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

• 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