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In the direct pathway, the motor cortices send activating signals to the caudate and putamen (which together form the dorsal striatum). The cells of the direct pathway in the caudate and putamen that receive these signals are inhibitory and, once they become activated, send inhibitory signals to the GPi and SNpr and stop activity there.
The striatum (pl.: striata) or corpus striatum [5] is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. [6] The striatum is a critical component of the motor and reward systems; receives glutamatergic and dopaminergic inputs from different sources; and serves as the primary input to the rest of the basal ganglia.
The direct pathway, originating in the dorsal striatum inhibits the GPi and SNr, resulting in a net disinhibition or excitation of the thalamus. This pathway consists of medium spiny neurons (MSNs) that express dopamine receptor D1, muscarinic acetylcholine receptor M4, and adenosine receptor A1. [33]
Indirect and direct pathways. Some neuroanatomy is excluded for simplicity. The two major input structures of the circuit are the striatum and the subthalamic nucleus (STN). The striatum receives inputs from both the cortex and the pars compacta of the substantia nigra (SNc), while the STN only receives cortical inputs. Two pathways emerge from ...
The balance of direct/indirect activity in movement is supported by evidence from neurodegenerative disorders, including Parkinson's disease (PD), which is characterized by loss of dopamine neurons projecting to the striatum, hypoactivity in direct pathway and hyperactivity in indirect pathway neurons, along with motor dysfunction. [21]
The substantia nigra is located in the ventral midbrain of each hemisphere. It has two distinct parts, the pars compacta (SNc) and the pars reticulata (SNr). The pars compacta contains dopaminergic neurons from the A9 cell group that forms the nigrostriatal pathway that, by supplying dopamine to the striatum, relays information to the basal ganglia.
As the pathway from the striatum to the medial globus pallidus is monosynaptic (containing one synapse), it is called the direct pathway. The indirect pathway, which contains the GPe and the subthalamic nucleus, functions to modulate the effects of the direct pathway. The GPe acts as an inhibitory "control device", adjusting subthalamic nucleus ...
The direct pathway consists of axons from medium spiny cells in the striatum that project directly to pars reticulata. The indirect pathway consists of three links: a projection from striatal medium spiny cells to the external part of the globus pallidus ; a GABAergic projection from the globus pallidus to the subthalamic nucleus , and a ...