The putamen, caudate, and nucleus accumbens are all referred to as the straitum. Their main cell types are the medium spiny neurons. The putamen and globus pallidus are referred to as the lenticular nucleus.
The putamen is coextensive with the insula, which is where the telencephalon and diencephalon first meet during development.
The putamen is sperated from the globus pallidus by the lateral medullary lamina.
The caudate tail is continuous with the amygdala, which, in turn, is continuous with the putamen.
The substantia nigra has two parts: compact, with closely packed pigmented neurons and the reticular part that is more loosely packed and nonpigmented. The compact is what sends dopaminergic projection and the reticular part serves as an output nuclei.
Globus Pallidus internal and Substantia nigra internal are the two output centers of the basal ganglia. Outputs are GABA(inhibitory).
Projections from the cerebral cortex reach the striatum and subthalamic nucleus. Inputs are glutamate.
Huntington’s is a hereditary disorder that is characterized by neuronal damage to the striatum and caudate and causes involuntary choreform movements and alteration of mood or cognitive function. Thought to knock out the D2 receptors(the ones that are inhibitory once they receive dopamine). This would account for the spastic movements.
Dementia- caudate and cortical destruction
Athetosis is a slow writhing movement with an inability to keep the affected limb in a fixed position. Thought to be caused by striatum problems.
Hemiballismus is characterized by wild flailing movements and we see it caused by lesions in the STN.
Parkinson’s is characterized by rigidity, slow, and reduced movements, stooped posture, and tremor. The rigidity is cause by an increase tone in all muscles. The resting tremor (pill rolling) shows that there is a diminished voluntary movement that increases during emotional stress.
Dystonia has hand cramping and twistic and is usually a result of corticostriate interruption.
Positive signs – motor neurons fire when they should not
Negative signs – motor neurons cannot easily be made to fire by their owner.
Parkinson’s disease has damage that is most consistently evident in the substantia nigra where we see a degeneration of pigmented nigral cells. L-dopa can help reverse some of the functional abnormalities. Sometimes lesions of the GPi can help relieve the tremor and rigidity and faliling movements.Deep brain stimulation to the SNc can help as well.
Decrease is parkinsons systems. With a loss of opamine, we get the loss of enhancement of the disinhibition circuit and an enhancement (loss of inhibition) of the brake since SNc goes to straitum, which has deifferent responses to dopamine.
The BG could be working a “center-surround” fashion that releases wanted movements and inhibits unwanted movements.