LIMBIC SYSTEM.pptx

Medical

1. LIMBIC SYSTEM CENTRAL NERVOUS SYSTEM

2. Nerve signals in brain stem activate cerebrum in 2 ways: Background neuronal activity Neurohormonal system

3. Without continuous transmission of nerve signals from the lower brain into the cerebrum, the cerebrum becomes useless Control of cerebral activity by continuous excitatory signals from the brain stem by reticular excitatory area of the brain stem—a driver of brain activity located in the reticular substance of the pons and mesencephalon. This area is also called the bulboreticular facilitory area Increased Activity of the Excitatory Area Caused by Feedback Signals Returning From the Cerebral Cortex A Reticular Inhibitory Area Is Located in the Lower Brain Stem The Thalamus Is a Distribution Center That Controls Activity in Specific Regions of the Cortex

4. NEUROHORMONAL CONTROL OF BRAIN ACTIVITY Neurohormonal Systems in the Human Brain Norepinephrine system Dopamine system Serotonin system Acetylcholine system

5. LIMBIC SYSTEM Ring of forebrain structures that surround the brain stem and are interconnected by intricate neuron pathways entire neuronal circuitry that controls emotional behavior and motivational drive

6. 2 routes of communication between limbic system and brain stem Medial forebrain bundle extending from the septal and orbitofrontal regions of the cerebral cortex downward through the middle of the hypothalamus to the brainstem reticular formation Short pathways among reticular formation of brain stem, thalamus, hypothalamus and most other contiguous areas of the basal brain

7. Limbic Means: border (border structures around basal ganglia) COMPONENTS OF LIMBIC SYSTEM Subcortical Cortical

8. THE HYPOTHALAMUS A MAJOR CONTROL HEADQUARTERS FOR THE LIMBIC SYSTEM

9. Less than 1% of the brain mass but, most important of the control pathways of the limbic system. Two-way communicating pathways with all levels of the limbic system Output signals in three directions backward and downward to the brain stem Upward toward diencephalon and cerebrum( anterior thalamus and limbic portions) Hypothalamic infundibulum

10. FUNCTIONS OF THE HYPOTHALAMUS

11. VEGETATIVE Homeostatic drives Endocrine NON-VEGETATIVE Emotion Behavior

12. VEGETATIVE FUNCTIONS Cardiovascular Regulation/Arterial pressure regulation Body Temperature regulation Body water regulation/Thirst and water conservation Regulation of Uterine Contractility and Milk Ejection from the Breasts Gastrointestinal and Feeding Regulation/Appetite and energy expenditure Hypothalamic Control of Circadian Rhythms—The Suprachiasmatic Nucleus

13. Cardiovascular Regulation Hypothalamic stimulation can cause changes in arterial pressure and heart rate Stimulated area/nucleus Arterial pressure & heart rate Posterior and lateral hypothalamus Increase Preoptic area Decrease

14. Body Temperature Regulation Preoptic area , anterior portion of hypothalamus responsible Increased temperature blood Flows through preoptic area Increases activity of temperature-sensitive neuron Decrease in temperature will decrease neuronal activity

15. Body Water Regulation Two ways 1Thirst Thirst center-lateral hypothalamus Fluid in this & surrounding area becomes concentrated Desire to drink/thirst sensation develop Intake of water from nearby source to compensate electrolyte

16. 2 Control of water excretion in urine Supraoptic nuclei control renal water excretion Stimulate when body fluids become too concentrated Nerve fibers pass to posterior pituitary Here ADH/vasopressin is secreted Transported via blood to kidneys Collecting tubules & ducts increase water reabsorption for electrolyte balance

17. Regulation of Uterine Contractility and Milk Ejection from the Breasts Paraventricular nuclei secrete the hormone oxytocin on stimulation Oxytocin released at the end of pregnancy Stimulates Uterine/ labor contractions Expels the baby

18. Baby suckles the mother’s breast Reflex signal from the nipple to the posterior hypothalamus releases oxytocin Contracts the ductules of the breast Expels milk through the nipples

19. Gastrointestinal and Feeding Regulation Lateral hypothalamic area (hunger area) stimulation extreme hunger a voracious appetite an intense desire to search for food Damage to it causes loss of desire for food, sometimes causing lethal starvation Ventromedial nuclei- satiety center Stimulation ceases food intake & indifference to food Bilateral destruction will cause overeating/voracious eating leading to tremendous obesity

20. Arcuate nucleus Stimulation causes increased or decreased appetite Mammillary bodies partially control the patterns of many feeding reflexes, such as licking the lips and swallowing

21. Hypothalamic Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland Blood flows first through lower part of hypothalamus than towards the pituitary gland Upon coursing through the hypothalamus, specific releasing and inhibitory hormones are secreted into the blood by various hypothalamic nuclei These are transported via the blood to the anterior pituitary gland Act on the glandular cells to control release of specific anterior pituitary hormones

22. Control of Circadian Rhythms—The Suprachiasmatic Nucleus(SCN) SCN located above the optic chiasm where the optic nerves cross underneath the hypothalamus SCN neurons serve as “master clock,” with a pacemaker firing frequency that follows a circadian rhythm This pacemaker function is critical for organizing sleep into a recurring 24-hour circadian pattern of sleeping and waking

23. The SCN receives direct innervation from the retina via the retinohypothalamic tract (RHT) to entrain/alter its activity to day–night cycles SCN neurons project to various brain centers, which contain local circadian clocks that direct feeding–fasting, sleep–wakefulness, autonomic and neuroendocrine circadian rhythms These systemic cues synchronize local molecular clocks in peripheral tissues These local clocks then direct circadian gene expression that regulates physiological rhythms, including those related to mental alertness and cognition, cardiovascular regulation, metabolism, and renal function

24. NON-VEGETATIVE FUNCTIONS BEHAVIORAL FUNCTIONS OF THE HYPOTHALAMUS AND ASSOCIATED LIMBIC STRUCTURES REWARD & PUNISHMENT

25. Overt rage/fighting Satiety, decreased eating tranquility

26. Fear and punishment

27. Hypothalamic stimulation affects behavior Lateral Overt rage, fighting + ( thirst and eating) Ventromedial nucleus Satiety, decreased eating, and tranquility Thin periventricular zone Fear and punishment Anterior and posterior regions Sexual drive

28. EEFECTS OF HYPOTHALAMIC LESIONS Bilateral lesions in the lateral hypothalamus Decrease drinking and eating almost to zero, often leading to lethal starvation. Extreme passivity with loss of most of its overt drives Bilateral lesions of the ventromedial areas Excessive drinking and eating Hyperactivity Frequent bouts of extreme rage on the slightest provocation

29. “REWARD” AND “PUNISHMENT” FUNCTION OF THE LIMBIC SYSTEM

30. Limbic system concerned with affective nature of sensory sensations Pleasant reward satisfaction Unpleasant punishment aversion Major reward centers Along medial forebrain bundle Lateral (weaker stimuli give reward) and Ventromedial nuclei of hypothalamus Minor/less potent Reward centers Septum Amygdala Certain areas of thalamus and basal ganglia Few parts of basal tegmentum

31. Major Punishment centers central gray area surrounding the Aqueduct of sylvius extending to periventricular zones Minor/less potent Punishment centers Amygdala hippocampus Effects Displeasure, fear, terror, pain, punishment, sickness Punishment and fear can take precedence over pleasure and reward

32. Association of Rage with Punishment Emotional pattern associated with punishment is Rage pattern Can be elicited by Strong stimulation of the punishment centers of the brain, especially in the periventricular zone of the hypothalamus and in the lateral hypothalamus Inhibition Ventromedial nuclei of hypothalamus, hippocampi and ant. limbic cortex Placidity and Tameness Stimulation of reward centers Effect opposite to that of punishment center

33. Importance of reward and punishment in Behavior Rewarding act is continued Punishing act is ceased Tranquilizers chlorpromazine, usually inhibits both the reward and the punishment centers, thereby decreasing the affective reactivity of the animal Learning and memory Habituation Reinforcement

34. HIPPOCAMPUS IMPORTANT IN MEMORY AND LEARNING

35. AMYGDALA Behavioral awareness areas that operate at a semiconscious level Project one’s current status into the limbic system in relation to both surroundings and thoughts Believed to make the person’s behavioral response appropriate for each occasion

36. Complex of multiple small nuclei Bidirectional connections with limbic system and hypothalamus Afferents Efferents Concerned with olfactory stimuli in lower animals In humans , Basolateral nuclei concerned with Behaviour Due to multiple connections, the amygdala has been called the “window” through which the limbic system sees the place of the person in the world

37. STIMULATION OF AMYGDALA/FUNCTIONS Effects from Amygdala via hypothalamus Arterial pressure & heart rate (Increase or decrease) GIT’s motility and secretion (Increase or decrease) Defecation or micturition Pupillary dilatation (rarely constriction) Piloerection Secretion of various anterior pituitary hormones

38. Other effects Involuntary movements tonic movements, such as raising the head or bending the body (2) circling movements (3) occasionally clonic , rhythmical movements (4) different types of movements associated with olfaction and eating, such as licking, chewing, and swallowing Rage, escape, punishment, severe pain, and fear Reward and pleasure Sexual activities

39. Kl ü ver-Bucy Syndrome Bilateral Ablation of the Amygdala Both Anterior temporal lobes destroyed in a monkey (rare in humans) results in Not afraid of anything Extreme curiosity about everything Forgets rapidly Puts everything in mouth and tries to eat Abnormal sex drive

40. FUNCTIONS OF THE LIMBIC SYSTEM

41. Emotional and motivational aspects of behavior Reward and punishment Autonomic functions Heart rate, Blood pressure, water and temperature regulation GI/Feeding habits- hunger & satiety Circadian Rhythms Endocrine function Memory/learning Sexual functions