THALAMUS

Dr. M. Anbarasi

ML

DM

IL

PUL

PL

VPL

DL

VL

VA

EXTERNAL MEDULLARY LAMINA

RETICULAR NUCLEUS

LGN

MGN

NUCLEI OF THALAMUS

PARTS OF THALAMUS

EPITHALAMUS

DORSAL THALAMUS

VENTRAL THALAMUS

EPITHALAMUS

Comprises of PINEAL BODY and HABENULAR COMPLEX

Receives projection from Supra chiasmatic nuclei Sympathetic nervous system Olfactory areas

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.

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.

Spinal lemniscus Medial lemniscus

Trigeminal lemniscus

VPM

VPL

3,1,2

MEDIAL & LATERAL GENICULATE BODIES

171819

41

THALAMUS

LGNMGN

RETINA

COCHLEA

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

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

v

SPECIFIC AREA

NONSPECIFIC CORTEX

NONSPECIFIC THALAMIC NU.SPECIFIC THALAMIC NU.

TECTUMAUDITORY

VISUAL

ARASSPECIFIC ASCENDING

TRACTS

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

PAPEZ CIRCUIT

ANTERIOR NU. CINGULATE GYRUS

HIPPOCAMPUSMAMILLARY BODY

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.

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

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

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

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