Final answer:
Parkinson's disease progresses through five stages, starting with mild symptoms affecting one side of the body, advancing to severe disabilities, and eventually leading to bedridden or wheelchair-bound state.
Step-by-step explanation:
The five stages of Parkinson's disease, a degenerative disorder of the central nervous system, describe the progression of symptoms that patients experience. In the first stage, symptoms such as tremors and other movement-related symptoms are mild and typically only affect one side of the body.
By the second stage, symptoms start to affect both sides of the body, although balance is still maintained. In the third stage, balance and mobility become significantly impaired, and the risk of falls increases. The fourth stage sees further decline, with severe disabilities; patients may still be able to walk, but movements are limited.
Throughout these stages, the motor symptoms result from the death of neurons in the midbrain area known as the substantia nigra, leading to a decrease in dopamine production. This loss of dopamine neurons manifests in symptoms like muscle tremor, rigidity, slowness of movement, and postural instability.