Chapter 38
Parkinson Disease
Loss of dopamine in the substantia nigra
What is Parkinson Disease?
Parkinson disease is a slowly progressive degenerative neurological disease characterized by tremor, rigidity, bradykinesia (sluggish neuromuscular responsiveness), and postural instability. First described by James Parkinson in 1817 as 'shaking palsy,' it has a prevalence of 1-2 per 1000 (2 per 100 over age 65), with onset usually in the 60s.
The core pathology: depigmentation of the substantia nigra and loss of dopaminergic input to the basal ganglia (extrapyramidal system). This creates an imbalance between the inhibitory neurotransmitter dopamine (deficient) and the excitatory neurotransmitter acetylcholine -- which is why treatment either boosts dopamine or blocks acetylcholine. Lewy bodies are the pathological hallmark.
The Dopamine-Acetylcholine Balance
Dopamine (inhibitory) is produced by neurons projecting from the substantia nigra to the neostriatum. Losing dopamine tips the balance toward excitatory acetylcholine, producing the motor disability. Every drug either raises dopamine or lowers acetylcholine.
📖 “Parkinson disease: progressive degeneration; tremor, rigidity, bradykinesia, postural instability. Depigmentation of substantia nigra, loss of dopaminergic input to basal ganglia. Dopamine (inhibitory) vs acetylcholine (excitatory) imbalance. Lewy bodies hallmark. Prevalence 1-2/1000, onset 60s.”