Introduction of Basal ganglia for the Students of Medical fraternity.pptx

It is power point presentation about the Basal Ganglia..for Medical Students written in crisp and clear manner

1. Basal ganglia By:- dr. vishwajit kumar

2. FUNCTIONS OF BASAL GANGLIA 1. The neurons of basal ganglia are observed to discharge before the movement begins. This indicates that basal ganglia is involved in planning and programming of motor activities 2. Basal ganglia controls posture . Basal ganglia- thalamiccortical projection to brainstem influences descending pathways that control posture. Diseases of basal ganglia result in profound postural abnormalities

3. 3. Basal ganglia inhibits stretch reflexes by stimulation of caudate nucleus. This is achieved by stimulation of inhibitory motor cortex through thalamocortical feedback pathway and by stimulation of inhibitory reticular formation 4. Neostriatum regulates subconscious gross movements 5. Basal ganglia also play a role in cognitive functions . This is especially performed by the caudate nucleus through its connections with the frontal portion of the neocortex. Lesion of caudate nucleus results in deficit in performance based on learning

4. 6. Lesion of head of the left caudate nucleus is associated with dysarthritic aphasia (difficulty in articulating words). 7. Globus pallidus provides inputs for appropriate muscle tone for skilled movements . 8. Substantia nigra is the center for coordination of impulses essential for skilled movements

5. 9. Basal ganglia controls associated movements that occur automatically and normally with various body movements 10. Lesion of basal ganglia in animals does not lead to significant motor deficit . However, diseases of the basal ganglia in humans result in severe motor dysfunctions .

6. ANATOMICAL ORGANIZATION On each side of the brain, these ganglia consist of the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus.

7. The caudate nucleus and putamen are together known as striatum (neostriatum ) Putamen and globus pallidus are combinely known as lenticular nucleus. Globus pallidus is divided into an external part (globus pallidus externus) and an internal part (globus pallidus internus). Substantia nigra is divided into two parts: pars compacta and pars reticulata

8. Inputs The main inputs to basal ganglia come from cerebral cortex Basal ganglia also receive inputs from thalamus, dorsal raphe nucleus and pedunculopontine region of the brainstem. Most afferent information enters basal ganglia via striatum (caudate nucleus and putamen).

9. The afferent fibers are Corticostriate projection Thalamostriate projection Raphestriate projection Pedunculostriate projection

10. Basal ganglia receive afferents from all parts of cerebral cortex via corticostriate projection. Putamen receives input mainly from the sensorymotor cortex and caudate nucleus receives inputs from remainder of the cortex . The centromedian nucleus of thalamus projects to the striatum via thalamostriate projections. Striatum also receives input from dorsal raphe nucleus Pedunculopontine nucleus of brainstem projects to basal ganglia

11. Outputs The principal output nucleus of basal ganglia is the internal segment of globus pallidus The fibers project mainly to the ventral-lateral, ventral-anterior, and centromedian nuclei of thalamus from where fibers project to prefrontal and premotor cortices (extrapyramidal pathways mainly originate from these cortical areas)

12. The output from the internal segment of the globus pallidus to the thalamus is inhibitory , whereas the output from the thalamus to the cerebral cortex is excitatory . Pars reticulata portion of substantia nigra projects to thalamus Basal ganglia also project to pedunculopontine nucleus, habenula and superior colliculus

13. motor loop The main feature of input and output of basal ganglia is that cerebral cortex projects to striatum, striatum projects to internal segment of globus pallidus, globus pallidus projects to thalamus, which projects back to the cortex, completing the motor loop

14. Connections within Basal Ganglia

15. Nigrostriatal projection The pars compacta portion of substantia nigra projects to striatum. The nigrostriatal projection is dopaminergic . Degeneration of this system produces Parkinsonism

16. Striatonigral projection Striatum also projects to substantia nigra. The striatonigral projection is inhibitory and neurotransmitter secreted in this pathway is GABA . Degeneration of this pathway produces Huntington’s disease .

17. Projection from subthalamic nucleus Projection from subthalamic nucleus to globus pallidus internus: Subthalamic nucleus projects to internal segment of globus pallidus. This projection is excitatory

18. Neural Pathways through Basal Ganglia The inputs, interconnections, and outputs constitute two important neural pathways through the basal ganglia that are involved in control of motor activities: the direct pathway, and the indirect pathway

19. Cortex projects to striatum. Striatum projects to globus pallidus internus, which projects to thalamus and thalamus in turn projects to motor cortex. This is the direct pathway In direct pathway, projection of striatum to globus pallidus internus is inhibitory (GABAergic), and from there to the thalamus is inhibitory (GABAergic). Therefore, stimulation of striatum results in stimulation of thalamus by disinhibition that leads to stimulation of cortical neurons.

20. The direct pathway is stimulated during movement Usually, neurons in the striatum have less resting background activity. • During movement, they are activated by inputs from cortex and thalamus. • Activation of striatum inhibits globus pallidus internus. • However, pallidal neurons themselves are inhibitory to thalamus. • Therefore, activation of striatum finally excites the thalamic neurons. • Consequently, the target neurons in the motor cortex are stimulated via thalamocortical projection.

21. DIRECT PATHWAY

22. Indirect Pathway

23. Modulation by Nigrostriatal Projections The direct and indirect pathways have opposite effects IN DIRECT PATHWAY activation of striatum finally excites the thalamic neurons. Where as the final output of striatum through this indirect pathway is inhibitory

24. . Alteration of activity in either of the pathways leads to imbalance in motor output from basal ganglia. Therefore, in basal ganglia disorders, both hypo- and hyperkinetic features are observed

25. The dopaminergic projections from pars compacta of substantia nigra to the striatum appear to have an excitatory influence on the direct pathway and inhibitory influence on the indirect pathway It also modulates the input from cortex to the striatum The neurons in the striatum are cholinergic. In striatum, the ratio of acetylcholine and dopamine keeps the striatal neurons active. Alteration in this ratio results in abnormalities in motor activities

26. DYSFUNCTIONS OF BASAL GANGLIA Parkinson’s Disease

27. 1. PARKINSON DISEASE 2. WILSON DISEASE 3. CHOREA 4. ATHETOSIS 5. CHOREOATHETOSIS 6. HUNTINGTON CHOREA 7. HEMIBALLISMUS „ 8 KERNICTERUS