LIMBIC SYSTEM (Anatomy) ppt

Anatomy

1. The Limbic System By J. Ochai Department of Anatomy College of Basic medical sciences Federal University of Health sciences, Otukpo 1

2. Learning Objectives To know the anatomy of the limbic system with reference to function and clinical conditions The constituent parts of the limbic system The connecting pathways . To understand the limbic system as the epicentre of emotional and behavioural expression. 2

3. Introduction Limbic system refers to structures which lies deep beneath cerebral cortex and above brainstem Structures includes; hippocampus , amygdala , hypothalamus , ant thalamic nuclei and limbic cortex Key functions; olfaction, emotional response, behavior, memory and learning 3

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5. The Limbic Cortex Comprises a wide portion of cortex on the inner side of each hemisphere including parts of frontal and temporal lobes C-shaped structure and includes; Orbitofrontal cortex Subcallosal (Paraolfactory)area Cingulate gyrus Parahippocampal gyrus 5

6. Components of the Limbic System (Grey Matter structures) Cingulate Gyrus : forms a curve around the corpus callosum Receives input from the anterior nucleus of thalamus and cortex and projects signals to hippocampal formation Plays a role in emotion formation and processing, learning and memory and autonomic functions 6

7. Components of the Limbic System contd.. Parahippocampal gyrus : cortical ridge located in the inferior medial temporal lobe It covers the hippocampus medially and amygdala anteromedially Involved in encoding and memory processing 7

8. Hippocampal Formation Located within the medial temporal lobe and lies medial to the Parahippocampal gyrus. Includes; Dentate Gyrus (information enters the hippocampus via the DG (afferent fibres ). Contributes to formation of memory and exploration of novel environment Hippocampus proper: Cornus Ammonis (CA1 and CA3) Plays crucial role memory consolidation from short to long term, spatial navigation Subiculum; pre and parasubiculum (information exit the hippocampus via the subiculum) gives rise to efferent from HF into fornix 8

9. Flow of information within the hippocampus 9 The hippocampus

10. Components of hippocampal formation Disorders of the hippocampus are associated with amnesia, Alzheimer’s, dementia etc 10

11. Amygdala Almond shaped structure located in the medial temporal lobe just anterior to the hippocampus. It is a paired structure with one located in each hemisphere of the cerebrum Involved in emotion and behavior; links our emotions to many other brain abilities; learning, memory and senses There are two important nuclei in the amydala ; Cortico medial nuclei group (emotional response to smell/olfaction) Besolateral nuclei group(largest group, responsible for other emotional and behavioral responses not associated with olfaction) 11

12. Hypothalamus and Thalamus The hypothalamus is a very important structure of the limbic system. Involved in sexual arousal, emotional response, endocrine regulation, sexual development, thermoregulation, regulation of hunger and satiety etc. It feeds information into the limbic system and serves as its final output as well The anterior nuclei and medial dorsal nuclei of thalamus plays a key role in the limbic system (covered in lecture on diencephalon) 12

13. Hypothalamus and Thalamus contd.. In the thalamus, the anterior thalamic nuclei is a component of the limbic system; supports spatial learning and memory The medial dorsal nuclei (medial group) involves in emotions and behaviors The anterior nuclei is a central component of the papez circuit responsible for the aforementioned function The papez circuit connects the hypothalamus to the cortex and plays a key role in control of memory and emotions Papez circuit 13

14. Hypothalamic Nuclei Nucleus Zones Functions Paraventricular Stimulate the releases of oxytocin Paraventricular and medial Fluid balance, parturition, sex drive, autonomic, ant pituitary control etc.. Arcuate Paraventricular and medial Control of anterior pituitary and feeding Preoptic Medial, lateral Thermoregulation, sexual behavior Anterior Medial Thermoregulation, sexual behavior Suprachiasmatic supraoptic Medial Circadian rhythm Supra optic Medial, lateral Fluid balance, parturition etc Dorsomedial Medial Emotion (rage) Ventromedial Medial Appetite(satiety), body weight, insulin regulation Posterior hypothalamic Medial Thermoregulation, fear Mamillary bodies Medial Emotion and short term memory lateral hypothalamic Lateral Appetite(hunger) and body weight control 14

15. Other structures of the limbic system Habenula : part of the epithalamus, located behind the thalamus Septal area : sits in the septum pellucidum; translucent, thin wall, triangular double membrane structure separating the frontal horns of the right and left lateral ventricle of the brain Together, the septal area and habenula are involved in reward pathway and emotional responses 15

16. Components of the Limbic System (White Matter structures/tracts) White matter tracts connects the limbic nuclei with one another. They include; Fornix : involved in memory pathway The fornix sends information from hippocampus to septal area and also sends information to mamillary bodies in hypothalamus as shown in image 16

17. Components of the Limbic System (White Matter structures/tracts) Striae terminalis : from the amygdala, this band of fibres goes up dorsally and underneath the corpus callosum and gives connection to septal area and hypothalamus Ventral amygdalo fugal pathway(VAFP): form the amygdala, it goes ventrally and gives connection to septal area In addition, VAFP also gives connection to the thalamus; medial dorsal nucleus and prefrontal cortex 17

18. Components of the Limbic System (White Matter structures/tracts) Striae medullaris thalami : connects the septal area and habenula Remember that t ogether, the septal area and habenula are involved in reward pathway and emotional responses 18

19. Components of the Limbic System (White Matter structures/tracts) Mammillo -thalamic tract: connection from mamillary bodies in hypothalamus to anterior nuclei of thalamus 19

20. Components of the Limbic System (White Matter structures/tracts) Medial forebrain bundle: is a 2-way connection that runs from prefrontal cortex through the hypothalamus(lateral) and connects with reticular formation of the brain stem 20

21. Components of the Limbic System (White Matter structures/tracts) Mammillo -tegmental tract : Connection between mamillary bodies in the hypothalamus and ventral tegmental area(VTA) in the midbrain The ventral tegmental area has a high concentration of dopaminergic neurons Mamillary peduncles :connection from VTA to mammillary bodies 21

22. Functions of the Limbic system 1. Olfaction smell stimulus activates olfactory epithelial cells Olfactory nerves run up to cribriform plate of ethmoid bone in nasal cavity Stimulate olfactory bulb which sends action potential to olfactory tract reaches Parahippocampal gyrus via lateral olfactory straie outcome = memory of smells experienced 22

23. Functions of the Limbic system 1. Olfaction smell stimulus activates olfactory epithelial cells Olfactory nerves run up to cribriform plate of ethmoid bone in nasal cavity Stimulate olfactory bulb which sends action potential to olfactory tract reaches amygdala via lateral olfactory straie outcome = emotions related to the smell 23

24. Olfaction and its tract 24

25. Functions of the Limbic system 2. Memory/ Learning : Papez circuit Information flow from dentate gyrus – hippocampus proper (CA 3-CA1-subiculum) information leaves via Fornix hypothalamus (mamillary bodies )- ant. Thalamic nuclei via mamiliary thalamic nuclei – cingulate gyrus- Parahippocampal gyrus and back to hippocampus (be informed that from cingulate gyrus fibres also reach the prefrontal cortex ) 25

26. Papez circuit 26

27. Functions of the Limbic system 3. Emotional responses and behaviors Emotional responses such as fear, anger, rage, sadness etc.. You are likely to react differently following each emotional experience. Behaviors associated with limbic system include; feeding behavior, sexual behavior and motivational behavior The amygdala in the epicenter for emotional responses and behaviors 27

28. Functions of the Limbic system contd The amygdala is in constant communication with prefrontal cortex and temporal lobes which are areas in the brain that carry out loads of functions Posterior association area (PAA) receives information from three different areas; somatosensory association cortex, visual association cortex and auditory association cortex and communicates the information to the amydala 28

29. Functions of the Limbic system contd Imagine a person approaches you holding and firing a gun to the air, what will happen to you? What areas of the cortex will create awareness of this situation ? What area of the limbic system do u think this information will reach and what kind of response will be triggered? 29

30. Hypothalamic Nuclei Nucleus Zones Functions Paraventricular Stimulate the releases of oxytocin Paraventricular and medial Fluid balance, parturition, sex drive, autonomic, ant pituitary control etc.. Arcuate Paraventricular and medial Control of anterior pituitary and feeding Preoptic Medial, lateral Thermoregulation, sexual behavior Anterior Medial Thermoregulation, sexual behavior Suprachiasmatic supraoptic Medial Circadian rhythm Supra optic Medial, lateral Fluid balance, parturition etc Dorsomedial Medial Emotion (rage) Ventromedial Medial Appetite(satiety), body weight, insulin regulation Posterior hypothalamic Medial Thermoregulation, fear Mamillary bodies Medial Emotion and short term memory lateral hypothalamic Lateral Appetite(hunger) and body weight control 30

31. Answer ? You will be afraid, you can visually see this threat and even hear the frightening sound coming from the gun ( all this visual and auditory information reaches the amygdala from the cortex through posterior association area The area responsible for fear is amygdala, it sends fibres to your septal area and hypothalamus ( although the hypothalamus will be playing the major role in this situation) 31

32. Functions of the Limbic system Posterior hypothalamic nucleic sends descending axons through hypothalamic- spinal tract and innervates preganglionic neurons located within thoraco lumbar region of spinal cord Sympathethic neurons will then get to specific organs Liver (glucose production) Heart ( increased heart rate)bp Lungs (respiratory rates and depth of breathing) Note : all these are autonomic response Paraventricular neuron in the hypothalamus releases Corticotrophin releasing hormone- ACTH released by anterior pituitary –cortisol released by adrenal cortex 32

33. Functions of the Limbic system Feeding behaviors (hunger and satiety ) Which area will be activated by amygdala ? 33

34. Functions of the Limbic system Motivational behaviors In the case of drug addiction, what happens ? Amygdala – spetal area and hypothalamus(via septum terminalis and ventral medial fugal pathway Both septal area and hypothalamus communicate with ventral tegmental area(area with lots of dopaminergic neurons ) in midbrain Axons from VTA reach nuclear accumbens (via meso-limbic pathway) and PFC(via meso-cortical pathway). This areas are reward areas 34

35. Thank You 35