The thalamus is divided into three parts: the epithalamus, dorsal thalamus, and ventral thalamus. The dorsal thalamus contains four types of nuclei: specific sensory relay nuclei, nuclei concerned with efferent control, nonspecific projection nuclei, and nuclei concerned with higher functions. The ventral thalamus contains the reticular nucleus. The thalamus acts as a relay center for sensory information and plays roles in motor control, arousal, consciousness, memory, and emotions. Damage to the thalamus can result in sensory deficits and symptoms like loss of sensation and memory.

1. THALAMUS
Dr. M. Anbarasi

3. NUCLEI OF THALAMUS
EXTERNAL MEDULLARY LAMINA
ML
IL
DM
VA RETICULAR NUCLEUS
DL
PL
VL
PUL VPL
MGN
LGN

4. PARTS OF THALAMUS
 EPITHALAMUS
 DORSAL THALAMUS
 VENTRAL THALAMUS

5. EPITHALAMUS
Comprises of PINEAL BODY and
HABENULAR COMPLEX
Receives projection from
 Supra chiasmatic nuclei
 Sympathetic nervous system
 Olfactory areas

6. DORSAL THALAMUS
FOUR TYPES OF NUCLEI
1. Specific sensory relay Nu.
2. Nu. Concerned with efferent control
3. Nonspecific projection Nu.
4. Nu. Concerned with higher functions.

7. SPECIFIC SENSORY RELAY NU.
projects to specific areas of neocortex.
VENTROBASAL GROUP [VBG]
ventroposterolateral
ventroposteromedial
- ventrolateral & ventromedial
Relay somaesthetic information to postcentral
gyrus from entire body.

8. 3,1,2
VPL
VPM
Trigeminal lemniscus
Spinal lemniscus
Medial lemniscus

9. MEDIAL & LATERAL GENICULATE
BODIES
17
18
19
41
THALAMUS
LGN
MGN
RETINA
COCHLEA

10. NUCLEI CONCERNED WITH EFFERENT
CONTROL MECHANISMS
 Mainly ventrolateral & MOTOR & ASSOCIATION AREAS
ventroanterior Nu.
 Relay motor impulses from
basal ganglia and cerebellum
 Projects to motor and
association cortex STRIATO
LENTICULAR NU
 Participate in
CEREBELLUM
cognition,planning and
coordination of motor
activities.
VA & VL
THALAMUS

11. NONSPECIFIC PROJECTION NUCLEI
 Receive inputs from diff. ascending tracts and projects to all parts
of neocortex, some specific cortical areas and also to limbic
system.
Examples –
 Midline – behavioural responses
 Intralaminar – thru reticulo-thalamo-cortical and
cortico-thalamo-reticular connections, thalamus
influences
 Alertness
 Sleep and wakefulness
 Consciousness
 EEG

12. NONSPECIFIC CORTEX
SPECIFIC
AREA
SPECIFIC THALAMIC NU.
NONSPECIFIC THALAMIC NU.
AUDITORY
TECTUM
v
VISUAL
SPECIFIC ASCENDING
TRACTS ARAS

13. NUCLEI CONCERNED WITH HIGHER
FUNCTIONS
Anterior nucleus:
participates in ‘PAPEZ CIRCUIT’
concerned with recent memory and emotions
Association Nu.
Dorso medial – AFFECTS THE MOOD
Dorsolateral
Pulvinar LANGUAGE & INTELLECTUAL FNS
Posterolateral Nu.

14. ANTERIOR NU. CINGULATE GYRUS
PAPEZ CIRCUIT
MAMILLARY BODY HIPPOCAMPUS

15. VENTRAL THALAMUS
{RETICULAR NUCLEUS}
 A thin curved sheet of cells present between
External Medullary lamina and the posterior
limb of Internal capsule.
 Modifies the exchange of signals between the
thalamus and the cortex thru thalamo-cortical
and cortico-thalamic fibres.

16. Comparison between specific &
nonspecific thalamic projections
NON SPECIFIC SPECIFIC
Thalamic Nu, Intralaminar & VPL,
Reticular Nu. VPM,MGB,
LGB.
Projection to Diffuse to all Specific
the cortex parts of the cortical areas
neocortex like 3,1,2,5 & 7,
41, 17,18 &19
No. of Multi {> 4} <4
synapses
Conduction Slow Fast
rate

17. Function Arousal Specific
sensation
Termination Mainly 1st layer Mainly 4th
in the layers layer
of the cortex
Effect of Coma or Loss of
lesion unconsciousness particular
sensation

18. FUNCTIONS OF THALAMUS
 Sensory relay center:
tactile, vibration, pressure, stereognosis, conscious
proprioception and sexual sensation.
 Centre for crude sensation – crude touch, pain and
temperature.
 Controls smooth, slow and coordinated movements
 Relay center for auditory and visual sensations:
lesion in both MGB – deafness
lesion of LGB – homonymous hemianopia
 Role in emotions and short term memory
 Role in sleep-wakefulness cycle, alertness and production
EEG

19. THALAMIC SYNDROME
Signs and symptoms:
 Loss of sensations
 Astereognosis
 Sensory ataxia
 Thalamic over-reaction
 Thalamic phantom limb
 Ameliognosia
 Hypotonia
 Choreoathetosis or tremor
 Loss of recent momory and emotions
 Sleep disturbances
 Thalamic hand