Biological Rhythms A01

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Outline somnambulism (4).	Somnambulism, otherwise known as sleep walking, is a parasomnia, which occurs during slow wave sleep (SWS). It is thought to be caused by an abnormal transition from NREM to REM. There's evidence to suggest that it could be inherited, based on gene HLA DQ51*05.
Outline the incomplete arousal explanation for somnambulism (4).	Recordings of brain activity during sleep walking show a mixture of delta waves, which occur during SWS, and high frequency beta waves, which are typical of an awake state. This suggests that a sleep walker is partly awake, partly asleep. Therefore, sleep walking may occur when a person in deep sleep is awakened but brain arousal is incomplete.
Define insomnia (2).	Insomnia is a type of sleep dyssomnia, which can be short-term or chronic. It is when a person experiences problems falling asleep, maintaining sleep and experiences reductions in sleep quality. This means that sleep becomes non-restorative, leading to daytime tiredness.
Outline one explanation of primary insomnia (2).	Primary insomnia is when the insomnia has no direct physical cause. It can be explained through genetics. The insomniac may have inherited a minor imbalance in their network of biological clocks and neural mechanisms, which may prevent neural sleep controls from operating correctly.
Outline a cause for secondary insomnia (4).	Secondary insomnia is when there is an underlying cause for the insomnia. The sleep disorder is viewed as a symptom. One cause for secondary insomnia is psychological disorders. These are often associated with high levels of arousal and anxiety (e.g: high levels of serotonin) that are incompatible with sleep. Some of the most common drugs prescribed to treat anxiety and depression are BZs (benzodiazepines), a form of hypnotic sleeping pill that can increase sleep time but reduce overall sleep quality, resulting in a direct interference with the brain's complex sleeping mechanisms.
Define narcolepsy (2).	Narcolepsy is a type of dyssomnia in which the individual suffers from random sleep attacks and abnormal sleep patterns, entering REM within the first 5 minutes of the sleep cycle.
Outline the REM explanation for narcolepsy (2).	Cataplexy, which occurs during narcolepsy, is similar to what is experienced during the paradoxical stage of sleep (REM - where the individual's body is paralysed but their brain activity is similar to when they are awake). During the day narcoleptics often experience hypnagogic hallucinations, which are like dreams typically experienced during REM. This suggests that there is a malfunction in the system that regulates REM, causing the disorder.
Outline the hypocretin explanation for narcolepsy (4).	Another explanation for narcolepsy may be low levels of hypocretin (orexin). This neurotransmitter regulates arousal and wakefulness. It integrates circadian and metabolic influences to determine whether an animal should be asleep or active. If this neurotransmitter is depleted then it will affect neural control over our biological sleep mechanisms, leading to the sleep attacks experienced in narcolepsy.
Define the ecological approach (2).	The evolutionary functions of sleep explanation can also be known as this, since it's based on the observations of animals in a natural environment. The evolutionary approach suggests that different environmental pressures lead to differences in sleep patterns between species.
Outline foraging requirements as an explanation for the function of sleep (2).	Carnivores eat food high in nutrients so they can afford to rest and conserve energy (e.g: lions). Herbivores (e.g: cows) eat plants that are poor in nutrients (e.g: grass) so they must spend a lot of time eating and less time sleeping. As a result, dietary requirements act as sleep constraints.
Outline predator avoidance as an explanation for the function of sleep (4).	Prey species have a reduced sleep time in order to remain vigilant against predators (e.g: giraffes sleep for 3 hours). They are best to sleep when least vulnerable. A predator however, can sleep for longer since their sleep isn't constrained by predation risk (e.g: lions). This suggests that sleep may be a function of predator avoidance.
Outline Oswald's theory of the restorative functions of sleep (4).	Oswald proposed that both NREM and REM sleep have specific and important functions. NREM restores bodily processes that have deteriorated during the day (body repair) and REM renews brain processes and replenishes neurochemicals that have been used up during the day (brain recovery). For example, the immune system consists of antibodies that are regenerated during cell growth and protein synthesis occurs during slow wave sleep. Growth hormone (GH) also enables restoration of body tissues. Therefore, sleep enables these restorative functions to be carried out.
Outline Horne's theory of the functions of restorative sleep (4).	Horne suggested that deep NREM (stages 3-4) and REM sleep are core. Light NREM has no obvious functions and is optional. Participants who have been sleep deprived use the core stages to further restoration and skip the optional stages. Horne also found proposed that the body doesn't necessarily need sleep to recover as this process can be achieved through periods of relaxed wakefulness (like microsleep).
Outline the sleep-wake cycle (8).	The sleep wake cycle is an ultradian rhythm (a pattern of behaviour that occurs more often than once a day). It consists of 5 main stages. The first 4 are NREM (non-rapid eye movement), which have been linked to body repair. As we move through the stages we experienced deeper slow wave sleep (SWS) until we make the transition to REM, a paradoxical stage of sleep (our body is paralysed but our brain activity resembles that of when we are awake) that has been linked to the restoration of brain functions. Afterwards we go back down through stages 2-4 and the cycle repeats every 90 minutes. Our time spent in stages 3 and 4 lessen until only stages 1, 2 and REM are returned to by the end of the night.
Outline sleep during infancy (2).	During infancy we sleep for an average of 16 hours a day and experienced an immature form of slow waves sleep (SWS) called active sleep. 50% of our sleep consists of this.
Outline sleep during childhood (2).	During childhood it is fairly common to experience a variety of parasomnias (e.g: night terrors). By the age of 5, EEG patterns start to be similar to adults but the child still has more sleep (12 hours) and up to 30% of this sleep is REM.
Outline sleep during adolescence (2).	During adolescence the need for sleep increases to 9-10 hours. Circadian rhythms change slightly to feel more awake at night (phase delay) and the individual experiences difficulties getting up in the morning (phase advance).
Outline sleep in the elderly (2).	In old age we typically sleep for 8 hours a night. REM decreases to 20% and slow wave sleep (SWS) to as little as 5%. Phase advance is often experienced as well as frequent night waking during this time (up to 6 times a night).
Outline the SCN as an endogenous pacemaker (4).	An endogenous pacemaker is an internal biological clock. For example, the SCN located in the hypothalamus sets the circadian rhythm of the sleep-wake cycle. The SCN receives information about how much light falls on the retina and when dusk falls it triggers the pineal gland to release melatonin. This makes us feel sleepy.
Outline exogenous zeitgebers (4).	Exogenous zeitgebers are external factors that may effect our circadian rhythms. They are often environmental in nature e.g: the presence/absence of sunlight. Exogenous zeitgebers often work with the endogenous pacemaker to help regulate the sleep-wake cycle through factors such as: noise, seasons, temperature etc.
Outline the disruption of biological rhythms (2).	Biological rhythms are controlled by endogenous pacemakers (EP - our internal, biological body clock) and exogenous zeitgebers (EZ - external, environmental factors e.g: light). These can be disrupted through a dislocation of EPs and EZs, which causes desynchronisation.
Outline shift work (2).	Shift work can disrupt biological rhythms because we are working when the body wants to sleep and vice versa. This is a reverse of our natural biological rhythm since melatonin is released in response to the darkness of night. As a result, we don't feel sleepy during the day and environmental stimuli, such as light, interrupts our sleep quality, (particularly affecting REM) when we try to sleep during the day.
Outline infradian rhythms (2).	An infradian rhythm is a rhythm with a cycle length usually longer than a day such as Seasonal Affective Disorder or the menstrual cycle.
Outline the menstrual cycle (2).	This infradian cycle regulates ovulation through hormone changes (FSH, LH, oestrogen and progesterone all contribute towards the process). PMS (pre-menstrual syndrome) is a physiological process that typically occurs 14-7 days before and can result in mood swings.
Outline Seasonal Affective Disorder (4).	Seasonal Affective Disorder (SAD) is a depressive condition in which the individual becomes depressed during winter and recovers in the summer. Melatonin is produced by the pineal gland when it's dark. Since melatonin is made from serotonin (a chemical associated with mood), more darkness means less serotonin and more melatonin, leading to low mood.
Define free running (2).	Free running is a term used to describe biological rhythms in the absence of exogenous zeitgebers e.g: the sleep-wake cycle - even in the absence of light cues, melatonin is released in a cyclical manner but the cycle disappears if the SCN is destroyed.
Define ultradian rhythm (2).	An ultradian rhythm is a pattern of behaviour that occurs more often than once a day such as the stages of the sleep wake cycle.
Outline jet lag (4).	Jet lag occurs when you cross time zones. It disrupts the natural rhythm of your endogenous pacemaker due to a dislocation between the body clock and local exogenous zeitgebers (EZs). Travelling from east to west results in phase delay. It easier to get up as it's like a lie in but travelling west to east results in phase advance. It becomes harder to get up as you're in a circadian trough. Symptoms of jet lag include: loss of appetite, nausea, fatigue and mild depression.

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