Basal Ganglia

Basic anatomy of basal ganglia

1. BASAL GANGLIA DR HARI RAM SEDAI 1 ST YEAR RESIDENT PSYCHIATRY

2. TOPIC OF DISCUSSION Neuroanatomy of basal ganglia Internal processing(direct and indirect pathways) Functional connections of basal ganglia Putamen circuit & caudate circuit Disorders associated with damage to basal ganglia Basal ganglia & Psychiatric implications

3. BASAL GANGLIA Collection of masses of gray matter situated within each cerebral hemisphere Important role in the control of posture and voluntary movement Major structure: Corpus striatum Putamen Globus pallidus (internal & external ) Subthalamic nuclei Substantia nigra

4. CORPUS STRIATUM Situated lateral to the thalamus Divided by a band of nerve fibers & Internal capsule into: Caudate nucleus Lentiform nucleus

5. Caudate Nucleus Large C-shaped mass Closely related to the lateral ventricle Lateral surface - related to the Internal capsule Head Large and rounded Forms the lateral wall of the anterior horn of the lateral ventricle

6. Body Long and narrow Continuous with the head in the region of the lnterventricular foramen Forms part of the floor of the body of the lateral ventricle Tail Long and slender Continuous with the body in the region of the posterior end of the thalamus Terminates anteriorly In the amygdaloid nucleus

7. Lentiform Nucleus Wedge shaped mass of gray matter Medially- Internal capsule, separates it from the caudate nucleus and the thalamus Laterally to a thin sheet of white matter, the external capsule Separates it from a thin sheet of gray matter, called the claustrum Claustrum separates the external capsule from the subcortical white matter of the insula

8. A vertical plate of white matter divides the nucleus into: Lateral portion- Putamen Medial portion- Globus pallidus

9. Putamen Telencephalic in origin. Lies in the brain medial to insula Bounded laterally by fibers of external capsule and medially by globus pallidus Separated from caudate by the anterior limb of internal capsule

10. Globus pallidus Diencephalic in origin. Inner component of lentiform nucleus. Cone like structure with tip directed medially. Bounded medially by posterior limb of internal capsule and laterally by putamen. Divided into external and internal segments by medial medullary lamina .

11. SUBTHALAMIC NUCLEUS Diencephalic origin. Lies dorso -medial to posterior limb of internal capsule. Situated dorsal to substantia nigra . Discrete lesions of subthalamic nucleus leads to hemiballism us

12. SUBSTANTIA NIGRA Mesencephalic in origin. Present in mid-brain Consists of 2 components: Pars compacta Pars reticulata

13. INPUTS OF BASAL GANGLIA Striatum is the major recipient of inputs to basal ganglia Three major afferent pathways are known to terminate in the striatum Corticostriatal pathway Nigrostriatal pathway Thalamostriatal pathway

14. i) Corticostriatal pathway Originates from all regions of neocortex predominantly from frontal and parietal areas Uses glutamate as neurotransmitter Afferents from sensorimotor cortex terminates predominantly in putamen Afferents from association regions of cortex preferentially terminate in caudate nucleus

15. ii) Nigrostriatal pathway Arises from pars compacta Uses neurotransmitter dopamine Different portions of striatum receive input from dorsal tier or ventral tier dopaminergic containing neurons of substantia nigra

16. iii) Thalamostriatal pathway Originates in thalamus Thalamic nuclei providing projections are intra-laminar nuclei, particularly the central median nucleus

17. CEREBRAL CORTEX STRIATUM PARS COMPACTA PARS RETICULATA THALAMUS THALAMOSTRIATAL PATHWAY CORTICOSTRIATAL PATHWAY NIGROSTRIATAL PATHWAY SCHEMATIC REPRESENTATION OF INPUTS OF BASAL GANGLIA 19

18. CONNECTION OF THE CORPUS STRIATUM Afferent Fibers Corticostriate Fibers All parts of the cerebral cortex send axons to the caudate nucleus and the putamen The largest input is from the sensory-motor cortex Glutamate is the neurotransmitter Efferent Fibers Striatopallidal Fibers Striatopallidal fibers pass from the caudate nucleus and putamen to the globus pallidus They have gamma- aminobutyric acid ( GABA ) as their neurotransmitter

19. Afferent Fibers Efferent Fibers Thalamostriate Fibers The intralaminar nuclei of the thalamus send large numbers of axons to the caudate nucleus and the putamen Nigrostriate Fibers Neurons in the substantia nigra send axons to the caudate nucleus and the putamen and liberate dopamine at their terminals as the neurotransmitter I nhibitory in function Striatonigral Fibers Striatonigral fibers pass from the caudate nucleus and putamen to the substantia nigra Some of the fibers use GABA or acetylcholine as the neurotransmitter, while others use substance P

20. Brainstem Striatal Fibers (Afferent fibers) - Ascending fibers from the brainstem end in the caudate nucleus and putamen - Liberates serotonin at their terminals as the neurotransmitter - Inhibitory in function

21. CONNECTIONS OF GLOBUS PALLIDUS AFFERENT FIBER Striatopallidal Fibers Striatopallidal fibers pass from the caudate nucleus and putamen to the globus pallidus As noted previously, these fibers have GABA as their neurotransmitter EFFERENT FIBERS Pallidofugal Fibers Divided into groups: the ansa lenticularis , which pass to the thalamic nuclei (2) the fasciculus lenticularis , which passes to the subthalamus (3) the pallidotegmental fibers, which terminate in the caudal tegmentum of the midbrain (4) the pallidosubthalamic fibers, which pass to the subthalamic nucleus

22. INTERNAL PROCESSIONG Direct pathway Indirect pathway

23. Direct Pathway Striatum receives major projection from cerebral cortex Within striatum , medium spiny neurons sends inhibitory projections to Globus pallidus internal ( GPi ) Reduces inhibitory output of Basal ganglia Promotes movement

24. Indirect Pathway Increases inhibitory output of basal ganglia Consequence leads to inhibition of movement

25. OUTPUTS OF BASAL GANGLIA Gpi is the source of much of the output of basal ganglia. Gpi provides projections to Ventral lateral(VL) and Ventral anterior(VA) nuclei of Thalamus and central median nuclei. Substantia nigra pars reticulata also provides projections to VL and VA nuclei These projections of VA and VL project to premotor and pre-frontal cortices Projections of premotor and prefrontal cortices project to primary motor cortex

26. PUTAMEN CIRCUIT PUTAMEN BEGIN IN THE PREMOTOR AND SUPPLEMENTARY AREAS OF THE MOTOR CORTEX AND IN THE SOMATOSENSORY AREAS OF THE SENSORY CORTEX INTERNAL PORTION OF THE GLOBUS PALLIDUS EXTERNAL GLOBUS PALLIDUS, SUBTHALAMUS SUBSTANTIA NIGRA VENTROANTERIOR AND VENTROLATERAL RELAY NUCLEI OF THE THALAMUS CEREBRAL PRIMARY MOTOR CORTEX, PREMOTOR AND SUPPLEMENTARY CEREBRAL AREAS

27. CAUDATE CIRCUIT ASSOCIATION AREAS OF THE CEREBRAL CORTEX CAUDATE NUCLEUS INTERNAL GLOBUS PALLIDUS RELAY NUCLEI OF THE VENTROANTERIOR AND VENTROLATERAL THALAMUS PREFRONTAL, PREMOTOR, AND SUPPLEMENTARY MOTOR AREAS OF THE CEREBRAL CORTEX

28. DISORDER OF BASAL GANGLIA 1. Hyperkinetic disorders There are excessive and abnormal movements seen with chorea, athetosis , and ballism 2. Hypokinetic disorders There is a lack or slowness of movement Parkinson disease includes both types of motor disturbances

29. TREMORS Regular oscillating movement about a joint due to synchronous contraction of agonist and antagonist muscles resulting from disequilibrium between Ach and dopamine activity in striatum . Resting tremors: movement occurs in a relaxed supported extremity, reduced by ambulation Postural tremors: Sustained posture elicit tremor eg . Outstretched hands Intention tremors: Active limb oscillates more predominantly when reaching target eg . Patient trying to touch examiner’s fingers.

30. Chorea Rapid semi-purposeful, graceful, dance like non-patterned involuntary movements involving distal or proximal muscle groups due to involvement of caudate nucleus and degeneration of GABAergic fibres Dystonia Sustained or repetitive involuntary muscle contractions frequently causing twisting movements with abnormal postures due to lesions in putamen circuit

31. Athetosis Slow, writhing, involuntary movements with a propensity to affect arms and hands primarily due to lesion of lenticular nucleus . Hemiballismus A violent form of chorea that comprises wild, flinging, large amplitude movements on one side of the body contralateral to the lesion in subthalamic nucleus

32. Parkinson’s Disease Neurodegenerative disease associated with loss of dopaminergic neurons in substantia nigra Characteristic triad: Resting tremor( pill rolling tremor) Rigidity ( cogwhell ) Bradykinesia Gait and postural disturbances Shuffling gait Small handwriting ( micrographia ) Psychiatric manifestation: Depression, apathy, anxiety, psychosis

33. Huntington Disease A utosomal dominant inherited disease characterized by midlife onset restlessly progressive course C ombination of motor , psychiatric and cognitive symptoms Caused by a CAG ( trinucleotide ) repeat expansion mutation of huntingtin gene on chromosome 4 Polyglutamine disease D egeneration of GABA-secreting , Substance P & acetylcholine - secreting neurons of striatonigral inhibiting pathway which inhibits the caudate nucleus & putamen leading to abnormal body movements

34. BASAL GANGLIA AND PSYCHIATRIC IMPLICATIONS Major depressive disorder Hyper-intensities in subcortical regions such as basal ganglia, thalamus and periventricular region Tourette’s disorder Reduced basal ganglia volume, prominently in putamen and Globus pallidus Obsessive-compulsive disorder Smaller basal ganglia volume associated with severity of OCD Most patient show increased blood flow to the caudate

35. REFERENCES Kaplan & Sadock’s Comprehensive Textbook Of Psychiatry, 10 th edition . Snell’s Clinical Neuroanatomy , 8 TH Edition Guyton and Hall Textbook of Medical Physiology 14 th edition