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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

(thalamus, hypothalamus, subthalamus & epithalamus) is the largest nuclear mass of the whole body

Formed of 2 oval masses of grey matter & is the largest nuclear mass of the body

Together with the hypothalamus, it forms the lateral wall of the 3rd ventricle.

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It is the gateway to the cortex and 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.

Thalamus

Thalamus has 4 surfaces & 2 ends.

Surfaces Lateral: Medial: frequently connected to

the thalamus of the opposite side by the interthalamic adhesion (massa intermedia)

Superior: Inferior:

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.

LLMM

SS

II

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interventricular foramen.

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Relations

LVLV

ICIC

CC

ThalamusThalamus

33rdrd

VV

FF

HHSTST

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 Structure

2 sheaths of white matter pass through the thalamic mass and divide it into nuclei:

External medullary lamina: lies laterally, separating the reticular nucleus from the rest of nuclei. It consists of thalamocortical & corticothalamic fibers.

Internal medullary lamina: Y-shaped bundle of myelinated fibers (afferent & efferent), dividing the thalamus into anterior, medial & lateral nuclear groups. Each group is subdivided into a number of named nuclei.

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Extrnal Medullary lamina

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Dorsal tier, which contains: lateral dorsal (LD) lateral posterior

nuclei (LP) pulvinar.

Ventral tier, which contains ventral anterior

(VA) ventral lateral

(VL) ventral posterior

(VP) nuclei medial & lateral

geniculate bodies.

Lateral group is divided into:

Functional Organization of Thalamic Functional Organization of Thalamic NucleiNuclei

All thalamic nuclei project to the ipsilateral cerebral cortex EXCEPT reticular nucleus.

Precise Point to Point projections sometimes 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.

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Classification of thalamic nuclei Classification of thalamic nuclei according to their projectionaccording to their projection

A) Simple sensory relay nuclei: receive sensory impulses, and relay them to the sensory cortex.

1. Ventral posterolateral nucleus (VPL).2. Ventral posteromedial nucleus (VPM).3. Lateral geniculate body (LGB).4. Medial geniculate body (MGB).

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They could be classified into 3 groups, each group contains 4 nuclei: Simple sensory relay nuclei Circuit relay nuclei Associative nuclei

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C) Associative nuclei: receive impulses from other thalamic nuclei, associate these impulses & then send processed information 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 (project to primary motor cortex).

2. Anterior ventral nucleus (project to premotor cortex).

3. Anterior nucleus (project 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 1ry auditory cortex

Lateral geniculate Specific nucleus

Left and right eyes 1ry visual cortex

Ventroposteromedial

Specific nucleus

Trigeminothalamic tract 1ry somatosensory

Ventroposterolateral Med. & spinal Lemnisci 1ry somatosensory

Posterior nucleus Sup. & Inf. Colliculi 1ry somatosensory

Ventral lateral Specific nucleus

Globus pallidus 1ry motor cortex

Ventral anterior Specific nucleus

Globus pallidus 1ry motor cortex

Intralaminar Diffuse nucleus Spinal cord, spinothalamic, reticular formation, cerebellar nuclei, globus pallidus, sup. Colliculus.

Cerebral cortex & stratum

Reticular Diffuse nucleus Reticular formation, corticothalamic, thalamocortical

Dorsal thalamic nuclei

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The term "limbic" is from the LatinLatin 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

It consists of a number of cortical & subcortical structures with complex and often looped connections that all project to the hypothalamus.

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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 includes:The limbic system includes:

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It 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.

FUNCTION OF THE LIMBIC SYSTEMFUNCTION OF THE LIMBIC SYSTEM

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

gyrus and the 5. 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.

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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 formation.

Dentate gyrus

Indusium grsium

Amygdala 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

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 nuclei

Korsakoff’s psychosis (retrograde & anterogdrade amnesia)

Temporal lobe epilepsy The hippocampus is a common focus site in epilepsy,

and can be damaged through chronic seizures. It is sometimes damaged in diseases such as herpes

encephalitis, Alzheimer’s disease: The hippocampus is one of the

first brain areas to show damage in Alzheimer's disease Schizophrenia.

Limbic lobe disordersLimbic lobe disorders