Basal Ganglia

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.

• 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)

Basal Ganglia

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 .

BASAL GANGLIA

TERMINOLOGIESNeurological structure

Basal nuclei

Corpus striatum Caudate nucleus + lentiform nucleus +Putamen

Amygdala Amygdaloid nucleus

Claustrum Claustrum

Neostriatum Caudate nucleus + putamen

Paleostriatum Globus pallidus

Caudate nucleus Caudate nucleus

Lentiform nucleus Globus pallidus + putamen

• 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.

Basal Ganglia: Organization

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.

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.

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.

Relations of Caudate Nucleus to lateral ventricle

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

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*.

* *

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

Connections of the basal ganglia

• Caudate nucleus • Putamen

• Globus pallidus – output leaves

receive input

• 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

Connections of the basal ganglia

Connections of the Striatum

Afferent Fibers

1. Corticostriatal2. Thalamostriatal3. Nigrostriatal4. Brainstem

striatal

Efferent Fibers

I. StriatopallidalII. Striatonigral

12

3

4

II

I

Connections of the Globus Pallidus

Afferent Connections:1. Striatopallidal fibers2. 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).

subthalamic fasciculus

Together with the pars reticulata of substatia nigra, the medial segment is regarded as output part of the basal ganglia.

2

1

subthalamic fasciculus

2

1

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:1. primarily to the thalamus

(pallidothalamic fibers)2. to the pedunculo-pontine

nucleus of the brain stem tegmentum (pallidotegmental fibers)

Midbrain

Connections of the Globus Pallidus

• Pallidothalamic fibers: • take two routes:1-Pass around the anterior margin of the internal capsule as the ansa lenticularis2-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).

• 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.

Connections

CN/

i/laminar thal

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

• 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.

Function Functions of the basal ganglia

Cerebral cortex

Corticospinal CorticobulbarCorticostriatal

Direct Indirect

StriatonigralStriatopallidal

inhibitory

Disinhibit neurone thalamus

Facilitate movement

Subthalamic NMed pallidalinhibitory

inhibitoryLat pallidal

Activate neurone

Inhibit unwanted movement

excitatory

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

Cerebral cortex

Corticospinal CorticobulbarCorticostriatal

Direct Indirect

StriatonigralStriatopallidal

inhibitory

Disinhibit neurone thalamus

Facilitate movement

Subthalamic NMed pallidalinhibitory

inhibitoryLat pallidal

Activate neurone

Inhibit unwanted movement

excitatory

Basal Ganglia-SummaryFunction - Dysfunction

• Its dysfunction Does NOT cause paralysis, sensory loss or ataxia, but leads to:I. Abnormal motor control: emergence of abnormal,

involuntary movements (dyskinesias) e.g. tremors, chorea, athetosis, myoclonus, tic or dystonia..

II. Alteration in muscle tone (hypertonia /hypotonia).

• Function• 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.