Biological Rhythms unit Flashcards
(26 cards)
How long do we spend asleep? What is this behaviour?
We sepnd at least a third of our lives asleep. Sleep is a behaviour, despite not being associated with any movement (except rapid eye movement). It is characterised by a motivational force - sleepiness. It drives us to find a quiet place and lie down for several hours
How did we find our that sleep consists of various stages?
Sleep studies involve placing electroencephalogram (EEG) electrodes on the scalp, and electrooculogram (EOG) electrodes around the eyes, and measuring electrical activity while the subject sleeps in a sleep lab. EMG on the face, sensors that measure heart rate and skin conductance etc. Stages can be identified by their distinct patterns of EEG (brain) activity and EOG (eye) activity
what are the different frequencies that are observed at wakefulness?
EEG data tends to show two basic patterns of activity: Alpha and Beta activity. Alpha (8-12 Hz) observed when a person is resting, not engaged in a task and are more prevalent with the eyes closed. Beta (13-30 Hz) observed when a person is alert/attentive, or engaged in a particular task.
Describe, what is the first stage of sleep?
As we enter S1, we see theta activity (3.7-7.5 Hz). Stage 1 is a transitional stage between wakefulness and sleep. Hypnic jerk may also occur (muscle contraction, followed by relaxation). (REM slep produces the smae pattern of EEG activity as stage 1 sleep)
Describe, what is the second stage of sleep?
After 10m, we enter S2, characterised by less regular EEF activity, sleep spindles and K-complexes.
Sleep spindles are short bursts of 12-14 Hz activity, and occur between 2 to 5 times a minute.
They may plat a role in episodic memory consolidation, and have been found to correlate with intelligence. K-Complexes (are sharp waveforms that occur once a minute, and represent periods of inhibition of cortical arousal)
Describe, what is the third stage of sleep?
After 30m, we enter S3, slow wave sleep, which is characterised by delta activity (<3.5 Hz).
(This is deep sleep) Whereas being awoken in stage 2 may produce a sensation of not having been asleep, in stage 3 we are likely to be awoken only by loud noises, and if awoken, we would feel groggy and confused.
Slow wave sleep was previouslt considered to consist of 2 stages, but the literature now considers these as sub-stages.
Describe, what is REM stage of sleep?
After 90 minutes we enter rapid eye movement (REM) sleep, high EOG activity and beta EEG activity (similar neural activity to stage 1). Each sleep cycle lasts 90m, with each having 20 to 30 minutes of REM. REM is also characterised by low muscle tone: aside from occasional twitching we are paralysed, however when awoken we are normally alert and attentive
When do vivid dreams happen?
During REM sleep, its been associated with high activity in the extrastriate cortex (visual association cortex) and low activity in the striate cortex (primary visual cortex). Low activity in the striate cortex demonstrates the eyes are not recieving visual input, whereas activity in the extrastriate cortex likely relfects the visual hallucinations during dreams.
What area of the brain do we see low activity from while dreaming?
The rapid eye movemets likely reflect to visual hallucinations, Dreaming is associated with low prefrontal cortex activity, which may be why dreams appear so unorganised (given the PFC is involved in planning, organisation, retrieving the context of memories, etc.)
How come all mamals and birds sleep, how it essential to our survival?
It appear to maintain brain functions rather than bodily functions: sleep deprivation doesn’t affect the ability to perform physical activities, but affects cognitive abilities and reduced concentration
What are the effects of sleep deprivation?
We don’t tend to recover all of the lost hours of sleep, after incurring a sleep debt of 8 hours, we may sleep an extra 4 hours the following night rather than an extra 8 hours. We tend to recover more hours of REM and slow-wave sleep than other sleep stages, suggesting that REM and slow-wave sleep are the most essential stages of sleep.
What is the function of slow-wave sleep?
It’s a recovery process. During wakefulness, the brain consumes a significant amount of the body’s energy. However, during slow-wave sleep, both its metabolic rate and cerebral blood flow drop to about 75% of waking levels. Interestingly, the brain regions that are most active during wakefulness exhibit the highest levels of slow-wave activity and the lowest metabolic activity during sleep.
What do slow-wave sleep faciliates?
The desctruction of free radicals. FR as chemicals that contain at least one unpaired electron, and appear as a waste product caused by the high metabolic activity of the brain during periods of wakefulness. Prolonged sleep deprivation = more FR = damage
What is involved in memory consolidation?
Slow-wave and REM sleep, memory consolidation is the strengthening of the formation of memories. REM benefit non-declarative memory (implicit) (learning automatic skills). Slow-wave sleep benefits declarative explicit memory, such as remembering spatial locations or a list of words.
What are the neuromodulator that controls sleep, and how does it work?
Adenosine is the main homeostatic factor regulating sleep. In the brain, astrocytes store small amounts of glycogen, which can serve as an energy source for neurons during periods of heightened activity. When glycogen levels decrease, adenosine levels rise.
How does adenosine produce sleepiness?
The high levels and the accumulation of adenosine during prolonged periods of wakefulness produces the cognitive and emotional effect of sleep deprivation. It produces its sleep effects by exciting neurones that produce sleep, and inhibiting neurones that maintain arousal. During slow-wave sleep, astrocytes renew their glycogen stores and adenosine is destroyed.
What are the five main neurotransmitters that play a role in maintaining arousal?
Acetylcholine, noradrenaline, serotonin, histamine, and orexin are key neurotransmitters involved in regulating arousal and wakefulness. Neurons from brain regions such as the pons, hypothalamus, and reticular formation project to widespread areas of the brain, releasing these neurotransmitters as part of distinct neural circuits.
What controls the transition from wakefulness to sleep?
It’s controled by inhibitoy neurones in the preoptic area of the hypothalamus. When active, preoptic area neurones inhibit the neurones that produce arousal, which cuases the onset of sleep.
What is the flip-flop circuit?
The preoptic area inhibits the neurones that maintain excitation, or the neurones that maintain excitation inhibit the preoptic area. It has this name because one set of neurones are active and not the other, meaning we are either in a state of wakefulness or a state of sleep
What controls our daily sleep rhythms?
The hypothalamus, these sleep rhythms are a type of biological clock, or enfogenous cycle. (from within)
What governs the circadian rhythms?
The suprachiasmatic nucleus in the hypothalamus.This brain area regulates the release of melatonin from the pineal gland. Melatonin is a hormone, which also regulates the onset of puberty
How does the suprechiasmatic nucleus function for sleep?
It communicates with the pineal gland via neurones belonging to the sympathetic nervous system in the spinal cord. He excites the pineal gland at night, causing it to secrete melatonin into the bloodstream. Melatonin increases sleepiness in humans, and wakefulness in nocturnal animals.
How does the suprechiasmatic nucleus function for wakefulness?
The suprachiasmatic nucleus inhibits the release of melatonin from the pineal gland, resulting in less sleepiness. Specialised retinal ganglion cells contain a special photopigment (melanopsin), which is sensative to light: when these cells are stimulated they send neural impulses along a small branch of the optic nerve that travels to the suprachiasmatic nucleus in the hypthalamus
How does the pineal gland end up secreting very low levels of melatonin?
The impulses sent along this branch of the optic nerve inhibit the suprachiasmatic nucleus, meaning it cannot excite the pineal gland. Resulting is that the pineal gland secretes very low levels of melatonin during the day.
