350 Neuroanatomy: Draw It to Know It
Thalamus: Anatomy & Function
Here, we will draw the egg-shaped anatomy of the thala-
mus and metathalamus and review their functional high-
lights. First, draw the back end of the thalamus and then
the front; we leave the thalamus open so we can label its
interior nuclei. Now, draw the anterior–posterior and
medial–lateral planes of orientation. Next, along the
anterior–posterior axis of the thalamus, draw the inter-
nal medullary lamina. Show that anteriorly it bifurcates
to envelop the anterior group nuclei; the length of the
internal medullary lamina separates the medial and lat-
eral thalamic groups. Now, indicate that the anterior
group nuclei communicate with the limbic system. Th en,
label the medial group nuclei (the most prominent of
which is the dorsomedial nucleus) and show that they
connect with the prefrontal cortex.
Next, let’s label the lateral group nuclei, which divide
into ventral and dorsal subgroups. First, label the ventral
subgroup nuclei: anteriorly, label the ventroanterior
nucleus, which connects with the basal ganglia; in the
middle, label the ventrolateral nucleus, which connects
with the cerebellum, red nucleus, and, to a lesser extent,
the basal ganglia; and posteriorly, label the ventroposte-
rior nucleus. Show that the ventroposterior nucleus fur-
ther divides into lateral and medial nuclei. Denote that
the ventroposterior lateral nucleus receives sensory aff er-
ent projections from the body whereas the ventroposte-
rior medial nucleus receives sensory aff erents from the
face; both nuclei then relay these sensory projections to
the somatosensory cortex.
Next, let’s label the dorsal subgroup of the lateral
group nuclei. First, anteriorly, label the dorsolateral
nucleus, which communicates with the limbic system
along with the anterior group nuclei; in the middle,
label the lateral posterior nucleus; and posteriorly, label
the pulvinar. Indicate that the pulvinar, which is part
of the extrageniculate visual pathway, is important for
visual attention (as is the lateral posterior nucleus).
Now, let’s address the two metathalamic nuclei: draw
the medial geniculate nucleus underneath the medial
aspect of the pulvinar and the lateral geniculate nucleus
underneath the lateral aspect of the pulvinar. Show that
the medial geniculate nucleus is part of the auditory
system and that the lateral geniculate nucleus is involved
in the visual system.
Next, beneath the pulvinar, label the posterior group
nuclei; they span posteriorly from the caudal pole of the
ventroposterior nucleus to the medial geniculate nucleus
and they also extend medial to the medial geniculate
nucleus. Th e most notable function of the posterior
group nuclei is nociceptive sensory processing. Although
it is not easy to appreciate the following from this dia-
gram, the pulvinar, which lies above the posterior group
nuclei, actually extends farther posterior than any of the
other thalamic nuclei or the metathalamic nuclei.
Next, in the center of the diagram, label the intrala-
minar group, which has widespread connectivity and is
involved in multiple functional roles but most notably
helps form the ascending arousal system for wakefulness.
Now, draw the midline group nuclei along the ventro-
medial portion of the thalamus in the midline of the
central nervous system; they function in limbic-related
processes. Th en, lastly, write out that the thalamic reticu-
lar nucleus forms a shell around the rostral/ventral/
lateral thalamus, and indicate that it modulates thalamic
output. Th e posterior limb of the internal capsule lies lat-
eral to the reticular nucleus and the external medullary
lamina lies in between the reticular nucleus and the lat-
eral border of the thalamus.