Upper motor neuron lesion

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2] Luke Rusowicz-Orazem, B.S.

An upper motor neuron lesion is a lesion of the neural pathway above the anterior horn cell or motor nuclei of the cranial nerves. This is in contrast to a lower motor neuron lesion, which affects nerve fibers traveling from the anterior horn of the spinal cord to the relevant muscle(s).

• Spastic increase in tone in the extensor muscles (lower limbs) or flexor muscles (upper limbs)
• Clasp-knife response where initial resistance to movement is followed by relaxation
• Weakness in the flexors (lower limbs) or extensors (upper limbs),^[1] but no muscle wasting
• Brisk tendon jerk reflexes
• Babinski sign positive, where the big toe is raised rather than curled downwards on stimulation of the sole of the foot

These are the neural tracts which descend in the spinal cord, in the lateral columns, carrying signals for voluntary movement of skeletal muscle. These nerve fibres usually originate in the cerebral cortex, then gather in the internal capsule before crossing over to the opposite side (decussation) in the medulla oblongata and proceeding down the spinal cord to meet lower motor neurons in the anterior horn.

• Upper motor neuron

• http://www.med.yale.edu/caim/cnerves/cn7/cn7_13.html
• http://www.lib.mcg.edu/edu/eshuphysio/program/section8/8ch3/s8ch3_34.htm

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