Download 21. Basal ganglion

And claustrum
And substantia
innominata
Nucleus accumbens
Basal Ganglia
It is a number of nuclear (grey matter) masses which lie within the cerebral hemisphere.
They are corpus striatum; amygdaloid nucleus and claustrum. Its major components are
caudate nucleus; putamen and globus pallidus . These structures are involved in the control
of posture and movement. They are sometimes referred to anatomically as the corpus
striatum but clinically, as basal ganglia. Notice that the function of amygdala is differ.
Gross anatomically, the putamen and globus pallidus are called the lentiform or lenticular
nucleus. The corpus striatum are connected with thalamus ; subthalamus of diencephalon
and substantia nigra of midbrain.
The lentiform nucleus is three- sided, having a convex lateral surface and 2 other
surfaces that converge to a medial apex which lies against the genu of the internal
capsule.
1- Putamen:
It lies lateral to the internal capsule and globus pallidus. It is separated from
the globus pallidus by a thin lamina of nerve fibers ( the lateral medullary lamina ).
Lateral to it lies a thin sheet of grey matter ( claustrum ) which separates the
white matter into 2 layers, the external capsule and the extreme capsule. Lateral to
the extreme capsule lies the cortex of the insula ( deep within the lateral fissure of
the hemisphere ).
2- Caudate nucleus:
It consists of a large head and body and a tapering, curved tail. The head of
the caudate is completely separated from the putamen by the internal capsule.
Rostrally, it is continuous with the putamen at the anterior limb of the internal
capsule. At this level, the most ventral portion of the striatum is the nucleus
accumbens which is connected to the limbic system.
The head of the caudate nucleus forms a prominent bulge in the lateral wall of
the anterior horn of the lateral ventricle.
The tail of the caudate
passes posteriorly and
follows the curvature of
the lateral ventricle then
descends into the
temporal lobe where it
lies in the roof of the
inferior horn of lateral
ventricle.
3- Globus Pallidus:
It lies medial to putamen, separated from it by the lateral medullary lamina. Its
medial apex nestles into the lateral concavity of the internal capsule.
It consists of 2 division which are separated by a thin sheet of fibers ( the
medial medullary lamina ). The medial segment is the smaller one.
The putamen and globus pallidus ( lentiform nucleus ) lie lateral to the internal
capsule and deep to the cortex of the insula.
4- Substantia Innominata:
It refers to the basal part of the rostral forebrain that lies beneath the corpus striatum.
It contains several groups of neurons. One of them is the nucleus basalis that project to
the cerebral cortex and utilize acetylcholine as their neurotransmitter. These neurons
undergo degeneration in Alzheimer’s disease.
5- Claustrum:
It is a thin plate of grey matter placed lateral to lentiform nucleus. Its anteroinferior part
fuses with the anterior perforated substance and the amygdaloid nucleus.
Connections of the striatum
The caudate nucleus and putamen together
referred as the striatum. They are the input
regions of the corpus striatum. Since the
majority of afferents from other parts of the
brain end here rather than in the globus pallidus.
Striatal afferents:
1. Corticostriatal fibers
They originate from the ipsilateral side of the
cerebral cortex.
Motor regions of the frontal lobe project mainly
to the putamem, where the body is represented
in an inverted fashion. The putamen , so
considered the most motor part of the striatum.
More anterior regions of the frontal lobe and
other association cortices project mainly to the
caudate nucleus. So, it has more associative
functions.
Corticostriatal fibers are excitatory to striatal
neurones and their transmitter is glutamic acid
2- Thalamostriatal projection:
Comes from the intralaminar nuclei of the ipsilateral thalamus ( centromedian and
parafascicular nuclei ) to caudate nucleus and putamen.
3- Nigrostriatal projection:
Originates from the pars compacta of the ipsilateral substantia nigra of the midbrain
tegmentum to caudate nucleus and putamen. The neurons of pars compacta contain the
dark pigment neuromelanin. Their transmitter is the monoamine dopamine which has both
excitatory and inhibitory effects upon striatal neurons.
4- The nucleus accumbens receives its dopaminergic input (afferent ) from the
ventral tegmental area which lies medial to the substantia nigra. This
projection is the mesostriatal pathway.
5- Other afferent to the striatum include a projection from the brain stem raphe
nuclei which utilize serotonin as its transmitter.
Striatal Efferents
1. Striatopallidal fibers
From the caudate nucleus and
putamen to globus pallidus. Their
neurotransmitter is gammaaminobutyric acid (GABA ). These
projections are inhibitory upon
pallidal neurons.
The cells that project to the medial
segment of globus pallidus contain
both substance P and dynorphin.
The projection to the lateral segment
of globus pallidus contains metenkephalin.
2. Striatonigral fibers
From the caudate nucleus and
putamen to the pars reticulata of the
substantia nigra. The cells that
project to it contains both substance
P and dynorphin.
+
M.segment; pars reticulata
-- L. segment
+ or -
-
Also, to pars reticulata
Connections of the Globus Pallidus
The medial segment of the globus pallidus is very
similar in structure and function to the pars
reticulata of the substantia nigra. They are
regarded as the output portion of the basal ganglia
Pallidal Afferents:
They arise from the striatum . Both utilize GABA as
transmitter. In addition each contains peptide
cotransmitters.
Subthalamopallidal projection:
It originates from small structure is located
beneath the thalamus, lying against the medial
surface of the internal capsule. It has the
appearance of a biconvex lens in coronal section.
They pass laterally through the internal capsule forming the subthalamic fasciculus and
terminate in both segments of globus pallidus mainly the medial.
They are excitatory to pallidal neurons using glutamic acid as their transmitter.
They also, sends fibers to the pars reticulata of the substantia nigra.
Pallidal efferents:
The lateral segments projects to the subthalamic
nucleus. They pass through the internal capsule
in the subthalamic fasciculus. They are
inhibitory and use GABA.
The medial segment together with the pars
reticulata project to the thalamus ( ventral lateral
;ventral anterior and centromedian nuclei ).
pallidothalamic fibers:
Some fibers pass round the anterior margin of
the internal capsule as ansa lenticularis, while
others pass through the internal capsule as
lenticular fasciculus. The fibers continue to
course medially then loop dorsally and laterally
as thalamic fasciculus to enter the ventral aspect
of the thalamus.
The thalamic project fibers are excitatory fibers
to the primary motor and supplementary motor
cortices
A smaller projection of the medial
pallidal efferent fibers passes
caudally to terminate in the brain
stem tegmentum in the nucleus
tegmenti pedunculopontinus which
lies at the boundary between
midbrain and pons, surrounding the
superior cerebellar peduncle.
Efferents of the pars reticularis of the
substantia nigra pass to the ventral
lateral thalamus to superior
colliculus and to brain stem reticular
formation including the
pedunculopontine nucleus.
The nigral cells control the axial
musculature including the
extraocular muscles.
Function of the Basal Ganglia
+
_
Or pars reticulata of the substantia nigra
The basal ganglia are referred as extrapyramidal
motor system. Their function is to facilitate
purposeful behaviour and movements and to
inhibit unwanted or inappropriate (not suitable )
movements.
When a movement is initiated from the cerebral
cortex, impulses discharge not only through
corticospinal and corticobulbar pathways but
also through the corticostriatal projection to the
neostriatum.
These glutamatergic fibers cause excitation of
striatal neurons.
The indirect pathway is via the
subthalamic nucleus.
Efferent from striatum inhibits lateral
plallidal neurons which becomes
disinhibited to subthalamus causes
activation of medial pallidal and nigral
neurons and inhibition of thalamus and
cortical cells. This pathway has the effect
of inhibiting unwanted movements.
The first route ( direct pathway ) induce the
inhibition of medial pallidal ( for limb
movements ) or pars reticulata neurons ( for eye
movements ). These output neurons are
inhibitory and lead to disinhibition ( loss
inhibition ) of the motor thalamus.
The resulting increase in the activity of the
thalamic neurons causes excitation of the cells
of cerebral cortex.
The direct pathway facilitate purposeful
behaviour and ongoing movement.
1- Huntington’s Disease
It is an degenerative autosomal dominant inherited disease with the onset occurring in
adult life. Within the striatum, there is progressive ; particular attrition of the cells that
project to the lateral segment of the globus pallidus ( indirect segment ).
This leads to disinhibition of the lateral pallidal neurons and inhibition of subthalamic
nucleus. Medial pallidal neurons , therefore ,become abnormally underactive and
unwanted; involuntary movements.The following signs is present:
1- Choreiform movements first appear as involuntary movements of the extremities and
twitching of the face (facial grimacing). Later, more muscle groups are involved so the
patient becomes immobile and unable to speak or swallow.
2- Progressive dementia occurs with loss of memory and intellectual capacity There is
degeneration of the GABA; P-secreting and acetylcholine-secreting.
2- Parkinson’s disease
It is a neurodegenerative disease of elderly, of unknown cause. It is
characterized by akinesia, flexed posture, rigidity and a resting tremor.
It is due to depletion of striatal dopamine levels. It is treated by levodopa which
restores normal striatal function. When drug therapy fails, neurosurgical ablation
or electrical stimulation of the subthalamic nucleu or medial segment of the
globus pallidus can help the patient.
3- Sydenham’s Chorea ( St Vitus’ dance )
The patient exhibits involuntary, quick,
jerky, spasmodic, irregular movements that are
nonrepetitive. Sudden movements of the head;
trunk or limbs. It is a common manifestation of
rheumatic fever.
4- Hepatolenticular degeneration (Wilson’s
disease)
It is an inherited disorder ( autosomal
recessive ) of copper metabolism.
5- Hemiballism
It is rare with choreiform movements of the
limbs on one side of the body. It caused by a
lesion of cerebrovascular origin of the
contralateral subthalamic nucleus.