Download BASAL GANGLIA

BASAL GANGLIA
OBJECTIVES

Functional anatomy of basal ganglia

Components of basal ganglia

Neuronal circuit of basal ganglia

Putamen circuit

Caudate circuit

Specific neurotransmitter in basal ganglia

Functions of basal ganglia

Abnormalities of putamen and caudate circuit

Disorders of basal ganglia
BASAL GANGLIA

The basal nuclei are masses of cerebral Gray matter buried deep in the white
matter, lateral to the thalamus deep within the cerebral hemispheres.

The term is debatable because these masses are nuclei rather than ganglia (cluster
of neurons outside the CNS).

Two of basal ganglia lie side by side, lateral to thalamus.

Globus pallidus is closer to thalamus and putamen is closer to the cerebral cortex.

The caudate nucleus has a large head connected to a smaller tail by long comma
shaped body.

The term corpus striatum refers to the striated appearance of internal capsule as it
passes among the basal ganglia.

The nearby structures that are functionally linked to the basal ganglia are associated
nuclei:
 Substantia nigra of the midbrain
 Subthalmic nuclei of diencephalon
 Ventral anterior and ventral lateral nuclei of thalamus
 Axons from Substantia nigra terminate in the caudate nucleus and putamen.
 Subthalmic nuclei interconnect with globus pallidus.
Anatomically the basal ganglia are derived from telencephalon of forebrain and
include the following nuclei:

1 - Corpus striatum.
A - caudate nucleus,
B - putamen,
C - globus pallidus

2 - Substantia nigra.

3 - Red nucleus.

4 - Subthalmic nuclei.

Caudate nucleus, putamen, globus pallidus are true basal ganglia because they are
derived from telencephalon of fore brain.

Substantia nigra, red nucleus and subthalmic nuclei are associated basal ganglia b/c
they work in association with true nuclei.

Putamen And Globus Pallidus Are Called Lentiform Nucleus.

Substantia nigra and Red nucleus are derived from mid bran and Subthalmic nuclei
derived from Diencephalon.

There is no universally accepted anatomical definition but for clinical purpose all
these nuclei are included in basal ganglia.

Caudate nucleus and lentiform nucleus are called the corpus striatum after their
striped appearance.

The putamen and globus pallidus are also collectively called the lentiform nucleus,

FUNCTIONALLY, the basal ganglia and their interconnections and neurotransmitters
form the extrapyramidal system.
COMPONENTS OF BASAL GANGLIA

Corpus Striatum
o Striatum ----- Caudate Nucleus & Putamen
o Pallidum ----- Globus Pallidus (GP)

Substantia Nigra
o Pars Compacta (SNc)
o Pars Reticulata (SNr)

Subthalamic Nucleus (STN)

Ventral Striatum and Ventral Pallidum
o Nucleus Accumbens Septi

Non cholinergic portion of Substantia Innominata

Corpus Striatum

Striatum ----- Caudate Nucleus & Putamen

Pallidum ----- Globus Pallidus (GP)

Substantia Nigra

Pars Compacta (SNc)

Pars Reticulata (SNr)

Subthalamic Nucleus (STN)

Ventral Striatum and Ventral Pallidum

Nucleus Accumbens Septi

Non cholinergic portion of Substantia Innominata
BASAL GANGLIA CONNECTIONS
Input Portion
STRIATUM
o (Caudate Nucleus and Putamen)
Output Portion

PALLIDUM (Globus Pallidus)

SNr (Substantia Nigra, Pars Reticulata)
BASAL GANGLIA
INPUT NUCLEI
o Caudate
o Putamen

caudate + putamen = striatum
o Nucleus accumbens

Output nuclei
o Globus Pallidus -external segment
o Subthalamic nucleus
o Substantia nigra
o Ventral tegmental area
o
Major inputs to the striatum come from the cerebral cortex & the thalamus

Globus pallidus sends GABAergic, inhibitory projections to the brainstem and
thalamus.

Subthalamic nucleus plays an important role in control of the basal ganglia’s output.
NEURONAL CIRCUIT OF BASAL GANGLIA

The pathway into and out of the basal ganglia are complex.

Almost all areas of cerebral cortex project on to the striatum, including a critical input
from the motor cortex.

The striatum then communicate with the thalamus and then back to the cortex via
two different pathways.
 Indirect pathway
 Direct pathway
INDIRECT AND DIRECT PATHWAY

The outputs of the indirect and direct pathway from the BG to the motor cortex are
opposite and carefully balanced.

A disturbance in one of the pathway will upset this balance of motor control and such
imbalance is characteristic of diseases of BG.

ADDITIONAL CONNECTION

There is an additional connection (in addition to the basic circuitry of the direct and
indirect pathways) between the striatum and the pars compacta of the substantia
nigra.

The NT for the connection back to the striatum is dopamine.

This additional connection b/w SN and the striatum means that dopamine will be
inhibitory (via D2 receptors) in the indirect pathway and excitatory (via D1 receptors)
in the direct pathway.

NEURONAL CIRCUIT OF BASAL GANGLIA
There are two major circuits regarding basal ganglia.

Putamen circuits

Caudate circuits

Afferent is corticostriat projection from cerebral cortex to putamen and caudate
nucleus then to globus pallidus.

Efferent is from globus pallidus to thalamic nucleus also from globus pallidus to
substantia nigra – brainstem reticular formation – reticulospinal tract.

Fibers from globus pallidus go to red nucleus then to rubrospinal tract.
TWO MAJOR CIRCUITS OF BG

Putamen circuit
o subconscious execution of learned patterns of movement

Caudate circuit
o large input into caudate from the association areas of the brain
o caudate nucleus plays a major role in cognitive control of motor activity.
PUTAMEN CIRCUIT

The principal pathway through basal ganglia begin mainly in premotor and
supplementary motor areas of motor cortex as well as in primary somato - sensory
areas of sensory cortex,

Then pass mainly to putamen by passing caudate nucleus,

Three ancillary circuits function in association with primary putamen circuit.

From putamen to external globus pallidus to sub thalamus, to the relay nucleus of
thalamus and back to motor cortex.

From putamen to internal globus pallidus, to substantia nigra to relay nuclei of
thalamus and also returning to motor cortex.

THREE ANCILLARY CIRCUITS

A local feed back circuit from external globus pallidus to sub thalamic nuclei and
again returning to external globus pallidus.

Globus pallidus projection is inhibitory due to NT GABA.

CAUDATE CIRCUIT

Caudate nucleus extends in all lobes of cerebrum starting anteriorly in frontal lobe.

then passing posteriorly through parietal and occipital lobes .

finally curving forward like the letter C into temporal lobe.

Caudate nucleus receives input from association area of brain.

Signals pass from cerebral cortex to caudate nucleus then transmitted to internal
Globus pallidus.

Then to the relay nucleus of ventroanterior and ventrolateral thalamus.

Finally back to prefrontal, promoter and supplementary motor areas of cerebral
cortex.
NEUROTRANSMITTERS IN BASAL GANGLIA
Some Neurotransmitters that are known to function with basal ganglia are:

A dopamine pathway from substantia nigra to caudate nucleus and putamen.

A gamma amino butyric acid (GABA) pathway from caudate nucleus and putamen to
globus pallidus and substantia nigra.

Acetylcholine pathway from cortex to caudate nucleus and putamen.

Multiple general pathways from brainstem that secrete nor epinephrine, serotonin,
epinephrine and other NT in the basal ganglia and in other parts of cerebrum.

In addition to all these are multiple glutamate pathways that provide most of the
excitatory signals that balance out a large number of inhibitory signals transmitted
specially by Dopamine, GABA, and Serotonin transmitters.

FUNCTIONAL CONSIDERATION

Functional Consideration

Selection of “Preprogramed (learned) motor plans”
OF BASAL GANGLIA
o Basal Ganglia Circuit ---- Selection Mechanism
o Selection Inability -------- Akinesia and Hypokinesia
o Faulty Selection ----------- Hyperkinesia

Generation (learning) of motor programs

Programming of several motor fragments into complex motor
routines
o Cerebral Palsy ------------- Disordered motor program

FUNCTIONS OF BASAL GANGLIA

The basal ganglia receive input from all lobes of cerebral cortex and have
projections via thalamus, to the frontal cortex to assist in regulating movements.

BG act as accessory motor cortex. It does not work alone but works in association
with cerebral cortex.

A major function of basal ganglia is to help regulate initiation and termination of
movements.

Activity of neurons in putamen precedes or anticipated body movements

Activity of neurons in caudate nucleus occurs prior to eye movements.

The globus pallidus helps regulate the muscle tone Required for specific body
movements.

The basal ganglia also control subconscious contractions of skeletal muscles.
DISORDERS OF BASAL GANGLIA
SYDENHAM’S CHOREA

Complication of Rheumatic Fever

Fine, disorganized , and random movements of extremities, face and tongue

Accompanied by Muscular Hypotonia

Typical exaggeration of associated movements during voluntary activity

Usually recovers spontaneously in 1 to 4 months
HUNTINGTON’S CHOREA

Clinical Feature

Predominantly autosomal dominant

inherited chronic fatal disease

(Gene: chromosome 4)

Insidious onset: Usually 40-50

Choreic movements in onset

Frequently associated with emotional disturbances

Ultimately, grotesque gait and severe dysarthria, progressive dementia ensues.
HEMIBALLISM

Usually results from CVA (Cerebrovascular Accident) involving subthalamic nucleus

sudden onset

Violent, writhing, involuntary movements of wide excursion

confined to one half of the body

The movements are continuous and often exhausting but cease during sleep

Sometimes fatal due to exhaustion

Could be controlled by phenothiazines and stereotaxic surgery
PARKINSON’S DISEASE

It is one of the most common neurodegenerative diseases and estimated to occur in
1-2% of individuals over age 65.

Familial cases also occur, but these are uncommon.

Dopaminergic neurons and dopamine receptors are steadily lost with age in the BG
in normal individual and acceleration of these losses apparently precipitates
parkinsonism

The characteristics of Parkinson’s Disease due to dysfunction of BG are :

Resting Tremor

Parkinsonian Posture

Rigidity-Cogwheel Rigidity

Slowness and delay of movement

Shuffling gait.


