Thalamus is a very important relay station.
All general and special sensory impulses (except smell) & afferent impulses from RAS are integrated here.
Thalamus however is the center of pain and protopathic sensations.
It has other non sensory functions as well, like motor control, sleep, wakefulness.
It is the largest structure deriving from the embryonic diencephalon, the posterior part of the forebrain situated between the midbrain and the cerebrum.
The thalamus is part of a nuclear complex structured of 4 parts, the hypothalamus, epithalamus, prethalamus (formerly called ventral thalamus) and dorsal thalamus.
2. Introduction
Thalamus is a very important relay station.
All general and special sensory impulses (except smell) & afferent
impulses from RAS are integrated here.
Thalamus however is the center of pain and protopathic sensations.
It has other non sensory functions as well, like motor control, sleep,
wakefulness.
It is the largest structure deriving from the embryonic diencephalon,
the posterior part of the forebrain situated between the midbrain and
the cerebrum.
The thalamus is part of a nuclear complex structured of 4 parts, the
hypothalamus, epithalamus, prethalamus (formerly called ventral
thalamus) and dorsal thalamus.
Name was first assigned by Wilhelm His,Sr. in 1893
Literally means ‘inner chamber’
It prepares a crude blue-print of the final product achieved by the
cortex.
3. Physiological Anatomy
Each thalamus is a large, ovoid diencephalic mass of grey matter.
Two thalami lie close together in the cephalic 2/3rd & separated by 3rd
ventricle.
Joined in the midline by mass intermedia.
Caudal 1/3rd are more divergent and the corpora quadrigemina lie
between them.
External medullary lamina consisting of thalamocortical and cortico
thalamic fibers covers the lateral surface.
Reticular nucleus separates internal capsule from External medullary
lamina.
Internal medullary lamina (‘Y’ shaped sheath of white matter) consisting
of internuclear thalamic connections dividing the thalamus into
lateral,medial and anterior nuclear masses.
It’s a afferent gateway of cerebral cortex.
5. Classification of Thalamic nuclei.
Anatomical
classification-
A. Lateral group of Nuclei
1.Ventral group-
Ventral anterior nu.
Ventral lateral nu.
Ventral posterior nu.
Medial geniculate body
Lateral geniculate body
2.Dorsal group-
Pulvinar nu.
Lateral posterior nu.
Lateral dorsal nu.
B. Medial group of Nuclei
Centro-median nu.
Dorso-median nu.
Midline nucleus
C. Anterior group of Nuclei
Anterior ventral nu.
Ant dorsal nu.
Ant medial nu.
6. Developmental classification
1.Dorsal thalamus
A) Extrinsic nuclei/Cortical relay nuclei--
a. Postero-vental nu.
b. Latero-ventral nu.
c. Anterior nu.
d. Medial geniculate body
e. Lateral geniculate body
B) Intrinsic nuclei--
Midline nu.
Intralaminar nuclei—
a. Centro-median nu.
b. Parafascicular nu.
c. Limitance nu.
d. Central nu.
e. Paracentral nu.
f. Centro-lateral nu.
2. Ventral thalamus
3.Epithalamus
Pineal body
Habenular complex
7. Functional Classification
1.Intrinsic nuclei/non specific Projection nuclei.
They receive impulses from RAS and project diffusely in whole neocortex
Comprises the midline and intralaminar nuclei.
2.Extrinsic nuclei/specific projection nuclei
From specific sensation to Neocortex or limbic system
Types-
Specific sensory
Motor
Visceral efferent
Integrative & perceptual
8. Specific Sensory Relay Nuclei
Medial geniculate body and Lateral geniculate body
Relay auditory and visual area of cerebral cortex.
Ventral posterior nucleus
from N. gracilis, cuneatus, Spinothalamic tract
to sensory cortex (post central gyrus)
i.e. somatosensory impulses from trunk & limbs
except face.
9. Nuclei concerned with Motor control mechanism
Ventral lateral nucleus.
Input from cerebellum and basal ganglia
Project to motor cortex
Dentatothalamic fibers from opposite side.
Proprioceptive information & voluntary motor functions.
Ventral anterior nucleus
Programming of movements
VA
BASAL
GANGLIA
SUBSTANTIA
NIGRA.
PREMOTOR
CORTEX
GLOBUS
PALLIDUS
10. Visceral efferent
Anterior nucleus.
From hippocampus through mammilary body.
Project to limbic cortex
Concerned with recent memory & emotions.
Dorsal medial nucleus.
Concerned with thinking, memory, judgement & emotional behavior.
11. Integrative & perceptual function control
Pulvinar nucleus
Integration of visual, auditory & other sensation.
Lateral posterior nucleus
Lateral dorsal nucleus
Project to cortical association area of cerebral cortex
Concerned with language function
12. Connections of Thalamus
1. Non specific Projection Nuclei
2. Specific Projection Nuclei
3. Reticular Nuclei
13. 1.Non - Specific group
Do not receive afferents from ascending tracts, but
have abundant connections with other diencephalic
nuclei. Project to cortical association areas in frontal &
parietal lobes.
Nucleus Afferent Efferent Functions
Anterior
nucleus
Mamillothalmic tract (Mamillary
body of hypothalamus))
Cingulate gyrus (24) 1.Part of Papez circuit.
2.Attention,emotion & Recent
memory.
Dorso-
medial nu.
Prefrontal cortex &
Hypothalamus
Prefrontal
area(8,9,10,11)
Synthesis of crude somatic
sensation.
Midline
nu.
Spinothalamic,trigeminothalamic
medial leminiscus,reticular
formation,hypothalamus
Hypothalamus,
neocortex, basal ganglia
Crude visceral and somatic
sensation
Intra-
laminar
nu.
RAS, basal ganglia, other
thalamic nu.
Prefrontal cortex Integrate somatic and visceral
sense.
Responsible for alerting affects
of RAS
14. 2.Specific Projection nuclei -
Nucleus Afferent Efferent Functions
Postero-
ventral nu.
Spinothalamic tract,medial
leminiscus.
Trigeminal,face,taste fibre
Sensory cortex(3,1,2) 1.Relay somatosensory impulse
(touch,pressure,pain,temp,proprioc-
eption,Kinesthetic) from trunk and limb.
2.Relay sensory impulse from Face.
Lateral
Ventral nu.
Dentate nu.of Cerebellum & Globus
pallidus
(dentato-rubro-thalamic fibres)
(Dentato-thalamic fibres)
Motor & premotor areas
Area 4 & 6
Relay proprioceptive information and
voluntary motor functions.
Dorso-
lateral nu.
Other thalamic nu.& parietal lobe
of cerebral cortex
Parietal lobe of cerebral
cortex
Speech & other complex integrated
function
Pulvinar nu. Other thalamic nu., cerebral
cortex(parietal, temporal,
occipital)
Cerebral cortex Integrate auditory, visual,somatic
informations.
MGB Topically organized project of
Auditory fibres from cochlear nu &
Inferior Colliculus
Primary auditory area 41
& 42, via internal
capsule
Auditory impulses/Hearing
LGB Optic tract Ipsilateral calcarine
cortex (Geniculate
Calcarine tract)
Visual impulses
15. 3. Reticular nuclei
Reticular nucleus, Intralaminar nuclei & Median nuclei
(Paraventricular nucleus)
Connected with Reticular formation
Nucleus Afferent Efferent Functions
Reticular Brain stem reticular
formation
Whole of cerebral
cortex
Forms part of reticular activating
system (RAS)
Intralaminar &
Centro
median
Brain stem reticular
formation
Other thalamic nuclei &
Corpus striatum
Involved in awareness of painful
stimuli at thalamic level
16. Functions of thalamus
1. Sensory relay station for all sensory pathways (Except olfaction)
2. It is a subcortical center for pain & protopathic sensation ( Pain perception is possible even
without cerebral cortex)
3. Responsible for maintaining conscious & alerting responses of RAS
4. Control of muscular movement by virtue of its connection with cerebellum, BG and motor cortex
5. Integrating center for sleep
6. Concerned with recent memory and emotion by virtue of Papez circuit.
7. Responsible for personality and social behavior because of its connections with hypothalamus &
prefrontal cortex.
8. Concerned with language and speech by virtue of its connection with hypothalamus & prefrontal
cortex.
9. Plays an important role in genesis of EEG
10. Perception of sexual sensations.
18. Thalamic syndrome.
Also known as Dejerine–Roussy syndrome
Disturbance of emotional response to sensory experience.
Cause
Thrombotic blockage of Thalamogeniculate branch of Posterior Cerebral Artery
Damage to Posteroventral & Posterolateral nuclei.
Symptoms and signs occurs on the opposite site of the body.
19. Signs & symptoms
Sensory symptoms
Thalamic Phantom limb.- unable to locate
position of limb with closed eye. Due to
loss of kinaesthetic sensation.
Asteriognosis.
Thalamic over-reaction.– sensation to
touch, pain , temp exaggerated.
Amelognosis. – illusion of absent limb.
Loss of tactile localization,discrimination.
Inability to produce an image of self within
self.
Motor symptoms
Thalamic hand or Athetoid hand –
Moderate flexion of the wrist with hyper
extended fingers.
Ataxia -- muscle tone & profound muscle
weakness.
Involuntary movements – chorea, athetosis
& intension tremors.
20. Korsakoff’s syndrome
Difficulty in remembering new information.
Due to – lesions of mediodorsal nucleus of thalamus.
Frontal lobotomy
To relieve intractable pain.
Dividing dorsal nuclei of thalamus from the frontal lobe
