Thalamus & Limbic System

1. Thalamus & Limbic System Prof. Saeed Abuel Makarem

2. Objectives By the end of the lecture, you should be able to: • Describe the anatomy and main functions of the thalamus. • Name and identify the different nuclei of the thalamus. • Describe the main connections and functions of the thalamic nuclei. • Name and identify different parts of the limbic system. • Describe main functions of the limbic system. • Describe the effects of lesions of the limbic system.

3. It is the largest part of the diencephalon • It is the largest nuclear mass of the whole body. • It is formed of • two oval masses of grey matter. • It is the gateway to the cortex. • Resemble a small hen. • It is in the shape and size of walnut. • Together with the hypothalamus they form the lateral wall of the 3rd ventricle. THALAMUS THALAMUS Corpus Callosum Midbrain PONS

4. THALAMUS It sends received information from different brain regions, to the cerebral cortex. Axons from every sensory system (except olfaction) synapse in the thalamus as the last relay site 'last stop'before the information reaches the cerebral cortex. There are some thalamic nuclei that receive input from: Cerebellar nuclei, Basal ganglia- and Limbic brain regions.

5. Relations It has 4 surfaces & 2 ends. Surfaces Lateral: (L) Posterior limb of the internal capsule. Medial: The 3rd ventricle The 2 thalami are connected by the interthalamic connexus, (adhesion) or Massa intermedia. Superior: (S) Fornix and lateral ventricle. Inferior: (I) Hypothalamus, anteriorly & Subthalamus posteriorly. • It is separated from the hypothalamus by the hypothalamic sulcus S T T L 3rd I

6. Anterior end: Forms a projection, called the anterior tubercle. It lies just behind the interventricular foramen. Posterior end: Broad and is called Pulvinar which lies above the superior colliculus and the lateral & medial Geniculate bodies.

7. Internal Structure • White matter: • External medullary lamina: • Covers the lateral surface. • It is formed of thalamocortical & corticothalamic fibers. • Internal medullary lamina: • Y- shaped bundle of myelinated (afferent & efferent) fibers. • It divides the thalamus into: anterior , medial, lateralnuclear groups. • Each of these group is subdivided into a number of named nuclei.

8. Lateral Nuclear Group It is divided into: Dorsal & Ventral tiers Dorsal tier: Which contains: Lateral Dorsal (LD)& Lateral Posterior (LP) Pulvinar. Ventral tier, Which contains: Ventral Anterior (VA) Ventral Lateral (VL) Ventral Posterior (VP) (VPLN, VPMN). Medial & Lateral geniculate nuclei.

9. Functional Organization of Thalamic Nuclei • All thalamic nuclei project to the ipislateral cerebral cortex, EXCEPT reticular nucleus (project to other thalamic nuclei) • Precise Point to Point projections sometimes found 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.

10. Output of thalamic nuclei MN AN VA VL (VPLN, VPMN) MGN LGN

13. Classification of thalamic nuclei according to their projection • They could be classified into 3 groups, each contains 4 nuclei, (12 nuclei). A) Simple Sensory Relay Nuclei: • They receive sensory impulses, and relay them to the sensory cortex. • PLVN (posterolateral ventral nucleus). • PMVN (posteromedial ventral nucleus). • LGB (lateral geniculate body). • MGB (medial geniculate body).

14. B) Circuit relay nuclei: • They receive impulses from different areas of CNS and relay them to specific areas in cerebral cortex, they include: 1. Anterior ventral nucleus (premotor cortex). 2. Lateral ventral nucleus (primary motor cortex). 3. Anterior nucleus (cingulate gyrus) 4. Part of dorsomedial nucleus (prefrontal cortex).

15. C) Associative nuclei: They receive impulses from other thalamic nuclei 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.

16. Functional Organization of the Thalamic nuclei

17. LIMBIC SYSTEM • The term "limbic" is from the Latin word Limbus, for "border" or "edge". • It separates the medial surface of the cerebral cortex from the diencephalon. • It consists of a number of cortical & subcortical structures. • All are connected with looped fibers. • That all project to the hypothalamus.

18. WHAT IS THE FUNCTION OF THE LIMBIC SYSTEM? Pleasure sensation It control a variety of functions including: • Emotions, and Emotional responses. • Behavior. • Mood (happy, cry, laugh, sad, afraid, aggression, depression). • Motivation. • Memory. • Visceral & Motor responses involved in (sex, pleasure, hunger, and reproduction). • Olfaction. OLFACTION MEMORY

19. The limbic system is a set of brain structures including The limbic system is formed of four main structures: 1. Limbic cortex. 2. Amygdala. 3. Hippocampus, 4. Septal area. These structures form connections between the limbic system and the hypothalamus, thalamus and cerebral cortex. The hippocampus is important in memory and learning, while the limbic system itself is central in the control of emotional responses.

20. CORTICAL STRUCTURES • Limbic lobe. • Hippocampus. • Septal areas. • Prefrontal area.

21. LIMBIC LOBE • C-shaped ring of grey matter on the medial side of each cerebral hemisphere, surrounding the corpus callosum. • It includes: • Subcallosal area • Cingulate gyrus • Isthmus • Parahippocampal gyrus. • Uncus.

22. HIPPOCAMPUS It is a limbic system structure that is involved in: Formation, Organization, and Storage of long lasting memories. It is important in forming new memories and connecting emotions and senses, such as smell and sound, to memories. It is a horseshoe paired structure, one in each cerebral hemisphere. It acts as a memory indexer by sending memories to the appropriate part of the cerebral hemisphere for long-term storage, consolidation and retrieving them when necessary.

23. HIPPOCAMPUS • Site: • It is a scrolled structure in the inferomedial part of the temporal lobe. • Function: • Memory (file new memories as they occur). • The hippocampus & its connections are necessary for consolidationof new short-term memories.

24. HIPPOCAMPUS • Its principal efferent pathway is called the: FORNIX: It is C-shaped group of fibers connecting the hippocampus with mammillary body. it consists of: 2 Fimbriae, 2 Crurae, 1 Body & 2 Column. • The Fornix is an important component of PAPEZ CIRCUIT

25. AMYGDALA • Site: • Almond shaped mass of nuclei. • It lies near the temporal pole, close to the tail of the caudate nucleus. • Function: • It is involved in • FEAR , • Emotions. • Anger, • Hormonal secretions.

26. CONNECTIONS OF AMYGDALA • Inputs: • Association areas of: • Visual cortex, • Auditory cortex, • Somatosensory cortex. • Outputs: • Hypothalamus & Autonomic nuclei in the brain stem, • Lesion: • Lack of emotional responses and docility.

27. Septal nuclei Site: Located anterior to the interventricular septum. Main connections: • To Hypothalamus • To Habenular nuclei Function: It is the pleasure zone.

28. Lesions associated with limbic lobe disorders • Korsakoff’s psychosis (Retrograde = loss of new memories at the time of lesion with retained old memories & anterograde amnesia= inability to gain new memories) • 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.

29. بسماللة الرحمن الرحيم ”واللة اخرجم من بطون امهاتكم لا تعلمون شيئا “وجعل لكم السمع والابصار والافئدة لعلكم تشكرون النحل78