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The loop has also been divided into limbic, associative, oculomotor, and motor circuits [4] to explain the role of dopamine in the basal ganglia on motivational states. [10] A five loop division based on primary cortical targets has been described as follows: [11]
The limbic loop is a functional pathway of the basal ganglia, in which the ventral pallidum is involved. It (and the internal globus pallidus and substantia nigra pars reticulata) receives input from the temporal lobes, and the hippocampus via the ventral striatum.
Cortico-basal ganglia-thalamo-cortical loop [ edit ] The dopaminergic pathways that project from the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) into the striatum (i.e., the nigrostriatal and mesolimbic pathways, respectively) form one component of a sequence of pathways known as the cortico-basal ganglia-thalamo ...
[7] [8] [9] Nuclei within the MLR receive inputs from the substantia nigra of the basal ganglia and neural centers within the limbic system. [10] Projections from the MLR descend via the medullary and pontine reticulospinal tracts to act on spinal motor neurons supplying the trunk and proximal limb flexors and extensors. [2] [5] [11]
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.
The basal ganglia (BG) or basal nuclei are a group of subcortical nuclei found in the brains of vertebrates. In humans and other primates , differences exist, primarily in the division of the globus pallidus into external and internal regions, and in the division of the striatum .
The “limbic loop” is very similar to the direct pathway motor loop of the basal ganglia. In both systems, there are major excitatory inputs from the cortex to the striatum (accumbens nucleus), the midbrain projects neuromodulatory dopamine neurons to the striatum, the striatum makes internuclear connections to the pallidum, and the pallidum ...
As the GPi is one of the direct output centers of the basal ganglia, this causes disinhibition of the thalamus, increasing overall ease of initiating and maintaining movement. As this pathway only contains one synapse (from the striatum to the internal globus pallidus), it is known as the direct pathway .