Biological explanations of eating behaviour.

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• Biological explanations of eating behaviour.

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Keywords you will come across in this topic.

• Satiation
• Aphagia
• Leptin
• Hyperphagia
• Neuropeptide Y
• Lateral hypothalamus
• Ventromedial hypothalamus
• Paraventricular nucleus
• Amygdala
• Inferior frontal cortex

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Do you remember this phrase from GCSE
science..Homeostasis

• It involves mechanisms that can detect and
  correct.
• Detect check whether the body has enough
  nutrients (internal environment)
• Correct restore the body to its optimal state.
• Body evolved 2 separate systems in order to cope
  with the time lag between restoring equilibrium
  and body registering their effect.
• Turning eating on and turning eating off!

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The role of neural mechanisms involved in
controlled eating satiation

• You should understand..
• Hunger is activated by many cues.
• All animals have a motivation to eat these
  motivations increase as energy levels decrease.
• An imbalance occurs when the energy expended
  exceeds the amount consumedthis is signalled in
  the brain in different ways.

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The Hypothalamus.
The hypothalamus is responsible for all of these
bodily functions. A bit like the fat controller!!
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Hunger pangs?
Water balloons ?
Stomach or neural mechanism?
What do balloons have to do with it?
What evidence is this based upon?
Who is Washburn cannon?
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Karl Lashley (1938)

• Mr Lashley was the first psychologists to suggest
  that stomach contractions were more of a strong
  incentive rather than indication of hunger.
• Hunger is not just a reflex to a empty stomach

Lets pause for thought!!! Q So if hunger is not
a reflex what is it??
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Karl Lashleys research

• He used rats to support his growing belief that
  neural mechanisms are involved in decision
  making.
• These were hungry rats!
• He cut out different areas of the brain to see
  the effect on their ability to negotiate a maze
  successfully and reach the food placed at the
  exit as a reward.

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Lashleys findings.

• He discovered how vital the role of the
  hypothalamus is in playing a part in the
  regulating of food intake.
• In particular the lateral hypothalamus, this was
  identified as the main hunger centre.
• The ventromedial hypothalamus as the main satiety
  centre.
• After the lesions to the lateral hypothalamus,
  animals stopped eating spontaneously, and the
  reverse occurred after the lesions to the
  ventromedial hypothalamus.

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The breakdown of the hypothalamus
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So what does this tell us???

• The hypothalamus is a very complex part of the
  brain.
• It contains a number of different types of
  specialised nerve cell and controls different
  physiological functions.
• There is a further section named the arcuate
  nucleus...this too plays a vital role.

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Theres more!!!!!!

• It contains a several different nerve cells, one
  of which makes a neuropeptide (called
  neuropeptide Y or NPY).
• Neuropeptides are small proteins that are encoded
  by genes- they serve as chemical messengers
  between neurons and the brain.

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So what is a peptidean example!
Leptide is secreted.

• The fat hormone leptide is an example of a
  peptide that is secreted from fat cells into the
  blood and signals the brain (via hypothalamus)
  that caloric storage is high.
• When you do not eat sufficient amounts of food
  fat storage is used up to fuel the body and the
  fat cells cease to secrete and these levels fall
  in the blood.
• The hypothalamus detects this drop and
  interprets the drop in leptin as lack of calories
  and generate the feeling of hunger.

Hypothalamus is Signalled.. calories are high
enough.
Body ceases to release fat cells
Hypothalamus detects this dropfeelings of
hunger.
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How do we know this???

• Studies have shown individuals with leptin
  deficiency have atypical eating behaviours.
• They cannot control their eating and frequently
  become obese, injecting leptin can help them
  return to typical weight.

Be mindfulthese cases are rare.
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Over to you.AO2 or not AO2, that is the
question.

• Zhang et al (1994)
• Yang et al 2008
• Kluver-Bucy syndrome
• Homeostasis
• Sakurai et al (1998)
• Marie et al (2005)
• Investigate these select pieces of research and
  apply them to the different mechanisms we have
  discussed so far.

How does each piece of research become an AO2
point. What research does it support or refute.
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Other Neuropeptides.

• Agouti-gene-related peptide (AGRP) appears to
  signal hunger.
• A rat that is food deprived has demonstrated
  levels of (NPY) and AGRP are...... increased in
  the brain.
• If the rat is satiated and AGRP/NPY is injected
  into the rat what do you expect to happen?
• He becomes ravenous.

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So are the the same or different?

• AGRP

• NPY

• Slow to increase during deprivation and slow to
  fall upon feeding.
• A single injection of AGRP will cause a rat to
  overeat for several days

• Increases levels rapidly food deprivation.
• NPY injections induce feeding for a few minutes.
• Gherlin is activated by NPY. A hormone that is
  secreted from a empty stomach..its concentration
  in blood falls after each meal and rises until
  the next.

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Glucose is another signal

• As glucose levels decrease hunger levels increase
• Increase in glucose levels means satiation
  reached.

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Satiation

• Eating stops when satiation is reached. This
  occurs when the stomach muscles stretch and
  become distended by food.
• Cholecystokinin (CCK) is secreted in the stomach
  during a meal and activates receptors.
• These signals reach the hypothalamus and the
  anorexigenic peptides are released.

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Set point hypothesis

• Everyone has a certain metabolic rate, a certain
  weight our bodies are set to, which determined by
  our hypothalamus, metabolism or rate at which we
  burn calories.
• This point can change due to other factors
  (exercise). When we diet our leptin levels
  decrease and this causes hunger pangs to be
  triggered by the hypothalamus.
• Thus the point maybe higher for obese people and
  lower for healthier people and thus is involved
  in many different aspects of eating behaviour.

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Overall evaluation.

• Neural mechanisms still unclear
• Influence of biological rhythms
• Set point theory
• Psychological hunger
• Evidence for other biological theories.
• Using these headings formulate at least two
  sentences for each heading to use as AO2
  evaluation.