The basal ganglia are a group of interconnected subcortical nuclei that include the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra. They are involved in motor control, learning, and cognitive functions through complex excitatory and inhibitory circuits between the cortex and thalamus. Disorders of the basal ganglia can result in movement disorders like Parkinson's disease, chorea, athetosis, and hemiballismus.

1. Basal ganglia These are a set of deep nuclei located in and around the basal part of the brain that are involved in motor control, action selection, and some forms of learning

2. Basal ganglia Caudate nucleus Putamen Globus pallidus (internal and external) Subthalamic nuclei Substantia nigra International Basal Ganglia Society

3. (Ref. Guyton)

4. thalamus globus pallidus putamen caudate

6. basal ganglia caudate nucleus putamen globus pallidus subthalamic nuclei substantia nigra corpus striatum lentiform nucleus

7. Interconnecting circuitry through these nuclei These circuits start from the cortex and ends in the cortex These circuits are very complex Their effect is excitatory or inhibitory on motor functions (depending on the neurotransmitter involved) They also have a role in cognitive functions.

8. PUTAMEN CIRCUIT Starts from premotor Cx, SMA & 1° sensory area. Then goes to putamen (striatum) Then to globus pallidus Then to thalamus Return to 1° motor Cx

9. Cortex Putamen globus pallidus Thalamus

10. PUTAMEN CIRCUIT This circuit functions to control complex patterns of movement in association with the motor Cx eg. writing letters of alphabet, cutting papers with scissors, hammering nails, passing a football, vocalisation

11. CAUDATE CIRCUIT Starts from all parts of the Cx: frontal, parietal, occpital, temporal. and association Cx Then to caudate nucleus Then to globus pallidus Then to thalamus Finally to Premotor Cx, SMA

12. Cortex Caudate globus pallidus Thalamus

13. CAUDATE CIRCUIT This circuit functions in the cognitive control of movement.

16. Some of these circuits are excitatory and some inhibitory This depends on the neurotransmitter involved. Inhibitory : dopamine and GABA Excitatory : Ach Others : glutamate (from cortical projections) enkephalin etc

17. Following pathways are known: Dopamine pathway from substantia nigra to caudate nucleus and putamen GABA pathway from caudate and putamen to globus pallidus and substantia nigra Ach pathway in the caudate and putamen

18. Cortex Putamen globus pallidus Caudate Substantia nigra Subthalamic nucleus Reticular formation Dopamine Thalamus Reticular formation glutamate GABA Interneurons: Ach striatum GABA + + Thalamus

20. Functions of Basal Ganglia Motor control Learning Sensorimotor integration Reward Cognition

23. Cortico–Basal Ganglia Motor Loop Basal ganglia receives information from cerebral cortex (frontal, prefronal and parietal) Complex mechanisms occur inside basal ganglia Output goes to the thalamus From the thalamus to the frontal cortex (premotor and supplementary motor areas) Basal ganglia inhibit muscle tone

24. Basal Ganglia disorders Parkinsonism Athetosis Chorea Hemiballismus Basal ganglia disorders are also called extrapyramidal disorders

25. Parkinsonism due to destruction of dopamine secreting pathways from substantia nigra to caudate and putamen. also called “paralysis agitans” or “shaking palsy” first described by Dr. James Parkinson in 1817. In the west, it affects 1% of individuals after 60 yrs Classical Clinical features: Tremor, resting Rigidity of all the muscles Akinesia (bradykinesia): very slow movements Postural instability

26. expressionless face flexed posture soft, rapid, indistinct speech slow to start walking rapid, small steps, tendency to run reduced arm swinging impaired balance on turning resting tremor (3-5 Hz) (pill-rolling tremor) diminishes on action cogwheel rigidity lead pipe rigidity impaired fine movements impaired repetitive movements

29. other areas

30. Cortex Putamen globus pallidus Caudate Substantia nigra Subthalamic nucleus Reticular formation Dopamine Thalamus Reticular formation glutamate GABA Interneurons: Ach striatum GABA + + Thalamus

32. Parkinsonism this could be caused by idiopathic causes (no definite cause) drugs toxins MPTP (1 methyl 4 phenyl tetrahydropyridine) experimentally induced parkinsonism associated with other disorders

33. Parkinsonism Treatment is to increase dopamine content by giving dopaminergic drugs Ldopa decrease Ach activity by giving anticholinergic drugs

34. Chorea Lesions in the caudate nucleus jerky movements of the hand, face and other parts patient is unable to control them may get worse with anxiety disappears in sleep video

36. Athetosis Lesions in putamen spontaneous slow writhing movements (twisting movements) of fingers, hands, toes, feet.

37. Hemiballismus Lesions in subthalamus violent, flailing movements of arm & leg on one side of the body