Final answer:
Parkinson's disease is a degenerative neurological disorder marked by resting tremor, bradykinesia, muscle rigidity, and impaired postural reflexes, caused by the loss of dopamine-producing neurons.
Step-by-step explanation:
Parkinson's disease is a degenerative disorder of the central nervous system that primarily affects movement and muscular control. The condition is characterized by four cardinal symptoms which include resting tremor, bradykinesia (slowness of movement), muscle rigidity, and impaired postural reflexes. A resting tremor typically presents in a limb when at rest and subsides during voluntary movement or sleep.
Bradykinesia affects the smoothness and velocity of movement, significantly slowing patients down and complicating daily tasks. Muscle rigidity leads to increased resistance to movement in the joints, while impaired postural reflexes contribute to balance difficulties and falls. Moreover, Parkinson's disease results from the progressive loss of dopamine-producing neurons in the midbrain, which ultimately causes these motor symptoms along with non-motor symptoms such as depression and dementia in advanced stages.