THALAMUS

Right Left

Transverse section thro’ upper part of pons

Sup.Cereb.Peduncle

Mid.Cereb.Peduncle

Main.sens.N.Trig.

Lat.Lemn.(Cochlear N. to Inf.Colliculi)

Spinal.Lemn.(ant.&Lat spinothalmic tracts) Pain, Temp, Crude touch

Trig.Lemn.(Chief sens.& spinal N.)Pain & Temp – faceProprioception – Muscles of Mast.

Medial.Lemn.(Gr. & Cun. N.)Touch,vibrationpoprioception0

MLF – integrates 3, 4, 6, 8 cranial nerves

DIENCEPHALON

Pars Dorsalis

Hypothalamic sulcus

Pars Ventralis

01.Thalamus (Dorsal thalamus)02.Metathalamus – Med Gen. Body - Lat. Gen. Body03.Epithalamus - Pineal body - Habenular Nuclei - Habenular Commissure - Post. Commissure - Stria Medullaris Thalami

01.Subthalums (Ventral Thalamus) – Sub-thalamic Nucleus - Zona Inserta02.Hypothalamus -

Thalamus = Gk - inner room

Midline paired structure within brainBetween cerebral cortex and brain stem(Both in location & neurological connections)Sends fibres out to cerebral cortex in all directions

FUNCTIONSRelay of sensation (Except olfactory system)Spatial senseRegulation of consciousnessRegulation of sleepand alertness

Main largest product of embryonic diencephalonGreat sensory gateway to cerebral cortexDamage to thalamus can lead to permanent coma

Two thalami on each side of slit like cavity of 3rd ventricle

3 cms length x 1.5 cms breadth

Long axis 30 deg. oblique to midline

30 300 0

Interthalamic adhesion

Cingulate gyrus

Corpus CallosumBody of caudate nucleus

TT

Hypothalamus

Stria Terminalis

Thalamostriate Vein

Third Ventricle

Right Left

External featuresTwo ends1. Anterior end – Tubercle of Thalamus2. Posterior end – Pulvinar – Overhangs Med & Lat.Gen.Bodies Sup.Colliculi & their brachiaSurfaces01.Sup. Surface – Lat. Part forms central part of lat. Vent. Med. Part is covered by tela choroidea of 3rd ventricle.02.Inf. Surface - Ant. part fused with subthalamus - Post. part free – inf. part of Pulvinar03.Med. Surface – Greater part of Lat. wall of 3rd ventricle04.Lat. Surface - Med.boundary of Post. Limb of internal capsule

Subthalamus

Thalamus

Internal capsule

Cad. Nucleus

Lat.Ventricle

Lat.Ventricle

Cad. Nucleus

Optic radiation

Lateral surface of Thalamus – Medial boundary of Post. Limb of Int.Capsule

Stria medullaris Thalamior Habenular stria

Taenia Thalami

Stria Terminalis

Thalamostriate vein

Body of caudatenucleus

WHITE MATTER - THALAMUS

Stratum Zonale

External MedullaryLamina

Internal MedullaryLamina

Nuclei of Thalamus

Anterior Nucleus

Hypothalamus

Medial Dorsal(Large)

Medial Ventral(Small)

Lateral Dorsal

Lateral Ventral

LD, LP, Pulvinar – Dorsal Tier nuclei

VA, VL, VPL, VPM – Ventral Tier nuclei

VPLVPM

CMN

ILN

PVN

EXT.Med.Lam

Ret.N

LGB

MGB

Stratum Zonale

MEDIALLATERAL

Functional group nuclei

1. Specific2. Non-specific3. Reticular

1. Specific - Input from certain specific ascending tratcs Project specific cortical areas Ventral tier, Med & Lat. Geniculate bodies

Ventral Posterior Nucleus:

VPM

VPL

Nucleus Afferent Efferent Relay station

VPM Trigeminal lemniscus

Solitariothalamic tract

Post central gyrus(3,1 & 2)

Impulses from face & headTaste buds

VPL Medial lemniscus

Spinal lemniscus

Post central gyrus(3,1 & 2)

Exteroception (Pain,Tocuh & Temp) Proprioception from whole body except face & head

Functional group nuclei1. Specific group -

Nucleus Afferent Efferent Relay station

Ventralanterior

Globus pallidus(subthalamic fasciculus)

Premotor cortexarea 6 & 8

Striatal impulses

Ventrallateral

Cerebellum(dentato-rubro-thalamic fibres)(Dentato-thalamic fibres)

Motor & premotor areasArea 4 & 6

Cerebellar impulses

MGB Auditory fibres from Inferior Colliculus

Primary auditory area 41 & 42

Auditory impulses

LGB Optic tract Primary visual cortex area 17

Visual impulses

Functional group nuclei2. Non - Specific groupDo not receive afferents from ascending Tracts, but have abundant connections with other diencephalic nuclei. Project to corticalassociation areas in frontal & parietal lobes.

Nucleus Afferent Efferent Relay station

Anterior nucleus

Mamillothalmic tract (Mamillary body)

Cingulate gyrus Attention & Recent memory

Medial dorsal

Other thalamic nuclei &Hypothalamus

Prefrontal area Mood & Emotional balance

Lateral dorsal

Ventral tier of thalamic nuclei

Precuneus & Cingulate gyrus

Integrate sensory information

Lateral posterior

Ventral tier of thalamic nuclei

Superior parietal lobule

Integrate sensory information

Pulvinar Ventral tier of thalamic nuclei

Association areas in parietal, occipital & temporal lobes

Correlates visual & auditory information with other sensations

Functional group nuclei3. Reticular nucleiReticular nucleus, Intralaminar nuclei & Median nuclei(Paraventricular nucleus)

Connected with Reticular formation

Nucleus Afferent Efferent Relay station

Reticular Brain stem reticular formation

Whole of cerebral cortex

Forms part of reticular activating system (RAS)

Intralaminar & Centro median

Brain stem reticular formation

Other thalamic nuclei & Corpus striatum

Involved in awareness of painful stimuli at thalamic level

Dorsal nerve root

N. of spinal tract of Trig. nerve

NG & NCSup. Sens. N. of Trigeminal

Dentate Nucleus

Sup. Cereb. Peduncle

MB

Hypothalamic Nuclei

Caudate N.

Prefrontal cortexCingulate gyrus

Somesthetic sensory area (3, 1, 2)

Parietal cortex

Inferior parietal lobule

RN

Spinal lemniscus(Spinothalamic tract)

Trigeminal lemniscus

Medial lemniscus

VPM

VPL

VPL

Anygdaloid body

Main connectionsof Thalamus

Premotor cortex Area 6

Motor cortexArea 4

Sensory cortex Area 3,1,2

Superior parietal lobule

Parietal, TemporalOccipital cortex

RNTrigeminal lemniscusSolitariothalamic tract

Medial lemniscusSpinal lemniscus

Globus pallidus

Cingulate gyrusCingulate gyrus

Subthalamic fascilulus

Connections of ventraland lateral group nuclei

VPMVP

L

Functions of Thalamus

1. Sensory integration relay station for all sensory pathways (Except olfaction)

2. Capable of recognition of pain, thermal & tactile sensations

3. Influences voluntary movements through basal ganglia & cerebellum – cerebral cortex – cortico-nuclear / cortico-spinal pathways

4. Through ascending activating system – maintains state of wakefulness and alertness

5. Impulses received from hypothalamus projected o prefrontal & cingulate gyrus – Determination of mood

6. Recent memory and emotions

7. Influences electrical activity of cerebral cortex (EEG)

METATHALAMUS

1. Medial Geniculate body – Relay station for auditory pathway

2. Lateral Geniculate body – Relay station for visual pathway

1. Medial Geniculate body Afferents – Through lateral lemniscus – inferior colliculus - brachium of inf. Colliculus Efferents - Geniculocortical fibres project as auditory radiation thru’ sublentiform of int. capsule to primary auditory area in temporal lobe of cerebral cortex (41 & 42)

Auditory radiationInferior thalamic radiation

Midbrain

Pulvinar

METATHALAMUS

1. Lateral Geniculate body – Relay station for visual pathway

Afferents – Lateral root of optic tract – retinal fibres of both eyes (temporal fibres of same side & nasal fibres of opposite side) Efferents - Geniculocalcarine fibres project as optic radiation trhu sublentiform part of int. capsule to visual cortex of occipital lobe (17, 18 & 19)

Optic radiationPosterior thalamic radiation

Midbrain

Pulvinar6 layers (laminae) of LGB& their afferents

1,4,6Retina ofopp.side

1

4

6

2,3,5Retina ofsame side

235

Sensory fibres are mostly thalamocortical fibre, radiate from thalamusIn different directions to reach wide spread areas of cerebral cortexConstitute – thalamic radiations

Sup. Thal. Radiation(Ventral tier to frontal & parietal lobes)

Inf Thal. Radiation(Auditory radiation)

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Ant.Thal.Radiation

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Post.Thal.Radiation

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