BASAL GANGLIASanaa Alshaarawy, PhD

Khaleel Alyahya, PhD, MEd

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.

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). Substantia Nigra (in midbrain).

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.

BASAL GANGLIA

No longer spoken of Basal Ganglia

Part of limbic system

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.

BASAL GANGLIA

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

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.

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).

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 substantia nigra of midbrain

BASAL GANGLIA

At the basal part of Rostral forebrain, Substantia Innominata lies (beneath corpus striatum). Containing nucleus basalis. Projects Acetylecholine to cerebral cortex.

Degeneration of this part leads to Alzheimer’s disease

CONNECTIONS OF CORPUS STRIATUM

Caudate and Putamen Input portion of Corpus Striatum. They receive afferents From

cerebral cortex, intralaminar thalamic nuclei & pars compacta of substantia nigera.

Globus Pallidus (Mededial Pallidum & Substantia Nigra)Output portion of Corpus

Striatum.

Red, Glutamatergic pathway. Green, GABAergic pathway. Purple, Dopaminergic

pathway.

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 Substantia Nigra.

Striato-Pallidal Fibres. Striato-Nigral Fibres (Pars Reticulata

Part). They utilise GABA (gamma

aminobutyric acid) as neurotransmitter (inhibitory)

Red, Glutamatergic pathway. Green, GABAergic pathway. Purple, Dopaminergic

pathway.

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.

BASAL GANGLIA DISEASES

Parkinson’s Disease: Is a neurodegenerative disease,

usually of the elderly.Unknown cause.

It is due to degeneration of dopaminergic neurones of Pars Compacta of Substantia Nigra 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.

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

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 the Paleostriatum

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

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 Substantia Nigra.Efferent fibers are directed to Globus Pallidus and Pars Reticulata

of Substantia Nigra

SUMMARY

Connections of Globus Pallidus:Globus Pallidus consists of 2 segments:

Medial (inner) & Lateral (outer).The Medial segment & Pars Reticulata of Substantia Nigra 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

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.

QUESTIONS

Which is TRUE regarding Parkinsons’s disease?

Is a hereditary undegenerative disease. It is due to degeneration of Pars Reticulata of Substantia Nigra. It leads to depletion of Striatal Dopamine levels. Its main feature is Chorea.

QueSTioN?