2. Learning Objectives
• At the end of the lecture, students would be
able to know
• The basic structure of thalamus
• Different groups of nuclei
• Functions of thalamus
• Thalamic syndrome
3. • The Thalamus is a large ovoid gray mass having
neurons arranged into nuclei.
• It is a part of diencephalon.
• The anterior tubercle of the thalamus is rather
narrow and lies close to the mid line.
• The posterior end is broader and its prominent
medial portion is called the pulvinar.
• Its lateral swelling is called the lateral geniculate
body.
4.
5.
6. • The medial surface of each thalamus forms the
lateral wall of the third ventricle on the
corresponding side and is connected with the
medial surface of the opposite thalamus by the
massa intermedia which is a short
communicating bar of gray matter.
7.
8. NUCLEI OF THALAMUS
• There are five major masses each containing
several nuclei; anterior ,posterior ,lateral and
midline group of nuclei.these nuclei are
intimately interconnected.
• 1:Anterior nuclei group:This group includes
anterior dorsal, anterior ventral, and anterior
medial nuclei.
• It receives fibers from the hippocampus both
directly through the fornix and relayed through
the mamillary body (mamillothalamic tract)
9.
10. • Impulses are also received from the cingulate-
gyrus and the hypothalamus.
• The function of anterior thalamic nuclei is
closely associated with that of the limbic
system and is concerned with the emotional
tone and mechanism of recent memory.
11. Posterior nuclear group
• It includes the following nuclei:
• 1:The pulvinar nucleus:It connects with the
temporal and parital lobes of the cerebral
cortex.
• 2:The lateral geniculate body:It receives
most of the fibers of the optic tract.
• The relay fibers project via the optic radiation
to the visual cortex around the calcarine sulcus
in the occipital lobe.
12.
13. • 3:The medial geniculate body:It receive
acoustic fibers from lateral lemniscus and
inferior colliculus.
• The relay fibers project via the acoustic
radiation to the temporal lobe cortex (auditory
area)
14. MEDIAL NUCLEAR GROUP
• 1:Intra laminar nuclei:These are brought to
receive some of the trigeminal fibers from the
medial lemniscus.
• They connect with many other thalamic nuclei
and also project to the globus pallidus.
• 2:Dorsomedial nucleus: It is a large nucleus and
had 2-ways connection with the whole pyramidal
cortex of the cerebral hemisphere and also with
the hypothalamus.
• It is interconnected with all other groups of
thalamic nuclei.
15.
16.
17. • 3:Nucleus of central medianum: It connects
the corpus striatum.
• The medial part of the thalamus is responsible
for the integration of large veriety of sensory
information including somatic, visual and
olfactory information.
18.
19. Lateral and ventral nuclear group
• 1:Ventral anterior nucleus :It receives fibers
from the cerebellum the globus pallidus and
the substantia nigra.
• It sends fibers to other thalamic nuclei and the
cortex of the frontal lobe including area 6.
• As it lies on the pathway b/w the corpus
striatum and the motor areas of the frontal
cortex it probably influence the activity of the
motor cortex.
20.
21. • 2:Ventral lateral neuclus: It is the motor
relay nucleus via dentato-thalamus tract. i.e;
proprioceptive impulses from the cerebellum,
and also impulses from the red nucleus
(cerebro-rubrothalamic tract) and also from the
globus pallidus ;it sends fibers to the cerebral
cortex.
22. • 3:Ventral posterior nucleus: Its subgroups are
Ventral posterolateralis(VPL)
• Ventral posteromedialis(VPM)
• Ventral posteroinferior(VPI)
• The VPL nucleus receives fibers from the medial
lemniscus and a part of the spinothamic tracts;it
projects to the postcentral gyrus.
• It also receives afferent fibers from the vestibular
nuclei which are relayed to the somesthetic cotex
I.
23.
24. • The VPM nucleus is closely associated with
VPL and together these two trigeminal
lemniscus ,trigeminothalamic projections and
some spinothalamic fibers
• It also receive taste impulses.
• Its portion that receives trigeminal nerve fibers
from the face is called the arcuate nucleus .
• The VPL nucleus probably receives impulses
from the vestibular nuclei.
25. NUCLEUS OF THE MIDLINE
• These are the oldest thalamic nuclei and are the
center of the most primitive form of sensation
• E.g.from the viscera and structures forming the
axial region of the body.
• These nuclei are diffuse groups in the
periventricular region resembling RF.
• These nuclei belong to the visceral control
system.
• They work in conjuction with the intralaminar
nuclei,nucleus of the central medianum and also
the thalamic reticular nucleus.
26. FUNCTIONS OF THALAMUS
• 1:Role of specific nuclei: The relay station and
has been called the great gateway to the sensory
cerebral cortex.
• All types of sensation including a fraction of
fibers connected with olfaction reach the cerebral
cortex after relaying in the thalamus.
• The nuclei that act as relay stations in the
thalamus are called specific nuclei.
• These include ventral posterior nuclei and medial
and lateral geniculate bodies.
27. • The thalamus can perceive crude sensation.
• The cerebral cortex is required for the
interpretation of sensation based on past
experiences as well as for finer perception of
sensations.
• Fibers from the thalamus reach the cerebral
cortex through thalamocortical tract;this tract
becomes divides into 2 parts:
28.
29. • 1:Anterior thalamic radiation: This passes
through the anterior limb of the internal
capsule and connect to the frontal lobe cortex
• 2:Posterior thalamic radiation: This passes
through the posterior limb of the internal
capsule and connects to the postcentral gyrus,
supramarginal gyri and to the temporal and
occipital lobes.
30. • 2:Role of diffuse nuclei: Its is a separate
system by which fibers from non-specific
nuclei connect with the cerebral cortex.
• It is also called diffuse thalamocortical system.
• These nuclei are intralaminar nuclei, midline
nuclei.
• These nuclei and the thalamic reticular.
31. • These nuclei connects with specific thalamic
nuclei and make connections with all parts of
the cerebral cortex except small portions on
the temporal lobes that are mainly associated
with the limbic system.
• This system also receives afferents from the
reticular formation .
• It is also the terminal center for pain of
burning and aching type.
32. • 3:Role in attention: The constant volley of
impulses from the thalamus to the cerebral cortex
contributes to the activation of the cortex thus
making it attentive.
• The thalamus it self is initiated by the afferent
volleys of impulses reaching it mainly from the
RF.
• All areas of the cerebral cortex have direct
afferent and efferent connections with the
thalamus,together called the thalamocortical
system.
33. • Role in motor system:The thalamus is a part of
the following circular pathways.
• Motor cerebral cortex pons
cerebellum thalamus
• red nucleus
• Motor cerebral cortex striatum globus
pallidus thalamus
34. • These circuits act as feed back mechanism for
controlling motor functions.
• lesions of the thalamus can cause athetosis and
dystonia just like lesions of putamen;effects are
produced on the contralateral side.
• In dystonia(torsion spasm)large muscle are
affected ,e.g.muscles of trunk and limb girdles.
• High frequency electrical stimulation of the
thalamus relieves rest tremors of parkinsonism
and also the bengin essential (familial) tremors.
• Thalamotomy is done in both diseases.
35. • 5:Role in limbic system: The anterior nuclei
of the thalamus are part of the limbic system
concerned with emotional expression.
• These nuclei have also some role in memory
consolidation.
36. THE THALAMIC SYNDROME
• Some times the blood supply of the
posteroventral portion of the thalamus supplied
by the posterolateral branches of the posterior
cerebral artery is blocked by a thrombus.
• The nuclei of the thalamus supplied by this
artery which include the VPL nucleus of the
lateral thalamus degenerate,while the medial
and the anterior nuclei of the thalamus remain
intact.
37.
38. • Following is the clinical picture which is
called the thalamic syndrome the nature and
extent of neurological disturbance depend
upon the site of the lesion and collateral
circulation.
• 1:Contralateral hemisensory loss: Loss of
almost all sensation from the opposite side of
the body b/c relay nuclei are destroyed
• 2:Ataxia (loss of control over movements)
39. • Spontaneous paresis and voluntary movements
are seen;the latter consist of tremors or choreic
athetosis or irregular dancing movements
• 3:Homonymous hemianopia
• 4:Some recovery of sensations may occur after
a few months.
• But most sensations including light touch and
cold will produce pain and unpleasent sensation.
• Pain is contralateral severe and persistent and is
frequently uncontrolable.
• It also has autonomic and emotional components.
40. • Another contributory factor may be the release
of thalamus from cortical control resulting in
an over –reactive thalamus.
• 5:Thalamic hand: This is seen on the
contralateral side .
• The wrist is pronated and flexed ,the
metacarpophalangeal joints are flexed and the
interphalangeal joints are extended.the fingers
can be moved actively,but the movements are
slow.
