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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EXTRA Reading:

http://en.wikiversity.org/wiki/Upper_vs_Lower_Motor_Neuron_Lesions

58 COMMENTS

  1. Greetings from Uni of Manchester, haha i am here for my quick scan through on UMN and LMN lesions for my 4th year OSCEs on Thursday. Fingers crossed.

  2. hey.. i have read most of your notes from MSK, CNS, and many other systems. they’re really good. i am from IMU as well and have shared it with most of my friends. most of whom really loved your site for the simplicity of the notes and the good diagrams.. really thanks!

  3. Please can someone explain the anatomical/physiological reasoning that spinal cord lesions above T6 are classified as UMN and below T6 are classified as LMN? Thanks!

  4. Hello! Great summary! Although I”m so confused why does Upper Motor Neuron lesion causes problesm for the lower quadrant of the face and Lower Motor Neuron lesion causes damage for half of the face? And I thought lower motor neuron is in the spinal cord?

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