Download basal ganglia

Vincenzo Perciavalle, M.D.
Professor of Physiology - University of Catania
BASAL GANGLIA
Reproduction of plate VII of book VII of De Humani Corporis Fabrica [1543] of Andreas
Vesalius (Andreas van Wesel, 1514-1564) with a rather accurate view of the basal ganglia.
Bundles of white matter (E), corresponding roughly to internal capsule, are shown
separating masses of grey matter (D), the lower medial one corresponding to the thalamus
and the upper lateral one to the putamen. The caudate nucleus is also clearly outlined as a
structure separated from the putamen by white matter. Also note, on the right side, the
unmarked line separating the putamen from the globus pallidus.
Vesalius A, De Humani Corporis Fabrica, Libri Septem, J. Oporinus, Basel, 1543.
Reproduction of plate VIII from Cerebri anatome [1664] by Thomas Willis (16211675) that shows a dorsal view of the brainstem and basal ganglia in a sheep. The
hemispheres have been removed to better illustrate the basal ganglia, and the corpus
striatum on the right side has been cut in half to show its characteristic striations.
Willis T., Cerebri Anatome Cui Accessit Nervorum Descriptio et Usus, Flesher, Martyn and Allestry, London,
1664.
Reproduction of plate XXII from Traité d’anatomie et de physiologie [1786] by Félix
Vicq d’Azyr (1746-1794) that depicts a horizontal section of the human brain. The
caudate nucleus, putamen and globus pallidus are clearly singled out, but not
specifically named by the author. The claustrum and the substantia nigra (locus niger
crurum cerebri) are also depicted. The insert at the bottom is a drawing taken from
palate XIV of Vicq d’Azyr’s treatise showing a sagittal view of the human basal
ganglia, with the putamen and the inner and outer pallidal segments.
Vicq d’Azyr F., Traité d’Anatomie et de Physiologie, Didot, Paris, 1786.
Reproduction of plate III (book III) of Von Baum und Leben des Gehirns [1819] by
Karl Friedrich Burdach (1776-1847) showing a coronal view of the right hemisphere
of a human brain with the first detailed view of the basal ganglia. The Streifenhügel
(caudate nucleus) is clearly separated from the Linsenkern (lenticular nucleus,
consisting at this rostral level only of its Schale or envelope that Burdach called
putamen) by the fiber of the innern Capseln (internal capsule). The Vormauer
(claustrum) is also well delineated, with the äussern Capseln (external capsule)
separating it from the Linsenkern (lentiform nucleus).
Burdach K.F., Vom Baue und Leben des Gehirns und Rückenmarks, Vol. 3, Dyk, Leipzig, 1819.
In strictly anatomical sense, the Basal Ganglia are constituted by three
nuclei: the Caudate Nucleus and the Putamen, which constitute the
Corpus Striatum, and the Globus Pallidus.
Subsequently, to these three structures were added the Substantia Nigra,
the Subthalamic Nucleus and, more recently, the Nucleus Accumbens.
The Putamen and the Globus Pallidus are so close that in the past were
called Lenticular Nucleus. Subsequently, it is seen that the Putamen has a
structure similar to that of the Caudate Nucleus to which was assimilated
for the characteristic striation.
The Caudate Nucleus resembles a C-shape structure with a wider "head"
(caput in Latin) at the front, tapering to a "body" (corpus) and a "tail"
(cauda). After the body travels briefly towards the back of the head, the
tail curves back toward the anterior, forming the roof of the inferior horn
of the lateral ventricle.
1 – 3 caudate nc.
4 – putamen
5 – globus pallidus
6 - amygdala
The substantia nigra (SN) is a brain structure located in the midbrain and is divided
into two parts: the pars reticulata (SNpr) and pars compacta (SNpc).
The SNpr bears a strong structural and functional resemblance to the internal part of
the globus pallidus. The two are sometimes considered parts of the same structure,
separated by the white matter of the internal capsule. Like those of the globus pallidus,
the neurons in pars reticulata are mainly GABAergic.
The SNpc is formed by dopaminergic neuron. In humans, these cells are coloured
black by the pigment neuromelanin; they degree receive striatal information and send
their axons along the nigrostriatal pathway to the striatum where they release the
neurotransmitter dopamine.
The subthalamic nucleus (STN) is a small lens-shaped nucleus in the brain where it
is, from a functional point of view, part of the basal ganglia system. It was first
described by the French neurologist Jules Bernard Luys (1928-1897), and the term
Corpus Luysi or Luys' body is still sometimes used.
The STN receives GABAergic, inhibiting inputs from the external part of globus
pallidus and excitatory, glutamatergic inputs from the cerebral cortex.
The efferent axons of STN are glutamatergic (excitatory) and reach the inner segment
of globus pallidus.
The nucleus accumbens (nucleus accumbens septi; latin for nucleus adjacent to
the septum) is a region in the basal forebrain rostral to the preoptic area of the
hypothalamus.
Major inputs to the nucleus accumbens include the prefrontal cortex, basolateral
amygdala, ventral tegmental area (VTA) and hippocampus.
The output neurons of the nucleus accumbens send axon projections to the ventral
pallidum, VTA, substantia nigra, and the reticular formation of the pons.
Excitatory (red) and inhibitory (black) connections forming the corticostrio-pallido-thalamocortical circuit. It can be seen that the Striatum
(Caudate + Putamen) act on the internal segment of Globus Pallidus
either directly (direct pathway) that by means of its external segment
and the Subthalamic Nucleus (indirect pathway).
The direct pathway exerts an excitatory effect on the thalamus and,
therefore, on the cerebral cortex. In the motor cortex the induced effect is
a facilitation of movements and a reduction of muscular tone.
The indirect pathway exerts an inhibitory effect on the thalamus and,
therefore, on the on the cerebral cortex. In the motor cortex the induced
effect is an increase of muscular tone and a reduction of movements .
Distribution of corticostriatal neurons in cortical layers
Large dots – striatum
Small dots - thalamus
Neurons of the basal ganglia
Basal Ganglia Loops
Convergence
– large dendritic trees
– decreasing cell
number
150,000,000
30,000
Cortex
Striatum
100
GPe
1
GPi/
SNr
500:1
300:1
100:1
Dopaminergic
cells
of
Substantia
Nigra
pars
compacta send their axons
the striatal medium spiny
neurons
from
which
originates both the direct
and the indirect strio-pallidal
pathways.
On striatal medium spiny neurons of origin of the direct pathway.
dopamine binds receptors D1-type, while on those of origin of the
indirect pathway binds receptors D2-type.
Activation of receptor D1-type induces an increase of cAMP, whereas
the activation of receptor D2-type produces a decrease of cAMP.
Therefore, nigrostriatal dopaminergic neurons activate the direct
pathway and inhibit the indirect one.
THE DOPAMINERGIC PATHWAYS
PARKINSON’S DISEASE
Parkinson's disease (PD) is a neurodegenerative disorder mainly affecting
the motor system. The motor
symptoms of PD result from the death
of dopamine-generating cells in the
substantia nigra. The early symptoms
include shaking, rigidity, slowness of
movement and difficulty with walking
and gait. Later, thinking and behavioral
problems may arise, with dementia and
depression commonly occurring in the
advanced stages of the disease. Other
symptoms include sensory, sleep and
emotional problems.
PD is more common in older people,
with most cases occurring after the age
of 50. In 2013 PD resulted in about
103,000 deaths globally, up from
44,000 deaths in 1990
HUNTINGTON’S DISEASE
Huntington's
disease
(HD)
is
a
neurodegenerative genetic disorder that
affects muscle coordination and leads to
mental decline and behavioral symptom. The
most characteristic initial physical symptoms
are jerky, random, and uncontrollable
movements called chorea exhibited as
general restlessness, small unintentionally
initiated or uncompleted motions, lack of
coordination, or slowed saccadic eye
movements. Physical symptoms usually
begin between 35 and 44 years of age.
The disease is caused by an autosomal
dominant mutation in either of an individual's
two copies of a gene called Huntingtin. The
most prominent early effects damage the
caudate
nucleus
and
putamen,
so
compromising the functioning of the indirect
pathway.
HYPO-FUNCTIONING OF INDIRECT PATHWAY
Athetosis
is
a
symptom
characterized
by
slow,
involuntary, convoluted, writhing
movements of the fingers, hands,
toes, and feet and in some cases,
arms, legs, neck and tongue.
Lesions to the Corpus Striatum
are most often the direct cause of
the symptoms.
Hemiballismus is a very rare
movement disorder, caused in
most cases by a decrease in
activity of the Subthalamic
Nucleus,
resulting
in
the
appearance of flailing, ballistic,
undesired movements of the
limbs.
The Basal Ganglia are involved not only in motor functions, but also
in cognition and emotion.