thalamus & limbic system
DESCRIPTION
Thalamus & Limbic System. Objectives. By the end of the lecture, the student should be able to : Describe main functions of the thalamus Name and identify different nuclei of thalamus. Describe the connections and functions of thalamic nuclei. - PowerPoint PPT PresentationTRANSCRIPT
By the end of the lecture, the student should be able to:
Describe main functions of the thalamus Name and identify different nuclei of thalamus. Describe the connections and functions of thalamic
nuclei. Describe the effects of lesions of the thalamus. Describe main functions of the limbic system. Name and identify different parts of the limbic
system. Describe the effects of lesions of the limbic system.
Objectives
Thalamus Part of diencephalon (other parts
are hypothalamus, subthalamus and epithalamus)
A midline symmetrical structure, formed of 2 oval masses of grey matter
Is the largest nuclear mass Situated between the cerebral
cortex and brainstem
Together with the hypothalamus, it forms the lateral wall of the 3rd
ventricle33rdrd ventricle ventricle
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It is the gateway to the cortex. It relays received information to the cerebral
cortex from diverse brain regions. Axons from every sensory system (except
olfaction) synapse in the thalamus as the last relay site before the information reaches the cerebral cortex.
There are some thalamic nuclei that receive input from cerebellar nuclei, basal cerebellar nuclei, basal ganglia and limbic-related brain regions.
Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness.
ThalamusThalamus
Thalamus has 4 surfaces
Superior Inferior Lateral Medial: frequently
connected to the thalamus of the opposite side by the interthalamic adhesion (massa intermedia)
LL MM
SS
II
RLVRLV
33rdrd V VICIC
LLVLLV
****InterventricularInterventricular
foramenforamen.
Thalamus has 2 ends.*Anterior: Forms a projection called
anterior tubercle which lies just behind the interventricular foramen.
*Posterior: Forms a projection called Pulvinar which lies above the superior colliculus and the lateral & medial geniculate bodies.
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PulvinarPulvinar.
RelationsRelations
Lateral: Posterior limb of the internal capsule (IC)
Medial: Together with hypothalamus, forms the lateral wall of the 3rd ventricle
Superior: Caudate nucleus (C) fornix (F) & lateral ventricle (LV)
Inferior: Hypothalamus (H) anteromedially & Subthalamus (ST) posterolaterally.
Internal StructureInternal Structure Thalamus is mainly formed of
grey matter divided by 2 sheets of white matter
External medullary lamina: Covers the lateral surface
separating the reticular nucleus from the rest of nuclei.
Consists of thalamocortical & corticothalamic fibers.
Internal medullary lamina: Bundle of Y-shaped
myelinated (afferent & efferent) fibers.
Divides the thalamus into: anterior , medial, lateral nuclear groups.
Extrnal Medullary lamina
Each of these nuclear Each of these nuclear groups is subdivided into a groups is subdivided into a
number of named nucleinumber of named nuclei
Anterior nuclear group: Anterior nucleus Medial nuclear group: Largest nucleus is medial dorsal
nucleus (MD) Intralaminar nuclei: Lie within the internal medullary lamina Midline nuclei: Lie deep to ependyma of 3rd ventricle
Thalamic NucleiThalamic Nuclei
Lateral nuclear group Lateral nuclear group is divided into Dorsal & Ventral tiers.
Dorsal tier contains: lateral dorsal n. (LD) lateral posterior n. (LP) pulvinar.
Ventral tier contains ventral anterior (VA) ventral lateral (VL) ventral posterior (VP)
nuclei, divided into lateral & medial parts
medial & lateral geniculate bodies.
Thalamic Nuclei cont’dThalamic Nuclei cont’d
Functional Organization of Thalamic NucleiFunctional Organization of Thalamic Nuclei All thalamic nuclei
EXCEPT reticular nucleus project to the ipsilateral cerebral cortex
Precise point to point projections exist between individual thalamic nuclei and restricted cortical zones. This type of nuclei are called ‘Specific nuclei’ All specific nuclei lie within the ventral tire of the lateral nuclear group.
All other nuclei are ‘Non-specific nuclei,
Classification of thalamic nuclei according to Classification of thalamic nuclei according to their projectiontheir projection
A) Simple sensory relay nuclei: receive well defined sensory impulses, and relay them to functionally distinct areas of the sensory cortex.
1. Ventral posterolateral nucleus (VPL).2. Ventral posteromedial nucleus (VPM).3. Lateral geniculate body (LGB).4. Medial geniculate body (MGB).
They could be classified into 3 groups, each group contains 4 nuclei:
C) Associative nuclei: receive impulses from other thalamic nuclei and relay these impulses to the association areas of the cerebral cortex, They include:1.Part of dorsomedial nucleus.2.Pulvinar.3.Lateral dorsal nucleus.4.Lateral posterior nucleus.
B) Circuit relay nuclei: receive impulses from different areas of CNS and relay them to specific areas in cerebral cortex. They include:1.Lateral ventral nucleus (projects to primary motor cortex).2.Anterior ventral nucleus (projects to premotor cortex).3.Anterior nucleus (projects to cingulate gyrus).4.Part of dorsomedial nucleus.
Functional Organization of the Thalamic nucleiNucleus Function Inputs Outputs
Anterior Association Hippocampus &mammillary body
Cingulate cortex
Medial nuclear group
Association Amygdala, olfactory cortex & hippocampus
Prefrontal cortex, hippocampus
Lateral dorsal Association Amygdala, olfactory cortex & hippocampus
Cingulate cortex and other limbic regions
Lateral posterior Association Superior colliculus, pretectum Occipital parietal, temporal association
Medial geniculate Specific nucleus
Inferior colliculus Primary auditory cortex
Lateral geniculate Specific nucleus
Left and right eyes Primary visual cortex
Ventroposteromedial
Specific nucleus
Trigeminothalamic tract Primary somatosensory
Ventroposterolateral Specific nucleus
Med. & spinal lemnisci Primary somatosensory
Posterior nucleus Sup. & Inf. colliculi Primary somatosensory
Ventral lateral Specific nucleus
Globus pallidus Primary motor cortex
Ventral anterior Specific nucleus
Globus pallidus Primary motor cortex
Intralaminar Diffuse nucleus Spinal cord, spinothalamic, reticular formation, cerebellar nuclei, globus pallidus, sup. colliculus.
Cerebral cortex & striatum
Reticular Diffuse nucleus Reticular formation, corticothalamic, thalamocortical
Dorsal thalamic nuclei
The term "limbic" is from the Latin word Limbus, for "border" or "edge".
The limbic system is a set of evolutionarily primitive brain structures located on top of the brainstem and buried under the cortex
It separates the medial surface of the cerebral cortex from diencephalon
Function of the limbic systemFunction of the limbic systemIt control a variety of functions including: Emotions, emotional responses Behaviour & mood (happy, cry, laugh, sad, fear, anger,
aggression, depression) Motivation. Memory. Visceral & Motor responses involved in sex, pleasure,
hunger, and reproduction. Olfaction.
The limbic system The limbic system includes:includes:
1. Limbic lobe.2. Hippocampal formation.3. Septal area.
4. Prefrontal area.5. Amygdala6. Anterior thalamic nuclei7. Hypothalamus
(mammillary body)8. Fornix9. Olfactory system.10. Habenular nuclei
The limbic system consists of a number of cortical & subcortical structures with complex and often
looped connections that all project to the hypothalamus.
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Limbic LobeLimbic Lobe C-shaped ring of
grey matter on the medial side of each cerebral hemisphere, surrounding the corpus callosum.
It includes:1. Subcallosal area 2. Cingulate gyrus3. Isthmus4. Parahippocampal
gyrus5. Uncus.
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It is a seahorse shaped paired structure, one in each hemisphere.
Located in the inferomedial part of the temporal lobe.
Involved in formation, organization, storage and retrieval of memory
HippocampusHippocampus
Its principal efferent projection is to the mammillary body via a C-shaped bundle of fibers called the Fornix.
Fornix consists of: 1. Fimbria2. Crus 3. Body4. Column The fornix is an
important component of PAPEZ CIRCUIT
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1937: Papez was the first to describe a relationship between limbic system components.
Papez’s circuit connects the parahippocampal gyrus, hippocampus, fornix, mamillary body, anterior thalamic nucelus and cingulate gyrus. Since the initial description,
connections to additional subcortical structures have been identified.
Papez CircuitPapez Circuit
The hippocampal formation is a compound structure in the medial temporal lobe of the brain
It consists of: Hippocampus Dentate gyrus: Which
lies between hippocampus & Parahippocampal gyrus.
Subiculum (at the base of the hippocampus)
Entorhinal area (area 28)
Induseum gresium (grey matter on the upper surface of the corpus callosum).
Hippocampal FormationHippocampal Formation
Dentate gyrusDentate gyrus
Indusium gersiumIndusium gersium
HippocampusHippocampusEntorhinal areaEntorhinal area
FornixFornix
AmygdalaAmygdala Almond shaped mass of
nuclei, lies near the temporal pole, close to the tail of the caudte nucleus.
Connections: Input: from association areas
of visual, auditory & somatosensory cortices.
Output: to hypothalamus & brainstem autonomic nuclei, to control the autonomic centers.
Function: It is involved in emotional responses, fear, anger, hormonal secretions, and memory.
Lesion: results in lack of emotional responses & docility
Site: Located anterior to the interventricular foramen below the rostrum of corpus callosum
Main connections:1. To hypothalamus
through medial forebrain bundle.
2. To habenular nuclei through stria medullaris thalami.
Function: It provides critical interconnections and it is the pleasure zone.
Septal NucleiSeptal Nuclei
Septal area
Korsakoff’sKorsakoff’s psychosispsychosis (Retrograde & anterogdrade amnesia)
Temporal lobe epilepsy: Temporal lobe epilepsy: The hippocampus is a common focus site in epilepsy, and can be damaged through chronic seizures.
Alzheimer’s diseaseAlzheimer’s disease: : The hippocampus is one of the first brain areas to show damage in Alzheimer's disease
The hippocampus is sometimes damaged in diseases such as herpes encephalitis & Schizophrenia.herpes encephalitis & Schizophrenia.
Limbic Lobe DisordersLimbic Lobe Disorders
Thank You & Good Luck