HMB200H1 Final: Lecture 9 Revision Guide

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Human Biology
Franco Taverna

Lecture 9 Revision Guide - Hypothalamus controls homeostatic mechanisms Homeostatic Loops - Lesions to ventromedial nucleus  overeating & extreme obesity o Required for feelings of ‘fullness’ - Lesions to lateral hypothalamic area  anorexia, may die of starvation o Required for feelings of hunger - Both behavioural triggers & homeostatic sensors in the hypothalamus-- to Dopamine Pathway maintain normal functioning - Activated by behaviours that ‘feel good’ o Dopamine release = experiencing pleasure Pathway: - Ventral tegmental area (VTA) of midbrain  Hippocampus  Nucleus Accumbens (of Basal Ganglia)  Frontal Cortex Pleasure: - Dopamine neurons in VTA neurons activate - Dopamine released by NAcc - Opioids / Endorphins o Also synapse onto the NAcc (perhaps even more rewarding than dopamine) Error Predictor: - Dopamine signals change only if something unexpected occurs - Something more rewarding occurs—more dopamine  increased liking - Something less rewarding—less dopamine  decreases liking Reward Mechanisms - The anticipation of pleasure, not the actual happiness, brings the most dopamine o Increasing the uncertainty of reward  dopamine surges 1. It Feels Good a. Operant conditioning a.i. Stimulation of VTA & medial forebrain – effective reinforcers of behaviour b. Dopamine pathways can activate motivated behaviours b.i. D e Innate Releasing Mechanisms (not only the o hypothalamus) p b.ii. Synapse onto motor areas  causes the movements a m 2. Motivation to obtain reinforcer i n a. Dopamine—critical for motivated behaviour e a.i. Dopamine is more related to drive/actions a c a.ii. Endorphins / opioids – more related to pleasure t i 3. Negative Affect a. Amygdala releases stress hormones v a t i o n c a n c a u s Drugs a.i. Inhibits/modifies these drives a.ii. Seen as top of the hierarchy (usually) Why are drugs 5. Classical & Operant conditioning addictive? a. Occurs unconsciously, without awareness a.i. Cannot be consciously controlled a. VTA neurons shift to fire at the predictors of rewards a.i. Association of earlier & earlier actions with pleasure a.ii. Easier to lead to the actual reward a.i. D Cocaine / Amphetamines (stimulants) r i - Strong activation of the VTA  NAcc pathway v e - Strong dopamine activation  motivated behaviour pathways s  Reduced dopamine receptors in the NAcc (down-regulation of dopamine b receptors) o d o Tolerance y  Sensitizes dopamine—motivational pathways t Morphine/ Heroin/ Fentanyl (opioid-like) o - Binds opioid receptors (endorphin pathways) a o Provides pain relief & euphoria c t - Binds GABA neurons 4. Cortical o Inhibit GABA neurons Control  Leads to Disinhibition of VTA neurons a. Frontal Cortex o Leads to Dopamine release —has Alcohol strong -
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