1. Basal Ganglia

2. Objectives
Understand the anatomical and functional definition of the basal ganglia.
Identify the different components of the basal ganglia.
Describe the connections of the different components of the basal ganglia and the indirect pathways from the basal ganglia to the lower motor neurons.
Describe signs and symptoms of lesions which affect different components of the basal ganglia.

3. Basal Ganglia Definition:
a group of nuclei, located deep within the cerebral hemispheres.
They are part of the extrapyramidal motor system, principally involved in the control of posture and movements (primarily by inhibiting motor functions)

4. Components The basal ganglia include: 1-Caudate nucleus 2-Putamen
3-Globus pallidus:
- external segment
- internal segment
Subthalamic Nucleus
Substantia nigra
Are functionally related to the basal ganglia
The Amygdala, located within the temporal lobe has a similar embryologic origin but functionally is part of the limbic system.

5. BASAL GANGLIA BASAL GANGLIA CORPUS STRIATUM NEOSTRIATUM
CAUDATE NUCLEUS
PUTAMEN
PALEOSTRIATUM
GLOBUS PALLIDUS
LENTIFORM NUCLEUS
AMYGDALA
CLAUSTRUM

6. TERMINOLOGIES Neurological structure Basal nuclei Corpus striatum
Caudate nucleus + lentiform nucleus +Putamen
Amygdala
Amygdaloid nucleus
Claustrum
Neostriatum
Caudate nucleus + putamen
Paleostriatum
Globus pallidus
Caudate nucleus
Lentiform nucleus
Globus pallidus + putamen

7. Basal Ganglia: Organization
Functionally the putamen is more closely allied to caudate nucleus and together constitute the neostriatum or simply STRIATUM.
The globus pallidus is the oldest part of corpus striatum and is called paleostriatum or simply PALLIDUM.
Anatomically the putamen and globus pallidus are together called the lentiform nucleus.
The striatum and the pallidum are collectively known as the corpus striatum.

9. Corpus Striatum Lies lateral to the thalamus.
It is divided by internal capsule into caudate nucleus and lentiform nucleus.
Bands of grey matter pass from lentiform nucleus across the internal capsule to the caudate nucleus, giving the striated appearance hence, the name corpus striatum.
The most ventral part of the corpus striatum is called the nucleus accumbens, which has connections with the limbic system.

10. Caudate Nucleus Large C-shaped or comma-shaped grey mass
It has a Head, a Body and a Tail.
Head : ( Anterior) Large, & rounded
Forms the lateral wall of the anterior horn of lateral ventricle.
Completely separated from the putamen by the internal capsule except rostrally where it is continuous with the putamen through and beneath the anterior limb of internal capsule.

12. Caudate Nucleus Body: Long & narrow continuous with head
lies in the floor of body of lateral ventricle.
Tail : Long, narrow & tapering,
descends posteriorly into the temporal lobe
lies in the roof of inferior horn of lateral ventricle.

13. Relations of Caudate Nucleus to lateral ventricle

14. Lentiform Nucleus
A three sided, wedge-shaped mass of grey matter, with a convex outer surface and an apex which lies against the genu of the internal capsule
Divided into a:
Larger darker lateral portion called Putamen &
Smaller, lighter medial portion called Globus pallidus
External capsule

15. Putamen * * Lies lateral to the internal capsule and globus pallidus
Separated from globus pallidus by a thin sheath of Nerve Fibers, the lateral medullary lamina
The white matter lateral to putamen is divided, by a sheath of GREY MATTER, the CLAUSTRUM, into two parts:
The part between the putamen and claustrum forms the external capsule*
between the claustrum and the cortex of insula (deep within the lateral fissure) forms the extreme capsule*. * *

16. Globus Pallidus
Lies medial to the putamen, separated from it by lateral medullary lamina
Consists of two divisions, the lateral & the medial segments, separated by a thin sheath of nerve fibers, the medial medullary lamina.
The medial segment is similar, in terms of cytology and connections with the pars reticulata of substantia nigra

17. Connections of the basal ganglia
Caudate nucleus
Putamen
Globus pallidus – output leaves
receive input

18. Connections of the basal ganglia
Connections of striatum
Caudate nucleus & putamen – INPUT
Receive afferent - cerebral cortex, intralaminar thalamic nuclei, subs nigra
Efferent – globus pallidus, subs nigra
Connections of globus pallidus
2 segments – med & lat
Med & subs nigra – OUTPUT
Receive afferent – striatum, subthalamic nucleus
Efferent
Lat – subthalamic N
Med – thalamus (VA, VM ,CM) – motor areas

19. Connections of the Striatum
Afferent Fibers
Corticostriatal
Thalamostriatal
Nigrostriatal
Brainstem striatal 1 2 I
Efferent Fibers
Striatopallidal
Striatonigral 4 II 3

20. Connections of the Globus Pallidus
Together with the pars reticulata of substatia nigra, the medial segment is regarded as output part of the basal ganglia.
Afferent Connections:
Striatopallidal fibers
Subthalamopallidal fibers: Originate from subthalamic nucleus of the diencephalon. Pass laterally through the internal capsule as subthalamic fasciculus and terminate in both segments of globus pallidus (more in the medial segment). 1 2
subthalamic fasciculus

21. Connections of the Globus Pallidus
Efferent connections:
The two segments have different projections
The lateral segment principally projects to subthalamic nucleus via the subthalamic fascicle.
The medial segment together with the pars reticulata of substatia nigra projects:
primarily to the thalamus (pallidothalamic fibers)
to the pedunculo-pontine nucleus of the brain stem tegmentum (pallidotegmental fibers) 1 2
Midbrain
subthalamic fasciculus

22. Pallidothalamic fibers:
take two routes:
1-Pass around the anterior margin of the internal capsule as the ansa lenticularis
2-Pass through the internal capsule as the lenticular fasciculus.
Both sets of fibers continue to course medially and then loop dorsally and laterally as thalamic fasciculus to enter the thalamus (VA, VL and centromedian nuclei).

23. All of this circuitry is on the same side of the brain—uncrossed.
Thus, the basal ganglia affect function mediated by the ipsilateral motor cortex.
Since motor cortex controls the movements of the contralateral body, the basal ganglia affects movements of the contralateral side of the body.

24. Connections
i/laminar thal
CN/

25. Functions of the basal ganglia
Cerebral cortex, basal ganglia, cerebellum and thalamus
motor activity
muscle tone
organization of movement
What type ? : cerebral cortex
How to perform? : basal ganglia + cerebellum
Assist in regulation : thalamus

26. Functions of the basal ganglia
Part of extra-pyramidal motor system
Facilitate behaviour & movement – required and appropriate
Inhibit unwanted & inappropriate
The deficits tend to fall into one of two categories:
1- The presence of extraneous unwanted movements OR
2- An absence or difficulty with intended movements.
The balance between the cerebellum and the basal ganglia allows smooth, coordinated movement, and a disturbance in either system will show up as movement disorders.

27. Cerebral cortex
Corticospinal
Corticobulbar
Corticostriatal
excitatory
Direct
Indirect
inhibitory
Striatonigral
Striatopallidal
Lat pallidal
inhibitory
Subthalamic N
inhibitory
Med pallidal
Activate neurone
Disinhibit neurone
thalamus
Facilitate movement
Inhibit unwanted movement

28. Diseases of basal ganglia
Change in muscle tone
Abnormal involuntary movement
Parkinsonism
Effect on the opposite side
Degeneration of dopamine-producing cells in substantia nigra-depletion of dopamine in striatum
Resting tremors
Rigidity – simultaneous contraction of flexors and extensors
Bradykinesia = Slowness of movement – brake cannot be released
No paralysis, sensory loss, ataxia

29. Cerebral cortex
Corticospinal
Corticobulbar
Corticostriatal
excitatory
Direct
Indirect
inhibitory
Striatonigral
Striatopallidal
Lat pallidal
inhibitory
Subthalamic N
inhibitory
Med pallidal
Activate neurone
Disinhibit neurone
thalamus
Facilitate movement
Inhibit unwanted movement

30. Basal Ganglia-Summary Function - Dysfunction
The corpus striatum assists in regulation of voluntary movement and learning of motor skills.
Their function is to facilitate behavior and movement that are required and appropriate, and inhibit unwanted or inappropriate movement.
Its dysfunction Does NOT cause paralysis, sensory loss or ataxia, but leads to:
Abnormal motor control: emergence of abnormal, involuntary movements (dyskinesias) e.g. tremors, chorea, athetosis, myoclonus, tic or dystonia..
Alteration in muscle tone (hypertonia /hypotonia).