348 Neuroanatomy: Draw It to Know It
The Thalamus, Part 2 ( Advanced )
Now, label the intralaminar nuclear group, which divides
into caudal and rostral subgroups. Th e caudal subgroup
is the most notable; it comprises the centromedian and
parafascicular nuclei. Th e rostral subgroup comprises
a cluster of closely related nuclei: the central medial, par-
acentral, and central lateral nuclei. Th e intralaminar
nuclei project to other thalamic nuclei, notably the
ventroanterior and ventrolateral nuclei; they have key
connections to the basal ganglia; and they project dif-
fusely to other cortical and subcortical areas. Th e intrala-
minar nuclei play an important role in a wide range of
processes; as an important example, indicate that they
participate in the ascending arousal system, which is fun-
damental to wakefulness.^13 , 14
Next, indicate the midline nuclear group, which, by
at least one defi nition, comprises the rhomboid, paratae-
nial, paraventricular, and reuniens nuclei — the reuniens
nucleus lies immediately ventral to the interthalamic
adhesion. Show that this group of nuclei is reportedly
involved in limbic-related processes and that it has
important hippocampal connections.^15
Now, label the thalamic reticular nucleus, which lies
along the rostral, ventral, and lateral aspects of the thala-
mus in between the thalamic external medullary lamina
and the posterior limb of the internal capsule. Show that it
contains GABAergic neurons, which modulate thalamic
output. Th e external medullary lamina is a white matter
layer that surrounds the lateral aspect of the thalamus.
Finally, indicate the metathalamus and show that it
comprises the medial geniculate and lateral geniculate
nuclei. Indicate that the medial geniculate nucleus forms
an important step in the auditory system pathway; it
receives aff erents from the inferior colliculus, which it
projects to the transverse temporal g yri (of Heschl).
Th en, show that the lateral geniculate nucleus forms an
important step in the visual system pathway; it receives
aff erents from the optic tract, which it projects to the
primary visual cortex.^8