The term basal nuclei is applied
to a collection of masses of gray matter situated within each cerebral
hemisphere. They are the corpus striatum, the amygdaloid nucleus, and the
claustrum. The basal nuclei play an important role in the control of posture and
voluntary movement.
The purpose of this is to
describe briefly the basal nuclei, their connections, and their functions.
(click to enlarge)
The corpus striatum is situated
lateral to the thalamus . It is almost completely divided by a band of nerve
fibers, the internal capsule, into the caudate nucleus and the lentiform
nucleus.
The caudate nucleus is a large C‑shaped
mass of gray matter that is closely related to the lateral ventricle and lies
lateral to the thalamus. The lateral surface of the nucleus is related to the
internal capsule, which separates it from the lentiform nucleus. For purposes of
description, it can be divided into a head, a body and a tail.
The head of the caudate nucleus
is large and rounded and forms the lateral wall of the anterior of the lateral
ventricle. The head is continuous inferiorly with the putamen of the lentiform
nucleus.* Just superiorly to this point of union, strands of gray matter pass
through the internal capsule, giving the region a striated appearance, hence the
term corpus striatum.
*The caudate nucleus and the
putamen are sometimes referred to as the neostriatum or striatum.
The body of the caudate nucleus
is long and narrow and is continuous with the head in the region of the
interventricular foramen. The body of the caudate nucleus forms part of the
floor of the body of the lateral ventricle.
The tail of the caudate nucleus
is long and slender and is continuous with the body in the region of the
posterior end of the thalamus. It follows the contour of the lateral ventricle
and continues forward in the roof of the inferior horn of the lateral ventricle.
It terminates anteriorly in the amygdalold nucleus.
The lentiform nucleus is a wedge‑shaped
mass of gray matter, whose broad convex base is directed laterally and its blade
medially. It is buried deep in the white matter of the cerebral hemisphere and
is related medially to the internal capsule, which separates it from the caudate
nucleus and the thalamus. The lentiform nucleus is related laterally to a thin
sheet of white matter, the external capsule, that separates it from a thin sheet
of gray matter, called the claustrum. The claustrum, in turn, separates the
external capsule from the subcortical white matter of the insula. A vertical
plate of white matter divides the nucleus into a larger, darker lateral portion,
the putamen, and an inner lighter portion, the globus pallidus. Inferiorly at
its anterior end, the putamen is continuous with the head of the caudate
nucleus.
The amygdaloid nucleus is situated in the temporal lobe close to the uncus.The amygdaloid nucleus is considered to be part of the limbic system.
(click to enlarge)
The claustrum is a thin sheet of gray matter that is separated from the lateral surface of the lentiform nucleus by the external capsule (Fig. Lateral to the claustrum is the subcortical white matter of the insula. The function of the claustrurn is unknown.
(click to enlarge - this one IS worth it!)
Afferent Fibers
CORTICOSTRIATE
FIBERS
All parts of the cerebral cortex send axons to the caudate nucleus and the putamen . Each part of the cerebral cortex projects to a specific part of the caudate.putamen complex. Most of the projections are from the cortex of the same side. The largest input is from the sensory‑motor cortex. Glutamate is the neurotransmitter of the corticostriate fibers.
THALAMOSTRIATE FIBERS
Intralaminar nuclei of the thalamus send large numbers of axons to the caudate nucleus and the putamen.
NIGROSTRIATE
FIBERS
Cells in the substantia nigra
send axons to the caudate nucleus and the putamen and liberate dopamine at their
terminals as the neurotransmitter. It is believed that these fibers are
inhibitory in function.
BRAINSTEM
STRIATAL FIBERS
Ascending fibers from the
brainstem end in the caudate nucleus and putamen and liberate serotonin at their
terminals at the neurotransmitter. It is thought that these fibers are
inhibitory in function.
Efferent Fibers
STRIATOPALLIDAL
FIBERS
These fibers pass from the
caudate nucleus and putamen to the globus pallidus. They have gammaaminobutyric
acid (GABA) as their neurotransmitter.
STRIATONIGRAL
FIBERS
Fibers pass from the caudate
nucleus and putamen to the substantia nigra. Some of the fibers use GABA as the
neurotransmitter, while others use substance P
Afferent Fibers
STRIATOPALLIDAL FIBERS
These fibers pass from the
caudate nucleus and putamen to the globus pallidus. As noted previously, these
fibers have GABA as their neurotransmitter.
Efferent Fibers
PALLIDOFUGAL FIBERS
These fibers can be divided into
four groups: (1) the lenticularis, (2) the fasciculus lenticularis, (3) the pa
tegmental fibers, and (4) the pallidosubtlialamic fiber.
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Basal nuclei are joined
together and connected with different regions of the nervous system by a
very complex number of neurons. |
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Basically the corpus
striatum receives afferent information from most of the cerebral cortex, the
thalamus, the subthalamus, and the brainstem, including the substantia
nigra. information is integrated within the corpus striatum and the outflow
passes back to the areas listed above. This circular pathway is believed to
function as follows. |
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The activity of the basal
nuclei is initiated by information received from the sensory cortex, the
thalamus, and the brainstem. The outflow from the basal nuclei is channeled
through the globus pallidus, which then influences the activities of the
motor areas of the cerebral cortex or other motor centers in the brainstem.
Thus the basal nuclei can control muscular movements by influencing the
cerebral cortex rather than through direct descending pathways to brainstem
and spinal cord. In this way the basal nuclei assist in the regulation of
voluntary movement and the learning of motor skills. |
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Destruction of the motor
cerebral cortex prevents the individual from performing fine discrete
movements of the hands and feet on the opposite side of the body However,
.the individual is still capable of performing gross crude movements. If
destruction of the corpus striatum then occurs paralysis of the remaining
movements of the opposite of the body takes place. |
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It has been shown that the
basal nuclei not only influence the execution of a particular movement of
say the limbs, but play a role in the preparation of the movements. This be
achieved by controlling the axial and girdle movements of the body and the
positioning of the proximal parts of the limbs. The activity in certain
neurons of the globus pallidus increases before movement takes place in the
distal limb muscles. This preparatory function enables the trunk and limbs
to be placed in appropriate positions before the primary motor part of the
cerebral cortex activates discrete movements of the hands and feet. |