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Thalamus“Gateway to cerebral cortex”

Dr Anil Dwivedi

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Thalamus

• Development• Functional Roles• parts• Relations• Internal Organization

• Anatomical & Functional Divisions

• Functional Organization• Connections of nuclei• Blood supply• Clinical correlation

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BRAIN:• Embryologically derived from

3 primary brain vesicles:– Prosencephalon (Forebrain)

• 5th week, • subdivide into :

– Telencephalon - Cerebrum– Diencephalon - Thalamus

– Mesencephalon (Midbrain)

– Rhombencephalon(Hindbrain)• subdivide into:

– Metencephalon - Pons, Cerebellum

– Myelencephalon - Medulla

Diencephalon

• Paired structure• Located between the

brain stem and the cerebral hemisphere

• Continuous with the rostral part of the midbrain

• Forms the lateral wall of the 3rd ventricle

Cmo

mbp

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• Almost entirely surrounded by cerebral hemispheres

• A little part seen externally on base of brain caudal to optic chiasma

• Other parts seen on sagittal & coronal sections

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• medial surface of diencephalon-– Subdivided by

hypothalamic sulcus (indicated by black line) into:

– Dorsal part– Ventral part

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Dorsal part Thalamus & Epithalamus

Subthalamus & HypothalamusVentral part H

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ThalamusFunctional Roles

• Four basic functional roles:– Sensory• All sensory information (except olfaction) is relayed to cortex

via the thalamus– Motor• Motor system outputs from basal ganglia and cerebellum

are relayed by thalamus– Emotion/memory• The thalamus is part of Papez circuit and helps control some

emotional and memory information going to limbic cortex (cingulate gyrus)

– Vegetative• The thalamus has some intrinsic nuclei associated with

alertness and arousal. Can be associated with disorders of consciousness

Thalamus

• Large mass of grey matter• Shape and size, resembles– small hen’s egg

• 80 percent of diencephalon• Forms lat wall of 3rd ventricle • Separated from hypothalamus– hypothalamic sulcus

• May be connected to opposite thalamus– interthalamic adhesion (massa

intermedia)

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Thalamus: In horizontal sections of brain

Higher level

Lower level

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• Anterior pole– Narrow– Close to midline– Tubercle of thalamus– form posterior

boundary of the interventricular foramen

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• posterior pole– Expanded– Pulvinar– Extend beyond 3rd ventricle– Overhang superior Colliculus– Sup quadrigeminal brachium

separates from MGB

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Relations

Medial: 3rd ventricle

Dorsal: lateral ventricle

Ventral: Subthalamus & Hypothalamus

Lateral: Internal capsule

Caudal: midbrain

Anterior: interventricular foramen

Surfaces

• 4 Surfaces:• Superior• Inferior• Medial• Lateral

S

lML

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Superior Surface

• Stratum zonale• Bounded laterally by– caudate nucleus– thalamostriate vein– stria terminalis

• Lateral part – lies in the floor of lat

ventricle– covered by ependyma

• Medial part-related to :– choroid plexus of the

3rd ventricle

caudate nucleus

LV

ependymachoroid plexusthalamo-striate vein

stria terminalis

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Lateral Surface• Related to the

internal capsule

Inferior Surface• Rests on the

Subthalamus & hypothalamus

Medial Surface

• Stria medullaris thalami (a fascicle of nerve fibers) courses along its dorsomedial margin

• hypothalamic sulcus• Interthalamic adhesion• Forms the upper part

of the lateral wall of the 3rd ventricle

Stria medullaris thalami

Hypothalamic sulcus

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Internal Organization

• composed of – grey matter– interrupted by two vertical

sheaths of white matter -medullary laminae.

• External medullary lamina: – Located laterally– separates reticular nucleus

from rest of the thalamic mass

– Contains thalamocortical & corticothalamic fibers

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Internal medullary lamina• Y- shaped band• divides thalamus into– Anterior– Medial– Lateral nuclear groups

• Contains:– Fibers connecting thalamic

nuclei with one another – Neuronal collections called

intralaminar nuclei

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Anatomical Divisions• Anterior Division

– Anterior nucleus• Medial Division

– Dorsomedial Nucleus (DM)• Lateral Division– Dorsal Tier

• Lateral dorsal (LD) • Lateral Posterior (LP)• Pulvinar

– Ventral Tier• Ventral Anterior (VA)• Ventral Lateral (VL)• Ventral Posterior (VP)

– Ventral posterolateral (VPL)– Ventral posteromedial (VPM)

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Anatomical Divisions

• Medial Geniculate Nucleus (MGN)

• Lateral Geniculate Nucleus (LGN)

• Intralaminar Nuclei– Centromedian (CM)– Parafascicular (PF)

• Reticular Nucleus

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Functional Divisions

• Relay Nuclei– Relay specific information from a particular tract

or modality– This is not just sensory information• Relay nuclei are part of several important modulatory

loops in the CNS

– This is not simple “passing on” of the signal• Relay nuclei engage in some complex condensing and

processing of the incoming raw information

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Functional Divisions

• Association nuclei– Support areas of association cortex• Prefrontal cortex• Parietal-occipital-temporal cortex

– Association cortex is involved in higher cognitive function

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Other Nuclei

• Intralaminar nuclei– Inputs are diverse!• Cortex, basal ganglia, cerebellum, brainstem reticular

formation, Spinothalamic tract – Project to • Widespread areas of cortex• Basal ganglia

– Produce general changes in cortical function

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Other Nuclei

• Reticular nucleus– Sheet-like layer of neurons partially covering the

thalamus– Receives input from widespread cortical areas– Only thalamic nucleus with no projections to the cortex– Inhibitory projections to specific thalamic nuclei– Regulates the activity of the thalamus in the form of

cortical feedback

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Functional Organization

• Thalamus is major route for-– Subcortical neuronal activity

influences the cerebral cortex• All nuclei of thalamus

except reticular nucleus, project to ipsilateral cerebral cortex

• whole of cerebral cortex receives input from thalamus

• All thalamic nuclei receive corticofugal fibers in a reciprocal fashion

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• Based on their connection with the cerebral cortex, the thalamic nuclei are divided into:Specific nucleiNonspecific nuclei

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• Specific nuclei:– Have well-defined

sensory and motor functions

– Have highly organized point-to-point connection with sensory & motor regions of cerebral cortex

– Lie within the ventral group of the lateral nuclear group

• Non-specific Nuclei:– Receive less

functionally distinct afferent input

– Connect with wider area of cortex, including associative and limbic regions

– Include nuclei of dorsal tier of lateral group, and whole of ant and med group

Anterior Nuclear Groups

• Enclosed bn arms of int medullary lamina

• 3 parts:– Anteroventral– Anteromedial– Anterodorsal

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Mammillary body of hypothalamus via mammillothalamic tract

Ant limbic areacingulate gyrusParahippocampal gyrus

•Functionally part of the limbic system•Involved in control of alertness & attention•Acquisition of memory

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Medial Nuclear Group

Integrates emotion, thought, and judgment

Hypothalamus, amygdala, other thalamic nuclei, prefrontal cortex

Prefrontal cortex post parietal cortex limbic structures

Mediodorsal nucleus & Nucleus reuniens

Lateral Nuclear GroupVentral Tier

• Ventral anterior• Ventral lateral• Ventral posterior:

• VPL• VPM

• Lateral geniculate • Medial geniculate

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Ventral Anterior Nucleus Influences motor activity

Premotor & supplementary motor cortex

Ipsilateral globus pallidus & substantia nigrapremotor cortexFrontal eye field

Ventral Lateral Nucleus

Planning & modulation of commands

Ipsilateral globus pallidus &substantia nigraContralateral dentate nucleusSpinothalamic tract & vestibular nuPrecentral motor cortical area

Primary motor cortexSupplementary motor area

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Ventral Posterior Nucleus principal thalamic relay for somasensory pathways

C/L Gracile &Cuneate nu,C/L Dorsal horn of spinal cord

Primary somatosensory cortex

C/L trigeminal sensory nuclei

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Medial Geniculate Body

Part of the Auditory Pathway

Inferior Colliculus

Primary auditory cortex

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Lateral Geniculate Body Part of the Visual Pathway

Ipsilateral temporal hemiretinaContralateral nasal hemiretina

Primary visual cortex

Lateral Nuclear Group Dorsal Tier

• Lateral Dorsal• Lateral Posterior• Pulvinar

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Lateral dorsal nucleus

Memory, interpretation of visual stimuli

Happocampal formationPretectal areaSuperior Colliculus

Cingulate gyrusVisual association cortex

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Lateral posterior nucleus

Superior Colliculus

Parietal, temporal,& occipitalassociation cortex

Interpretation of visual & other sensory stimuli

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Pulvinar

Visual, perceptive, cognition & memory

Pretectal area, superior Colliculus,retinas

Association area of parietotemporal cortexVisual areas in occipital &post temporal lobe

Intralaminar Nuclei

Cortical activation, Sensorimotor integration

Brainstem reticular formationSpinothalamic tractCerebellar nuPallidum

Frontal & parietal lobesstriatum

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Midline Nuclei

Brainstem reticular formationHypothalamusSpinothalamic tractmidbrain

Hippocampal formationAmygdalaNucleus accumbensCingulate gyrus

Part of limbic system, memory & arousal

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Reticular Nucleus

Inhibitory modulation of thalamocortical transmission

Collaterals of Thalamocortical, Corticothalamic , thalamostriatal , pallidothalamic fibers

Body of thalamusC/L thalamus

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•Perforating branches of post cerebral a.

• Posteromedial group(thalamo-perforating a) supply medial and anterior part.

• Posterolateral group ( thalamo-geniculate br) supply posterior and lateral part of thalamus.

•Also receives br from-• posterior communicating• anterior choroidal• posterior choroidal• middle cerebral a.

Blood supply of thalamus

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• Thalamus – important relay and integrative center – lesions will have profound effects

• 3 common etiologies:– Invasion of neoplasm– Degeneration following disease of

its arterial supply– Damage by Hemorrhage

Clinical correlation

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• Manifestations:1. Sensory loss• damage to the VPM and VPL

nucleus – loss of all forms of sensation » light touch» tactile localization &

discrimination» muscle joint sense from

opposite side of body

2. Thalamic pain• may be aroused by light touch

or by cold – occurs on the opposite side of

the body

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3. Abnormal involuntary movements-

4. Thalamic hand-• due to altered muscle tone:– wrist is pronated and

flexed– metacarpophalangeal

joints are flexed– interphalangeal joints are

extended

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Thalamic syndrome

• Also known as "Dejerine-Roussy disease", after Joseph jules dejerine & Gustave Roussy.• Vascular lesion-• ventral post part of thalamus (PCA)

• Disturbance of• somatosensory aspect

• C/L impairment of-• Proprioception• Touch• Pain & temp.

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Thalamic syndrome

• Sensation is-• Exaggerated• Painful &perverted• exceptionally disagreeable

• Development of spontaneous pain• Emotional instability• spontaneous or forced• laughing or crying

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Fatal familial insomnia• Caused by prions• Mediodorsal & ventral ant nu• Dementia & other neurological

symptoms

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Thalamic cauterization• Surgical relief of pain in terminal

cancer• Intralaminar nu –relay of pain to

cortex

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DISCUSSION