Functional anatomy of the basal ganglia
Ahmad Hany Tatwany
The Basal Ganglia
Basal ganglia are collections of neurons Found within
the white matter of each cerebral hemisphere.Play an
important role in the control of posture & initiation of
voluntary movement. This would include the caudate
nucleus, the putamen, the Globus pallidus,substabtia
nigra, and the subthalamic
The caudate and putamen are also called the
neostriatum, histologically these are the same
neurons but in the human brain they are
partially separated from each other by
projection fibers.
The putamen and Globus pallidusare
anatomically grouped together in the human
brain and are called the lentiform or lenticular
nucleus because of the lens-like configuration of
the two nuclei.
The striatum & pallidum (globus pallidus) are
known as the corpus striatum
Caudate nucleus
Large C-shaped mass of gray mater.
The caudate nucleus is anatomically associated
with the lateral ventricle and follows its curvature.
Anterolateral, superior, posterior and inferior to the
thalamus.
Medial to the anterior limb of the internal capsule.
It is described as having three portions :
• The head, located deep within the frontal
lobe
• The body, located deep in the parietal lobe
• The tail, which goes in to the temporal lobe
The head of the caudate nucleus is large and
rounded and intrudes into the space of the anterior
horn of the lateral ventricle.
The body of the caudate nucleus tapers and
becomes considerably smaller and is found beside
the body(floor)of the lateral ventricle.
The tail is long and slender follows the inferior horn
of the lateral ventricle into the temporal lobe .
Terminates anteriorly in the amygdala.
The lentiform
The Putamen It is darker and lateral and closely
intertwined with the caudate nucleus and
globus pallidus, which are together known as
the corpus striatum.
Signals are transmitted through these structures
to the motor thalamus, brain stem, and motor
neocortex, which helps the body with all aspects
of physical movement.
The lentiform
The globus pallidus, is lighter and immediately
medial to the putamen and has a medial and
lateral segment. There's a small rind of cells
called the claustrum which is separated from the
putamen by the external capsule and from the
insular cortex by the extreme capsule.
has two components, a medial (internal) and
lateral (external) segment
SUBSTANTIA NIGRA
• The substantia nigra is a large pigmented
cluster of neurons that consists of two parts,
the pars reticulata and the pars compacta.
Cells of the pars compacta contain the dark
pigment melanin(neurmelanin)these cells
synthesize dopamine and project to either the
caudate nucleus or the putamen.
Subthalamic nucleus
Are small paired structures that are part of the
functional basal ganglia. They are located inferior to
the thalamus, dorsal to the substantia nigra and
medial to the internal capsule.
Made of the cranial ends of the red nucleus and
substantia nigra and subthalamic nucleus.
The subthalamic nucleus has the shape of the
biconvex and receives its main input from the
lateral pallidum (external segment of the Globus
pallidus).
Medially
The lentiform nucleus is now seen to be
composed of its two portions, the putamen,
laterally, and the globus pallidus, which is
medially placed
HORIZONTAL SECTION OF
HEMISPHERES
This brain section exposes the white matter of
the hemispheres, the basal ganglia, and parts of
the ventricular system. Understanding this
particular depiction of the brain is vital to the
study of the forebrain. The structures seen in
this view are also of immeasurable importance
clinically, and this view is most commonly used
in neuroimaging studies, both CT and MRI
Connections
All part of the cortex send axons (glutamate
secreting) to the specific part of the
striatum(corticostriate)
Fibers from intralaminar nuclei of thalamus to
the striatum (thalamostriate)
Dopamine-secreting inhibitory fibres from
substantia nigra (nigrostriate)
Serotonin-secreting ascending inhibitory fibres
from the brain stem to striatum
Lenticulostriate arteries
Middle cerebral artery
Blood supply
Blood supply
Basal ganglia pathways
There are two described pathways for
transmission of signals through the basal
ganglia, a direct and an indirect pathway.
These pathways have competing effects on
movement and there is often thought to be a
balance between these systems that is involved
in establishing and regulating tone. In both the
direct and indirect pathways, the caudate and
putamen represent the first synapse in the
system
Direct pathway
In the direct pathway excitatory input from the
cerebral cortex project the striatal neurons in
the caudate nucleus and putamen. Through
disinhibition, activated inhibitory neurons in the
striatum , which use GABA as their
neurotransmitter , project to and inhibit
additional GABA neurons in the internal
segment of the Globus pallidus.
Then the GABA axons of the internal segment of
the globus pallidus to the thalamus. Because
their input to the thalamus is disinhibited the
thalamic input excites the motor cortex. The net
effect of the disinhibition in the direct pathway
result in increased level of cortical excitation
and promotion of the movement.
Indirect pathway
In the indirect pathway , excitatory input from
the cerebral cortex also projects to striatal
neurons in the caudate nucleus and putamen.
These inhibitory neurones in the striatum which
also use GABA as their neurotransmitter project
to and additional to GABA neurons in the
external segment of the Globus pallidus
The GABA axons of the external segment of the
Globus pallidus project to the subthalamic nucleus.
Through disinhibition the subthalamic nucleus
excites inhibitory GABA neurones in internal
segment of the Globus pallidus which inhibit the
thalamus. This decrease the level of cortical
excitation ,inhibitory movement .The net effect of
the disinhibition of the indirect pathway result in
DECREASED level of cortical excitation and
suppression of the unwanted movement.
Dopamine and cholinergic effects
In addition to the GABA neurons, 2 other chemically
significant neurons enhance the effect of the direct or
indirect pathways.
Dopaminergic neurons in the substantia nigra in the
mid brain project to the srtiatum.the effect of
dopamine excites or drive the direct pathway
increasing the cortical excitation. Dopamine excites the
direct pathway through D1 receptors and inhibit the
indirect pathway through D2 receptors
Cholinergic neurons found within the striatum
have the opposite effect . Acetylcholine drives
the indirect pathway ,decreasing cortical
excitation