Neuroanatomy, Upper Motor Neuron Lesion

A vast network of nerve tracts in the central nervous system (CNS) which spans the cerebral cortex, brainstem, cerebellum, and spinal cord control the initiation and modulation of movements. The nerves in the CNS which carry the impulses for movement are known as upper motor neurons (UMN). The primary tract which carries signals for voluntary movement is known as the pyramidal tract. The pyramidal tract divides further into the corticospinal tract and the corticobulbar tract. Injury or lesions to UMN’s are common because of the vast areas covered by the motor neuron pathways. UMN lesions are designated as any damage to the motor neurons that reside above nuclei of cranial nerves or the anterior horn cells of the spinal cord. Damage to UMN’s leads to a characteristic set of clinical symptoms known as the upper motor neuron syndrome. These symptoms can include weakness, spasticity, clonus, and hyperreflexia. UMN’s lesions have a wide differential diagnosis which ranges from cerebrovascular accidents, traumatic brain injury, malignancy, infections, inflammatory disorders, neurodegenerative disorders, and metabolic disorders.