Neuro: Motivation

Question 1

What is motivation?

Answer 1

Motivation is a driving force driven by either a physical need or the wanting/liking of something

Question 2

Briefly explain process of anabolism

Answer 2

• After eating absorbed nutrients from food enter bloodstream and get converted into glucose, ketones and fatty acids which provide energy to the cells of body
• Excess absorbed nutrients get converted into triglycerides which get stored as adipose tissue
• They also get converted into glycogen which get stored in liver and skeletal muscle

Question 3

Briefly explain process of catabolism

Answer 3

• During period of starvation triglycerides in adipose tissue get broken down to glucose, ketones and fatty acids
• Glycogen in liver and gets broken down into glucose
• These substances provide energy to cells of body

Question 4

How do we know that bodyweight is regulated?

Answer 4

• If you put an animal through a period of starvation it will lose weight
• If you then re-introduce that animal to a normal diet it will then gain weight until its bodyweight goes back to the level it was before the level of starvation
• If you put an animal through a a period of force-feeding it will gain weight
• If you then put it back onto a normal diet it lose weight until its body weight goes to back to pre-force feeding levels

Question 5

Explain how the parabiosis experiment proved that hormones in the blood are able to regulate bodyweight

Answer 5

• Parabiosis: sharing of blood circulation between animals
• Experiment involved connecting obese mouse, with no copies of ob gene, with normal mouse, which had 2 copies of ob gene.
• Normal and obese mice shared blood circulation and leptin produced from expression of ob gene of normal mouse was able to effect hypothalamus of obese mouse as well
• Obese mouse couldn’t produce leptin before as it didn’t have ob gene
• Production of Leptin meant obese mouse losing bodyweight

Question 6

Briefly explain the feedback leptin produces on the brain to cause someone to stop eating

Answer 6

• After feeding adipose tissue reserves get replenished due to conversion of nutrients into triglycerides
• When adipose tissue gets replenished it secretes leptin into the bloodstream
• Leptin travels to arcuate nucleus of hypothalamus and binds to leptin receptors
• This tells the brain that person is full and causes them to stop eating

Question 7

Where specifically within the brain is the arcuate nucleus found?

Answer 7

• It’s found in the hypothalamus
• Specifically it’s found at the bottom of the third ventricle of the brain

Question 8

Apart from the arcuate nuclei what other nuclei are found surronding the third ventricle of the brain?

Answer 8

• On either side of the third ventricle there’s a nucleus called the paraventricular nucleus
• Directly underneath both paraventricular nuclei is the lateral hypothalamus

Question 9

What happens to the body weight of a mouse in which its ventromedial hypothalamus is lesioned? What does this show?

Answer 9

• Body weight increased massively
• This shows ventromedial hypothalamus important for preventing too much weight gain

Question 10

What happens to the body weight of a mouse in which its lateral hypothalamus is lesioned? What does this show?

Answer 10

• Body weight reduced dramatically
• This shows lateral hypothalamus important for preventing too much weight reduction

Question 11

Explain how elevated leptin levels in the body cause inhibition of feeding behaviour (stop eating)?

Answer 11

• Leptin binds to leptin receptors on arcuate nucleus leading to activation of arcuate neurons
• Activated arcuate neurons release αMSH and CART peptides
• Arcuate nucleus neurons project to the lateral hypothalamus so release of αMSH and CART peptides leads to inhibition of lateral hypothalamus
• Inhibition of lateral hypothalamus inhibits feeding
• Release of αMSH and CART peptides from activated arcuate nucles neurons also leads to activation of paraventricular nucleus
• This leads to release of ACTH and TSH from anterior pituitary which causes big increase in metabolism

Question 12

What is the collective term for αMSH and CART peptides?

Answer 12

Anorectic peptides

Question 13

Explain how reduced leptin levels lead to stimulation of feeding behaviour (start eating)?

Answer 13

• In response to low levels of leptin neurons of the arcuate nucleus that secrete NPY and AgRP become activated
• Secretion of NPY and AgRP peptides from these neurons leads to activation of lateral hypothalamus
• Activation of lateral hypothalamus stimulates feeding behaviour
• Low leptin levels also leads to inhibition of paraventricular nucleus via neurons that project to it from arcuate nucleus
• Inhibition of paraventricular nucleus inhibits release of ACTH and TSH from anterior pituitary
• This leads to decrease in metabolism

Question 14

What is the collective term for the NPY and AgRP peptides?

Answer 14

Orexigenic peptides

Question 15

What is the name of the receptor on the lateral hypothalamus that both αMSH and AgRP bind to?

Answer 15

MC4 recptor

Question 16

What effect do αMSH and AgRP have on the MC4 receptor?

Answer 16

• αMSH is an agonist and so activates MC4 receptor
• AgRP is an antagonist and so inhibits the MC4 receptor

Question 17

Apart from the anorectic and orexigenic peptides released from the arcuate nucleus what other peptides can affect feeding behaviour? Where are the released from?

Answer 17

• Melanin-concentrating hormone (MCH)
• Orexin
• Both released from neurons of lateral hypothalamus

Question 18

What effect do MCH and orexin have on feeding behaviour?

Answer 18

• Melanin-concentrating hormone (MCH) - prolongs food consumption so increases feeding behaviour
• Orexin - Promotes meal initiation so increases feeding behaviour

Question 19

As well as the long-term regulation of feeding provided by the hypothalamus there is also short-term regulation of feeding (satiety or feeling full) What are the 3 stages of satiety?

Answer 19

• Cephalic phase
• Gastric phase
• Substrate phase

Question 20

What occurs during the cephalic phase of satiety?

Answer 20

• Increased saliva and gastric secretions
• Increased secretion of ghrelin from stomach

Question 21

Explain the effect ghrelin release has on feeding

Answer 21

• Ghrelin release from stomach causes secretion of NPY and AgRP from neurons in the arcuate nucleus
• This leads to activation of lateral hypothalamus leading to stimulation of feeding behaviour

Question 22

What occurs during the gastric phase of satiety?

Answer 22

• Eating leads to gastric distention
• Gastric distention leads to activation of the vagus nerve
• Activated vagus nerve sends signals to nucleus of the solitary tract which causes you to stop eating
• CCK is also released from the gut and also activates vagus nerve

Question 23

What happens to serotonin levels in the hypothalamus before and during feeding?

Answer 23

• 5-HT (Serotonin) release into hypothalamus rises in anticipation of food
• Then during a meal there’s a spike in serotonin release

Question 24

How is mood associated with food and feeding?

Answer 24

• Disorders connected to eating such as anorexia nervosa and bulimia are associated with depression with one of the causes of depression being low serotonin levels

Question 25

Why do we eat even when we aren't hungry?

Answer 25

* We like food - eating food is pleasureable * We want food - motivational drive to go get food

Question 26

Name some natural rewards

Answer 26

* Food * Sex * Water * Nuturing

Question 27

What pathway of the brain do rewards activate?

Answer 27

Mesolimbic pathway - from ventral tegmental area (VTA) to the nucleus accumbens and then frontal cortex

Question 28

Explain how release of dopamine due to a drug results in addiction to that drug

Answer 28

* Addictive drugs hyperstimulate mesolimbic pathay to cause massive release of dopamine from ventral tegmental area into nucleus accumbens and pre-frontal cortex * This causes massive high/makes you feel good * After that experience you remeber the high so you get increased motivation to feel the same high again which leads to repeat use * Eventually repeat use leads to a person needing more of a drug to feel same high * This leads to dependence

Question 29

During later stages of addiction the motivation for someone taking a drug changes. What is this change of motivation?

Answer 29

* When someone is addicted to drug and they don't take it for a particular length of time they experience withdrawal symptoms * At this point in addiction motivation for somebody taking the drug changes from wanting to feel the high it caused to just trying to offset the withdrawal symptoms

Question 30

What is positive reinforcement?

Answer 30

When a desirable stimulus is presented as a consequence of a behavior and the chance that this behavior will manifest in similar environments increases

Question 31

What is negative reinforcement?

Answer 31

When a response or behavior is strengthened by stopping, removing or avoiding a negative outcome or aversive stimulus