By

Dr Manah Chandra Changmai

Thalamus is a part of diencephalon

Diecephalon divided into 4 regions

Thalamus

Hypothalamus

Epithalamus

Ventral thalamus(or subthalamus)

Diencephalon

Thalamus

Thalamus Large mass of grey matter,lies immediatelylateral to third ventricle

The thalamus is an ovoid nuclear mass, c.4cm long, which borders the dorsal part of third ventricle

Two polesAnterior pole(or end) -Lies behind the interventricular foramenPosterior pole(or end) -Also called PULVINAR -Lies just above and lateral to superior colliculus. Thalamus

Anterior pole

Posterior pole or pulvinar

Thalamus

Superior colliculus

Interventricular foramina

Thalamus

Superior(dorsal) surface -The superior (dorsal) surface of the thalamus is covered by a thin layer of white matter, the stratum zonale

-It extends laterally from the line of reflection of the ependyma (taenia thalami), and forms the roof of the third ventricle

-This curved surface is separated from the overlying body of the fornix by the choroid fissure with the tela choroidea within it.

-More laterally it forms part of the floor of the lateral ventricle.

-related laterally to caudate nucleus

-Seperated from caudate nucleus stria terminalis and thalamostriate vein.

Superior surface

Superior surface

Inferior surface

Medial surface

Surfaces of the thalamus

The medial surface of the thalamus is the superior (dorsal) part of the lateral wall of the third ventricle.

It is usually connected to the contralateral thalamus by an interthalamic adhesion behind the interventricular foramina.

The boundary with the hypothalamus is marked by an indistinct hypothalamic sulcus, which curves from the upper end of the cerebral aqueduct to the interventricular foramen.

The thalamus is continuous with the midbrain tegmentum, the subthalamus and the hypothalamus

Medial surface

The medial surface

Medial surface of thalamus

Hypothalamus

Midbrain tegmentum

Inferior surface of the tegmentum is relatedto hypothalamus anteriorly and to ventralthalamus posteriorly.

The ventral thalamus seperates the thalamusfrom tegmentum of midbrain

Inferior surface of thalamus

Internally, the thalamus is divided into anterior, medial and lateral nuclear groups by a vertical Y-shaped sheet of white matter, the internal medullary lamina

Nuclei of the anterior part.Anterior nucleus.

Nuclei in the medial partLargest nuclei among them medial dorsal nucleus.

Internal structure of the thalamus

Thalamus consists of mainly of grey matter

Superior surface is covered by a thin layer ofwhite matter called stratum zonale

Lateral surface is covered by a similar layer called externalmedullary layer.

Nuclei in the lateral part

Ventral group Lateral group

Ventral anterior nucleus

Ventral lateral nucleus OrVentral intermediate nucleus

Ventral posterior nucleus

Lateral dorsal nucleus

Lateral posteriornucleus

Pulvinar

Other thalamic nuclei

Intralaminar nucleiEmbedded within the internal medullaryLamina

Midline nucleiScattered cells between medial part of thethalamus and ependyma of third ventricle.

Medial and lateral geniculate bodiesNow included under the thalamus.

Connections of the thalamus

Afferent impulses from large number ofSubcortical centres converge to the thalamus.

Visual and aduditory impulses reach the lateralAnd medial geniculate bodies.

Sensation of taste are conveyed to the thalamus Through solitariothalamic fibres

Thalamus does not receive direct olfactory impulsesThey probably reach through amygdaloid complex.

Thalamus receive profuse connections from all partOf cerebral cortex,cerebellum and corpus striatum.

Thalamus is there fore regarded as integrating centreWhere information of all sources is brought together.

The information from thalamus is projected to wholeOf the cerebral cortex through thalamo-cortical projection.

Thalamocortical fibres form large bundles known as Thalamic radiations or thalamic radiation.

Thalamic radiations

Superior thalamic radiation (dorsal )

Posterior thalamic radiations ( caudal )

Ventral thalamic radiation

Anteriorthalamic radiations

Superior thalamic radiations

Posterior thalamic radiation

Thalamus

Connection of ventral group of nuclei

Most important connection of thalamus are from ventral posteriornucleus

cerebral cortex (somatosensory area,3 1 2)

ventral posterior nucleus

medial part lateral part

Trigeminothalamic tractSolitariothalamic tract

Medial leminiscusSpinothalamic tract

cerebral cortex

premotor and supplementary motor area

Area 4

ventral lateral nucleus

Anterior part Medial part Posterior part

From globus pallidus

From substantianigra

FromCerebellar nucleiVestibular nucleiSpinal cord

Ventral lateral nucleus

cerebral cortexGyrus cinguli

Parahippocampal gyrus

Parietal lobe

Prefrontal & orbitofrontal

Temporal Occipital lobe

Lateral dorsal

Lateral posterior pulvinar

Superior colliculus& Pretectal area

Retina

Connection of lateral group of nucleuses

Medial and lateral geniculate bodies are ovalCollection of grey matter

Situated below the posterior part of thalamus.

Traditionally under metathalamus,functionallyUnder thalamus.

The medial geniculate bodies-Relay station of the auditory pathway.-Medial geniculate body recieves fibres of lateral leminiscus.-Fibres arising in the medial geniculate bodies constitute the acoustic radiation.

Medial geniculate body

Acoustic area of cerebral cortex

Medial geniculate body

pulvinar

Inferior colliculus

Superior olivary nucleus

Opposite superior olivary nucleus

Inferior brachium

Lateral leminiscus

Connection of medial geniculate body

Lateral geniculate body

Relay station for visual pathway

Recieves fibres from retinae of both the eyes

Efferent fibres arising in the body constitute optic radiation.

Sections through lateral geniculate body shows partially split six lamellae seperated by nerve fibres.

Lateral geniculate body also recieves fibres from primary visual cortex.,superior colliculus,and from the reticular formation of pons and medulla.

Lateral geniculate body

Lateral geniculate body

Raphe nuclei

Locus coeruleus

Other areas in pons & medulla

Reticular formation

Pulvinar

Retina Ipsilateral & Contralateral

Visual areas of cerebral cortex

Superior colliculus

Connections of lateral geniculate body

Blood supply of thalamus

Perforating branches of the posterior cerebral artery

Posteromedial group(thalamo-perforating arteries) supplymedial and anterior part.

Posterolateral group ( thalamo-geniculate branches) supplyposterior and lateral part of thalamus.

Also recieves branches from posterior communicatinganterior choroidal,posterior choroidal and middle cerebralartery.

Thalamic syndrome

Thalamic syndrome (or thalamic pain syndrome) is a condition that can be associated with inadequate blood supply from the posterior cerebral artery.

Rare neurological disorder in which the body becomes hypersensitive to pain as a result of damage to the thalamus, a part of the brain that affects sensation

Primary symptoms are pain and loss of sensation, usually in the face, arms, and/or legs.

Pain or discomfort may be felt[1] after being mildly touched or even in the absence of a stimulus.

The pain associated with thalamic syndrome may be made worse by exposure to heat or cold and by emotional distress. Sometimes, this may include even such emotions as those brought on by listening to music.

It is also known as "Dejerine-Roussy disease", after Joseph Jules Dejerine and Gustave Roussy

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