biological rhythms

rem sleep

10 minutes at start of night and up tp an hour later in the night. sometimes referred to as stage 5 or paradoxical sleep. brain becomes very active almost indistinguishable from a waking brain. the pons in the midbrain throws out bursts of electrical activity. heart rate and blood pressure increase as does body temperature and eyes twitch rapidly. body remains motionless, cut off from the brain by pons. paralysis occurs to prevent acting out dreams and endangering lives. cats who have had lesions to their pons typically act out their dreams. our first visit to rem = 10mins. start journey back down. cycle repeats throughout the night cycle repeats throughout the night, but we spend most of the first haf of the night in deep sleep. and most of the second half in rem.

stage 3

15 minutes brain waves start to slow and become higher in amplitude and wavelength. these are called delta waves and are associated with deep sleep. we are now more difficult to wake. first time round in the night this stage is brief, only a few minutes, spend longer in this stage later on in the night.

stage 1

15 minutes occurs at the start of a nights sleep. it lasts a matter of minutes, we often wake from this stage. e.g. watching a film late at night, we may nod off. we may wake from this stage and think that we have been dreaming. intact these hallucinations are referred to as hypnogogic phenomena and usually comprise of fleeting images. the eyes may roll slowly. sometimes we may wake without even realisning that we have nodded off. brain waves are slower and are called theta waves. other times we may wake with a jerk or twitch.

stage 2

20 minutes characterised by bursts of high frequency waves called sleep spindles. we are still aware of sounds and activity around us and the brain responds to this with k complexes. still very easily woken.

stage 4

30 minutes in many respects this is a continuation of stage 3, however delta waves now constitute most of the brains activity and we are now at our most relaxed. at this stage we are very difficult to wake up. however a quiet but meaningful sound such as a baby crying can be sufficient, indicating that the brain still retains some degree of awareness of external stimuli. heart rate and blood pressure fall, muscles are very relaxed and temp at its lowest. we have now been asleep for abut an hour in the 1st cycle. we start to ascend back through these stage in reverse order, but instead of going back to stage 1 we enter a bizarre stage of consciousness.

the details of a typical first cycle of sleep awake

AWAKE the brain is active and shows beta activity, when we relax shows alpha activity. alpha waves are slower with higher amplitude and indicate the beginning of sleep.

conclusion

Conclusion: It appears that both exogenous zeitgebers and endogenous pacemakers usually work together to regulate our 24 hour sleep wake cycle. We know that the SCN is a main endogenous pacemaker, and will keep a sleep wake cycle regulated in the absence of light, although it is unlikely to stick to a rigid 24 hours. There are ethical concerns about such research, as the invasive surgery on animals may be seen as unfair by critics of animal research, although such research maybe vital for helping people with sleep disorders.

social cues affect on sleep wake cycle

For example, mealtimes, work times, use of social media, and external noise levels may play an active role on changing people's sleep/wake cycle. For example, Folkard et al (1985) investigated the effect of manipulating exogenous zeitgebers on the sleep-wake cycle. The researchers placed 12 participants in temporal isolation (isolated to only the time cues within their environment and not external time cues) for 3 weeks. The environment was a cave with no external light and a single large clock that the researchers were able to control. The participants agreed to go to bed when the clock showed 11:45PM and get up at 7:45AM. Initially the researchers set the clock to run at a normal 24 hour cycles, however they gradually increased its speed so that eventually a day passed of the participants synchronized their sleep-wake cycles to the pace of the clock. This shows that the sleep-wake cycle can be influenced by exogenous zeitgebers, at least gradually

how the scn works

How the SCN works is not precisely understood, but according to Kalat (1998) the SCN generates its own internal rhythm as a result of protein production. It is likely that what happens is that the cells in the SCN produce a protein for a period of hours until the level inhibits further production, again for hours; next when the protein level drops below the threshold, the SCN starts producing the protein again. The SCN passes information about light and dark to just behind the hypothalamus to a structure called the pineal gland. This secretes melatonin when it gets dark which induces sleep. This does not occur during times of wakefulness.

entrainment

Light is a key zeitgeber in humans. It a process known as entrainment, it can reset the main endogenous pacemaker, the SCN. Hormone secretion and blood flow are also influenced indirectly by light. Research has shown that light not necessarily be detected by the eyes to have an influence, as researchers were able to change some participants' sleep/wake cycle by up to three hours by waking 15 participants and shining a light pad on the back of their knees (Campbell and Murphy, 1998). In studies where participants are placed in isolation, their sleep wake cycle can change a little. Michel Siffre is a classic example, and this case study has been replicated with similar results.

further support for exogenous zeitgebers

McClintock and Stern (1998) aim= show that the menstrial cycle is influenced by phermonal secretions form other women. sample= female university students, not taking birth control pills. design= longitudinal with independent measures. method= a control group of women wore alcohol soaked pads under their armpit, the fumes of these were inhaled by another group of women ( the experimental group) and their menstrual cycles were monitored. result: when the experimental group inhaled secretions from women who had just ovulated, their menstrual cycles became longer. the experimental groups mentrual cycles were affected by the secretions of the control group . 68% of occasions the resipitents of the sweat donation had responded to the pheromones. conclusion: this explains why when a group of women live in close proximity their menstrual cycles tend to synchronise and provides support for the role of exogenous zeitgebers.

what is the cycle referred to?

a 28 day cycle.

biological rhythms

are cyclical changes in the way biological systems behave. one of the most obvious is the sleep wake cycle. = we will typically spend 16 hours of every 24 hours in varying degrees of consciousness, and 8 in every 24 hours in varying degrees of unconsciousness.

sensations experienced during the infradium rhythm

backache, pain in the inner thighs, bloating, nausea, diarrhoea, constipation, headaches, breast tenderness, irritability and other mood changes. positive sensations include- relief, release, euphoria, new beginning, invigoration, connection with nature, creative energy, exhilaration, increase sex drive.

negatives with this research

confounding variables that could have contributed to these findings: change of diet, exercise, stress and chance= any of these could explain the findings. furthermore recent research has not found synchrony between women in close proximity, questioning the reliability of these findings.

supporting evidence for the different stages of sleep

dement and kleitman aim= eye movements and dreaming mthod- 9 participants 7m 2f, studied under controlled lab conditions, had to report to the lab at bedtime where they were connected to an reg. reg took measurements throughout their time asleep as at night, were asked not to drink caffeine. results= show that rem predominantly associated with dreaming, non rem associated with periods of non dreaming sleep,ps were able to recall dreams when woken during rem. awaken during other stages = less likely conclusions- stags of sleep follow a pattern

other arguments

dreaming does occur in other stages, but in these studies they were unable to report them. additionally large variations between individuals 20 yrs= long sessions of stage 4 sleep. over 80 virtually none

effects of endogenous and exogenous on sleep wake cycle

endogenous pacemakers= the svn and the pineal gland scn=a tiny bundle of nerve cells in the hypothalamus, is the primary endogenous pacemaker in humans and other mammals one function = regulate the sleep wake cycle. nerve fibres connected to the retina cross the optic chasm and into the svn tells us when it is day or night. however any established rhythm will continue in the absence of the exogenous zeitgeber for a short time whilst the svn adjusts to the new time

case study of michel siffre

it is clear that exogenous zeitgebers play a key role in the regulation of circadian rhythms. the case study shows that the absence of external cues such as light and contact with others, the biological clock can drift as his did to a longer 25 hour clock , some people blind at birth have difficulties adjusting to the 24 hour day because of the lack of light cues.

evaluation

it is unclear whether the menstrual cycle is effected by endogenous pacemakers or exogenous zeitgebers

what does light do?

light influences our internal clock through specialised light sensitive cells in the retina of our eyes.these cells tell the brain if its day or night, our sleep patterns are adjusted accordingly. so although sleep wake cycle exists without light, light does influence the cycle. e.g. travelling across time zones = shift in external cues, the sleep wake cycle becomes aligned to new cues. this is called entrainment.

circadian rhythms

most obvious circadian rhythm in humans in the sleep wake cycle, this appears to be a 24 hour rhythmic cycle where there are different levels of consciousness. people sleep for a certain time every 24 hours and conduct other activities during wakefulness. these patterns are repeated regularly and are persisted even when the environment changes. for example people will often feel jet lagged.

how does the SCN work?

not precisely understood, but according to kalat the SCN generates its own internal rhythm as a result of protein production. it is likely that the cells in the SCN produce a protein for a period of hours until the levels inhibits further production, again for hours. when the protein level drops below the threshold the SCN starts producing the protein again.

evidence supporting the role of exogenous zeitgebers in mesntrual cycles.

reiberg- conducted a study where one female participant spent three months in a cave, with only light from a small lamp. as a result her days lengthened to 24.9 hours and her mentrual cycle shortened to 25.7 days. this shows that the levels of light in the cave could have affected the womens menstrual cycle suggesting infradian biological rhythms could be influenced by exogenous zeitgebers such as light.

morgan

removed and transplanted the SCNs from hamsters and shows support for the importance of the SCN as when it was removed their nocturnal circadian rhythms disappeared. transplanting the svn cells re established the rhythm. furthermore when nocturnal hamsters had their SCNs replaced with non nocturnal hamsters, the hamster followed the new routine of the new hamster. further evidence shows that the lsioning of the SCN in rats showed a complete disruption in the sleep wake cycle.

evidence

removed and transplanted the SCNs from hamsters and shows support the importance of the SCN as an endogenous pacemaker. When the SCN was removed from hamsters their nocturnal circadian rhythms disappeared. Transplanting with SCN cells re-established the rhythms. Furthermore, when hamsters with nocturnal patterns of activity (usual) had their SCNs replaced with SCNs from mutated hamsters which slept through the night and were active during the day (unusual), the hamsters followed the new daytime activities of the donor's patterns. Further evidence from lesioning (cutting) the SCN in rats showed a complete disruption to the animals sleep/wake cycle

what has research into circadian rhythms repeatedly found?

that circadian rhythms remain even when there are changes to the environment. if no clues are offered about daylight and night time, and other environmental factors are kept constant, the biological clock will continue to regulate our bodies, on approximately a 24 hr cycle. suggests it is built in, and regulated by what scientists had called endogenous pacemakers. suspected to be found in the brain, and structures such as the pineal gland and the suprachiasmatic nuclei (SCN) are thought to be influential in the regulation. the neurotransmitter serotonin and the hormone melatonin are though to be influent; in the regulation of the sleep wake cycle.

details of the cycle

the hypothalamus releases the chemical messenger follicle stimulating hormone releasing factor (FSHRF) which triggers the pituitary gland to secrete follicle stimulating hormone (FSH) and leutanizing hormone (LH) into the blood stream which causes the follicles to begin to mature.

emergent sleep

the last cycle of sleep, as during this one that we wake up. contains no stage 3 or stage 4 so under normal conditions we will emerge from either rem or stage 2 and waking process may be accompanied by hypnogogic images as was mentioned in stage 1

then what happens

the maturing follicles then release another hormone, oestrogen. as the follicles ripen over a period of about 7 days, they secrete more and more oestrogen into the blood stream. when the oestrogen level reaches a certain point, the pituitary gland releases a further amount of leutanizing hormone (LH) . this surge of lh triggers the one most mature follicle to burst open and release an egg. this is called ovulation. many birth control pills work by blocking the lh surge. after ovulation, the hormone progesterone causes the womb linig to thicken which redoes the body for pregnancy. if the women does not become pregnant the unfertilised egg is absorbed back into the body and the womb lining comes away from the body= the menstrual flow.

ultradium rhythms: the cycles of sleep

these occur more than once in a 24 hour cycle. most are confined to either day or night, e.g. the stages of sleep. a typical nights sleep takes you from stage 1 to 4 then back to 2 and finally into REM sleep. this whole cycle then repeats itself 3 or 4 times during the night, each cycle lasting about 90 minutes. sleep is the perfect example of an ultradian rhythm, that is one that repeats itself over a period of less tham 24 hours. the cycle of sleep typically lasts 90 minutes and during a typical nights sleep we will repeat this cycle 4 or 5 times, although the cycles do differ throughout the night.

what is generated when the production of protein starts again?

this generates the biological rhythm which activates the pineal gland, since the SCN is connected to the pineal gland via a pathway; when the pineal gland is activated by the svn it produces melatonin, which causes drowsiness. it continues to be emitted throughout the night provided it is dark; when it becomes light the SCN and its protein production is affected, so a pathway from the SCN to the pineal gland is activated and the secretion of melatonin stops

what has research suggested about endogenous pacemakers?

what is also interesting is that research has suggested that endogenous pacemakers are not perfect, when deprived of external influences, the circadian rhythm can become a little longer or shorter, so people require these exogenous zeitgebers if circadian rhythms are to be fully co ordinated with the external world. the most influential exogenous zeitgeber is light, and its role is fine-tuning bodily rhythms has been reliably demonstrated in research.

infradian rhythms: the menstrual cycle

when a baby girl is born she has all the eggs her body will ever use. they are stored in her ovaries, each inside its own sack known as a follicle. as she matures into puberty her body begins producing various hormones that cause her eggs to mature. this is the beginning of her first cycle; it is a cycle that will repeat throughout her life until the end of menopause.