Indirect pathway of movement

The indirect pathway sometimes known as the indirect pathway of movement is a neuronal circuit through the basal ganglia and several associated nuclei within the central nervous system (CNS) which helps to prevent unwanted muscle contractions from competing with voluntary movements. It operates in conjunction with the direct pathway.2° (Spinomesencephalic tract → Superior colliculus of Midbrain tectum) The indirect pathway sometimes known as the indirect pathway of movement is a neuronal circuit through the basal ganglia and several associated nuclei within the central nervous system (CNS) which helps to prevent unwanted muscle contractions from competing with voluntary movements. It operates in conjunction with the direct pathway. The indirect pathway passes through the caudate, putamen, and globus pallidus, which are parts of the basal ganglia. It traverses the subthalamic nucleus, a part of the diencephalon, and enters the substantia nigra, a part of the midbrain. In a resting individual, a specific region of the globus pallidus, known as the internus, and a portion of the substantia nigra, known as the pars reticulata, send spontaneous inhibitory signals to the ventrolateral nucleus (VL) of the thalamus, through the release of GABA, an inhibitory neurotransmitter. Inhibition of the excitatory neurons within VL, which project to the motor regions of the cerebral cortices of the telencephalon, leads to a reduction of activity in the motor cortices, and a lack of muscular action. When the pre-frontal region of the cerebral cortex, which is generally involved in decision making and planning, determines that motor activity be executed, it sends activating signals to the motor cortices. The motor cortices send activating signals to the direct pathway through the basal ganglia, which stops inhibitory outflow from parts of the globus pallidus internus and the substantia nigra pars reticulata. The net effect is to allow the activation of the ventrolateral nucleus of the thalamus which, in turn, sends activating signals to the motor cortices. These events amplify motor cortical activity that will eventually drive muscle contractions.