Biology of fear, thermoregulation and eating behaviour Flashcards
ADAPTIVE FUNCTIONS OF EMOTIONS
Fear → alerts us to escape from danger
Anger → directs us to attack an intruder
Disgust → tells us to avoid things that may cause illness
EMOTIONS PROVIDE USEFUL GUIDE IN:
- making quick decisions &
- understanding/communicating needs & probable
actions
WHAT IS FEAR?
- integral part of brain’s defensive mechanism
- evolved to protect animals & humans from predation
& other ecological threats
CLASSICAL FEAR CONDITIONING
TO STUDY EMOTION (LeDoux)
- Fear conditioning is used as a behavioural
measure of ‘fear’ that humans experience - Studies using lab rats & other mammals have
helped map how the fear system of the brain
works
Very old in evolutionary terms
- Existed before humans experienced ‘fear’
- To understand fear system, neuroscientists
study underlying neural systems evolved as
behavioural solutions to problems of survival
MANY COMMON PSYCHIATRIC DISORDERS ARE
‘EMOTIONAL’ DISORDERS:
- many of these are related to the brain’s ‘fear system’
Public Health Service in US: ≈50% of ‘mental’ problems
(not related to substance abuse) are anxiety disorders:
* Phobias
* Panic attacks
* Post traumatic stress disorder
* Obsessive compulsive disorder
* Generalised anxiety
FEAR SYSTEM OF THE BRAIN
Pathways connecting emotional processing system of fear
(amygdala) with the thinking brain (neocortex) are not
symmetrical
Connections from neocortex → amygdala are much
weaker than those from amygdala → neocortex
This ‘double wiring’ creates problems in humans- we have
problems controlling our emotions:
- once an emotion is aroused it is hard for us to turn it
off at will and may explain why psychotherapy is a
difficult & lengthy process
AMYGDALA (Dr Joseph LeDoux)
In humans a visual stimulus (e.g., snake on
path) travels to the amygdala in a few
thousandths of a second
HUMAN AMYGDALA CONTAINS CELLS THAT
FIRE IN RESPONSE TO:
* Expressions of fear on faces of other
humans
* Objects of fear
- Most of the time the amygdala is quiet
- Amygdala is designed to detect predators
- A strong stimulus can result in:
- Piloerection (hair standing on end)
- Heart racing
- Fight/flight hormones flooding body
Amygdala has connections to stimuli processing cortexes and forms associations between different stimuli for adaptive and conditioned learning.
EMOTION VS FEELING OF ‘FEAR’
Amygdala is specialised for reacting to stimuli &
triggering physiological response (i.e., emotion of
fear)
- Different to conscious feeling of fear, which arises
from slower 2nd pathway (ear→ amygdala
→higher cortex) - Higher cortex analyses frightening stimulus in
detail (using info from many parts of brain) &
message is sent back down to amygdala
PHYSIOLOGY VS FEELING OF ‘FEAR’
‘FEAR’ IS USED SCIENTIFICALLY IN TWO WAYS:
* conscious feelings and
* behavioural and physiological responses.
Joseph LeDoux suggests that:
* ‘fear’ should denote feelings and
* ‘threat-induced defensive reactions’ should
be used for responses
EFFECTS OF FACIAL EXPRESSIONS ON AMYGDALA
- response pattern of intracranial event-related
potentials (ERPs) recorded from depth-electrodes in
the human amygdala - Amygdala presented a preferential response to eyes
expressing fear and joy- especially fear - special role of the amygdala in processing emotions
conveyed by the eye region of the face
Amygdala and sound
- If rats are threatened they emit very high
frequency screams - If another rat hears this scream, a signal
goes from auditory cortex (where sounds
are processed) directly to amygdala - When these sound waves penetrate rat
brain: - amygdala is instantly activated even though
rat does not ‘know’ the sound is coming
from another rat
ULTRASONIC RAT VOCALISATIONS (>ABOVE 20 KHz)
- Infant distress calls: Infants cannot regulate their
own body temperature & when they are cold they
emit high pitched (40 kHz) distress calls - Long distress calls (20 kHz): when unhappy or
stressed (e.g. when defeated socially, see a predator,
experience/anticipate pain). - Short, chirping calls: higher pitched (50 kHz) &
thought to be positive (e.g. during play, courtship, in
anticipation of feeding, when tickled by personlaughter?)
AMYGDALA & OTHER EMOTIONS?
- Amygdala has 12─15 distinct regions (only 2
clearly implicated in fear)
AMYGDALA & MEMORY
For traumatic memory, two memory systems are
important:
- EXPLICIT (CONSCIOUS) MEMORIES:
- Mediated by hippocampus & other parts of
temporal lobe memory system and - Blood pressure & heart rate rise, begin to sweat
& muscles tighten up - IMPLICIT (UNCONSCIOUS) MEMORIES:
- Mediated by amgydala & neural connections
anandamide
released by oxytocin and activates cannabinoid receptors to induce states of bliss.
Thermoregulation
Thermoregulation is the regulation of body temperature, usually within a specific range. In animals, there are two different types of thermoregulators: endotherms and ectotherms.
Animals are also either poikilotherms or homeotherms.
Endotherms
Endotherms can regulate their body temperature via metabolic processes. Endothermic animals can stay active in cold weather, but they need more energy to heat their bodies and therefore need more food. Maintain thermal
homeostasis irrespective of ambient temperature.
Ectotherms
Ectotherms have a body temperature that is influenced by the external environment (incorrectly known as ‘cold blooded’). Ectothermic animals do not need energy to heat themselves but as a result they are inactive in cold weather. Internal temperature
varies with ambient environmental temperature
Poikilotherms
Poikilotherms do not need a fixed body temperature to survive, and most terrestrial ectotherms are poikilotherms (e.g. snakes & many lizards) but the naked mole rat is a mammal poikilotherm.
Homeotherms
Homeotherms are animals that need to maintain a constant body temperature to survive and are usually endotherms (some ectotherms, e.g. desert lizards, are homeotherms).
THERMOREGULATION maintained with:
- Insulation
- Metabolic heat production/physiological
thermoregulation - Countercurrent heat exchange
- Behaviour
INSULATION
- Fur (piloerection hair stands on end)
- Feathers
- Blubber
- Colouration
PHYSIOLOGICAL THERMOREGULATION
Altering metabolic generation of heat to regulate
temperature
For example:
Metabolism increases to raise internal body
temperature in a colder environment
METABOLIC ACTIVITY
- Shivering
- Panting
- Evaporation of water
from respiration
and/or sweating
COUNTERCURRENT HEAT EXCHANGE
Warm and cold blood flow in opposite directions
to regulate the temperature (arteries & veins)
* Usually around the brain/head region
* e.g. Leatherback Turtle, Sea Gull
BEHAVIOURAL THERMOREGULATION
Using posture, orientation and/or microclimate selection
to regulate body temperature
e.g. lizard increases temperature by “spread eagle”
posture on top of a hot rock (microclimate) & turning its
back to the sun (orientation)
TORPOR (mini-hibernation)
Reduced metabolic activity and body temperature for
less than a day (endotherm)- governed by circadian
rhythm
* Animals continue foraging
e.g. bats, hummingbirds, small Australian marsupials
(stripe-faced dunnarts)
HIBERNATION
Long-term torpor (can be 6 months) occurring in the
winter months (endotherms & ectotherms), to
conserve energy
* animals usually do not forage but rely on energy
stores (food caches or body energy reserves)
e.g. European ground squirrels, adders, some bears
ESTIVATION
Long-term torpor (can be 6 months) occurring in the
summer months (ectotherms)
* To avoid damage from high temperatures
(dessication-extreme dryness or drying out)
e.g. lungfish, salamanders, land snails, Australian
water-holding frog, cane toads
OTHER BEHAVIOURS
- Torpor, hibernation, estivation
- Timing of activities
- “Cooling off” techniques
TIMING OF ACTIVITIES
NOCTURNAL–active at night
e.g. owl, mice, koala
DIURNAL–active during daytime
e.g. “grazers” –gazelles, elephants
CREPUSCULAR–active at dawn & dusk
e.g. deer, rabbits, most birds, red pandas, cats
CATHEMERAL –active at periods throughout 24-hours
e.g. some lemurs
‘COOLING OFF’ TECHNIQUES
- Rolling or wallowing in mud
- Taking a “dip” or standing in the water
- Going underground, using caves or lying in shade
- Flying in high altitudes
Biology of Thermoregulation
Focus on humans
Energy Balance: About 50%
used for Body Heat
37 degrees is optimal due to balance of hot enough that most fungi cannot survive for long in our body and cool enough that we do not need to spend most of our time consuming food to stay warm.
BODY TEMPERATURE BALANCE IN HOMEOTHERMS
- Metabolic heat production is usually required
to maintain balance - Balance is very narrow range, usually higher
than environment - Thermo neutral zone represents ambient
conditions where heat gain by animal equals
heat loss (= thermal comfort; 28-31 degrees C in naked
humans)
BODY TEMPERATURE BALANCE IN HUMANS
2 degree + Higher temperatures: temperature of the extremities close to the body core temperature
sweat evaporation and vascular dilation
2 degree - lower temperatures: vascular contriction
temperature of extremities falls
muscle contraction and shivering
BODY TEMPERATURE BALANCE IN HOMEOTHERMS
Peripheral & body core receptors – sense change
HYPOTHALAMIC THERMOREGULATORY CENTER
integrates & initiates:
* Shivering
* non-shivering thermogenesis
* vasoconstriction
THERMOREGULATION: PATHOLOGIES
HYPERTHERMIA: body temperature too high
Fever: pyrogens fight pathogens
Heat exhaustion (1020F/38.80C)
Heat stroke (1060F/410C) → death
Malignant hyperthermia – defective Ca++ release
HYPOTHERMIA: body temperature too low
Metabolism slows → loss of consciousness, death
Surgical applications: heart surgery
THERMOREGULATION SUMMARY
- Eatingprovides carbohydrates, proteins, & fats for
metabolism - Energyis used for body heat & work: transport,
synthesis, storage - Metabolic rate changes with age, sex, body fat,
activity & diet - Insulin regulates anabolic cell activities & glucose
uptake in cells - Maintaining homeothermy takes 50% of our
energy - Hypothalamic thermoregulatory center controls
heat homeostasis
FEEDING STRATEGIES ACROSS SPECIES
REPTILES
* Eat a huge meal & sometimes don’t eat again
for weeks or months
BEARS THAT HIBERNATE
* Huge feasts, ‘fatten up’, periods of ‘starvation’
SMALL BIRDS
* Eat what they need & store almost no fat
HUMANS
* Eat more than we need
* Influenced by learned & unlearned mechanisms
Human biological influences on eating behaviour
Hypothalamus sends cues to start or stop eating
Appetite hormones insulin, leptin, orexin, and ghrelin control eating and hunger
individual differences in basal metabolic rate
Human socio-cultural influences on eating behaviour
Norms about appropriate body weight
culturally preferred and available foods
Human psychological influences on eating behaviour
Sight and smell of food
Time elapsed since last meal
Individual differences in self-esteem, mood, and perfectionism
HUMAN DIGESTIVE SYSTEM
- Function of digestive system is to break food down
into smaller molecules that cells can use - Glucose is the body’s main ‘fuel’
ADULT PROBLEMS WITH MILK CONSUMPTION
- Newborn mammals rely on mother’s milk
- After weaning most mammals lose intestinal enzyme
lactase ─ needed for metabolising lactose (sugar in milk) - In humans, about two thirds of adults have low levels
lactase (recessive gene) & can eat small amounts dairy
but then get cramps or ‘gas’
TASTE & DIGESTION CONTROL HUNGER & SATIETY
ORAL FACTORS
* Humans like to eat: like to taste & chew even when not
hungry (e.g., chewing gum)
STOMACH & INTESTINES
* Main signal to stop eating is distention of stomach: stomach
sends satiety messages to brain via vagusnerve (info about
stretching stomach walls) & splanchnic nerves (info about
nutrient contents of stomach)
- Also stop when duodenumpartly distended (part of small
intestine adjoining stomach) & hormone cholecystokinin
(CCK) limits meal size
HUNGER: BODY CHEMISTRY
GLUCOSE
* form of sugar that circulates in the blood
* provides major source of energy for body tissues
* Insulin (a hormone) levels go up, glucose goes down
* when level is low, we feel hunger
SET POINT
* an individual’s natural level or “weight thermostat” for
weight regulation
* when the body falls below this weight, an increase in
hunger & a lowered metabolic rate may act to restore the
lost weight
BASAL METABOLIC RATE
* body’s base rate of energy expenditure
HUNGER & THE BRAIN
The hypothalamus controls eating & other body
maintenance functions
monitors appetite hormone levels
THE LATERAL HYPOTHALAMUS CONTROLS:
- Insulin secretion
- Alters taste responsiveness
Electrical stimulation of this area:
* Animal increases eating & food-seeking
behaviours
Damage to this area:
* Animal refuses food & water as if food distasteful
* Animal may starve to death if not force-fed
VENTROMEDIAL HYPOTHALAMUS:
- Tumors lead to overeating & weight gain
- Alters taste responsiveness
Damage to areas in or around the ventromedial
hypothalamus:
* Animal has increased appetite, gains lot of
weight, then becomes ‘finicky’ eater
* Eat normal meals more often (overeat)
Damage to paraventricular nucleus of hypothalamus:
* Animal eats larger meals (overeats)
Insulin
Hormone secreted by pancreas, controls blood sugar
Leptin
Protein secreted by fat cells; when abundant, causes brain to increase metabolism and decrease hunger
Orexin
Hunger triggering hormone secreted by hypothalamus
Ghrelin
Hormone secreted by empty stomach; sends hungry signal to brain
PYY
Digestive tract hormone; sends not hungry signal to brain
EATING DISORDERS
OBESITY (considered medical condition)
ANOREXIA NERVOSA (considered psychiatric condition)
* Unwilling to eat as much as they need; become extremely
thin & may die
BULIMIA NERVOSA (considered psychiatric condition)
* Alternate between extreme dieting and binges of
overeating
EATING DISORDERS (ALL OF THEM)
* Include elements of biology(e.g., hunger) & psychology
(e.g., social factors, customs, advertising- think can eat
more if ‘low fat’, alcohol with meal increases calories)
PSYCHOLOGY OF HUNGER
Factors other than biological ones influence
hunger & eating:
* Memories of last meal
* Taste preferences: cultural
* Social eating; trends; food security
* Cravings as a result of mood
EFFECTS OF CULTURE & HABITS ON BODY WEIGHT
‘SETTLING POINT’: cluster of genetic &
environmental factors cause a person’s weight to
settle within a given range
* Children more likely to be obese if parents are
obese
* Weight can be affected by diet, exercise, daily
habits (e.g., use stairs instead of lift)
In the US, research based on 7-day diary of all
meals & circumstances showed:
* People eat more when with others than
alone
* Size of meal depends on time of day &
local customs (e.g. US have big meal at
night & small meal at lunch; France have
bigger meal at lunch & smaller meal at
night)
* People eat more on weekends, especially
Saturdays; when food is ‘low fat’, tastes
good & if drink alcohol with meal
OBESITY IN MICE: LEPTIN?
- Fat cells throughout body produce peptide
leptin (more fat cells, more leptin) - Mice with ‘obese’ gene do not make leptin
- Gene exists that increases eating, decreases
metabolic rate & increases weight gain
OBESITY IN HUMANS: LEPTIN?
Most obese people produce plenty of leptin & have
normal leptin receptors, so they overeat for other
reasons
OBESITY IN AUSTRALIA
Heart Foundation of Australia:
* obesity & inactivity are 2 largest contributors to
developing heart disease– Australia’s biggest
killer
- ≈ 55,000 people die from heart disease each year
(1 every 12 minutes) - being active for at least 30 minutes a day reduces
risk of heart disease - physical inactivity is a leading contributor to
burden of chronic disease in Australia- estimated
total cost to health budget of $1.5 billion
Obesity has reached epidemic proportions globally
At least 2.8 million people die each year as a result of
being overweight (BMI> or =25) or obese (BMI>30);
In 1995 an estimated:
* 200 million obese adults worldwide
* 18 million under-five children overweight.
Since 2000:
* over 300 million obese adults
Once associated with high-income countries, obesity is
now also prevalent in low- and middle-income countries
WORLD HEALTH ORGANIZATION:
CRISIS OF CHILDHOOD OBESITY
Commission on Ending Childhood Obesity
* In 2016, >41 million children under 5 years old
were overweight or obese.
* 70 million young children will be overweight or
obese by 2025 if current trends continue.
* The rate of increase is 30% higher in low- and
middle-income countries, than that of developed countries.
RESEARCH ON WEIGHT REGULATION & DIETING
- No consistent personality trait differences found
between obese and non-obese people (e.g.,
willpower, anxiety) - Dieters and obese are more likely to eat in
response to stress than non-dieters - Family environment of little importance in
determining body weight - genetics plays a large
role
PHYSIOLOGY OF OBESITY
- Number of fat-storage cells is a major determinant of
body weight - Fat cells are determined by genetics & food intake
- They increase with weight gain, but merely shrink with
weight loss - may stimulate hunger - Weight loss causes a decline in basal metabolism
OBESITY & INACTIVITY
Obesity has been found to be more common
among those who watch the most television
gut-brain connection (‘second brain’)
the gut microbiome produces neurotransmitters, such as, serotonin and dopamine in greater quantities than our brain, which means that we need to nurture our gut health to enhance our mental and physical wellbeing.
