Physiological mechanisms

Question 1

Preoptic area (POA)

Answer 1

the region of the hypothalamus involved in temperature (only mammals and birds can regulate their body temperature)

Question 2

Endotherms

Answer 2

animals that can regulate their body temperature through internal mechanism

Question 3

Ectotherms (also called cold blooded animals)

Answer 3

animals that have no internal mechanism to regulate their body temperature

• therefore they do it by external means.
  (ex: lizards warm their bodies by basking in the sun)

Question 4

negative feedback

Answer 4

a mechanism by which a stimulus input causes a system to react by causing an opposite output to maintain a desired set point
- thermoregulation is achieved through negative feedback

Question 5

Thermoregulation and negative feedback

Answer 5

two negative feedback loops.
- body temperature rises, stimulus is heat, then it is picked up by temperature sensitive receptors in the skin and brain, then an afferent pathway goes towards the control center, preoptic area of the hypothalamus, to affect our organs it could be sweat glands, the stimulus input

Question 6

Cold defense

Answer 6

• output from the hypothalamus in response to potentially threatening cooling of the body
• decrease heat loss
• include the constriction of blood vessels of the skin
• results in increasing blood circulation to the core of the body preventing it from losing too much heat

Question 7

Heat defense?

Answer 7

output from the hypothalamus in response to potentially threatening heating of the body

• increase heat loss
  another way the body loses heat is by evaporative cooling, which you may know as sweating

Question 8

Shivering ?

Answer 8

shaking of skeletal muscles that generate heat through the expenditure of energy

–> reaction automatically triggered by the hypothalamus are combined with behavioural responses such as putting a warm sweater or generating heat by moving around

Question 9

Thermoregulatory circuits in the nervous system

Answer 9

• body temperature is detected by thermoreceptors deep in the body
  &
• temperature of the immediate surrounding is detected by thermoreceptors near surface of skin

Question 10

Spino Thalamo Cotrical pathway (STC)

Answer 10

• the pathway through which body temperature is conveyed to the somatosensory cortex via the thalamus for the perception of temperature
• if you touch a hot plate and say ouch thats because you are perceiving that the object is hot, this is called the spina thalamo cortical pathway

Question 11

Lateral parabrachial nucleus (LBN_

Answer 11

This is a pathway that runs from the lateral parabrachial nuclus - the region of the brainstem to the preoptic area of the thalamus involved in temperature regulation

Question 12

LBN-POA pathway?

Answer 12

The pathway through which body temperature is conveyed to the LPB and POA for temperature regulation
- this pathway leads to the regulation of body temperature by producing heat defense and cold defense behaviours

Question 13

Preoptic Area

Answer 13

was the major thermoregulatory structure in the brain in the hypothalamus

Question 14

thermoregulation

Answer 14

thermoreceptors under skin –> process starts in the spinal cord then goes to the LBN and then gets to POA.

Question 15

Energy homeostasis

Answer 15

• the brain consumes 20% of the body’s energy
• neurons consume twice the amount of energy as other cells in the body
  two-thirds of the energy used by neurons is for neurotransmission
• the process that maintains cellular metabolism depends on continuous supply of calories and oxygen
  food energy comes from macronutrients: carbohydrates, fats, and proteins

Question 16

Two states of energy homeostasis

Answer 16

Prandial state and Post-absorptive state

Question 17

Prandial state

Answer 17

a state in which energy stores are replenished as nutrients are absorbed in the bloodstream and stored

Question 18

Post-absorptive state

Answer 18

a state in which nutrients are no longer entering the bloodstream and when the body relies on the the release of stored energy from the lover as glucose and from fat cells and fatty acids and ketones

Question 19

what are energy is used for your muscles ?

Answer 19

• glucose used by cells and neurons

- fatty acids and ketones used by all cells for energy

Question 20

hormones

Answer 20

substances that can have effects on cells distant from the cells that released them

• hormones are chemical messengers
• some of them involved in satiety

Question 21

hunger ?

Answer 21

the drive generated when energy stores are not sufficient to sustain energy balance

Question 22

Satiety

Answer 22

refers to the state of being fed or to the feeling of satisfaction that follows a meal

Question 23

arcuate nucleus

Answer 23

a region of the hypothalamus involved in the regulation of food intake

Question 24

nucleus of the solitary tract (NST)

Answer 24

a bundle of nerve fibers that caries excitatory messages from the stomach to the hypothalamus

Question 25

neuropeptides

Answer 25

• molecules that can act as neurotransmitters or hormones

Question 26

hunger and Satiety depend on ?

Answer 26

they depend on the actions of hormones released from the gut, adipose cells (fat cells) and the hypothalamus

Question 27

Hunger or what makes you start eating ? GHERLIN

Answer 27

Gherlin is a hormone found mainly in the stomach. It is orexigenic meaning that it is an agent such as a drug or hormone that stimulates appetite

Question 28

Gherlin

Answer 28

• binds to receptors on neurons that contain two peptide neurotransmitters
  (Neuropeptide Y, and Agouti-gene-related peptide - AgRP)
• binding to these released into another regions of the hypothalamus called the paraventricular nucleus - PVN
• this also bings to receptors on the vagus nerve, which carries excitatory messages to the hypothalamus through the nucleus of the solitary tract of the brainstem

Question 29

Leptin (satiety or what makes you stop eating)

Answer 29

• produced and released from the stomach adipose tissue (fat cells)
• receptors for leptin are found on the same cells of the accurate nucleus to which Gherlin binds, that is cells containing NPY and AgRP
• it suppresses hunger by having excitatory effects on neurons containing neuropeptides
• stimulates norcartic hormones
• secreted in response to high level son insulin and glucose
• maintaining weight
• levels increase with body mass and with the size of fat cells

Question 30

Insulin

Answer 30

• anorexigenic
• released by cells of the pancreas
• the release of insulin is directly related to glucose levels
• it is secreted shortly after meals
• like leptin, it inhibits AgRP and NPY neurons in the arcuate nucleus and has excitatory effect on POMC and cART neurons

Question 31

Cholecytokinnin (cck)

Answer 31

• released from the small intestine when the stomach is full
• CCK binds to receptors on the vagus nerve, which carries inhibitory messages to the hypothalamus through the NST, to suppress appetite

Question 32

Peptide Tyrosine (PPY)

Answer 32

• released from the large intestine
• released in the circulation after meals and is reduced during fasting
• it suppresses appetite by inhibiting AgRP and NPY neurons in the arcuate nucleus but has no effect on POMC and cART neurons

Question 33

Regulation of eating

Answer 33

• not all eating fulfills a homeostatic need

- eating is also driven by the rewarding properties of food

Question 34

Incentive - Salience theory and eating

Answer 34

• environmental cues associated with the memory of certain food can induce a feeling of “wanting” that food
• eating the food will make you feel sated
• wanting and liking are dependent on two distinct systems
• wanting : the mesolimbic dopamine system
• liked reactions are associated with the release of endorphins in hedonic hotspots within the nucleus accumbens, ventral pallidum, parabrachial nucleus, obrifrontal cortex, insular cortex and amygdala