BASAL GANGLIA

1. BASAL GANGLIA Sanaa Alshaarawy, PhD Khaleel Alyahya, PhD, MEd

2. OBJECTIVES • At the end of this lecture, students should be able to: • List the subdivisions of Basal Ganglia and state the function of each . • List the important relations of Corpus Striatum (Caudate & Lentiform Nuclei). • List the important connections of Corpus Striatum. • Describe briefly the main effects in cases of lesion of Basal Ganglia.

3. BASAL GANGLIA • The term “Basal Ganglia’’ refers to interconnected nuclear masses of grey matter in the forebrain. • deeply situated in the Cerebral Hemispheres, Diencephalon, and Midbrain. • Basal Ganglia functionally are “Extrapyramidal Motor System”. • Control posture and regulate voluntary movements. • It refers now to those structures whose damage causes movement disorders. • Abnormalities of basal ganglia result in movement disorders. • Parkinsonism and Huntington Diseases. • The Basal Ganglia are: • Corpus Striatum (in cerebral hemisphere). • Subthalamic Nucleus (in diencephalon). • SubstantiaNigra (in midbrain).

4. BASAL GANGLIA • Corpus striatum is subdivided anatomically into two large nuclei : • Caudate & Lentiform Nuclei (lenticular = Latin word lentil). • Lentiform Nucleus consists of several segments that form : • Putamen & Globus Pallidus. • Globus Pallidus is divided into : • Lateral (Outer) segment. • Medial (Inner) segment.

5. BASAL GANGLIA No longer spoken of Basal Ganglia Part of limbic system

6. CORPUS STRIATUM • Caudate Nucleus lies in the wall of lateral ventricle and is divided into head, body & tail. • Head is the largest part, protrudes into anterior horn of lateral ventricle in cerebral hemispheres. • Head is separated from putamen by the anterior limb of internal capsule, and is continuous inferiorly with putamen. • The body is long & narrow continuous with head at interventricular foeamen. • The curved tapering tail becomes continuous with amygdaloid nucleus in the temporal lobe, where it lies in the inferior horn of lateral ventricle.

7. BASAL GANGLIA • Nucleus accmbens lies where the Caudate Nucleus & Putamen are continuous beneath anterior limb of internal capsule. • It has connections with limbic system.

8. CORPUS STRIATUM • Lentiform Nucleus consists of Putamen (lateral) & Globus Pallidus (medial). • Is separated from thalamus by posterior limb of internal capsule. • Is separated from head of caudate nucleus by anterior limb of internal capsule.

9. CORPUS STRIATUM • Putamen lies lateral to internal capsule & Globus Pallidus. • It is separated from globus pallidus by a thin lateral medullary lamina. • Clastrum is a thin sheet of grey matter lying lateral to putamen, and divides the white matter into: • the external capsule (inner). • the extreme capsule (outer).

10. CORPUS STRIATUM • Globus Pallidus lies medial to putamen, between putamen & internal capsule. • Divided into outer lateral & inner medial parts, separated by thin sheet of medial medullary lamina. • The medial part has connections with pars reticulata of substantianigra of midbrain

11. BASAL GANGLIA • At the basal part of Rostral forebrain, SubstantiaInnominatalies (beneath corpus striatum). • Containing nucleus basalis. • Projects Acetylecholine to cerebral cortex. • Degeneration of this part leads to Alzheimer’s disease

12. CONNECTIONS OF CORPUS STRIATUM • Caudate and Putamen • Input portion of Corpus Striatum. • They receive afferents From cerebral cortex, intralaminar thalamic nuclei & pars compacta of substantianigera. • Globus Pallidus (Mededial Pallidum & SubstantiaNigra) • Output portion of Corpus Striatum. • Red, Glutamatergic pathway. • Green, GABAergicpathway. • Purple, Dopaminergicpathway.

13. CONNECTIONS OF CORPUS STRIATUM • Striatal Afferents (Input): • Cortico-Striatal Fibres. • Glutamic acid (exitatory). • Thalamo-Striatal Fibres (exitatory). • Nigro -Striatal Fibres (Pars Compacta Part). • Dopamine (inhibitory). • Lesion of Nigro-Striatal Fibers. • Stops release of dopamine into corpus striatum leading to Parkinsonism. • Striatal Efferents (Output): • From Corpus Striatum to Globus Pallidus & Pars Reticulata of SubstantiaNigra. • Striato-Pallidal Fibres. • Striato-Nigral Fibres (Pars Reticulata Part). • They utilise GABA (gamma aminobutyric acid) as neurotransmitter (inhibitory) • Red, Glutamatergic pathway. • Green, GABAergicpathway. • Purple, Dopaminergicpathway.

14. CONNECTIONS OF GLOBUS PALLIDUS • Pallidal Afferents: • Subthalamo-Pallidal Fibres. • Excitatory. • Striato-Pallidal Fibers. • Inhibitory. • Pallidal Efferents: • Pallido-Subthalamic Fibres . • Inhibitory (GABA). • Pallido-Thalamic Fibres. • The Thalamus in turn sends fibers to the motor areas of the frontal lobe.

15. BASAL GANGLIA DISEASES • Parkinson’s Disease: • Is a neurodegenerative disease, usually of the elderly. • Unknown cause. • It is due to degeneration of dopaminergicneurones of Pars Compacta of SubstantiaNigra and so depletion of Striatal dopamine levels. • Lesion of Nigro-Striatal Fibres. • Characterized by: • Akinesia (lack of movement): absence of swinging arm during walking, mask face & shuffling gait. • Rigidity: a flexed posture. • Tremors: a resting (static) tremors.

16. BASAL GANGLIA DISEASES • Huntington’s Disease: • A degenerative hereditary disease. • It is due to progressive degeneration of striatum and cerebral cortex. • Leading to Chorea & progressive dementia. • Chorea (dance): involuntary, quick, jerky, irregular, non repetitive & purposless movement. e.g. sudden movement of head or limb

17. SUMMARY • Corpus Striatum includes: • Caudate nucleus. • Putamen. • Globus Pallidus. • These structures are primarily concerned with control of posture & movement. • Topographically, Putamen & Globus Pallidus constitute the Lentiform Nucleus. • Functionally, Caudate Nucleus & Putamen form a single entity, the Neostriatum (Striatum), while Globus Pallidus forms thePaleostriatum

18. SUMMARY • Head of Caudate Nucleus lies medial to internal capsule and forms a prominent bulge in lateral wall of anterior horn of lateral ventricle. • Putamen & Globus Pallidus lie lateral to internal capsule, deep to cortex of insula

19. SUMMARY • Connections of Striatum: • Caudate Nucleus & Putamen are “INPUT’’ regions of Corpus Striatum. • They receive Afferents from Cerebral Cortex, Intralaminar Thalamic Nuclei & Pars Compacta of SubstantiaNigra. • Efferent fibers are directed to Globus Pallidus and Pars Reticulata of SubstantiaNigra

20. SUMMARY • Connections of Globus Pallidus: • Globus Pallidus consists of 2 segments: • Medial (inner) & Lateral (outer). • The Medial segment & Pars Reticulata of SubstantiaNigra are ‘OUTPUT’ regions of Corpus Striatum. • Striato-Nigral Fibers. • Globus Pallidus receives afferents from Striatum and Subthalamic Nucleus. • Lateral segment projects to Subthalamic Nucleus. • Medial segment projects primarily to Thalamus. • Thalamus in turn sends fibers to motor areas of frontal lobe

21. QUESTIONS • Which is WRONG regarding the Basal Ganglia? • Corpus Striatum is divided into Caudate Nucleus & Lentiform Nucleus. • Lentiform Nucleus consists of Putamen & Globus Pallidus. • It is a collection of white matter. • Amygdaloid nucleus is connected to the tail of Caudate Nucleus.

22. QUESTIONS • Which is TRUE regarding Parkinsons’s disease? • Is a hereditary undegenerative disease. • It is due to degeneration of Pars Reticulata of SubstantiaNigra. • It leads to depletion of Striatal Dopamine levels. • Its main feature is Chorea.

23. QueSTioN?