Chapter 9: Homeostasis, Motivation & Reward

Question 1

what is homeostasis?

Answer 1

steady internal balance or equilibrium, regulatory systems actively defend certain values or set points

Question 2

what part of the brain is essential to homeostasis?

Answer 2

the hypothalamus

Question 3

what kind of mechanisms regulate body temperature?

Answer 3

a precisely defined set point, mechanisms that can detect deviations away from the set point, internal and behavioral elements designed to regain the set point

Question 4

what are the two solutions for maintaining internal temperature in animals?

Answer 4

endotherms: internal metabolic activity
ectotherms: external factors, such as sunlight or warm surfaces

Question 5

what are the autonomic internal responses to low or high body temperature?

Answer 5

low: shivering, blood vessels contract, thyroid hormones increase to boost metabolic rate
high: perspiration, licking, panting, blood vessels dilate near skin surface

Question 6

what part of the brain is responds to higher temperatures?

Answer 6

preoptic area (POA) of the hypothalamus has warm-sensitive neurons
POA -> paraventricular nucleus (PVN) -> lateral hypothalamus (LH) -> parasympathetic activity = cool down

Question 7

what part of the brain is responds to lower temperatures?

Answer 7

posterior hypothalamus has cold-sensitive neurons, receive inhibitory input from the warm-sensitive neurons
POA -> PVN -> sympathetic activity = conserve/generate heat

Question 8

what are the body fluids made up of?

Answer 8

electrolytes: sodium, calcium, potassium, chloride, and magnesium

Question 9

what are the three major fluid compartments in our body?

Answer 9

1. extracellular fluid: higher concentrations of Na and Cl (blood supply and CSF)
2. intracellular fluid: higher concentrations of K
3. interstitial fluid

Question 10

what are the mechanisms of osmotic thirst?

Answer 10

drop in the intracellular fluid volume detected by osmoreceptors located in the organum vasculosum of the lamina terminalis (OVLT)

Question 11

what are the mechanisms of hypovolemic thirst?

Answer 11

drop in blood volume, baroreceptors in heart and kidneys measure blood pressure

Question 12

how does the body respond to thirst?

Answer 12

osmoreceptors and baroreceptors stimulate release of vasopressin from the posterior pituitary gland, this stimulates our kidneys to reduce urine productions and constrict blood vessels

Question 13

how does the body initiate drinking?

Answer 13

angiotensin II acts on subfornical organ (SFO), the SFO then communicates with the medial POA which receives input from the nucleus of the solitary tract (NST), the NST receives input from baroreceptors and osmoreceptors and the zona incerta stimulates drinking to the motor system

Question 14

what are some important neurochemicals involved in hunger?

Answer 14

insulin, glycogen, glucagon, leptin, ghrelin, NPY, POMC, and orexins

Question 15

what does digestion do?

Answer 15

breaks down foods into usable chemicals by the digestive tract, excess glucose is stored as glycogen in the liver and excess fat is stored in adipose tissue

Question 16

how do glucagon and insulin regulate glucose levels?

Answer 16

glucagon converts stored glycogen back into glucose
insulin helps store glucose as glycogen (assists in moving glucose from the blood supply into cells)

Question 17

type 1 vs type 2 diabetes

Answer 17

type 1: disorder of insulin production, diagnosed in childhood or early adulthood
type 2: disorder of insulin recognition by cells, adult onset, obesity is a major risk factor

Question 18

what are the hunger and satiety neural circuits?

Answer 18

• PVN, LH, arcuate nucleus, VMH
• VMH lesions produce hyperphagia
• LH lesions inhibit eating (homeostatic set-point changes)
• hunger activates the vagus nerve and raphe nuclei -> PVN and LH
• hormones in the arcuate nucleus -> LH, VMH, PVN
• PVN -> arcuate nucleus, VMH, LH

Question 19

how do leptin/insulin, NPY/AGRP, and ghrelin influence eating behavior?

Answer 19

leptin and insulin communicate with the arcuate nucleus when glucose levels are low
NPY/AGRP activation stimulates feeding via PVN -> PNS activation, high leptin inhibits hunger via POMC
ghrelin increases when hungry and stimulates feeding

Question 20

what role does orexin play in hunger?

Answer 20

orexins are produced in the LH, neurons that release orexins project widely in the cerebral cortex, midbrain, and pons, injection of orexins into the LH results in increased eating in rats, leptin, glucose, and ghrelin levels appear to regulate orexin signaling, orexin activates NPY

Question 21

what is the medial forebrain bundle brain reward pathway?

Answer 21

contains both ascending and descending fibers that pass through the lateral hypothalamus, connecting with the ventral tegmental area (VTA)

Question 22

what is the mesostriatal brain reward pathway?

Answer 22

innervated with dopamine neurons, most addictive substances act as dopamine agonists, especially in the nucleus accumbens

Question 23

how was the reward circuit discovered?

Answer 23

Olds and Milner study which found that rats would press a lever in order to receive a small joint of current in the LH, indicating that there are reward mechanisms in the brain involved in positive reinforcement

Question 24

what neurotransmitters contribute to reward?

Answer 24

dopamine contributes to reward-seeking and learning, essential to “wanting” but not necessarily “liking”, serotonin, glutamate, and GABA signaling are also important in processing reward and promoting goal-directed behavior

Question 25

wanting vs liking

Answer 25

wanting is characterized by more motivational factors such as desire and craving (dopamine is key to wanting), liking describes pleasure and hedonic responses to a reward, such as our enjoyment of foods (opioid and endocanabinoid systems are key in liking)

Question 26

how does SUD alter the brain?

Answer 26

becoming intoxicated activates the reward circuits in the VTA and basal ganglia (mediated by dopamine and endorphins), withdrawal is associated with increased amygdala activity (increased CRF and dynorphin activity), withdrawal leads to preoccupation (mediated by PFC deficits)

Question 27

how does SUD alter homeostasis?

Answer 27

chronic drug use causes dopamine responses to become blunted and body struggles to maintain homeostasis, stress symptoms become overactive during drug withdrawal

Question 28

how does SUD alter impulsivity?

Answer 28

chronic drug use blunts activity in the frontal cortex, reduced volume of the OFC is associated with impulse behavior

Question 29

what role does orexins play in SUD?

Answer 29

orexins are stimulated by morphine conditioned place preference (CPP), stimulating orexins reinstates morphine seeking behavior in rats

Question 30

how is food addiction similar and different to addiction?

Answer 30

same: increased activity in salience and reward networks, reduced activity in executive control networks
differences: drugs work directly on the brain, not all individuals with obesity can be diagnosed with a food addiction