Bio Rhythms 8

Bio Rhythms 8: 

Rhythms can be categorized by periodicity (the time between one peak of maximum value and the next peak of maximum value.  

Three main types: 

  • Infradian rhythm (greater than 24 hours) e.g. hibernation/menstruation.  

  • Circadian rhythm (every 24 hours) e.g. the sleep wake cycle.  

  • Ultradian rhythm (less than 24 hours) e.g. the stages of sleep.  

Different biological rhythms can be influenced by many factors, both internal and external. 

  • Endogenous pacemaker (the biology clock): Moderates hormones, internal temperature, etc. INSIDE 

  • Exogenous Zeitgebers (external influences): Light, external temperatures, etc. OUTSIDE 

 

Infradian rhythm: 

  • Periodicity more than 24 hours 

Examples: 

  • The menstrual cycle has a periodicity of 28 days. It is under physiological control from hormones whose release is primarily controlled by the hypothalamus in the brain. However, there are some exogenous zeitgebers that can have a slight influence on timing. 

  • Hibernation is an infradian rhythm with a seasonal periodicity. Hibernation occurs in response to exogenous zeitgebers Associated with the onset of winter, such as outside temperature and day length. 

  • McClintock found that women who live or spend considerable time together can have synchronized menstrual cycles. This may be due to pheromones that are released into the air rather than the bloodstream. These are chemical messengers and so may coordinate the female's synchronization. 

  • Russel, Switz and Thompson’s female pheromones study provides support for the effect of pheromones. 

  1. Participants had donor pheromones rubbed onto their upper lips daily for five months. 

  1. A control group went through the same procedure, but instead of pheromones, plain alcohol was used. 

  1. After five months, four out of five women in the experimental group had menstrual cycles that synchronized with the donor. 

 

Ciradian Rhythm: 

Periodicity every 24 hours. 

Examples: 

  • Body temperature has a periodicity of 24 hours. It peaks at midafternoon (4-6pm) and is the lowest at 4:00 AM. It is regulated by endogenous pacemakers which release hormones (such as thyroxine), in addition to the exogenous zeitgbers of temperature.  

  • The sleep wake cycle has a periodicity of 24 hours which is synchronized with the day night cycle. It is controlled by endogenous pacemakers which release hormones (such as melatonin) but are also influenced by exogenous zeitgbers, such as light and temperature. 

Aschoff & Weber: 

Placed participants in a bunker with no natural light. They settled into a sleep/wake cycle of between 25 and 27 hours, suggesting that internal endogenous pacemakers control the sleep wake cycle in the absence of light cues. 

Evaluation of Asohoff & Weber: 

  • Some participants maintain normal cycles while others strongly differ. 

  • An issue with isolation studies is that they have few participants making generalization problematic, and studies tend to suffer from poor external validity due to this. Overall, this impacts negatively on the ability to generalize the findings to wider society. 

Michel Siffre: 

Spent six months in a cave with no time cues. He settled into a sleep wake cycle of 25 to 30 hours. After 179 days, he thought 151 days had passed supporting Aschoff and Webers findings that Endogenous pacemakers exert an influence on circadian rhythms.  

Evaluation of Michel Siffe: 

Artificial light and temperature in the cave could have been confounding variables, perhaps leading to inaccuracies which were never considered. 

The settling itself could be argued to have very low ecological validity. 

Ultradian Rhythm: 

Periodicity is less than 24 hours.  

 

Pacemakers and zeitgbers: 

  • The human cicadian sleep wake rhythm is regulated by our endocrine pacemaker (internal). The endogenous pacemaker for the sleep wake cycle is a brain area called the superchiasmatic nucleus which is located in the hypothalamus. 

  • However, we use Exogenous zeitgbers such as light to synchronize our internal body clock with the outside world.  

  • In this way the endogenous pacemaker and the exogenous zeitgbers work together to make sure that we are awake and alert during the day and sleep at night.  

 

The Superchiasmatic Nucleus (SCN): 

The SCN is a tiny cluster of cells in the hypothalamus just above optic chiasm, which obtains information about light via optic nerve. This tiny cluster of cells is vitally important for keeping biological time. 

 

 

Endogenous Pacemakers: 

Sleep wake studies pointed to the existence of an internal body clock or endogenous pacemaker for Ciradian rhythms. 

In 1972 two studies demonstrated the SCN rose by damaging the Super charismatic nucleus in rats. When the SCN was damaged it abolished circadian rhythms in rats and in later studies in hamsters. 

Superchiasmatic Nucleus (SCN): 

The Clinching Evidence of the Role of the SCN as the key endogenous pacemaker was the finding that SCN neurons removed and kept alive outside the brain still showed a circadian rhythm in their electrical activity. 

This demonstrates that the Circadian activity of SCN neurons is intrinsic or inbuilt. 

 

Retinohypothalamic Pathway: 

There is a direct pathway from the center of the eye to the SCN, a pathway called the Retinohypothalamic tract. 

This pathway alerts the SCN to the status of light in the outside world especially on set of light in the morning. 

Pacemakers and Zeitgebers: 

The SCN exerts its regulatory role in the sleep wake cycle via the Retinohypothalamic pathway. 

In response to its input (light rays onto the retina), the SCN signals the pineal gland to suppress the hormone melatonin that is known to control sleep wake behavior.  

Through this pathway, daylight suppresses the release of melatonin, while darkness leads to an increase. 

 

Pollino gland and melatonin. 

During the day, the Palino Gand is inactive. However, when the sun goes and it becomes dark, it begins to produce melatonin.  

As the levels of melatonin rise in the blood, you begin to feel less alert, and sleep becomes more inviting. 

The levels of the blood stay elevated throughout the night and drop back down in the day. 

 

Ultradian rhythm – stages of sleep: 

The sleep cycle has a periodicity of 90 minutes. 

In the sleep cycle you begin in light sleep, pass through several stages of non R.E.M. slow wave sleep before entering REM sleep. 

The sleep cycle is controlled by endogenous pacemakers which release or inhibit different hormones and neurotransmitters. 

Sleep Cycle: 

  1. Change over from wakefulness to sleep, a short period of light Sleep in which your heart rate, breathing, eye movements and brain waves slow, and your muscles relax. 

  1. A period of light sleep before you enter deeper sleep, your heart rate and breathing continue to slow, and your muscles further relax. Your body temperature drops, and eye movements stop. Brain wave activity slows but is marked by brief bursts of electrical activity. 

  1. A period of deep sleep. It occurs in longer periods during the first half of the night, your heartbeat and breathing slow to their lowest levels. Your muscles are relaxed, and it may be difficult to awaken you. Brain waves become even slower. 

  1. REM sleep - Occurs 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids. Mixed frequency brain wave activity becomes closer to that seen in wakefulness. Your breathing becomes faster and irregular, and your heart rate/blood pressure increases to near waking levels. Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep. Your arm and legs muscles become temporarily paralyzed which prevents you from acting out your dreams. 

The impact of sleep deprivation: 

  • After several sleepless nights, the mental effects become more serious. Your brain will fog, making it difficult to concentrate and make decisions. Your risk of injury and accidents at home, work and on the road also increases. 

  • If it continues, lack of sleep can affect your overall health and make you prone to serious medical conditions such as obesity, heart disease, high blood pressure and diabetes. 

  • But the detrimental impact of losing sleep not only affects you but can also impact others. For example, Rogers 2008 reviewed multiple research papers demonstrating a link between the effects of sleep deprivation and increased medical errors in medical staff. 

Circadian Misalignment (shift/night work): 

Our bodies and brains evolved to relax and cool down after dark, and to spring back into action come morning. People who work the night shift must combat their bodies natural rest and the impact of exogenous zeitgebers.  

However, it is now understood that doing so can have a negative impact on cognitive performance, mood and heart health. 

The impact of sleep deprivation on your immune system: 

  • While you sleep, your immune system produces protective infection fighting substances like antibodies and cytokines. It uses these substances to combat foreign invaders such as bacteria and viruses. 

  • Sleep deprivation prevents your immune system from building up its forces. If you don't get enough sleep, your body may not be able to fend off invaders, and it may also take you longer to recover from illnesses. 

 

The impact of sleep deprivation on physical health: 

  • Memory issues. 

  • Trouble with thinking and concentration. 

  • Mood changes. 

  • Accidents. 

  • Weakened immunity. 

  • High blood pressure. 

  • Risk for diabetes? 

  • Weight gain. 

  • Low sex drive. 

  • Risk of heart disease. 

  • Poor balance. 

 

Sleep and autism: 

  • Findings suggested autistic subjects often present sleep disturbances, particularly short sleep duration, low sleep quality/efficiency and circadian sleep desynchronization, such as delayed phases and or evenings. 

  • Sleep disturbances and circadian Sleep alterations have been related to the severity of autistic symptoms. Genetic studies have shown polymorphism in circadian clock genes and in genes involved in melatonin pathways in subjects with ASD. 

Sleep and dementia: 

The association between sleep and dementia is bidirectional. 

  • Stopa - Damage to the SCN may be an underlying. Anatomical substrate for the clinically observed changes in circadian rhythmicity that have been observed in Alzheimer's patients. (Brain pathology underlying dementia may lead to disturbed sleep). 

  • Hauglund - Sleep is for clearing the brain from the potential neurotoxic waste products that accumulated during wakefulness. This includes the substance that forms plaques which damage the brain in dementia. (Sleep disturbance may contribute to the development of dementia).