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THALAMUS &ITS CONNECTIONSDr. Talha- Sami- Ul- HaqueHonorary Medical OfficerDept. of NeurologyDhaka Medical College Hospital

CONTENTSIntroductionDevelopmentAnatomical ArrangementConnectionsBlood supplyFunctionSummary

WHAT IS THALAMUS?

situated between the cerebral cortex and midbrain.Thalamus is a large egg shaped mass of grey matterThalamus (from the Greek word "inner chamber")A midline symmetrical structure within the brains of vertebrates including humans.Thalamus is located on each side of third ventricle.From it, nerve fibers projecting out to the cerebral cortex in all directions.

Coronal Section

DevelopmentThe thalamus is the largest structure deriving from the embryonicdiencephalon, the posterior part of the forebrain situated between the midbrain and the cerebrum.The thalamic complex is composed of the perithalamus/ prethalamus, the mid-diencephalic organiser and the thalamus (dorsal thalamus).

Development

Twotranscription factors, Fez and Otx are required for proper development of the thalamus

Location of the Thalamus

Narrow

forms the posterior end of the interventriculer foramina.BoundariesAnterior:

Expanded to form the pulvinar.

which overhangs the superior colliculus.BoundariesPosterior:

covered medially by the tela choroidea and fornix laterally it is covered by ependyma and forms the part of the floor of the lateral ventricle.

BoundariesSuperior:

Continuous with the tegmentum of the midbrainBoundariesInferior:

Boundaries

Forms part of the lateral wall of the third ventricle

Connected to the opposite side by a band of grey matter called interthalamic connection.Medial:

Separated from the lentiform nucleus by the band of white matter called internal capsule.

Lateral:Boundaries

SUB DIVISIONs OF THE THALAMUS

Sub division of the ThalamusAnterior partMiddle partLateral partSubdivided into three main parts.

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Nucleus of Thalamus

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CONNECTIONS OF THALAMUS

Thalamic nuclei and their connections and functionsThalamic NucleusAfferent connectionsEfferent connectionsFunctionsAnteriorMammillothalamic tract, singulate gyrus, hypothalamussingulate gyrus, hypothalamusEmotional tone, mechanism of recent memoryDorsomedialPrefrontal cortex, hypothalamus, other thalamic nucleiPrefrontal cortex, hypothalamus, other thalamic nucleiIntegration of somatic visceral and olfactory information and relation to emotional feelings and subjective stageLateral dorsal, lateral posterior, pulvinarCerebral cortex, other thalamic nuclei Cerebral cortex, other thalamic nucleiUnknown

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Thalamic nuclei and their connections and functionsThalamic NucleusAfferent connectionsEfferent connectionsFunctionsVentral anteriorReticular formation, substantia naigra, corpus striatum, Prefrontal cortex, other thalamic nucleiReticular formation, substantia naigra, corpus striatum, Prefrontal cortex, other thalamic nucleiInfluences activity of motor cortexVentral lateralAs in ventral anterior nucleus also from cerebellum and red nucleusAs in ventral anterior nucleus also from cerebellum and red nucleusInfluences activity of motor cortexVentral postero medialTrigeminal lamniscus, gustatory fibersPrimary somatic sensory cortex (Area 3,1,2)Relays common sensation to consciousnessVentral postero lateralMedial and spinal lemnisciPrimary somatic sensory cortex (Area 3,1,2)Relays common sensation to consciousness

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Thalamic nuclei and their connections and functionsThalamic NucleusAfferent connectionsEfferent connectionsFunctionsIntra lamminarReticular formation, spino-thalamic and trigemino thalamic tractCerebral cortex via other thalamic nuclei, corpus striatumInfluences level consciousness and alertnessMidlineReticular formationUnknownUnknownReticularcerebral cortex, reticular formationOther thalamic nuclei? regulates thalamus

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Thalamic nuclei and their connections and functionsThalamic NucleusAfferent connectionsEfferent connectionsFunctionsMedial geniculate bodyInferior colliculus, lateral lemniscus from both ears but predominantly contra lateral earsAuditory radiation to superior temporal gyrusHearingLateral geniculate bodyOptic tractOptic radiation, visual cortex of occipital lobeVisual information from opposite field of vision

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BLOOD SUPPLY

From four arteries The polar artery (posterior communicating artery),Paramedian thalamic-subthalamic arteries,Inferolateral (thalamogeniculate) arteries andPosterior (medial and lateral) choroidal arteries.

BLOOD SUPPLY

Function of Thalamus

Thalamus is an important relay and integrative center.

A vast amount of sensory information of all types except smell converge to the thalamus and integrated through the interconnections between the nuclei. The resulting information pattern is distributed to other part of the CNS.

Anatomically and functionally the thalamus and the cerebral cortex are closely linked. The thalamus can appreciate crude sensation even after the removal of the cortex. Function of Thalamus

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It is concerned with subjective feeling state and the personality of the individual.

5. The intra laminar nuclei are able to influence the level of conciseness and alertness in an individual.

6. The thalamus also plays an important role in regulating states ofsleepand wakefulness.

7. Many of the sensory systems (except for the olfactory system), such as theauditory,somatic,visceral,gustatoryandvisual systemswhere localized lesions provoke specific sensory deficits.Function of Thalamus

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SUMMARY

Every thalamic nucleus (except reticular nucleus) sends axons to specific parts of cerebral cortex and every part of cerebral cortex sends reciprocal fibres back to the thalamic nuclei. This would indicate that information received by the thalamus is always shared with the cerebral cortex and that the cortex and the thalamus can modify each others activities.

SUMMARY

The thalamus is an important relay station for two sensory-motor axonal loops involving the cerebellum and the basal nucleiThe cerebellar-rubro-thalamic-cortical-ponto-cerebellar loopThe corticalstriatal-pallidal-thalamic-cortical loop

Both are necessary for normal voluntary movement.

SUMMARY

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