Limbic System human physiology mbbs 1styear.pptx

Physiology

1. Limbic System

2. SCHEME Physiological Anatomy Functions of Limbic System Physiology of Emotions Emotional behaviors Motivation and Addiction Physiological Basis of Psychotic Disorders

3. Introduction Limbic lobe or limbic system is the part of the brain that consists of a rim of cortical tissue around the hilum of the cerebral hemisphere and a group of associated deep structures. First described by Paul Broca in 1878 The region was formerly called the rhinencephalon . Also called as the “Visceral Brain” by Mclean in 1949

4. Physiological Anatomy Components of Limbic System Limbic Cortex Orbitofrontal cortex Subcallosal gyrus Cingulate gyrus Parahippocampal gyrus Uncus

5. Subcortical Structure Hypothalamus Septum Paraolfactory area Anterior nuclei of thalamus Amygdala Portions of basal ganglia Hippocampus

6. Connections Bundle of axons connecting the various components of limbic system are Fornix Mammillothalamic tract Stria terminalis Stria medullaris thalami Medial forebrain bundle

7. Afferent Connections Autonomic afferents from spinal cord and brain stem Reticular formation to various parts of the limbic system Visceral as well as some somatic sensations from the body wall, mouth, smell ,taste and from eyes and ears.

8. Efferent Connections Efferent fibers to autonomic centers in the brain-stem directly or through the hypothalamus Efferent fibers to the reticular formation From hippocampus to the hypothalamus and the anterior nucleus of the thalamus Few to and fro connections to the neocortex Interconnections between parts of the limbic system

9. Papez circuit Cingulate cortex Hippocampus Mammillary bodies Anterior nuclei of thalamus Via Fornix Via Mammillo- Thalamic tract

10. Cingulate gyrus Thalamus Hypothalamus Septal region Amygdala Hippocampus Bulbar reticular formation Spinal cord Bulbar Autonomic centers Spinal cord

11. Characteristic features of Limbic system connections The paucity of the connections between it and the neocortex. Functional point of view, neocortical activity does modify emotional behavior but cannot be turned on and off at will. Prolonged after discharge following stimulation.

12. Functions of Limbic System Autonomic functions Feeding behavior Learning and Memory Biological rhythm Regulation of sexual behavior Maternal behavior Emotions of Rage, fear and placidity Motivation and Addiction

13. Behavioral Functions of the Hypothalamus and Associated Limbic Structures Lateral hypothalamus: overt rage and fighting. Ventromedial nucleus: a sense of satiety, decreased eating, and tranquility. Periventricular nuclei: fear and punishment reactions. Sexual drive: most anterior and most posterior portions of the hypothalamus.

14. Physiology of Emotions Emotions refers to an aroused state involving intense feeling, autonomic activation and related behavior which accompany many of our conscious experiences. Emotions have both mental and physical components.

15. Mental or Sensory component Cognition : It refers to a phenomenon by which one becomes aware and recognizes a situation. Mere seeing but not recognizing is not cognition. Affect : the development of feeling. Conation : It is the urge to take action.

16. Physical or Expressive or Peripheral component It is the motor side of emotional behavior. Somatic part basically comprises changes in the skeletal muscles. Autonomic part involves the coordinated activity of sympathetic and parasympathetic nervous system. In many instances the somatic part of the emotions maybe absent.

17. Arnold theory of Genesis of Emotions By cognition one becomes aware and recognizes a situation. By unconscious evaluation the situation is judged as to be harmful or beneficial. Affect is conscious reflection of unconscious appraisal. A feeling thus generated consciously in response to unconscious evaluation of a situation. Such a feeling may be in the form of fear, joy, grief or rage. Autonomic responses are not an essential component of emotions.

18. SEXUAL BEHAVIOR Sexual activity comprises two components. The behavioral components that accompany it, the basic sex drive (urge to copulate), and the coordinated sequence of events in the male and female. It is the function of limbic system and Hypothalamus, which in turn are influenced by gonadal hormones and cerebral cortex. Learning plays a part in the development of mating behavior.

19. Neural Control Role of neocortex and limbic cortex: removal abolishes the excitement reaction during oestrous (heat period) without affecting the other aspects of heat. Role of hypothalamus: Anterior hypothalamus and median forebrain bundle stimulation elicits sex behaviour. Role of encephalization: i.e. the perception that sexual act produces pleasure is a big cause of sex behaviour.

20. Kluver Bucy Syndrome Effects of Bilateral Ablation of the Amygdala Is not afraid of anything Has extreme curiosity about everything Forgets rapidly Has a tendency to place everything in its mouth and sometimes even tries to eat solid objects Often has a sex drive so strong that it attempts to copulate with immature animals, animals of the wrong sex, or even animals of a different species.

21. Relation to Endocrine Function Removal of the gonads leads eventually to decreased or absent sexual activity. Injection of gonadal hormones in castrated animals revive sexual activity. Large doses of testosterone and other androgens in castrated females initiate female behavior, and large doses of estrogen in castrated males trigger male mating responses.

22. Relation to Endocrine Function Testosterone increases libido in males, and so does estrogen used to treat carcinoma of prostate. The behavioral pattern that was present before treatment is stimulated but not redirected. Thus, administration of testosterone to homosexuals intensifies their homosexual drive but does not convert it to a heterosexual drive.

23. Pheromones Substances produced by an animal that acts at a distance to produce hormonal, behavioral, or other physiologic changes in another animal of the same species. The odorant pheromones that act via the vomeronasal organ play a prominent role in the sexual and dominance behavior of rodents. In humans, pheromones also have effect.

24. Maternal behavior Maternal behavior is depressed by lesions of the cingulate and retrosplenial portions of the limbic cortex in animals. Hormones do not appear to be necessary for its occurrence. In female mice, knockout of the fos-B gene is associated with failure to retrieve and care for pups after delivery.

25. Fear The fear reaction can be produced in conscious animals by stimulation of the hypothalamus and the amygdaloid nuclei. Amygdaloid nuclei are concerned with the encoding of memories that evoke fear. Fear learning is blocked when LTP is disrupted in pathways to the amygdala.

26. Anxiety Anxiety is associated with a bilateral increase in blood flow in a discrete portion of the anterior end of each temporal lobe. α 2 GABA A receptor mediates anxiety.

27. “Reward” and “Punishment” Function of the Limbic System