Thalamus and Limbic System

Neuroanatomy block-Anatomy-Lecture 18

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At the end of the lecture, students should be able to:

● Describe the anatomy and main functions of the . ● Name and identify different nuclei of the thalamus. ● Describe the main connections and functions of 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. Color guide

● Only in boys slides in Green ● Only in girls slides in Purple ● important in Red ● Notes in Grey Thalamus

● It is the largest nuclear mass of the whole body. ● It is the largest part of the . ● It is formed of two oval masses of . ● It is the gateway to the cortex. ● Together with the they form the lateral wall of the 3rd ventricle. ● It sends received information to the from different regions. ● from every sensory system (except olfaction) synapse in the thalamus as the last relay site ‘’Last Pit Stop’’ before the information reaches the cerebral cortex. ● Resemble a small hen.

There are some thalamic nuclei that receive input from:

1 Cerebellar nuclei

Basal ganglia 2

3 Limbic-related brain regions

3 Relations of the Thalamus

It has 4 surfaces and 2 ends :

Surfaces

Lateral Medial Superior\Dorsal Inferior\ ventral

Posterior limb of the The 3rd ventricle. Lateral ventricle Hypothalamus Anteriorly . In some people the 2 thalami are and . & posteriorly. connected to each other by (connexus,) or Massa. intermedia, which crosses through the 3rd ventricle.

Ends

Anterior Posterior

Forms a projection, called the anterior tubercle. Broad and forms a projection called the Pulvinar which It lies just behind the inter-ventricular foramen. lies above the superior colliculus and the lateral & medial Geniculate bodies.

4 Internal Structure of the Thalamus

White matter:

External medullary lamina: ● Covers the lateral surface. ● It consists of thalamocortical and corticothalamic fibers. Internal medullary lamina: ● Bundle of Y-shaped myelinated (afferent and efferent) fibers. ● It divides the thalamus into 3 nuclear groups: 1. Anterior 2. Medial 3. Lateral ● Each is subdivided into a number of named nuclei.

Lateral Nuclear Group

It is divided into Dorsal and Ventral tiers: Dorsal tier: Ventral tier:

which contains; 1. Ventral Anterior (VA) 1. Lateral Dorsal (LD) 2. Ventral Lateral (VL) 2. Lateral Posterior (LP) 3. Ventral Intermediate (VI) 3. Pulvinar (PUL) 4. Ventral Posterior (VP) (PLVNT, PMVNT) 5. Medial & Lateral geniculate bodies or nuclei.

5 Projection of thalamic Nuclei

Nuclear Group Afferent Efferent

Cingulate Anterior Thalamic Nucleus Mamillary body (limbic system)

Prefrontal/ Frontal Medial Nucleus Hypothalamus cortex

Globus pallidus body and

Primary motor Ventral Lateral Nucleus Dentate nucleus cortex

Ventral posterior Lateral Nucleus Medial and spinal leminisci Sensory cortex

Ventral Posterior Medial Nucleus Trigeminal leminiscus Sensory cortex

Lateral Geniculate Nucleus Optic tract

Medial Geniculate Nucleus Lateral Leminiscus

6 Limbic system

● Limbic from ” Limbus” in Latin,means “border or edge”.

It separates the medial surface of It consists of a number of cortical & subcortical the cerebral cortex from the Limbic system structures with looped connections that all project to diencephalon the hypothalamus (particularly mammillary bodies.)

Functions of limbic system

Emotions: emotional response,behaviour Visceral & Motor responses Motivation Memory 5 Olfaction & Mood (happy, cry, laugh, sad, afraid, 2 3 4 involved in(sex,pleasure,hunger) 1 aggression, depression)

Structures of Limbic system

Septal area 1 Limbic cortex (Lobe) 2 3 4

❖ 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 important in the control of the emotional responses. ❖ Cortical structure : 1-. 2-Hippocampal formation. 3-Septal areas. 4-Prefrontal area (Olfactory cortex).

7 Structures of Limbic system

1 Limbic cortex (Lobe) 2 Hippocampus

❖ involved in: Formation, Organization, and Storing of memories (FOS of memories) ● C-shaped ring of grey matter on the It is important in forming new memories and connecting emotions and senses, such as smell and sound, to memories. medial side of each cerebral

hemisphere, surrounding the corpus ❖ It is a horseshoe paired structure, one in each . It acts as a memory callosum indexer by sending memories to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary.

● It includes: ❖ Site: It is a scrolled(infolding) structure in the inferomedial part of the 1. ❖ Function: 2. Cingulate gyrus ● Memory (file new memories as they occur). 3. Isthmus (behind splenium of ● The hippocampus & its connections are necessary for consolidation of new ) short-term memories. 4. ● its principal efferent pathway is called the FORNIX 5. . ❖ Fornix: It is C-shaped group of fibers connecting the hippocampus with (and then to the anterior nuclei of thalamus) ➔ It consist of: 2 Fimbria 2 Crus 1 Body 2 Column ➔ The Fornix is an important component of PAPEZ CIRCUIT (based on connecting the hypothalamus with limbic lobe to control emotions ) (is a neural circuit for the control of emotional expression)

8 Structures of Limbic system

3 Amygdala 4 Septal nuclei

❖ Site: It almond shaped mass of nuclei that lies near the temporal pole (deep within the temporal lobes)close to the tail of the . ❖ Site: Located anterior to the interventricular ❖ Function: It is involved in septum (septum pellucidum) and ❖ 1. FEAR anterior to hypothalamus. 2. Emotions ❖ 3. Anger, Aggression Function: It is the pleasure zone. 4. Release of Hormonal. ❖ Main connections: ❖ CONNECTIONS OF AMYGDALA 1. To Hypothalamus. ❖ Inputs: Association areas of visual, auditory & somatosensory cortices. 2. To (lies in of ❖ Outputs: Hypothalamus & Autonomic nuclei in the brain stem. diencephalon)

❖ Lesion: ➢ Lack of emotional responses ➢ docility (reduced emotional expression).

9 Lesions associated with limbic lobe disorders

Korsakoff’s psychosis Temporal lobe epilepsy Alzheimer’s disease Schizophrenia

A chronic memory disorder caused the hippocampus is one of by severe deficiency of thiamine The hippocampus is a common focus the first brain areas to mental disorder with (vitamin B-1) & alcoholic site in epilepsy, and can be damaged show damage in abnormal behavior + through chronic seizures. intoxication. Alzheimer’s disease inappropriate actions Patient has anterograde and feelings It is sometimes damaged in diseases Inability to remember recent such as herpes encephalitis amnesia”= inability to gain events and long-term memory gaps and retain new memories.

“Retrograde” = loss of retained old memories occurred before the injury & “anterograde amnesia”= inability to gain new memories.

10 Practice Q5: The efferent of the ventral anterior nucleus goes to? Q1: Which one of these is NOT cortical structure? A. Somatosensory area A. Septal areas B. Sensory cortex B. Limbic lobe. C.Premotor cortex C. Amygdala D. Auditory cortex D. Hippocampal formation Q6: Which of the following is a part of the dorsal tier of the lateral nuclear Q2: Which area is responsible for pleasure? group? A.Septal area A.Ventral intermediate B. Limbic cortex B.Ventral posterior C.Amygdala C.Lateral posterior D.Hippocampus D.Medial geniculate nuclei Q3: FORNIX connects? Q7: What is anterograde amnesia? A. Hippocampus with fimbria A.The inability to make new memories B. Mammillary body with fimbria B. The inability to retain old memories C. Mammillary body with cingulate gyrus C . The inability to retain new memories D. Hippocampus with mammillary D. A & C Q4: what is true about the amygdala? Q8 : Which one of these is not a function of the limbic system? A. Close to the tail of the caudate nucleus A. Memory B. Lies far away from the temporal pole B. Feeling C. Almond shaped mass C. Behavior D. A and c D. Pleasure

Answers: Q1(C) Q2(A) Q3(D) Q4(D) Q5(C) Q6(C) Q7(D) Q8(B) 11 Members board

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