Thalamus
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THALAMUS
Dr. M. Anbarasi
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ML
DM
IL
PUL
PL
VPL
DL
VL
VA
EXTERNAL MEDULLARY LAMINA
RETICULAR NUCLEUS
LGN
MGN
NUCLEI OF THALAMUS
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PARTS OF THALAMUS
EPITHALAMUS
DORSAL THALAMUS
VENTRAL THALAMUS
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EPITHALAMUS
Comprises of PINEAL BODY and HABENULAR COMPLEX
Receives projection from Supra chiasmatic nuclei Sympathetic nervous system Olfactory areas
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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.
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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.
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Spinal lemniscus Medial lemniscus
Trigeminal lemniscus
VPM
VPL
3,1,2
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MEDIAL & LATERAL GENICULATE BODIES
171819
41
THALAMUS
LGNMGN
RETINA
COCHLEA
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NUCLEI CONCERNED WITH EFFERENT CONTROL MECHANISMS
Mainly ventrolateral & ventroanterior Nu.
Relay motor impulses from basal ganglia and cerebellum
Projects to motor and association cortex
Participate in cognition,planning and coordination of motor activities.
THALAMUS
CEREBELLUM
STRIATOLENTICULAR NU
MOTOR & ASSOCIATION AREAS
VA & VL
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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
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v
SPECIFIC AREA
NONSPECIFIC CORTEX
NONSPECIFIC THALAMIC NU.SPECIFIC THALAMIC NU.
TECTUMAUDITORY
VISUAL
ARASSPECIFIC ASCENDING
TRACTS
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NUCLEI CONCERNED WITH HIGHER FUNCTIONS
Anterior nucleus: participates in ‘PAPEZ CIRCUIT’ concerned with recent memory and emotions
Association Nu.
Dorso medial – AFFECTS THE MOOD
DorsolateralPulvinar Posterolateral Nu.
LANGUAGE & INTELLECTUAL FNS
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PAPEZ CIRCUIT
ANTERIOR NU. CINGULATE GYRUS
HIPPOCAMPUSMAMILLARY BODY
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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.
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Comparison between specific & nonspecific thalamic projections
NON SPECIFIC SPECIFIC
Thalamic Nu, Intralaminar & Reticular Nu.
VPL, VPM,MGB, LGB.
Projection to the cortex
Diffuse to all parts of the neocortex
Specific cortical areas like 3,1,2,5 & 7, 41, 17,18 &19
No. of synapses
Multi {> 4} < 4
Conduction rate
Slow Fast
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Termination in the layers of the cortex
Mainly 1st layer Mainly 4th layer
Effect of
lesion
Coma or unconsciousness
Loss of particular sensation
Function Arousal Specific sensation
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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
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THALAMIC SYNDROMESigns 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
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