Motivation Flashcards
What is motivation?
→ A physical need
→ Wanting/liking something
What does the hypothalamus do?
→ Maintain homeostasis by regulating three interrelated functions
What are the 3 things that the hypothalamus controls?
→ Endocrine secretion
→ Autonomic nervous system
→ Emotions and drive
Describe anabolism
→ glucose goes to the liver
→ Skeletal muscle stores glucose as glycogen
Describe catabolism
→ Glycogen gets broken down to glucose
What is parabiosis?
→ Sharing of blood circulation between animals
What do obese mice not produce?
→ leptin
What happens if you connect an ob/ob mouse and a normal mouse via parabiosis?
→ the ob/ob mouse will decrease in size
Where does leptin bind?
→ Leptin receptors on the arcuate nucleus
When is leptin released and why?
→ When you finished eating
→ to stop feeding
Where is the hypothalamus?
→ At the base of the brain
What happens when you lesion the VMH?
→ weight gain
What happens during lateral hypothalamic syndrome?
→ Diminished appetite for food
→ Anorexia
What happens during ventromedial hypothalamic syndrome?
→ Overeating
→ Obesity
What are the anorectic peptides?
→ Alpha MSH
→ CART
Describe the anorexic response
→ Leptin increases in circulation
→ Leptin binds to receptors on the arcuate nucleus
→ Alpha MSH and CART neurons in arcuate nucleus are activated which project to the lateral hypothalamus
→ These neurons release alpha MSH and CART peptides
→ Peptides inhibit feeding
Describe how the basal metabolic rate is increased during the anorexic response
→ Leptin stimulates the Alpha MSH and CART neurons of the Arcuate Nucleus.
→ These neurons extend from the Arcuate Nucleus to the Paraventricular Nucleus.
→ The Paraventricular Nucleus is stimulated and stimulates the release of ACTH and TSH from the Anterior Pituitary.
→ ACTH and TSH increases the basal metabolic rate.
Describe the orexigenic response
→ Leptin levels are low.
→ CART and alpha MSH neurons of the Arcuate Nucleus are inhibited.
→ NPY and AgRP neurons in Arcuate Nucleus are activated which project to the lateral hypothalamus.
→ These neurons release NPY and AgRP peptides.
→ Peptides stimulate feeding.
Describe how the basal metabolic rate is decreased during the orexigenic response
→ Low Leptin levels inhibits the Alpha MSH and CART neurons of the Arcuate Nucleus whilst activating the AgRP and NPY neurons.
→ These neurons extend from the Arcuate Nucleus to the Paraventricular Nucleus.
→ AgRP and NPY inhibit the Paraventricular Nucleus thus it cannot stimulate the release of ACTH and TSH from the Anterior Pituitary.
→ A lack of ACTH and TSH means a decreased basal metabolic rate.
What do alpha MSH and AgRP bind to?
→ MC4 receptor
What does alpha MSH do to the MC4 receptor?
→ It activates the receptor
→inhibits feeding
What does AgRP do to the MC4 receptor?
→ Inhibits the receptor
→ Increases feeding
What are the 2 lateral hypothalamic peptides?
→ Melanin concentrating hormone (MCH)
→ Orexin
What are the 3 functions of orexins?
→ Promotes meal initiation
→ Decreases sleep and increases arousal
→ Promotes drug addition
What is the function of MCH?
→ Prolongs consumption
What does disruption of the hypothalamus cause?
→ Hyperphagia
→ Anorexia
→ bulimia
What happens during the cephalic phase?
→ Secretion of saliva
→ Gastric juices secreted in the stomach in preparation for food
→ Activated NPY/AgRP
What happens during the gastric phase?
More secretion of saliva
→ More secretion of gastric juice
→ Distension signals via the vagus nerve
What two other substances are released during the gastric phase?
→ CCK
→ Insulin
What is the connection between serotonin and food?
→ 5-HT rises in anticipation of food
→ Spikes during a meal
What are the natural rewards?
→ Sex
→ Food
→ Water
→ nurturing
What is the reward pathway in the brain?
→ Dopaminergic neurons that project from the VTA to the nucleus accumbens
What do nicotine, cocaine and heroin cause?
→ Activation of the mesolimbic pathway
How does cocaine work?
→ Blocks dopamine transporters in the nucleus accumbens
How does heroin work?
→ Activates new opioid receptors in the VTA
How does nicotine work?
→ Activates nicotinic receptors in the VTA
What is positive reinforcement?
→ Anything added that follows a behaviour and makes it more likely that the behaviour will occur again in the future
What is negative reinforcement?
→ A response or a behaviour that is strengthened by stopping, removing or avoiding a negative outcome
What classifies someone as being an addict?
→ They suffer from physical and emotional withdrawal symptoms when the drug is taken away
What do people who suffer from addiction have?
→ Suppressed reward systems
What is wanting something driven by?
→ Dopamine
What is liking something driven by?
→ Opioid system
What is the prefrontal cortex involved in?
→ Willpower
Why don’t leptin injections work in humans?
→ Addiction is driven by many factors
How are gut hormones involved in feeding behaviour?
→ acting via vagal afferents act on nuclei within the brainstem (NTS) which in turn signal to the hypothalamus.
→ Some gut hormones may also act directly on the hypothalamic nuclei via the circulation and across the blood-brain barrier
How is the pre-frontal cortex involved in feeding behaviour?
conditioned taste aversion
How is serotonin linked with food?
→ 5HT in hypothalamus
→ Rises in anticipation of food
→ Spike during a meal (carbohydrates in particular)
What is low serotonin levels associate with?
→ anorexia nervosa, → bulimia with depression
What is dopamine release in the nucleus accumbens correlated with?
→ correlated with motivation but not liking (hedonic)
What is microdialysis?
→ Measuring neurotransmitter release in vivo
→ Association with behaviour parameters
How is the hippocampus involved in feeding behaviour?
→ involved in memory and learning. Memory of reward is strong in people developing dependence on food and drugs
How is the amygdala involved in feeding behaviour?
emotionality. Extended amygdala in dependence
What is observed in D2 receptor labelling of obese people?
→ downregulation of D2 receptors.
→ So they increase feeding in order to get back to control normal states of satisfaction
What are the short term regulation of feeding?
→ Gastric distension signals brain via vagus nerve.
→ CCK released in intestines in response to fats
→ Insulin also released by β cells of the pancreas— induces satiety by acting on arcuate nucleus of the hypothalamus
What are the short term regulations of feeding in the cephalic phase?
→ Ghrelin released when stomach is empty
→ Activates NPY/AgRP-containing neurons in arcuate nucleus
What does removal of ghrelin-secreting cells in the stomach lead to?
loss of appetite
What is the hypothalamus adjacent to?
Adjacent to third ventricle of the brain
