⚖️ 1. Homeostasis - The Balance Keeper
Definition:
Body's automatic system to maintain stable internal environment → Works through feedback loops → Essential for survival!
Key Principle (Bridgeman 1988):
"All animal activities are motivated by homeostatic needs" → Behaviors serve to restore balance
Two Types of Feedback:
- Feedback Systems: Report current status back to brain
- Feed-Forward Systems: Anticipate needs before they become critical
Your brain CONSTANTLY monitors: Temperature, Hunger, Thirst, Sleep - all for survival!
🌡️ 2. Temperature Regulation
🦎 Ectotherms
Amphibians, Reptiles
Depend on ENVIRONMENT
"Solar powered"
Move to regulate temp
🦁 Endotherms
Mammals, Birds
INTERNAL control
Have SET POINT
Metabolically regulate
Set Point:
Internal thermostat → Body works to maintain ~37°C → Has "neutral zone" (small range of acceptable variation)
When You're HOT 🔥:
- Sweating (dogs: tongue, humans: skin glands)
- Vasodilation (blood vessels expand)
- Behavioral: seek shade, drink cold water
When You're COLD ❄️:
- Shivering (muscle activity)
- Vasoconstriction (blood vessels narrow → cold hands/feet)
- Piloerection (goosebumps/fur standing)
- Increased metabolism, adrenaline, thyroid
- Behavioral: huddle, seek warmth, wear clothes
Brain Control Center:
Preoptic Area (Anterior Hypothalamus) = Master thermostat
Heat it → Sweating | Cool it → Shivering
🍽️ 3. Hunger & Eating
🛑 VMH
Ventromedial Hypothalamus
SATIETY CENTER
"STOP eating signal"
Damage = Overeating
🍴 LH
Lateral Hypothalamus
HUNGER CENTER
"START eating signal"
Damage = Starvation
Hunger Signals:
- Glucose levels: Low glucose → hunger signals
- Leptin: Fat hormone → signals "enough stored"
- Ghrelin: Stomach hormone → signals "feed me!"
- Insulin: Regulates glucose uptake
Classic Experiments:
VMH lesion → Rat becomes OBESE (can't stop eating)
LH lesion → Rat STARVES (won't eat even with food available)
VMH = "Stop" center | LH = "Start" center → They BALANCE each other!
💧 4. Thirst & Fluid Regulation
Two Types of Thirst:
1️⃣ Osmotic Thirst:
- Caused by: Eating salty food
- Mechanism: Water leaves cells → cells shrink
- Detected by: Osmoreceptors in hypothalamus
- Solution: Drink water (not saline!)
2️⃣ Hypovolemic (Volume) Thirst:
- Caused by: Blood loss, sweating, diarrhea
- Mechanism: Total body fluid decreases
- Detected by: Baroreceptors in heart/kidneys
- Solution: Need water AND salt replacement
Brain Control:
Anterior Hypothalamus monitors fluid levels
ADH (Antidiuretic Hormone) released from pituitary → Tells kidneys to retain water
⏰ 5. Circadian Rhythms (Bio-Rhythms)
Definition:
~24-hour biological cycles → Control sleep-wake, hormones, temperature, metabolism
Master Clock:
SCN (Suprachiasmatic Nucleus) in hypothalamus
Located above optic chiasm → Receives light information directly from eyes!
Key Features:
- Free-running: Without light cues, cycle is ~25 hours
- Entrainment: Light resets clock daily to 24 hours
- Melatonin: Released by pineal gland at night → "darkness hormone"
Jet Lag: SCN not synced with new time zone → Takes days to adjust
SCN damaged = No circadian rhythm → Random sleep patterns!
😴 6. Sleep - Stages & Functions
Two Main Types of Sleep:
| Feature |
NREM (Non-REM) |
REM (Rapid Eye Movement) |
| Brain Waves |
Slow, synchronized |
Fast, desynchronized (like awake!) |
| Body |
Can move, relaxed |
Paralyzed (atonia) |
| Eyes |
Still |
Rapid movements |
| Dreams |
Rare, simple |
Vivid, story-like |
| Function |
Physical restoration |
Memory consolidation |
NREM Stages:
- Stage 1: Light sleep, easily awakened
- Stage 2: Deeper, sleep spindles appear
- Stage 3 & 4: Deep/slow-wave sleep, delta waves
Sleep Cycle:
~90 minutes per cycle → NREM → REM → Repeat 4-5 times per night
More deep sleep early, more REM later in night
🧠 7. Brain Areas Controlling Sleep
| Structure |
Role |
Key Fact |
| Reticular Formation |
Arousal/awakening |
RAS keeps you awake |
| Raphe Nuclei |
Sleep initiation |
Serotonin = sleep promoting |
| Locus Coeruleus |
Waking/REM control |
Norepinephrine system |
| Hypothalamus |
Sleep-wake switch |
Contains sleep neurons |
| Basal Forebrain |
Sleep promotion |
Adenosine accumulates → sleepy |
Adenosine builds up while awake → Makes you sleepy → Caffeine BLOCKS adenosine receptors!
⚠️ 8. Sleep Disorders
Insomnia:
Can't fall/stay asleep → Most common disorder → Causes: stress, caffeine, irregular schedule
Sleep Apnea:
Breathing stops during sleep → Wake briefly to breathe → Feel exhausted despite "sleeping"
Medulla controls breathing during sleep
Narcolepsy:
Sudden sleep attacks during day → Can include cataplexy (sudden muscle weakness)
Problem with hypocretin/orexin system in hypothalamus
REM Sleep Behavior Disorder:
Act out dreams (paralysis doesn't work) → Can be dangerous → Often precedes Parkinson's
Sleepwalking (Somnambulism):
Walking during NREM sleep (not REM!) → More common in children → Eyes open but not aware
❤️ 9. Sexual Behavior & Hormones
Hypothalamus Role:
Controls pituitary → Releases hormones → Affects gonads → Sexual development & behavior
Key Hormones:
- Testosterone: Male hormone → Aggression, libido, male characteristics
- Estrogen/Progesterone: Female hormones → Menstrual cycle, female characteristics
- Oxytocin: Bonding, orgasm, trust, maternal behavior
Brain Areas:
Hypothalamus (hormones) + Limbic system (emotional) + Cortex (social/cognitive)
😡 10. Aggression & Emotion
Brain Areas Involved:
- Amygdala: Fear, aggression center → Stimulation = rage, Removal = docile
- Hypothalamus: "Fight or flight" response
- Septum: Damage = "Septal rage" (extreme aggression)
- Prefrontal Cortex: Inhibits aggression (damage = impulsive)
Neurochemistry:
Low Serotonin = More aggression
High Testosterone = More aggressive tendencies
Phineas Gage case: Damage to prefrontal cortex → Changed from calm to aggressive!
🎁 11. Reward & Pleasure
The Reward Circuit:
VTA (Ventral Tegmental Area) → Nucleus Accumbens → Prefrontal Cortex
All connected by DOPAMINE pathway!
Olds & Milner (1954) Discovery:
Rats with electrodes in "pleasure centers" → Pressed lever 7000 times/hour → Even chose stimulation over food!
Located in: Medial Forebrain Bundle, Nucleus Accumbens
What Activates Reward System:
- Food 🍕
- Sex ❤️
- Drugs of abuse 💊
- Music 🎵
- Social approval 👍
- Winning/Achievement 🏆
All addictive drugs hijack the dopamine reward system → That's why addiction is so powerful!
⚡ QUICK EXAM CHECKLIST
- ✅ Homeostasis definition and principle
- ✅ Ectotherms vs Endotherms
- ✅ Set point and temperature regulation
- ✅ VMH (satiety) vs LH (hunger)
- ✅ Two types of thirst (Osmotic, Hypovolemic)
- ✅ SCN = master clock for circadian rhythms
- ✅ NREM vs REM sleep characteristics
- ✅ Sleep stages and cycles
- ✅ Sleep disorders and their features
- ✅ Brain areas for aggression (Amygdala, Septum)
- ✅ Reward pathway (VTA → NAc → PFC)
- ✅ Dopamine's role in pleasure