Chapter 14: Biological rhythms, sleep, and Dreaming Flashcards
What is a circadian rhythm?
A pattern of behavioral, biochemical, or physiological fluctuation that has a 24-hour period.
How is a circadian rhythm measured?
By tracking the running wheel in a hamster’s cage and having it mark it’s duration during the 24 hours of a day
What is free-running?
The added activity to maintain a hamster’s cycle because it is a few minutes longer than 24 hours.
Define Phase shift:
The shift of activity produced by a synchronizing stimulus.
Define entrainment:
The proces of shifting the rhythm
Define Zeitgeber
Literally time giver: The outside stimulus that entrains (entrainment) the circadian rhythm.
Where is the circadian clock located?
Within the suprachiasmatic nucleus of the hypothalamus (SCN). Located above the optic chiasm
How does light biologically affect the SCN?
Photoreceptor cells in the eyes. Certain retinal ganglion cells send their axons along the retinohypothalamic pathway.
What is different about the retinal ganglion cells?
These cells contain a photopigment, called melanopsin, that makes them sensitive to light.
They do not rely on rods and cones, even transgenic mice lacking rods and cones, and thusly are blind, entrain their to light.
Genes affecting the circadian rhythm
Period: Discovered in experiments with fruit flies whose became arrythmic without the gene. Affects free-running
Genes coding for Clock, Cycle, Bmal1, and cryptochrone(cry)
How does the molecular clock function?
5 steps:
- Clock and Cycle (Bmal1 in mammals) bind forming a “dimer”
- The dimer binds to DNA, enhancing the transcription of period (per) and cryptochrome (cry) proteins.
- per and cry bind together and inhibits the production of the clock/cycle dymer.
- The cry/per dimer eventually degrades, thus no longer inhibiting clock/cycle production
- Retinal ganglion cells release glutamate which enhances production of the per gene hereby entraining the molecular clock to the day-night cycle.
What is an infradian rhythm?
A rythmic biological event whose period is longer than a circadian rhythm - 24hours
What is an ultradian rhythm?
A rythimic biological event whose period is shorter than a circadian rhythm -24 hours
what is special about the circannual clock?
It is a clock whose cycles does not arise from the circadian clock. They involve a mechanism that is separate from SCN
What is the primary method when studying sleep/waking cycles in humans?
EEG measurements coupled with electrooculography (EOG) and Electromyography (EMG).
Describe the different classes of sleep
Overall there is two classes of sleep: Slow-wave sleep (SWS) and Rapid-eye-movement sleep (REM).
SWS: Widespread synchronization of cortical activity in slow waves.
REM: Small amplitude, high-frequency activity, similar to an awake individual, coupled with completely relaxed and limp muscles.
Describe the different stages of sleep and which EEG patterns characterize them
SWS stage 1 sleep: Closing of eyes, drowsiness, alpha rhythm 8-12 hz, sharp waves called vertex spikes, slowing of heart rate, reduced muscle tension, eyes rolling.
Stage 2 sleep: 12-14 HZ called sleep spindles, K complexes. Not yet aware of sleeping condition.
Stage 3 Sleep: Large amplitude very slow waves called delta waves 1 per second. The old definition of stage 4 is now removed because of similarity with stage 3
REM stage: Small amplitude, high-frequency activity, similar to an awake individual, coupled with completely relaxed and limp muscles. Brainstem regions are inhibiting motoneurons
The humans sleep in cycles…
Repeating cycles of 90-110 minutes recurring usually 4-5 times in a night.
Cycles consists of a stage 1 -> 2 -> 3 -> 2 -> REM
Then shifting between REM, stage 2, and stage 3 sleep. With more repeated cycles comes longer REM phases and shorter stage 3 phases.
There are also a few brief awakenings during the cycles.
What is the difference between a nightmare and a night terror?
Nightmare is a long frightening dreams which wakes the subject during REM sleep.
Night terror is sudden arousal in stage 3 sleep marked by intese fear and autonomic activation
The length of a sleeping cycle is associated with?
Metabolic rate and size of animals.
Small animals with high metabolic rate have short sleeping cycles and vice versa
As we grow older we sleep …
Less.
Less overall sleep, less REM sleep, and more brief awakenings
What is the importance of Stage 3 sleep?
Secretion of growth hormone.
Lack of stage 3 sleep is associated with coginitive deficits
What is the primary feeling and consequence of sleep deprivation?
SURPRISE!
You feel sleepy
What are the actual consequences of sleep deprivation?
Irritability, difficulty in concentrating, and episodes of disorientation.
Hallucinations in severe cases
Does getting too little sleep for a given amount of time eventually yield the same consequences as total sleep deprivation?
Yes and no, they may yield some similar consequences as this pattern can be sustained longer than total sleep deprivation. Studies of airline employees showed deficits in cognitive tasks and reduced volume of the temporal lobe compared to controls.
Total sleep deprivation in long periods is fatal as it compromises the immune system and yields thalamic degeneration.
What are the four major functions of sleep proposed?
Energy conservation, Niche adaptation, body restoration, and memory consolidation.
What is meant by Niche adaptation?
The circadian rhythm is adapted to the animals ecological niche. Meaning the unique assortment of environmental opportunities and challenges to which the animals has adapted. Eg. A mouse being nocturnal to hide from diurnal predators.
What is associated with body restoration?
Restoration of meterials used during waking, such as proteins. It helps ward against various forms of disease.
How was consolidation of memory studied? And what is the general conclusion on the studies?
Various behavioral studies testing declarative memory has been made. In general subjects get taught something before bed time and then the next day they get tested. These are then compared to a group who was taught during the early day and tested later in the afternoon.
Generally the before bedtime groups showed a larger effect suggesting that sleep contributes to stronger memory. In this case it is particularly stage 3 sleep that consolidates memory
Which parts of the forebrain are important for what aspects of sleep?
SWS in the cortex for the forebrain is generated by the basal forebrain as shown by electrical stimulation of that area. Gaba-a receptors from tuberomammillary nucleus in posterior hypothalamus seem to induce slow waves in the EEG.
Which parts of the brainstem are important for what parts of sleep?
The brainstem generally promotes wakefulness and alertness but also REM sleep.
The reticular formation, specifically the pons, has axons which project towards the brain and activates it. Lesions here will produce constant sleep states.
ventral to the locus coeruleus is an area with axons projecting towards the spinal cord. This area inhibits motoneurons thus promoting the limp muscle state in REM sleep. This is the Pontine REM Sleep Center
What is the Hypothalamic sleep center?
A region in the hypothalamus, including neurons that use hypocretin as a neurotransimtter, sends axons to the other three sleep centers and seems to coordinate them, enforcing the patterns of sleep. Loss of hypocretin can lead to disorganized sleep, such as REM-like muscle atonia while still awake (in narcolepsy)
What causes narcolepsy?
Malfunctioning of hypocretin receptors. Losing hypocretin neurons seem to cause innapropriate activation of the cataplexy pathway. It keeps sleep at bay and prevents transition from wakefulness directly to REM sleep.
