ventral grey horn

NB: 2nd order neurons (LMNs) leave spinal cord as ventral rootlets to form spinal
nerve

20
Q

what are some causes of LMN lesions?

A

peripheral nerve injury (crush or cut)

poliomyelitis

21
Q

what is the clinical presentation of a LMN?

A

Diminished (hyporeflexia) or absent (
areflexia) tendon reflexes at level of
lesion (= Flaccid paralysis)

  • muscle wasting/atrophy
  • muscle weakness/reduced power
  • hypotonia
  • Fasciculation/fibrillation
22
Q

what is hyporeflexia?

A

diminished reflexes

23
Q

what is areflexia?

A

absent reflexes

24
Q

flaccid paralysis is a feature of what type of motor lesion?

A

LMN

25
Q

hypertonia is a feature of what type of motor lesion?

A

UMN

26
Q

how does a UMN lesion present?

A

initially:

  • flaccid paralysis
  • loss of tendon reflexes

long term:

  • hypertonia
  • hyperreflexia
  • spastic paralysis
  • loss of fine motor control
27
Q

spastic paralysis a is a feature of what type of motor lesion?

A

UMN

28
Q

why would axial muscle groups be spared if there was a UMN lesion?

A

bi-lateral innervation

29
Q

where do Corticonuclear pathway fibres originate?

A

laterally within pre-central gyrus

30
Q

what do Corticonuclear pathway fibres act on?

A

Influences LMNs in
cranial nerve motor
nuclei

31
Q

which pathway Influences LMNs in
cranial nerve motor
nuclei?

A

Corticonuclear pathway

32
Q

with reference to the Corticonuclear pathway, is innervation largely bilateral or contralateral?

A

largely bilateral

  • except for lower facial and extrinsic tongue muscles which are under contralateral control
33
Q

with reference to the corticospinal pathway, is innervation largely bilateral or contralateral?

A

largely contralateral

34
Q

Corticonuclear pathway innervation is largely bilateral - what is the exception?

A

except for lower facial (facial CNVII)

extrinsic tongue muscles which are under contralateral control (hypoglossal CNXII)

35
Q

what is supranuclear lesion？

A

Unilateral damage to corticobulbar fibres

  • Results in paralysis of the lower half of the face on the opposite
    side to the lesion
36
Q

How could you differentiate between a supranuclear and facial nerve lesion?

A

supranuclear lesion：
paralysis of the lower half of the face on the opposite
side to the lesion

Paralysis of the whole of one side
of the face indicates damage to
the facial nerve itself

37
Q

how would a UMN lesion to facial innervation present?

A
  • Contralateral lower quadrant weakness
  • Angle of the mouth
  • Opposite side
38
Q

how would a LMN lesion to facial innervation present?

A
  • Ipsilateral half of face
  • orbicularis oculi muscle and facial muscles involved
  • unable to close eyes
  • weakness of angle of the mouth
  • cannot elevate eyebrows
  • Same side
39
Q

Where do you think the tongue will deviate if we

lesion the left hypoglossal nerve?

A

The tongue will deviate to the left (ipsilateral to the lesion)

40
Q

Where do you think the tongue will deviate if
we lesion the fibres coming from the right side
of the cortex?

A

The tongue will deviate to the left (contralateral to the lesion)

41
Q

how would a UMN lesion to hypoglossoal innervation will present?

A

tongue deviation is contralateral to lesion

42
Q

how would a LMN lesion to hypoglossoal innervation will present?

A

tongue deviation is ipsilateral to the lesion

43
Q

Muscles can be controlled by what structures other than the cerebral cortex?

A
  • Basal ganglia & red nucleus
  • Reticular formation
  • Vestibular system
44
Q

which Extrapyramidal pathway controls muscle tone?

A

Rubrospinal pathway

45
Q

which Extrapyramidal pathway controls posture?

A

Vestibulospinal pathway

46
Q

which Extrapyramidal pathway controls voluntary movement/breathing/consciousness?

A

reticulospinal pathway

CM - Control (20 decks)

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