Light hits your eyelids in the morning, activating light sensitive retinal proteins that trigger signals to the brain’s suprachiasmatic nucleus in the hypothalamus. Then it triggers the pineal gland to decrease melatonin levels in the body.

The opposite happens at night. The darkness triggers the suprachiasmatic nucleus to signal to the pineal gland to increase melatonin levels in the body, making you sleepier.

Disruptions to the circadian rhythm

Jet lag: Travelling across many time zones
Shift work: Working irregular hour shifts (morning or night shifts)

Brain Waves:

Waves Mental State

Delta waves → Deep Sleep

Theta waves → Drowsy

Alpha waves → Relaxed

Beta waves → Focused

B A T D T A B

Beta → Awake

Alpha → NREM1

Theta → NREM2

Delta → NREM3

Theta → NREM2

Alpha → NREM1

Beta → REM

Sleep Cycle

-NREM1: Lightest sleep (5-10 mins):

Hypnogogic sensations and sleep hallucinations occur

-NREM2: Light sleep (10-20 mins):

Sleep spindles (bursts of neural activity)

-NREM3: Deep sleep (approx. 30 mins):

Body is in its most restful state (heart rate, blood pressure, and body temperature drop.)

Sleep talking/walking usually occurs during this stage.

-REM (approx. 10 mins):

Person exhibits rapid eye movement

In REM, the brain but the body is asleep (muscle atonia)

Walking up during REM causes sleep paralysis.

REM Rebound occurs when someone is REM sleep deprived.

Dreaming occurs during this stage.

Sleep Disorders

Insomnia → Most common:
Persistent difficulty falling asleep, staying asleep, or obtaining restorative sleep.
Results in daytime fatigue.
- Treatments:
  - Lifestyle changes
  - Stress management
  - Medication → Melatonin
Narcolepsy → Rare:
Uncontrollable urge to fall asleep that may occur at any time at any instant. They fall into a direct REM sleep
- Symptoms:
  - Cataplexy (sudden muscle weakness)
  - Sleep Paralysis
  - Hallucinations
- Treatments:
  - Medications
  - Strategic napping hours
REM Sleep Behavior Disorder (RBD):
Muscle atonia during REM sleep is incomplete or completely absent, causing people to enact their dreams physically
- Symptoms: Dream enactment → May cause injuries
- Treatments:
  - Medications → Clonazepam
  - Safety measures
Sleep Apnea:
Breathing stops and starts repeatedly during sleep
Leads to daytime fatigue and never feeling well rested
- Types:
  - Obstructive Sleep Apnea (OSA): The throat muscles relax, obstructing the airway passage
  - Central Sleep Apnea: The brain fails to send proper signals to control breathing
  - Complex Sleep Apnea Syndrome: Combination of OSA and central sleep apnea
- Symptoms:
  - Loud snoring
  - Gasping for air
  - Never feeling well rested
- Treatments:
  - Weight loss
  - CPAP machine
  - Surgery → Severe cases
Somnambulism:
Sleep walking / Sleep talking
- Treatments:
  - Safety measures
  - Medications
  - Regulating sleep schedule.

Why Do We Sleep And Dream?

Sleep Theories:

Restoration Theory: States that sleep serves to restore cognitive and physical resources that were used up while awake.
Memory Consolidation Theory: States that sleep is essential for strengthening and stabilizing new memories.

Dream Theories:

Activation-Synthesis Theory: States that dreams are just the brain’s attempt to make sense of random neural activity while asleep. Saying that dreams have no meaning
Consolidation theory of dreams: States that dreams play a role in processing new information into existing networks

Note