Motivation Flashcards
What is motivation?
Driving force
Physical need
Wanting, liking
How odes the hypothalamus regulate motivation?
Maintain homeostasis by regulating three interrelated functions
- endocrine secretion
- autonomic nervous system
- emotions and drive/behaviour
- > Motivated behaviour, e.g. drinking, eating
What happens to the energy taken in by our food?
Energy from food is broken down to be taken up by cells. Any excess is stored as glycogen in the liver and muscles. Triglycerides are stored in adipose tissue
Explain how energy is released during periods of starvation
During periods of starvation, glycogen is broken down into glucose
In both, anabolic and metabolic reactions are tightly regulated.
How is feeding behaviour regulated long term?
Normal energy balance leads to normal adiposity
Prolonged positive energy balance leads to obesity
Prolonged negative energy balance leads to starvation
How does the hypothalamus regulate homeostasis?
Transduction of physiological stimuli in blood in specialized region of hypothalamus
Humoral and visceromotor responses are initiated by activation periventricular and medial hypothalamus
Behavioural action depends on lateral hypothalamus
How is body weight regulated around a set value?
Body weight is normally stable
If an animal is force fed, it will gain weight
The weight is lost, however, as soon as the animal can regulate its own food intake
Similarly weight lost during a period of starvation is rapidly gained when food is freely available
What is parabiosis?
sharing of blood circulation between animals.
Blood borne signals are shared and can affect the hypothalamus.
Which hypothalamic nucleus regulates feeding?
Arcuate Nucleus: important for control of feeding (effect of leptin on arcuate nucleus)
Describe the role of the arcuate nucleus in regulating feeding
After feeding, fat adipose tissues get replenished and release leptin into the blood circulation.
Leptin binds to its receptors in the arcuate nucleus (hypothalamus) signalling to the brain to stop eating - ‘full sensation’
What is the significance of the VMH and Lateral hypothalamus?
Important for the regulation of
- Body weight/food intake
- Blood volume/osmolarity: drinking
Where is the hypothalamus located?
Hypothalamus located under the thalamus at the base of the brain
Where in the hypothalamus is the arcuate nucleus found?
At the bottom part of the third ventricle is where the arcuate nucleus is found
Describe the location of other hypothalamic nuclei
The paraventricular nuclei is adjacent to the third ventricle and below it is the lateral hypothalamus area
How was the significance of VMH proved?
VMH lesion caused excessive eating to the point where the mouse became obese - showing the ventral medial hypothalamus is crucial in regulating body weight
What is the consequence of VMH lesion?
VMH plays a role in controlling the cessation of eating
Damage to the VMH results in prolonged and dramatic weight gain
What are the effects of lesions to the VMH and LH?
Lateral hypothalamic syndrome: diminished appetite for food; anorexia
Ventromedial hypothalamic syndrome: overeating and obesity
Both related to leptin signaling
What is the effect of elevated leptin levels?
Anorexic response
Rise in leptin levels in blood is detected by arcuate nucleus neurons that contain the peptides 𝜶MSH and CART
These neurons project axons to the lower brainstem and spinal cord, paraventricular nucleus of the hypothalamus, and inhibit the lateral hypothalamus
What is the role of the projections to the LH?
Each of these connections contributes to the coordinated humeral, visceromotor and somatic motor responses to increased leptin levels
What is the result of decreased leptin levels?
Orixegenic response
Reduction on blood levels of leptin detected by arcuate nucleus neurons containing peptides NPY and AgRP
These arcuate nucleus neurons inhibit paraventricular nuclei controlling release of TSH and ACTH from pituitary (via 𝜶MSH and CART)
They activate neurons in lateral hypothalamus that stimulate feeding behaviour
Some of the activated lateral hypothalamic neurons contain the peptide MCH (melanin-concentrating hormone)
Describe the competition for the MC4R
One way 𝜶MSH (anorectic peptide) and AgRP (orexigenic peptide) exert opposite effects on metabolism and feeding behaviour is via interaction with the MC4 receptor on some hypothalamic neurons
Describe how leptin levels effect MC4R competition
When you’ve eaten well there is increased leptin in blood circulation causing an increase in 𝜶MSH and decrease AgRP stimulation. 𝜶MSH then binds to MC4R to inhibit feeding
How is the MC4R activated?
While 𝜶MSH (agonist) stimulates the MC4 receptor, AgRP (antagonist) inhibits it
What are the 2 other factors contained in LH neurons that stimulate feeding?
- Melanin-concentrating hormone (MCH)
- Orexin
