The symptoms of Parkinson’s disease include:
- Slowness in carrying out different motor functions (bradykinesia)
- Difficulty in initiating movements (akinesia)
- Increased muscle tone (rigidity)
- Involuntary and unwanted movements (resting tremors)
The organic basis of Parkinson’s disease occurs in the basal ganglia. Degeneration of the pigmented dopaminergic neurons from the substantia nigra results in a decreased amount of dopamine at the caudate accompanied by a loss of pigmentation in the substantia nigra.
The net effect of the corto–basal ganglia motor control loop is excitation of the cortex. With the loss of dopamine producing neurons, the globus pallidus becomes overactive, resulting in inhibition of the VL nucleus of the thalamus and consequently there is reduced excitation of the cortex. This leads to a condition called hypokinesia.
Compare the diagram of a hypokinetic motor loop above with the normally functioning motor loop below, explained on the corto–basal ganglia motor loop page.
