Meta
thalamus
The meta
thalamus consists of the medial and lateral geniculate bodies, which are
situated on each side of the midbrain,
below the thalamus.
Medial
geniculate body :
It is an
oval elevation situated just below the pulvinar of the thalamus and lateral to
the superior colliculus. The inferior brachium connects the medial geniculate
body to the inferior colliculus.
The
connections of the medial geniculate body are as follows.
1.
Afferents
:
v
Lateral
lemniscus
v
Fibres
from both inferior colliculi.
2.
Efferents
:-
It gives rise to the acoustic radiation
going to the auditory area of the cortex through the sublentiform part of the
internal capsule.
Lateral
geniculate body :
This is a small oval elevation situated
anterolateral to the medial geniculate body, below the thalamus.
It is
overlapped by the medial part of the temporal
lobe, and is connected to the superior colliculus by the superior
brachium. Its connections are as follows.
Afferents
:-
The
lateral geniculate body receives fibres
concerned with vision, from both eyes ,through the optic tract.
Efferents
: -
Fibres arising in the lateral geniculate body
from the optic radiation.
This
radiation passes through the retrolentiform part of the internal capsule, to
reach the visual area of the cerebral cortex.
SUBTHALAMUS
:
The
subthalamus lies between the midbrain and the thalamus, medial to the internal
capsule and the globus pallidus. It consists of the following:
A.
Grey
matter :
1.
The
cranial ends of the red nucleus and substantia nigra extend into it.
2.
Subthalamic
nucleus
3.
Zona
incerta.
B.
White
matter :
1.
Cranial
ends of lemnisci lateral to the red
nucleus;
2.
Dentatothalamic
tract along with the rubrothalamic fibres;
3.
Ansa
lenticularis
4.
Fasciculus
lenticularis
5.
Subthalamic
fasciculus.
The
subthalamic nucleus is biconvex and is situated dorsolateral to the red nucleus
and ventral to the zona incerta.
The zona
incerta is a thin lamina of grey matter situated between the thalamus and the
subthalamus
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