Diencephalon
Diencephalon has
four major
divisions
Epithalamus:
– a. Pineal gland
(=epiphysis cerebri)
– b. Habenula nuclei:
Subthalamus
Hypothalamus:
The thalamus:
Thalamus
Greek word thalamos, meaning an
inner room or storeroom of a
Greek or Roman house
Its nuclei are conventionally
divided into groups based on their
anatomical locations
internal medullary lamina
– This is a curved thin sheet of
myelinated fibers. It divides most
nuclei into medial and lateral
groupings
– Rostrally, the lamina bifurcates to
enclose the anterior nucleus,
which may be divided into smaller
groupings (However, all of these
subdivisions of the anterior
nuclear complex have similar
connections).
Thalamus cont..
1.Lateral Grouping:
This is the bulk of the
thalamus. This
collection of nuclei is
divided into a dorsal
tier and a ventral
tier.
– a. Dorsal tier: Pulvinar,
lateral posterior, and
lateral dorsal nuclei.
– b. Ventral tier: ventral
anterior, ventral lateral,
ventral posterior medial
(VPM), ventroposterior
lateral nuclei (VPL).
2. Medial Group:
There is only one
nucleus, the dorsal
medial nucleus,
3. Medial and lateral
geniculate bodies:
– The nuclei are caudal
extensions of the
thalamus and receive
auditory and visual
inputs, respectively
(Metathalamus)
Intralaminar nuclei:
The largest is the
centromedian nucleus
Thalamus
Connections
Thalamus
Functional Subdivisions
1. Specific relay:
These nuclei receive incoming sensory or
motor information on its way to the
cortex.
–
–
–
–
a. Medial geniculate: audition
b. Lateral geniculate: vision
c. VPM/VPL: somatosensory
d. VA/VL motor: cerebellum, basal ganglia to
cortex (motor and premotor cortices). VL
thalamectomy for Parkinson's disease helps
reduce rigidity, but not tremor. This suggests
that the VL is involved in the control of muscle
tone.
Thalamus
Functional Subdivisions
2. Association:
– a. Pulvinar/Lateral Posterior Complex
– b. Lateral Dorsal (LD):
– c. Dorsal medial (DM):
3. Nonspecific nuclei:
– a. Part of VA:
– b. Intralaminar:
– i. Centromedian nucleus:
– a . Reticular Nucleus
Thalamic
syndromes
Tumors and especially vascular lesions
related to the middle and posterior
cerebral arteries may involve thalamus
to some extent.
A typical condition is known as
thalamic pain syndrome, which is
caused by destruction of the sensory
relay nuclei in the posterior half of the
thalamus.
It is most often caused by occlusion of
the thalamogeniculate branches of the
posterior cerebral artery.
In addition to injury of the internal capsule
with transitory hemiparesis and
homonymous hemianopsia, there is
usually impairment of superficial sensation
of the opposite side of the body.
Position sense may be affected more
frequently than other sensory systems. An
agonizing concomitant of this syndrome is
a burning or knife-like pain, which usually
appears after several weeks or months
when other sensory functions are
beginning to return.
Clinical Case
A 45 year old woman started month earlier
with sudden weakness and numbness down the
whole of the left side. There was a family
history of diabetes and high blood pressure.
When examined locally she was weak and
numb on the left side with chorea of the left
arm.
Over the next month her weakness and sensory
loss improved but she developed an unpleasant
burning sensation on the left side, which
persisted.
She also experienced two episodes of transient
dizziness on head movements.