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).
|cation and external resources
|The motor tract.
- Spasticity, 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), but no muscle wasting
- Brisk tendon jerk reflexes
- Babinski sign is present, where the big toe is raised (extended) rather than curled downwards (flexed) upon appropriate stimulation of the sole of the foot. The presence of the Babinski sign is an abnormal response in adulthood.
- increase deep tendon reflex (DTR)
- Pronator drift
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 fibers usually originate in the cerebral cortex, then gather in the internal capsule before crossing over to the opposite side (decussation) in the medullary pyramids and proceeding down the spinal cord to meet lower motor neurones in the anterior horn.