Thalamus “Gateway to cerebral cortex” Dr Anil Dwivedi 1
Nov 02, 2014
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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