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Thalamus
Dr. G. R. Leichnetz
Divisions of the Diencephalon
Thalamus
Hypothalamus
Subthalamus: prerubral fields of Forel,
zona incerta, subthalamic nucleus
Epithalamus: pineal gland, habenula
EPITHALAMUS
(Habenula, Pineal Gland)
THALAMUS
HYPOTHALAMUS
MB
Coronal Section: Thalamus/ Subthalamus/ Hypothalamus
Thalamus
Subthalamus
Mammillary Bodies
(hypothalamus)
Third
ventricle
Thalamus/ Subthalamus/ Hypothalamus
Posterior limb,
internal capsule
Thalamus
Subthalamus
Subthalamic
nucleus
Mammillary
bodies
(hypothalamus)
Third
ventricle
EPITHALAMUS
THALAMUS
Zona
Incerta
Subthalamic
nucleus
Prerubral
Fields of Forel
SUBTHALAMUS
MB
HYPOTHALAMUS
Epithalamus:
Pineal Gland and
Habenular Complex
Epithalamus
Pineal
Stalk
Pineal
Gland
Habenular
complex
Habenular
Complex
Pineal
gland
Posterior
commissure
Pineal
stalk
The epithalamus consists of the pineal gland and habenular
complex. The pineal gland contains modified glial cells, called
pinealocytes, that synthesize melatonin, which is released in a
biological rhythm that affects activities such as sleeping and
waking (jet lag).
Recent evidence has shown that the suprachiasmatic nucleus of
the hypothalamus (the brain’s “biological clock”), which receives
direct visual input from the retina, projects to the habenular
complex, which projects to the pineal gland through the pineal
stalk. In the reverse direction, the pineal sends fibers to the
habenular complex through the stalk to deposit melatonin in the
habenula. This could represent a more direct pathway for light to
influence pineal function (release of melatonin).
Retina
Suprachiasmatic
Nucleus
(“biological clock”)
Habenular
Complex
Pineal Gland
(melatonin)
Thalamus
The two egg-shaped
thalami are joined
across the third
ventricle by the
massa intermedia
(interthalamic
adhesion).
Caudate
Third
ventricle
Thalamus
The massa intermedia is
not a commissure.
Stria
terminalis
Pineal
gland
Anterior thalamic
tubercle
Caudate
The two thalami
are separated
from each other
by the third
ventricle.
The stria
terminalis
ST
(from amygdala)
Thalamus
IIIrd
vent
Pineal
gland
Pulvinar
SC
IC
runs in a groove
on the floor of
the lateral
ventricle that
separates the
thalamus from
the caudate
nucleus.
The internal medullary lamina of the thalamus
divides the thalamus into medial and lateral nuclear
groups. The lateral nuclear group is further
subdivided into dorsal and ventral tiers.
DorsalT
ier
Ventral
Tier
Ventral
Tier
The internal medullary lamina (containing intralaminar
nuclei) divides the thalamus into a medial nuclear group
(primarily MD nucleus) and lateral nuclear group (which
consists of a dorsal & ventral tiers).
Medial nuclear
group
Lateral nuclear
group
Internal medullary
lamina
Intralaminar
complex
Carpenter: Human Neuroanatomy
Thalamus:
Sectional Anatomy
(from rostral to caudal levels)
At rostral thalamic levels:
anterior nucleus is encapsulated by
the internal medullary lamina;
ventral anterior nucleus (VA) is in
the ventral tier.
Interventricular
foramen of Monro
Anterior thalamic
tubercle
ANT
VA
MTT
MD
IIIrd
Vent
SUBTHALAMUS
The last part of the
mammillothalamic tract
(MTT) from mammillary
body to anterior nucleus
courses through the
internal medullary lamina
of the thalamus.
The anterior nucleus receives
the MTT and projects to the
cingulate gyrus.
Thalamic
reticular
nucleus
ANT
MTT
Thalamic
reticular
nucleus
ANT
VA
The thalamic reticular nucleus consists of clusters
of cells within the external medullary lamina of the
thalamus. It is the only GABA-ergic (inhibitory)
nucleus in the thalamus, and is the only thalamic
nucleus that does not project to the cortex. It has
intrinsic thalamic connections; involved in the
generation of sleep “spindles” in the EEG.
MTT MD
When the MD nucleus is small,
the VA nucleus is transitioning into
the rostral part of the VL nucleus in
the ventral tier.
ANT
MD
VA/VL
MI
The massa intermedia
(interthalamic adhesion)
is an adhesion of
ependymal and glial cells
across the third ventricle
(not a commissure).
When the MD nucleus is largest,
the VL nucleus is present in the ventral tier.
A
LD/LP
VL
MD
MI
The ventrolateral nucleus
(VL) primarily receives
input from the
contralateral deep
cerebellar nuclei and
projects to the primary
motor cortex.
The mediodorsal nucleus
(MD) is the largest
nucleus of the medial
thalamus. It receives
limbic input from the
amygdala and projects to
the prefrontal cortex.
In the caudal third of the
thalamus, the ventral posterior
nucleus (VPM/VPL) are present
in the ventral tier, and the
CM/Pf intralaminar nuclei are
seen within the internal
medullary lamina.
LP
PUL
MD
VPL
CM
Subthalamus
Pf
VPM
The ventral posterolateral
(VPL) and ventral
posteromedial (VPM)
nuclei receive the spinal
and medial lemnisci. They
are somatotopically
organized.
The centromedian (CM) and
parafascicular (Pf) nuclei are
the largest nucleus of the
intralaminar complex. CM
projects to the putamen. The
Pf projects to the caudate
nucleus.
The pulvinar, medial geniculate, and
lateral geniculate nuclei are located in
the posterior (caudalmost) thalamus.
PUL
Pineal
gland
Posterior commissure
MGN
Pretectum
LGN
The lateral geniculate
nucleus receives direct
visual input from the
retina and projects to the
primary visual cortex.
The medial geniculate
nucleus receives auditory
input thru the brachium
of the inferior colliculus
and projects to the
primary auditory cortex.
Thalamic Connections
Basic Pattern Of Thalamic Connections
Thalamocorticals
Thalamus
Subcortical
Afferents
Corticothalamics
From: Kiernan and Barr
All thalamic nuclei
(except the thalamic
reticular nucleus) have
reciprocal connections
with the cerebral
cortex.
Thalamocorticals
project to lamina IV of
the cortex.
Corticothalamics that
project back to the
thalamus originate in
lamina VI of the cortex.
All thalamic nuclei are
glutamatergic (excitatory),
except the thalamic reticular
nucleus (GABA).
The principal source of cortical afferents is the thalamus.
Thalamocortical projections traverse the internal capsule
to reach the cortex.
From Noback & Demarest
The thalamus is the
principal source of direct
cortical afferents
(corticopetal projections).
The ventral tier of the
lateral group contains the
specific relay nuclei of the
thalamus.
motor relay nuclei
(VA/VL) rostrally,
sensory relay nuclei
(VPM/VPL, MGN, LGN)
caudally.
Organization of projections from the ventral tier
(specific relay nuclei) to the cortex.
Cortical Efferents
Corticofugal
projections
originate from
layer V pyramidal
neurons, including
corticospinals,
corticobulbars,
corticopontines,
corticostriates.
Only
corticothalamics
originate in
layer VI.
Associational
Corticostriate
Commissural
Corticopontine
Corticospinal
Corticobulbar
Corticothalamic
There are
reciprocal
connections
between thalamus
and cortex.
The intralaminar complex is made up of subnuclei
within the internal medullary lamina of the thalamus.
The intralaminar nuclei receive input from the
brainstem reticular formation, and project to the
striatum (thalamostriates) and to the cerebral cortex
(thalamocorticals).
The largest of the intralaminar nuclei is the
centromedian/parafascicular complex.
The centromedian nucleus projects to the putamen
and sensorimotor cortex.
The parafascicular nucleus projects to the caudate and
associational cortex.
MD
Intralaminar
nuclei are cell
groups within
the internal
medullary
lamina of the
thalamus.
MD
Intralaminar Nuclei at Caudal Thalamic Levels: CM/Pf
MD
Parafascicular
Nucleus
The centromedian and
parafascicular nuclei are
the largest of the
intralaminar nuclei. They
give rise to thalamostriates
to putamen and caudate.
Centromedian
Nucleus
CM
Pf
MD
The thalamic reticular nucleus is the only GABA-ergic nucleus
of the thalamus. It has intrinsic thalamic connections (does not
project to the cortex). Involved in generation of sleep spindles in
the EEG.
Thalamic
reticular
nucleus
ANT
Thalamic
reticular
nucleus
VA
MTT
Intrinsic
thalamic
conn.’s
ZI
Clinical Correlations
Thalamic Pain Syndrome
Central neurogenic pain (not caused by
activity in peripheral sensory fibers)
can be caused by lesions that interrupt the
somatosensory pathway at any level.
A destructive lesion that involves the ventral
posterior nucleus of the thalamus may result
in the thalamic pain syndrome characterized
by exaggerated and exceptionally disagreeable
responses to cutaneous stimulation.