This medical schematic diagram illustrates the functional neuroanatomy of the human basal ganglia circuitry, detailing the classic motor loops. The diagram displays key anatomical structures including the cerebral cortex, thalamus (violet), neostriatum (red/orange), globus pallidus externa (GPe, light blue), globus pallidus interna (GPi, bluish-gray), subthalamic nucleus (STN, dark blue), and substantia nigra pars compacta (SNc, dark gray). Three primary functional pathways are highlighted: the Direct Pathway (solid black lines from neostriatum to GPi), which facilitates movement via disinhibition of the thalamus; the Indirect Pathway (dashed black lines connecting neostriatum to GPe, then STN, and finally GPi), which serves to inhibit motor activity; and the Hyperdirect Pathway (solid blue line from cortex directly to STN), which provides rapid inhibition of motor output by bypassing the striatum. Arrows indicate the direction of signal flow between these nuclei and the thalamocortical circuit, providing a visual model for understanding movement disorders like Parkinson's and Huntington's disease where these pathways are imbalanced.

A pathophysiology diagram providing a schematic overview of the human basal ganglia motor circuits, specifically illustrating the indirect (left) and direct (right) pathways. The main illustration uses a coronal brain section to map anatomical structures: the cortex, striatum (caudate nucleus and putamen), thalamus, globus pallidus external (GPe) and internal (GPi) segments, subthalamic nucleus (STN), and substantia nigra (pars compacta, SNpc; pars reticulata, SNpr). Neurotransmission is color-coded: green arrows denote excitatory glutamatergic (GLU) or dopaminergic (DA) signals, while red T-bars signify inhibitory GABAergic (GABA/SP, GABA/ENK) signals. The direct pathway is labeled 'Motor Facilitation' and shows inhibitory projections from D1-receptor striatal neurons directly to the GPi/SNpr. The indirect pathway is labeled 'Motor Cessation' and highlights connections from D2-receptor striatal neurons to the GPe, subsequently influencing the STN and GPi/SNpr. An inset details projections to the SNpc, including inputs from the cortex, STN, and pedunculopontine nucleus (PPN). This educational material demonstrates the neuroanatomical basis for motor control and the circuit dysfunction relevant to Parkinson's disease (PD).

Educational medical diagram illustrating the pathophysiology of Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS) within the basal ganglia. The image is divided into three sections. On the left, a sagittal view of the human brain maps the four major dopaminergic pathways: nigrostriatal (blue), mesolimbic (red), tuberoinfundibular (green), and mesocortical (purple). The center and right panels provide a comparative schematic of basal ganglia circuitry. The 'Normal' circuit shows the functional balance between the direct and indirect pathways, highlighting the roles of the striatum (caudate and putamen), medium spiny neurons (MSNs), acetylcholine (Ach) interneurons, and the globus pallidus (externus and internus). In contrast, the 'PANDAS' circuit depicts neuroinflammation and cholinergic disruption in the dorsal striatum. This pathological state results in decreased Ach modulation and fewer distinct MSNs, leading to hyperactivity of the direct pathway. The diagram concludes by linking this physiological imbalance to clinical manifestations, including tics, obsessions, and compulsions typical of PANDAS syndrome.

This composite educational graphic details the neuroanatomy and connectivity of the basal ganglia network, specifically focusing on the fronto-striatal circuit. It consists of a functional schematic diagram paired with MRI diffusion tractography images. The schematic illustrates key nodes including the Striatum (containing D1 and D2 pathways), Substantia Nigra, Thalamus (VL/VA/MD nuclei), Globus Pallidus (EP/IP), and the Subthalamic Nucleus (STN). Arrows indicate excitatory and inhibitory pathways, highlighting the indirect and direct pathways of motor control relevant to Parkinson's disease. The accompanying MRI panels (coronal, sagittal, and axial views) show white matter fiber reconstruction using tractography. These panels visualize axonal connections between the striatum and thalamic nuclei, color-coded in blue and yellow to represent distinct fiber bundles. The resource is designed to teach the neurobiological basis of extrapyramidal signs and the localization of basal ganglia dysfunction in clinical neurology.