Download Basal Ganglia . نور عريقاتد الرا عبدربّه جرايدة Anatomy

‫‪Basal Ganglia‬‬
‫نور عريقاتد‪.‬‬
‫الرا عبدر ّبه جرايدة‬
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‫‪Anatomy‬‬
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Basal Nuclei
Definition:1
Clusters of gray matter that are located within the cerebral hemisphere, they
consist of Corpus striatum, Claustrum and Amygdaloid nucleus.
As you can see here, the corpus striatum and the amygdaloid nucleus.
- Corpus striatum is divided in two ways:
 Anatomically:
1. Lentiform nucleus
A wedge-shapednucleus located lateral to the thalamus,
consists of lateral Putamen and medial Globus pallidus.
____________________________________________________________________________________1:
some books may consider substantia nigra and subthalamic nucleus as one of the basal nuclei. However,
we will follow the aforementioned definition for basal nuclei.
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2. Caudate nucleus
Large nucleus which is closely related to lateral ventricle,
consists of head, long body and long tail.
The head forms the lateral wall of the anterior horn of the
lateral ventricle.
The body forms part of the floor of the body of the lateral
ventricle.
The tail continues into the roof of the inferior horn of the
lateral ventricle and terminates anteriorly into the
amygdaloid nucleus.
 Functionally:
1. The striatum
Consists of caudate and putamen nuclei and the strands of
gray matter connecting them.
Forms the major site for input or afferent fibers to basal
nuclei.
2. Pallidum
It’s the globus pallidus itself but this is a functional name.
Forms the major site for output from basal nuclei.
- The amygdaloid nucleus:
As you can see in the previous picture, the lateral side has been removed.
It’s situated in the temporal lobe and it is part of the limbic system.
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Notes about this figure:
o Note the head of caudate nucleus and the anterior horn of the lateral
ventricle.
o The paleness of the globus pallidus is due to the presence of a high
concentration of myelinated nerve fibers.
o The lentiform nucleus is separated from thalamus by the posterior limb of
internal capsule which is a band of nerve fibers (white matter).
o The lentiform is separated from the caudate by the anterior limb of internal
capsule.
o The lentiform is separated from the claustrum (strand of gray matter) by
the external capsule.
o Lateral to the claustrum is the subcortical white matter of the insula.
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**Connections between Cerebral Cortex, Basal Nuclei, Thalamic Nuclei, and Spinal
Cord
This illustrated figure shows different pathways
o From the cerebral cortex we have the corticostriate fibers which are
somatotopically organized, they are arising from all parts of the cerebral
cortex.
Somatotopical arrangement: a term in neuroscience means each part of the
cerebral cortex projects axons to a specific part of the caudate-putamen complex
(striatum), so it’s not a random connection but point to point correspondence.
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o Fibers projecting from substantia nigra1 to striatum, striatonigral fibers.
o Fibers arising from the intra laminar nuclei of the thalamus,
thalamocortical fibers.
o Fibers ascending from the brainstem to the striatum.
o Note those fibersbetween striatum and substantia nigra. The pathway is
mutual in both ways. There are fibers arising from striatum and terminating
in substantia nigra called striatonigral fibers and the vice versa are called
Nigrostriate fibers.
So there is input coming into the striatum being processed and then there is
outputfrom the striatum to the output areaof basal nuclei again referred to as
globus pallidus or pallidum.
There are fibers from globus pallidus that are collectively called pallidofugal fibers
which are divided into four groups:
 Two groups terminating eventually in the thalamus and join in the
subthalamus to form what is called thalamic fasciculus:ansa
lenticularis and fasciculus lenticularis.
 pallidotegmental fibers, which terminate in the caudal tegmentum
of the midbrain.
 pallidosubthalamic fibers, which pass to the subthalamic nuclei.
From the thalamus axons are projected to the cerebral cortex, there is no direct
connection between the basal nuclei and the spinal cord. The influence exerted
by the basal nuclei to the spinal cord is being through the cerebral cortex.
As you know there is pre-central gyrus which is the site for the primary motor
cortex those neurons projecting their fibers as a corticospinal tract to command
the lower motor neurons located in the spinal cord.
: substantia nigra that divides the cerebral peduncles of the midbrain into
posterior tegmentum and anterior crus cerbri.
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Regarding brainstem lecture there will be only two questions. Focus on what
mentioned here.
It’s very important to know the level at
which the key landmarks are located i.e.
you can look at the section you can find
structures or landmarks. By recognizing
them you can say this is from this level so
you need to know.For example:
o Thedecussation of the pyramid
occurs in the caudal part of medulla
oblongata.
o At the level of the facial colliculus
which passes through the caudal
part of pons you need to know
that you can see the roots and the
nuclei of the facial nerve and the
abducent nerve, 7th and 6th
respectively.
The question is: the structure that is
present at the level of facial colliculus is?
You need to know that the winding of
the root of the facial nerve round the
nucleus of the abducent nerve is what
produces the facial colliculus. The facial
colliculus is the inferior end of the median eminence which is present at the
posterior aspect of pons.
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Through the cranial part of pons
you need to know there are the
motor and the principle main or
chief sensory nuclei of
trigeminal nerve.
At the level of inferior colliculiof
midbrain you can see the
decussation of the superior
cerebellar pedunclesand you can
identify the trochlear nerve and
nucleus.
Through the superior colliculiof midbrain
there is the red nucleus you can also
identify the nuclei of the oculomotor
nerve.
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