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Clinical Neuroscience > Upper And Lower Motor Neurones > Flashcards

Upper And Lower Motor Neurones Flashcards

1
Q

Where are the cell bodies of the upper + lower motor neurones located?

A
  • upper: primary motor cortex
  • lower: brain stem + ventral horn of spinal cord
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2
Q

Distribution of upper + lower motor neurones in CNS and PNS

A
  • upper: only in CNS
  • lower: cell bodies in CNS + axons in PNS
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3
Q

Where can lower motor neurones be damaged?

A

Severed axon
Destruction of cell body

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4
Q

List lower motor neurone lesion signs

A
  • weakness
  • hyporeflexia
  • areflexia
  • hypotonia
  • muscle atrophy
  • fasciculaitons
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5
Q

Define hyperreflexia, areflexia + hyporeflexia

A
  • hyperreflexia: excessive reflex
  • areflexia: no reflex
  • hyporeflexia: reduced reflex
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6
Q

What are fasciciualtions?

A

Uncoordinated muscle contraction

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7
Q

Why does muscle atrophy occur in lower motor neurone lesions?

A

Reduce ACh to muscle at neuromuscular junction + reduction of growth factor

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8
Q

Why do fasciculations occur in lower motor neurone lesions?

A
  • reduction of ACh to muscle
  • upregulation of Ach receptors
  • causes hypersensitivity
  • uncoordinated muscle contraction
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9
Q

In the knee jerk reflex, for the quadriceps to contract, the hamstrings must relax. Explain the mechanism behind how this happens

A
  • upper motor neurones at L3 cause contraction of quadriceps at
  • the same UMN sends a projection to L5 + synapse at inhibitory interneurones > relaxation of hamstrings
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10
Q

Describe the inputs to lower motor neurones

A
  • majority of inputs via inhibitory interneurones from upper motor neurones
  • a strong excitatory input is needed to overcome inhibition to elicit a response
  • net effect of UMNs on LMNs is inhibition
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11
Q

What pathway allows for communication between CN 3,4+6 for extra ocular eye muscle innervation?

A

Medial longitudinal fasciculus

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12
Q

What are signs of upper motor neurone lesion?

A
  • weakness
  • spasticity: hypertonia, hyper reflexia + clasp knife rigidity
  • (atrophy)
  • spinal shock
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13
Q

What is clasp knife rigidity?

A
  • Flexed limb
  • resistance to being pulled out then sudden relaxation
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14
Q

What is considered spasticity?

A

Hypertonia
Hyper reflexia
Clasp knife rigidity

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15
Q

What is spinal shock?

A

A phenomenon that occurs hours-days post upper motor neurone lesion
- initially flaccid paralysis with areflexia
- then hypertonia +hyperreflexia

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16
Q

What is meant by the saying ‘upper spares upper’?

A

Upper motor neurones lesion spare upper face (forehead is spared)

17
Q

Describe the descent of upper motor neurones

A
  • UMN cell body in primary motor cortex
  • travel down through corona radiata
  • compress together at internal capsule
  • travels to medulla via cerebral peduncles
    TWO PATHWAYS:
  • 85% decussate at decussation of pyramids in caudal medulla
  • form lateral corticospinal tract
  • synapse to LMN > limb musculature
    OR
  • 15% travel down ipsilaterally
  • form anterior corticospinal tract
  • cross at level of LMN + synapse > trunk musculature
18
Q

What pathway do 85% of upper motor neurones take at the medulla?

A
  • 85% decussate at decussation of pyramids in caudal medulla
  • form lateral corticospinal tract
  • synapse to LMN > limb musculature
19
Q

What pathway do 15% of upper motor neurones take at the medulla?

A
  • 15% travel down ipsilaterally
  • form anterior corticospinal tract
  • cross at level of LMN + synapse > trunk musculature
20
Q

What is referred to as the upper + lower face?

A

upper: above eyes (frontalis)
lower: below eyes

21
Q

Where does the lower half of the facial motor neurone receive input from?

A

Contralateral upper motor neurones

22
Q

Where does the upper half of the facial motor neurone receive input from?

A

Bilateral upper motor neurones

23
Q

What is the clinical significance of the bilateral input to the upper facial motor nuclei?

A

Lesion prior to facial motor neurone is forehead sparing as there is another input from the opposite hemisphere

24
Q

Distribution of upper motor neurones in the internal capsule

A
  • only in posterior limb of internal capsules
  • face at genu (bend)
  • arms
  • trunk
  • legs

Clinical Neuroscience (20 decks)

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