How would you describe the damage to the motor pathway in the brain of a person with Parkinson's Disease?

     What causes Parkinson's disease is still unknown today, however with the development of an animal model of Parkinson’s disease much is learned about the disease (Knierim, 2013). Knierim (2013), "Parkinson’s disease results from the death of dopaminergic neurons in the substantia nigra pars compacta" (para. 14). Which, is the cause of the damage to the motor pathways in an individual with Parkinson's disease. When the substantia nigra neurons are lost this puts a hold on or stops the output of motor cortex, which inhibits voluntary motor commands from descending to the spinal cord and brain stem (Knierim, 2013). Substantia nigra activity excites the direct pathway and inhibits the indirect pathway (Knierim, 2013). The direct pathway excites the motor cortex and the indirect pathway inhibits motor cortex. Which, disrupts the inhibition and excitation balance in the basal ganglia and the excitation of motor cortex is reduced. The resulting symptoms that occur include resting tremors, and severe bradykinesia or akinesia. In the advanced cases of individuals with Parkinson's disease there is difficulty initiating movements. However, what may still be normal are involuntary, reflexive movements. 

Reference

Knierim, J. (2013). Neuroscience Online. Retrieved from http://neuroscience.uth.tmc.edu/s3/chapter06.html