Motivation Flashcards
What are the three components in homeostasis?
- Humoral response - pituitary hormones
- Visceromotor response - sympathetic and parasympathetic
- Somatic Motor Response - behavioural response
Define motivated behaviour
Behaviour that is incited to achieve a goal
What is the prandial state?
Blood is filled with nutrients
During and immediately after a meal
How is energy stored?
Glycogen and triglycerides
Define anabolism
The biosynthesis of organic molecules from nutritive precursors
Define catabolism
The breaking down of complex nutrient molecules into simpler molecules
When is the energy reserves balanced?
When the energy reserves are replenished at the same average rate that they are expended.
What happens when the intake and storage of energy consistently exceed the usage?
Obesity
How does starvation occur?
When the intake of energy consistently fails to meet the body’s demand.
What neurons incite feeding behaviour?
Hypothalamic cells in the periventricular zone in the lateral hypothalamus
What is the lipostatic hypothesis?
A hypothesis proposing that body fat is maintained homeostatically at a specific level
What is the purpose of leptin?
To regulate body mass by acting directly on neurons of the hypothalamus that decreases appetite and increase energy expenditure.
What does leptin deficiency stimulate?
Hunger and feeding
Suppresses energy expenditure
Inhibits reproductive competence
What causes anorexia?
Bilateral lesions on the lateral hypothalamus
What causes animals to overeat and become obese?
Bilateral lesions on the ventromedial hypothalamus
Define lateral hypothalamic syndrome
Anorexia associated with lesions of the lateral hypothalamic area
Define ventromedial hypothalamic syndrome
Obesity associated with lesions of the ventromedial hypothalamic area
What does leptin activate?
Leptin receptors on neurons of the arcuate nucleus
When leptin levels begin to rise, what do the neurons of the arcuate nucleus release?
aMSH - alpha-melanocyte-stimulating hormone
CART - cocaine- and amphetamine-regulated transcript
What is the body’s integrated response to excessive adiposity, high leptin levels, and activation of the aMSH/CART neurons of the arcuate nucleus?
- Humoral response: increased secretion of TSH and ACTH to raise the metabolic rate of cells throughout the body
- Visceromotor response: increase the sympathetic division of the ANS to further raise the metabolic rate, in part by raising the body temperature
- Somatic motor response: decreases feeding behaviour
How do aMSH/CART neurons trigger the Humoral response?
Activating neurons in the paraventricular nucleus of the hypothalamus which in turn causes the release of the hypophysiotropic hormones that regulate the secretion of TSH and ACTH from the anterior pituitary.
Define anorectic peptides
Diminish appetite
How does a fall in leptin affect the arcuate nucleus?
Turn off responses mediated by aMSH/CART neurons
Stimulate NPY/AgRP neurons
What connections do the NYP/AgRP have?
PVN and the lateral hypothalamus
What role do NPY/AgRP perform?
Inhibit the secretion of TSH and ACTH
Activate the parasympathetic division of the ANS
Stimulate feeding behaviour
Define orexigenic peptides
A neuroactive peptide that stimulates feeding behaviour
What does AgRP and aMSH bind to?
MC4 receptor on the postsynaptic neurons in the hypothalamus.
AgRP inhibits it - stimulates feeding
aMSH activates it - inhibits feeding
Define lateral hypothalamic area
A poorly defined region of the hypothalamus that has been implicated in the motivation of behaviour
What does electrical stimulation to the lateral hypothalamus area result in?
Triggers feeding behaviour, even in satiated animals
What is the role of melanin-concentrating hormone (MCH)
Informs the cortex of leptin levels in the blood
What does motivation to eat depend on?
How long since last meal and how much we ate
Define satiety signals
A factor that reduces the drive to eat without causing sickness
Examples: gastric distension and cholecystokinin released by the intestinal cells in response to food
When does satiety signal occur and when does it terminate?
Occurs when we eat and begin the process of digestion (prandial period)
Slowly dissipates during post absorptive (fasting) period
Name the three digestive phases
- Cephalic phase
- Gastric phase
- Substrate (intestinal) phase
Describe the cephalic phase
The sight and smell of food triggers a number of physiological processes that anticipate the arrival of a meal. The parasympathetic and enteric division of the ANS are activated, causing secretion of salvia into your mouth and digestive juices into your stomach
Describe gastric phase
Responses grow more intense when you start chewing, swallowing and filing your stomach with food
Describe the substrate phase
Stomach fills and partially digested food moves into the intestines, nutrients begin to be absorbed into the blood stream
What peptide is highly concentrated in the stomach and is released into the blood stream when the stomach is empty?
Ghrelin
What role does ghrelin play?
Stimulates hunger and food consumption by activating NPY/AgRP containing neurons of the actuate nucleus
Where is CCK located and when is it released?
Intestinal cell walls
Released in response to stimulation of the intestines by certain types of food, especially fatty ones
What role does CCK play in motivation?
Inhibits feeding behaviour
What tract inhibits feeding behaviour?
Nucleus if the solitary tract in the medulla
Where is insulin released from?
Pancreas by B cells
What role does insulin play with glucose transport?
Glucose is easily transferred to brain without a transporter however, other cell of the body require insulin
What is the relationship between glucose and insulin
Blood glucose levels are elevated when insulin levels are reduced
Blood glucose levels fall when insulin levels rise
When does the pancreas release insulin?
Cephalic phase - Parasympathetic innervation of the pancreas stimulates b cells to release insulin
Gastric phase - stimulated by CCK
Substrate phase - highest release of insulin during absorption
How does insulin inhibit feeding behaviour
Acts directly on the actuate and ventromedial nuclei of the hypothalamus
Define electrical self stimulation
Electrical stimulation that an animal can voluntarily deliver a portion of its brain
What happened to rats when the found the electrical self stimulator?
Shun food and water
How does dopamine play a role in self stimulating behaviour?
Most effective site for self stimulation was along the dopaminergic axons arising in the ventral tegmentum area, projecting through the lateral hypothalamus to several brain regions
Blockers = reduced self stimulation
What levels of serotonin are seen during food consumption?
Low during post-absorptive phase
Rise in anticipation of food
Spike during a meal
Abnormalities in serotonin cause what eating disorders?
- Anorexia nervosa - compulsion to maintain body weight at an abnormally low level
- Bulimia Nervosa - frequent eating binges, often compensated by forced vomiting
What two physiological signals stimulate drinking?
Hypovolemia (drecrease in blood volume)
Hypertonicity (increase in the concentration of dissolved substances in the blood)
How is thirst triggered?
Volumetric thirst - hypovolemia
What is released during volumetric thirst?
Vasopressin is released by the posterior pituitary. Acts directly on the kidneys to increase water retention and inhibit urine production.
What triggers the release of vasopressin?
Rise in Angiotensin II occurring in response to reduced blood flow to kidneys
Mechanoreceptors in the major blood vessels that signal the loss of blood pressure - signal via the vagus nerve and the nucleus of the solitary tract
What does reduced blood volume stimulate?
- The sympathetic division of the ANS - constricts arterioles
- Motivation
What senses hypertonicity?
Vascular organ of the lamina terminalis
What role does OVLT play in drinking?
- Directly excites the magnocellular neurosecretory cells that secrete vasopressin
- Stimulates osmometric thirst - motivation to drink
What causes diabetes insipidus?
Selective loss of the vasopressin secreting neurons of the hypothalamus
What neurons are sensitive to temperature changes?
Anterior hypothalamus
What happens when there is a fall in temperature?
TSH released by anterior pituitary which stimulates the release of thyroxin from the thyroid gland.
Visceromotor response - constricted blood vessels in skin and piloerection
