Neurological Disorders: Parkinson's and Alzheimer's Diseases

Parkinson's disease and Alzheimer's disease are both progressive (worsening over time), currently incurable disorders of the nervous system that become considerably more common with advancing age, but they differ substantially in their underlying cause and in the symptoms they primarily produce.

Parkinson's disease results from the progressive degeneration of a specific group of neurons in a part of the midbrain called the substantia nigra; these neurons normally produce the neurotransmitter dopamine, which is essential for the smooth initiation and control of voluntary movement, so as they are progressively lost, dopamine levels in the brain fall. The characteristic symptoms of Parkinson's disease are therefore predominantly motor in nature: a resting tremor (rhythmic shaking, often most noticeable in the hands when they are at rest), rigidity (increased stiffness and resistance in the muscles), bradykinesia (a general slowness in initiating and carrying out movement), and postural instability (difficulty maintaining balance, especially when starting to walk or turning). There is no cure for Parkinson's disease, but its symptoms can often be managed for some years with medication that helps restore or substitute for dopamine's action in the brain.

Alzheimer's disease is a different kind of degenerative brain disorder, mainly affecting older individuals, and it is associated with the abnormal build-up of two kinds of protein deposits within brain tissue — amyloid plaques accumulating between neurons, and neurofibrillary tangles forming within neurons — which together are believed to disrupt normal neuron function and communication and eventually cause widespread loss of neurons, particularly in brain regions important for memory, such as the hippocampus, and later across much of the cerebral cortex. The characteristic symptoms of Alzheimer's disease are therefore predominantly cognitive rather than purely motor: progressive loss of memory (especially for recent events, in the earlier stages), increasing confusion and disorientation, changes in mood and behaviour, and increasing difficulty with language, reasoning and everyday tasks, eventually leading to severe overall cognitive decline. …