LIMBIC SYSTEM VENTICLES OF BRAIN CSF AND ITS FUNCTIONS

LIMBIC SYSTEM VENTRICLES OF BRAIN CSF AND ITS FUNCTIONS

1. LIMBIC SYSTEM AND HIGHER MENTAL FUNCTIONS - HIPPOCAMPUS, THALAMUS, AND HYPOTHALAMUS

2. LIMBIC SYSTEM AND HIGHER MENTAL FUNCTIONS - HIPPOCAMPUS, THALAMUS, AND HYPOTHALAMUS LIMBIC SYSTEM The limbic system is a compound system of cortical and subcortical structures that form a ring around the hilus of the cerebral hemisphere. Limbus means a ring and is also known as the limbic lobe. It combines higher mental functions and it is often referred to as the emotional nervous system.

3. The term limbic system is the entire neuronal circuitry that controls emotional behaviour and motivational drives. The limbic system is mostly associated with the emotional part of our life and is connected with memory. FUNCTIONS OF LIMBIC SYSTEM 1. Olfaction: Olfactory centre is formed by Piriform cortex and amygdaloid nucleus of limbic system. 2. Regulation of endocrine glands: Hypothalamus plays a very important role in regulation of endocrine secretions.

4. Regulation of autonomic functions: Hypothalamus regulates the heart rate, blood pressure, electrolyte balance and body temperature. Regulation of food intake: Hypothalamus regulates the food intake. Regulation of sexual functions: Hypothalamus is responsible in maintain sexual functions. Role in emotional state: Hippocampus is responsible in maintaining emotion stability in humans. Role in memory: Hippocampus and Papez circuit involved in memory.

5. 8. Role in motivation: Hypothalamus has the reward and punishment, which are responsible for motivation of humans. The significant structures within the limbic system: The Hippocampus. The Amygdala. The Thalamus. The Hypothalamus. The Fornix and Parahippocamp. The Cingulate Gyrus.

6. I. The Hippocampus: It is situated in the temporal lobe, the shape of the hippocampus is seahorse. It consists of two horns that curve back from the amygdala The prefrontal area of the brain consults the hippocampus to use memories to modify our behaviour. The hippocampus is responsible for memory. It is very important in the transition of information from short to long term memory. As it is the part of the Temporal Lobe, damage to this portion of the brain result in memory loss.

7. Hippocampus also involved in various processes of cognition. The first and most widely researched area concerns memory, spatial memory in particular. Spatial memory is found in sub- regions of hippocampus, such as the dental gyrus (DG) in the dorsal hippocampus, the left hippocampus, and the Para hippocampus regions. The dorsal hippocampus was found to be an important component for the generation of new neurons, called adult- born granules (GC).

8. II. The Amygdala: It is located in anteroinferior regions of the temporal lobe, it connects with hippocampus, septinuclie and dorsal nucleus of the thalamus. The main function of the amygdala is to control of feelings such as love, friendship, affection, and expression of mood. It is an important center for identification of danger.

9. III. The Thalamus: Thalamus is a small structure, which is located in the brairs, just above the brain stem, between the cerebral cortex and the midbrain with extensive nerve connections. The main function of the thalamus is to transmit motor and sensory signals to the cerebral cortex The stimulation of medial, dorsal, and anterior nuclei of the thalamus are associated with changes in emotional reactivity

10. Physiological classification of thalamic nuclei: Midline nuclei. Intralaminar nuclei. Medial mass of nuclei. Lateral mass of nuclei. Posterior group of nuclei. The midline nuclei are a group of small nuclei located on the medial surface of the thalamus near the midline.

11. The intralaminar nuclei are smaller nuclei in the medullary septum of the thalamus, The medial mass of the nuclei is located medial to the septum and consists of two nuclei: anterior nucleus and dorsomedial nucleus. Lateral mass of nuclei is located on the side of the septum. It consists of the dorsolateral nucleus, the posterolateral nucleus, the anterior ventral nucleus, the lateral ventral nucleus, and the posterior ventral nucleus. Posterior group of nuclei are the extension of lateral mass of nuclei.

12. Functions of thalamus: The thalamus is primarily responsible in performing the somatic functions and has a minor role in visceral activities. Following are the some of the functions; Relay Center: Almost all sensory impulses reach the thalamic nuclei. After processing in the thalamus, the impulses are sent via the thalamocortical fibers to the cerebral cortex. Center for processing of sensory information: All peripheral sensory impulses that reach the thalamus are assimilated and altered before they are sent to certain areas of the cerebral cortex.

13. Center for determining quality of sensations: Thalamus center for defines the quality of sensations, ie., for determining the affective nature of sensations. It has the ability to identify the kind, place and other sensations details and to determine whether a sensation is pleasant or unpleasant. Center for sexual sensations: The thalamus is involved in generating sexual sensations. Role in excitation and alarm reactions. Center for reflex activity: It is one of the main centers for performing reflex functions.

14. 7. Center for integration of motor activity: The thalamus serves as the center for the integration of motor functions. IV. The Hypothalamus: The Hypothalamus is a small part of the brain located just below the thalamus. It connects with the midbrain with the cerebral hemisphere and encircles the third ventricle. It spreads from optic chiasma to mamillary body. It is formed with the group of nuclei in the wall and floor of 3rd ventricle.

15. Nuclei of hypothalamus: Branches of nuclei of hypothalamus are: Anterior or preoptic group. Middle or tuberal group. Posterior or mamillary group.

16. Functions of hypothalamus: The hypothalamus is the vital portion of the brain that is responsible for the homeostasis of the body. Many vital functions of the body such as endocrine functions, visceral functions, metabolic activities, hunger, thirst, sleep, wakefulness, emotions, sexual functions, etc, are maintained by the hypothalamus. 1. Secretion of posterior pituitary hormones: The hypothalamus is the main place for the production of hormones from the posterior lobe of the pituitary gland.

17. Control of anterior pituitary: Hypothalamus controls the secretions of anterior pituitary gland by secreting releasing hormones and inhibitory hormones. It secretes seven hormones: Growth hormone- releasing hormone (GHRH). Growth hormone- releasing polypeptide (GHRP). Growth hormone-inhibiting hormone (GHIH). Thyrotropin- releasing hormone (TRH). Corticotropin- releasing hormone (CRH). Gonadotropin- releasing hormone (GnRH).

18. vii. Prolactin-inhibiting hormone (PIH). Control of adrenal cortex: Adrenal cortex is controlled by anterior pituitary gland by relasing adrenocorticotropic hormone (ACTH). ACTH again controlled by corticotrophin- releasing hormone (CRH), which is released by paraventricular nucleus of hypothalamus. Control of adrenal medulla: Dorsomedial and posterior hypothalmic nuclei are excited by emotional stimuli.

19. Regulation of Autonomic nervous system: Hypothalamus controls the ANS: The sympathetic division is regulated posterior and lateral nuclei. The para supathetic division controlled by anterior group of nuclei. Regulation of heart rate: Stimulation of posterior and lateral nuclei of hypothalamus increases the heart rate. Stimulation of preoptic nucleus in anterior group decreases the heart rate. Regulation of blood pressure: Stimulation in posterior and lateral hypothalamic nuclei, increases the arterial blood pressure. Stimulation in the preoptic area decreases the blood pressure.

20. Regulation of body temperature: Hypothalamus sets the normal range of body temperature. The body temperature in normal physiological condition 37°C. Regulation of body temperature takes place by two centers; heat loss centers present in preoptic nucleus of anterior hypothalamus and heat gain center present in posterior hypothalamic nucleus. Regulation of hunger and food intake: Regulation of hunger and food intake is regulated by feeding center and satieity center.

21. Feeding center: Stimulation of this center leads to uncontrolled hunger and causes obesity. Destruction of this center leads to anorexia. Satiety center: The stimulation of its center leads to a complete loss of appetite and to the cessation of food intake. The destruction of the satiety center leads to hyperphagia and the animal becomes obese. Regulation of water balance: The hypothalamus regulates the body's water content through two mechanisms: Thirst mechanism. Antidiuretic hormone (ADH) mechanism.

22. Thirst mechanism: When the ECF volume is reduced osmolality of ECF is raised. Thereby osmoreceptors are stimulated and activate the thirst center to initiate the thirst. Antidiuretic hormone (ADH) mechanism: ADH causes retention of water by facultative reabsorption in the renal tubules. Regulation of sleep and wakefulness: Stimulation of anterior hypothalamus also leads to sleep. Regulation of sexual function: Hypothalamus regulates the sexual functions by secreting gonadotropin- releasing hormones.

23. Hypothalamus is responsible for smell. Hypothalamus is responsible for maintaining circadian rhythm. Role in behaviour and emotional changes: It has two centers reward center and punishment center. Reward center: Electrical stimulation of this center in hypothalamus in animals pleases or satisfies the animals. Punishment center: The electrical stimulation of these nuclei in animals causes pain, fear, defenses, escape responses, and other origins of punishments.

24. V. The Fornix and Para hippocampus: This region plays an important role in memory encoding and retrieval. It has been involved in some cases of hippocampal sclerosis. VI. The Cingulate Gyrus: The Cingulate Gyrus is located in the medial side of the brain between the cingulated sulcus and the corpus callosum. There is still much to be learned about this gyrus, but it is already known that its frontal part coordinates smells and sights, with pleasant memories of previous emotions.