Behavioral and Motivational mechanisms of Brain. Limbic system and the Hypothalamus

Transcription

1 Behavioral and Motivational mechanisms of Brain Limbic system and the Hypothalamus 1

2 General functions 1. Control of behavior 2. Control level of activities in different parts of brain 3. Motivational drives 4. Motivational control of learning process 5. Feelings of pleasure and punishment 6. Control of chemical constancy of body 7. Control of body temperature 2

3 Limbic system Limbic= border Border structures around basal regions of cerebrum Neuronal circuitry to control (Functions) 1. vegetative functions +many internal conditions e.g. body temperature, osmolality, drives to eat and drink, control of body weight 2. emotional behavior and motivational drives 3. Behavioral functions HYPOTHALAMUS and related structures 3

4 Functional anatomy of Brain key position of Hypothalamus 4

5 Hypothalamus Hippocampus Mamillary body 5

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7 behavioral functions from hypothalamus and limbic structures ----mediated through the reticular nuclei in the brain stem and their associated nuclei hypothalamic signals for controlling the autonomic nervous system are also transmitted through synaptic nuclei in the brain stem between limbic system and the brain stem is the medial forebrain bundle -- extends from the septal and orbitofrontal regions -- middle of the hypothalamus to brain stem reticular formation. 7

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9 short pathways among the reticular formation of the brain stem, thalamus, hypothalamus--- areas of the basal brain 9

10 Hypothalamus is major control HEADQUARTER for the limbic system Two way connections with all levels of limbic system Output signals in three directions 1. Downward into Brain stem mainly into the reticular areas of the mesencephalon, pons, and medulla-- into the peripheral nerves of the autonomic nervous system 2. Upward into Diencephalon and cerebrum-- anterior thalamus and limbic portions of the cerebral cortex 10

11 3. Into hypothalamic infundibulum (to control/partially control secretory functions of anterior and posterior pituitary gland) 11

12 Hypothalamus is major control HEADQUARTER for the limbic system Diencephalon and Cerebrum and to limbic portions of cerebral cortex Hypothalamus Ant/ post Pituitary Brain stem 12

13 Functions of Hypothalamus Hypothalamus (less than 1 percent of the brain mass) is one of the most important of the control pathways of the limbic system 1. Vegetative functions 2. Endocrine control 3. Behavioral functions 13

14 Vegetative and endocrine control functions of Hypothalamus 14

15 Hypothalamus helps to regulate arterial pressure thirst and water conservation appetite and energy expenditure temperature regulation endocrine control 15

16 Physiological anatomy of Hypothalamus 16

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18 Cardiovascular Regulation Stimulation in the posterior and lateral hypothalamus increases the arterial pressure and heart rate Stimulation preoptic area --a decrease in heart rate and arterial pressure-- transmitted through cardiovascular control centers in the reticular regions of the pons and medulla 18

19 Body Temperature Regulation Preoptic area (anterior hypothalamus)--- regulation of body temperature. An increase in temperature of the blood flowing through this area increases activity of temperature-sensitive neurons whereas a decrease in temperature decreases their activity 19

20 Body Water Regulation The hypothalamus regulates in 2 ways 1. Creating thirst 2. Control excretion of water in urine supraoptic nuclei---nerve fibers---- infundibulum ----into the posterior pituitary gland -- nerve endings secrete the hormone ADH 20

21 Regulation of Uterine Contractility and Milk Ejection from the Breasts paraventricular nuclei ----oxytocin Causes increased contractility of the uterus at the end of pregnancy and during labour Milk let down reflex 21

22 Gastrointestinal and Feeding Regulation lateral hypothalamic area hunger Stimulation thirst, eating, rage damage to this area on both sides of the hypothalamus --- lose desire for food satiety center---ventromedial nuclei stimulation --complete indifference to food, tranquility If destroyed bilaterally--hypothalamic hunger centers become overactive-- voracious appetite--obesity 22

23 mammillary bodies-- control partially the patterns of many feeding reflexes--- licking the lips and swallowing Arcuate nuclei---two types of neurons Stimulation causes increased or decreased apetite 23

24 Hypothalamic Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland The anterior pituitary gland receives blood supply ---flows first through the lower part of the hypothalamus --- then anterior pituitary vascular sinuses secrete releasing and inhibitory hormones into the blood by hypothalamic nuclei 24

25 Physiological anatomy of Hypothalamus 25

26 Behavioral functions of Hypothalamus 1. To control general level of activity 2. Sexual drive (stimulation of most anterior and most posterior portions) 3. Fear (stimulation of periventricular nuclei located immediately adjacent to the third ventricle) 4. Punishment (Punishment centre) 5. Reward (Reward centre) 6. Anger stimulation lateral hypothalamus 26

27 Reward Centers located along the medial forebrain bundle especially in the lateral and ventromedial nuclei of the hypothalamus Punishment Centers ---the central gray area surrounding the aqueduct of Sylvius in the mesencephalon and the periventricular zones of the hypothalamus and thalamus 27

28 a new sensory stimulus ---- excites multiple areas in the cerebral cortex No sense of either reward or punishment- -- habituation to that specific sensory stimulus repeated stimulation creates sense of reward or punishment ---reinforcement 28

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30 FUNCTIONS OF THE HIPPOCAMPUS sensory experience causes activation of hippocampus--- signals go to the anterior thalamus, hypothalamus, and other parts of the limbic system---- through the fornix which is a major communicating pathway stimulation ---- different behaviours as pleasure, rage, passivity or excess sex drive etc 30

31 hippocampus can become hyperexcitable- - give off prolonged output signals even under normal functioning conditions Weak electrical stimulation can cause focal epileptic seizures ---hallucinations 31

32 Anterograde Amnesia After Bilateral Removal of the Hippocampi can recall most previously learned memories satisfactorily are capable of retaining short-term memory for seconds up to a minute or two only ability to establish memories lasting longer than a few minutes --- completely abolished (anterograde amnesia) causes translation of short-term memory into long-term memory 32

33 Functions of the Amygdala complex of multiple small nuclei located immediately beneath the cerebral cortex of the each temporal lobe anteriorly The amygdala receives signals from limbic cortex, auditory and visual association areas amygdala is said to be the window 33

34 Function of the Amygdala Produce behavioral awareness at a semiconscious level. relation to both surroundings and thoughts. make the person s behavioral response appropriate 34

35 Summarize Q.1 Write down functions of the following Lateral hypothalamus Lateral and posterior hypothalamus Medial preoptic area Anterior portion of hypothalamus esp preoptic area Supraoptic nuclei Paraventricular nuclei 35

36 Q.2 Where is thirst and hunger center present? What happens when it is Stimulated Lesion causes Q.3 Where is satiety center present? What happens when it is Stimulated Lesion causes 36

37 Q.4 Where are the following centers mainly present? A) Reward center B) Punishment center 37

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