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Upper Limb Neuro

Motor Assessment

February 15th, 2021
On this page:The Motor Pathway


Neurological causes of weakness may be delineated into upper motor neuron (brain, brainstem or spinal cord) or lower motor neuron (nerve root, plexus or peripheral nerve) causes. These two broad groups manifest with specific findings elicitable on examination.
  • Causes of Weakness

  • Upper Motor Neuron

  • CNS lesions - decreased power with increased tone, clonus and reflexes.Ischaemia, SAH / ICH, tumour, trauma, encephalitis, vasculitis, MS, ADEM, PML, sarcoidosis, prions
  • Lower Motor Neuron

  • Nerve root pathology - loss of a single myotomeTrauma, radiculopathy, neoplasm
  • Focal peripheral nerve pathology - in the muscles supplied by a single nerveTrauma, entrapment, focal ischaemia, sarcoidosis, neoplasia, Bell's palsy (face)
  • Axonal pathology (peripheral neuropathy)Diabetes, motor neurone disease, hypothyroidism, B12 / folate deficiency, alcoholism, connective tissue disease, amyloid / sarcoidosis, toxins
  • Peripheral demyelinationGuillain-Barré syndrome, Charcot-Marie-Tooth
  • Other

  • Neuromuscular pathologyMyasthenia gravis, amyloidosis
  • Muscular pathologyPolymyositis, rhabdomyolysis
  • Poor compliance with examination

The Motor Pathway

Upper Motor Nucleus
Primary motor cortex (precentral gyrus)
Central Pathway
Corticobulbar tract
(via cerebral peduncle)
Medullary Pyramids
Spinal Pathway
Lateral corticospinal tract
Lower Motor Nucleus
Ventral horn at the level of entry into the spinal cord
Neuromuscular Junction
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