Thalamus and its functions

1. THALAMUS

3. Introduction
• It constitutes the main part of the
Diencephalon.
• The thalamus (from a GREEK word = inner
chamber) is a paired and symmetric Large
ovoid mass of grey matter or cluster of the
nuclei above midbrain, separated by
subthalamus
• Two thalami lies on each side of slit like third
ventricle and are joined by mass intermedia .

6. Introduction
• Functionally considered as the great sensory
gateway to the cerebral cortex
• All general and special sensation , except SMELL,
synapse here.
• Afferent impulse from RAS also synapse here.
• It is an important integrating center for
most input before relaying them to
cerebral cortex.

7. Introduction

8. External Features
End : Anterior & Posterior
Surface : Superior
Inferior
Medial
Lateral

9. EXTERNAL FEATURE
• ANTERIOR-just behind the interventricular foramen.
• POSTERIOR – just above and lateral to the superior
colliculus.
• DORSAL – forms the part of floor the lateral ventrical.
• VENTERAL – related to hypothalamus and sub
thalamus.
• MEDIAL - two thalamus are connected by
interthalamic adhesion .
• LATERAL – related to internal capsule.

10. INTERNAL STRUCTURE
• White Matter-
Stratum Zonale covering Superior Surface
External Medullary Lamina covering lateral
surface
Internal Medullary Lamina-“Y”shaped &
dividing thalamus in to three parts Anterior,
Medial and Lateral groups of nuclei

11. NEUROANATOMIC CLASSIFICATION
The thalamus is divided into three nuclear
groups by internal medullary lamina
• Lateral group
• Anterior group
• Medial group

12. THALAMIC NUCLEI
• Lateral group of nuclei
􀁺 Dorsal group of nuclei
• Pulvinar
• lateral posterior
• lateral dorsal
􀁺 Ventral group of nuclei
ventral anterior
ventral lateral
ventral posterior
(VLP & VPM)
medial geniculate body
lateral geniculate body

14. Thalamic Nuclei
• Medial
medial/dorso medial
midline nuclei
Intralaminar
centromedian
• Anterior group of nuclei

16. DEVELOPMENTAL CLASSIFICATION
A. Dorsal thalamus – divided into two group
1. Extrinsic nuclei – receive afferent from extra
thalamic sources and distributed to the
primary cortical areas;
(1) postero-ventral nucleus
(2) latero-ventral nucleus
(3) anterior nucleus
(4) medial and lateral geniculate bodies

17. 2. Intrinsic nuclei – They are the nuclei which
interconnect each other;
– Mid line nucleus
– Intralaminar nuclei
B. Ventral thalamus – consists of reticular
nucleus
C. Epithalamus –connected with olfactory
system.

18. FUNCTIONAL CLASSIFICATION
nonspecific projection nuclei
• Are those which receive impulses from RAS
and project diffusely to whole of cortex.
• These include –
– MIDLINE NUCLEI
– CENTROMEDIAN NUCLEUS

19. Functional classification
nonspecific projection nuclei
NUCLEUS FUNCTIONS
Midline nuclei Forms part of ascending reticular
activating system ,center for
crude visceral and somatic
sensations
Intralaminar
(Including
centromedian)
Awareness of painful stimuli at
thalamic level

20. Specific sensory relay nuclei
NUCLEUS FUNCTIONS
VPM Relay station for impulses from face, head & taste
buds
VPL Relay Station for exteroceptive& proprioceptive
from all body EXCEPT head & face
VA Relay station for attention & recent memory
VL Relay station for cerebellar impulses
MGB Relay station for Auditory impulses
LGB Relay station for Visual impulses

21. NUCLEUS FUNCTIONS
Anterior Attention & recent Memory ,receive afferent from
mammillary bodies and project to limbic cortex
Medial
dorsal
Associated with mood & emotional balance
Lateral
Dorsal
Integrates Sensory information concern with
speech
Lateral
Posterior
Integrates Sensory information
Pulvinar Correlates auditory & visual information with
sensations

23. Arterial supply
• Mainly by four branch of Posterior
cerebral artery
–Polar artery
–Paramedian thalamic –subthalamic
arteires
–Thalamogeniculate arteries
–Posterior choroidal arteries

24. Functions of Thalamus
• Thalamus is a SENSORY RELAY STATION and
INTEGRATING CENTER for most input before
relaying them to the cerebral cortex (except
Olfactory pathway).
– Relay station for somesthetic sensations coming
from opposite side of the body.
– Relay station for impulse from opposite cerebellum
to motor cortex .
– Relay station for impulse coming from the reticular
formation.
– Relay station for auditory and visual pathways.
•

25. Functions of Thalamus
• Recognition of crude pain, temperature &
touch
• Influences voluntary movements by receiving
impulses from basal ganglia & cerebellum &
relaying them to motor cortex , influence LMN
• Participates in maintenance of state of
wakefulness & alertness through RAS
• Role in emotions & recent memory
• Concern with speech

26. Thalamic syndrome
• Due to vascular lesion or thrombosis
of thalamogeniculate artery which is
branch of posterior cerebral artery.
• It usually damage the posteroventral
and posterolateral neclei of the
thalamus.
• The symptom and sign occur on
opposite side of the body.

27. POSTEROVENTRAL NUCLEUS –
• Its involvement leads to loss of discriminative
aspect of sensation.
• Loss of tactile localization , tactile
discrimination and stereognosis .
• Loss of kinesthetic sensation , so when eyes
are closed patient finds difficult to locate his
body parts . This condition is known as
THALAMIC PHANTOM LIMB .
• Over reaction to painful stimuli .

28. POSTEROLATERAL NUCLEUS –
• It relay cerebellar impulses to motor cortex.
• Profound muscular weakness, decrease in
muscle tone ataxia.
• Intention tremor
• Involvement of fiber coming from globus
pallidus leads to choreoathetosis [quick jerky
movement].

29. Thalamic hand
• Opposite hand shows abnormal posture
• Forearm is pronated, wrist flexed,
metacarpophalangeal joints flexed &
interphalangeal joints extended
• Fingers can move actively, but movements are
slow
• Due to altered muscle tone in different muscle
groups