Biological Rhythms & Sleep

Definitions of different types of rhythms:

Ultradian: Periods longer than 24 hours. Examples include heart rate, multiple sleep cycles during the night 

Circadian: rhythms with a period of about 24 hours. E.g.: daily rhythm of sleeping and wakefulness 

Infradian rhythm – Menstrual cycle 

Circannual= hibernation 

Definitions of terminology associated with rhythms 

  • Rhythm = A repeating event that occurs with a regular pattern  

  • Period: Duration of time it takes one cycle of the rhythm to occur  

  • Phase: describes a marker or point in a daily rhythm  

  • Mesor: the average level of the rhythm across a full cycle 

  • Amplitude: the difference between the peak and trough of that rhythm  

  • Frequency: how often the rhythm occurs within a period of time 

 

What is a zeitgeber? What is the strongest for humans? 

Zeitgeber = external or env cue that synchronizes a biological rhythm  

Strongest for humans: Light 

What does it mean for a rhythm to be endogenous? 

  • Part of the particular organism, innate 

Characteristics of chronotypes: 

Morning lark's vs night owl: 

Night owl = higher levels of energy, most productive later in day/night 

Early bird = most productive in early morning, focused and efficient with routine tasks in the morning, higher energy in the morning, often dips later in day 

  • Women tend to be early larks than night owls and vice versa with men although it is 50/50 

 

Why do we need sleep? 

  • Restoration of physical and mental energy  

  • Reduced energy demand 

  • Protection from predators 

  • Support plasticity for learning  

  • Support of growth and development 

Characteristics of different sleep stages - including what the waves look like 

Awake 

Stage 1: NREM = lightest stage of sleep, slowing heart rate, breathing and eye movements 

Stage 2: NREM – most of time sleeping, drop in body temp, breathing slows,  

  • Sleep spindle = increase in activity in sleep, learning and memory is being worked on  

Stage 3,4 NREM = decreased breathing rate and heart rate, slowed brain waves  

REM = get irregular breathing, increased heart rate, memory consolidation, emotional processing and brain development 

  

Know brain areas and NTs involved in the "flip flop switch" for sleep regulation: 

  • Raphe Nuclei (serotonin) 

  • Locus Coeruleus (norepinephrine) 

  • TMN (histamine) 

  • VLP (GABA, galanin) 

  • LDT/PPT (Acetylcholine) 

  • Thalamus  

Sending projections using various neurotransmitters to cortex, that is when we are awake  

VLPO = sleep promoting region, when we are wake it inhibits these areas and as a result maintains sleep  

Wake= Neurotransmitters that maintain awakeness by sending projections through the rest of the brain  

Characteristics of narcolepsy 

  • Can happen while driving or sitting at desk talking to someone 

  • Had adequate sleep during the night  

Characteristics in terms of sleep: 

  • During night frequent wakening's  

  • Sleep during the day = enter REM sleep very quickly (not normal) 

  • Obstructive sleep apnea  

Treatments: 

  • Melatonin 

  • Antidepressants can be used 

Effects of DST and shift work on sleep patterns and health 

DST: 

  • Changing from one time to another is disruptive  

  • Can disrupt sleep = higher risk of heart attack, increase in depression, higher risk of stroke, rise is fatal car accidents  

  • Worry of parents 

  • Transition is bad 

Shift Work: 

7am-6pm 

Effects of working night shifts: 

  • Disruption in circadian rhythm  

  • Melatonin suppression = exposure to light at the wrong time  

  • Heart problems 

  • Obesity and diabetes 

  • Digestive problems  

  • Breast cancer = nurses staying night shifts  

  • Mental health issues = change in sunlight exposed during day 

  • Vitamin d deficiency  

  • Risk of injury 

Sleep hygiene strategies: 

  • Consistent sleep and wake times (weekend and summer) 

  • No screens 1 hour before bed 

  • Dark, cool bedroom  

  • Limit alcohol and caffeine 

  • Exercise