Upper motor neuron & Lower motor neuron lesions

Upper motor neuron & Lower motor neuron lesions

 

Definitions

Upper motor neuron

  • Corticospinal neuron
  • Corticonuclear neuron

Cerebral cortex (pyramidal tract) –> Precentral gyrus (motor strip) → internal capsule (posterior limb) → brainstem → spinal cord

  • 85% cross to opposite side

Upper motor neuron lesions

  • Interruption of the corticospinal and corticonuclear tract along its course

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Lower motor neuron

  • Neurons from the brain stem & spinal cord
    • efferent motor fibres
    • terminal axons & motor end plates
    • muscle fibres

Anterior horn cells in spinal cord→nerve roots→nerve plexus →peripheral nerves

Lower motor neuron lesions

  • Degeneration of the motor neuron & peripheral nerves

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Clinical features – Upper motor neuron lesion

  • Initial phase
    • limbs flaccid
    • loss of tendon reflexes
  • Several days to a week
    • return of motor function, but tone increases
  • Long term
    • Spasticity
    • Hyperreflexia
  • Ankle & patella clonus
  • Barbinski sign +ve
    • extensor plantar response
  • Absent abdominal reflexes

Examples of UMN lesion

  • Cerebrovascular accident
    • stroke! most common
  • Intracranial tumour
  • Cervical spine injury

Clinical features – Lower motor neuron lesion

  • Muscle wasting
  • Muscle weakness
    • reduced power
  • Hypotonia
  • Loss of reflexes
  • Fasciculations
  • Fibrillations
  • Associated changes in
    • skin, nail, hair

Examples of LMN lesion

  • Motor neuron disease
  • Peripheral nerve neuropathy
    • Diabetic neuropathy?
  • Poliomyelitis
    • anterior horn cell affected
  • Spinal cord injury
    • with nerve root compression

Examples of BOTH UMN & LMN lesion

  • Demyelinating disease
    • Multiple sclerosis

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Spinal cord injury

  • C1 – C5
    • Upper limbs: UMN
    • Lower limbs: UMN
  • C6 – T2
    • Upper limbs: LMN
    • Lower limbs: UMN
  • T3 – L3
    • Upper limbs: normal
    • Lower limbs: UMN
  • L4 – S2
    • Upper limbs: normal
    • Lower limbs: LMN

Facial nerve lesion

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  • Upper motor neuron lesion
    • Contralateral lower quadrant weakness
      • Angle of the mouth
      • Opposite side
  • Lower motor neuron lesion
    • Ipsilateral orbicularis oculi muscle and facial muscles involved
      • Half of face
        • unable to close eyes
        • weakness of angle of the mouth
        • cannot elevate eyebrows
      • Same side

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