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

TT

HH

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