Thalamus Limbic System Objectives By the end of

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. 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.

Thalamus Ø Part of diencephalon (other parts are hypothalamus, subthalamus and epithalamus) A midline symmetrical structure, formed of 2 oval masses of grey matter Ø Is the largest nuclear mass Ø Situated between the cerebral cortex and brainstem Ø Together with the hypothalamus, it forms the lateral wall of the 3 rd ventricle T H 3 rd ventricle

Thalamus 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 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.

Thalamus has 4 surfaces Superior q Inferior q Lateral q Medial: frequently connected to the thalamus of the opposite side by the interthalamic adhesion (massa intermedia) q RLV LLV S L M I IC 3 rd V

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. Interventricular foramen. * * Pulvinar.

Relations Lateral: Posterior limb of the internal capsule (IC) § Medial: Together with hypothalamus, forms the lateral wall of the 3 rd ventricle § Superior: Caudate nucleus (C) fornix (F) & lateral ventricle (LV) § Inferior: Hypothalamus (H) anteromedially & Subthalamus (ST) posterolaterally. §

Internal 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 groups is subdivided into a number of named nuclei

Thalamic 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 3 rd ventricle

Thalamic Nuclei cont’d Lateral nuclear group is divided into Dorsal & Ventral tiers. Ø Dorsal tier contains: Ø lateral dorsal n. (LD) Ø lateral posterior n. (LP) Ø pulvinar. Ø Ventral tier contains Ø ventral anterior (VA) Ø ventral lateral (VL) Ø ventral posterior (VP) nuclei, divided into lateral & medial parts Ø medial & lateral geniculate bodies.

Functional 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 ‘Nonspecific nuclei,

Classification of thalamic nuclei according to their projection A) 1. 2. 3. 4. They could be classified into 3 groups, each group contains 4 nuclei: Simple sensory relay nuclei: receive well defined sensory impulses, and relay them to functionally distinct areas of the sensory cortex. Ventral posterolateral nucleus (VPL). Ventral posteromedial nucleus (VPM). Lateral geniculate body (LGB). Medial geniculate body (MGB).

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. 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.

Functional Organization of the Thalamic nuclei Nucleus 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 Sup. & Inf. colliculi Primary somatosensory Posterior nucleus 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 LIMBIC SYSTEM

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 system It control a variety of functions including: v Emotions, emotional responses v Behaviour & mood (happy, cry, laugh, sad, fear, anger, aggression, depression) v Motivation. v Memory. v Visceral & Motor responses involved in sex, pleasure, hunger, and reproduction. v Olfaction.

The limbic system consists of a number of cortical & subcortical structures with complex and often looped connections that all project to the hypothalamus. The limbic system includes: 1. Limbic lobe. 2. Hippocampal formation. 3. Septal area. Prefrontal area. 5. Amygdala 6. Anterior thalamic nuclei 7. Hypothalamus (mammillary body) 8. Fornix 9. Olfactory system. 10. Habenular nuclei 1 8 4 4. 6 10 3 7 9 5 2 1

Limbic Lobe C-shaped ring of grey matter on the medial side of each cerebral hemisphere, surrounding the corpus callosum. It includes: 1. 2. 3. 4. 5. Subcallosal area Cingulate gyrus Isthmus Parahippocampal gyrus Uncus. 2 1 3 5 4

Hippocampus 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

1. 2. 3. 4. Its principal efferent projection is to the mammillary body via a C-shaped bundle of fibers called the Fornix consists of: Fimbria Crus Body Column The fornix is an important component of PAPEZ CIRCUIT 3 2 4 1

Papez Circuit 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.

Hippocampal Formation § § § 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). Indusium gersium Entorhinal area Hippocampus Fornix Dentate gyrus

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

Septal Nuclei 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 area

Limbic Lobe Disorders 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. Alzheimer’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.

Thank You & Good Luck