Chapter 14: Biological Rhythms, Sleep, and Dreaming Flashcards
What is an example of a short rhythm?
Pacemaker cells in the heart
What is an example of a long rhythm?
Seasonal cycles (circannual rhythms)
Circadian Rhythms
A pattern of behavioral, biochemical, or physiological fluctuation that has a 24-hour period.
What is NOT TRUE about circadian rhythms?
The light/dark cycle can influence them.
What is true about a TRUE circadian rhythm?
It is independent and cannot be influenced.
Free Running
An animal maintaining a circadian rhythm without external cues.
What are example of external cues in free running?
- Outside noises
- Temperature
- Barometric Pressure
Phase Shift
A shift in activity of a biological rhythm, provided by a synchronizing environmental stimulus.
Synchronizing Stimulus
A signal that can cause people to temporarily align their movements/brain activity.
Entertainment
The process of synchronizing a biological rhythm to an environmental stimulus.
Zeitgeber
The external cue that an animal uses to synchronize its activity with the environment.
What is the Zeitgeber also known as?
The “time giver”
What is an example of a zeitgeber?
Light
What do circadian rhythms provide in connection to animal behavior?
Temporal organization
Suprachiasmatic Nucleus (SCN)
A small region in the hypothalamus above the optic chiasm that sets the circadian rhythm.
Explain the hamster experiment in relation to the SCN.
- Hamsters that had damage to the SCN were placed in constant conditions, causing their natural rhythms to be completely disrupted.
- The hamsters received transplants of SCN tissue from fetal hamsters with the same tau mutation.
- After a week, the transplanted hamsters started showing a new rhythm. However, this rhythm was shorter than the usual 24 hour cycle, which matches those of the donor hamsters SCN.
What happened to the hamsters that had the tau mutation in a gene?
They usually had short circadian rhythms.
What provides evidence for the SCN to be an endogenous rhythm maker?
The hamster experiment
What do most vertebrates have outside their eyes?
Photoreceptors that are associated with circadian rhythms.
What is an example of photoreceptors being outside the eye?
The pineal gland in amphibians is sensitive to light.
What type of cells do mammals have in their eyes?
Cells that provide light/dark information to the SCN
What do the special ganglion cells do?
Form the retinohypothalamic pathway due to the presence of melanopsin.
Melanopsin
A photopigment found in some retinal ganglion cells that project to the suprachiasmatic nucleus.
Retinohypothalamic Pathway
The projection of retinal ganglion cells to the suprachiasmatic nuclei.
Explain how the SCN has an endogenous rhythm in relation to fruit flies.
- Fruit flies display diurnal circadian rhythms in activity.
- Flies with a mutation that disabled the gene called per were arrhythmic when transferred to a constant dim light.
= internal clock is not running
What is the importance of the fruit fly experiment?
It was discovered that mammals have mechanisms that underly SCN circadian rhythms due to similar genes in fruit flies.
What do SCN related genes in flies and mice provide?
A molecular clock, regulating a 24-hour expression based off of protein products working together.
What two proteins do cells in the SCN make?
Clock and Cycle
Explain the process of genes in the SCN.
- Two proteins, Clock and Cycle, bind together to form dimer.
- The Clock/Cycle dimer binds to the DNA, enhancing the transcription of the genes for Per and Cry.
- Per and Cry bind together as a complex that inhibits the activity of the Clock/Cycle dimer.
= Slows production of Per and Cry genes, and production of Per and Cry proteins. - The Per/Cry proteins eventually break down/modified so they no longer inhibit the Clock/Cycle, allowing the process to start again. (process takes 24)
- Retinal ganglion cells detect light with melanopsin, and their axons in the retinohypothalamic tract release glutamate onto neurons in the SCN. The glutamate stimulation leads to increased transcription of the Per gene
= Synchronized molecular clock to the day/night schedule.
What can mutations in the SCN genes cause?
Issues to circadian rhythms
Dimer
A complex of two proteins that have bound together.
What happens when there is a mutation to the Clock gene?
The mouse is able to maintain rhythm until it is in dim light. After 27 hours it completely loses rhythm but an ultradian rhythm remains.
What causes some people to be night owls/early birds?
Different alleles (version) of Clock or Per gene
What can we take away from time zones?
Light still entrains humans
Ultradian Rhythms
Frequency is greater than once/day
What is an example of ultradian rhythms?
The basic rest activity cycle in humans
- about 90 minutes
Infradian Rhythms
Frequency is less than once/day
What is an example of infradian rhythms?
The menstrual cycle (humans and apes) or estrous cycle (other mammals)
Circannual Rhythms
Frequency is about a year
What can affect circannual rhythms?
Light
What are circannual rhythms not dependent on?
SCN
What is the most prominent circadian rhythm?
The sleep/wake cycle
How long does the free running sleep/wake rhythm last?
About 25 hours in humans.
What 3 tests can help investigate sleep in humans?
- EEG
- EMG
- EOG
EEG
The recording and study of gross electrical activity of the brain recorded from large electrodes placed on the scalp.
What does an EEG indicate?
An “awake” brain as musculature is relaxed/limp
EMG
The electrical reading of muscle activity. -
EOG
The electrical recording of eye movements.
What are the 5 stages of sleep?
Awake
1. NREM
2. Basic alpha rhythm
3. Slow wave sleep (SWS)
4. REM
Rapid-Eye Movement Sleep (REM)
A stage of sleep characterized by small amplitude, fast EEG waves, no postural tension, and rapid eye movements.
What is REM sleep also known as?
Paradoxical sleep
Non-REM (NREM) Sleep
Sleep without rapid eye movements.
What is NREM sleep divided into?
Stages 1, 2 and 3 of sleep
Awake Stage
EEG is out of its usual patten
- 15 to 20 Hz and low amplitude
Stage 1: NREM
- 8 to 12 Hz activity (alpha rhythm)
- Vertex spikes (sharp spikes in EEG)
- “Hypnic Jerks”
“Hypnic” Jerks
People can experience the sensation of falling and jerk into wakefulness
Stage 2: Basic Alpha Rhythm
- Sleep spindles
- K complexes
Sleep Spindles
12-14 Hz bursts that occur periodically
K Complexes
Sharp negative EEG potentials
What happens when people are awoken in stages 1 or 2 of NREM?
They will deny having been asleep.
Stage 3: Slow Wave Sleep (SWS)
- Delta waves
- Large amplitude and very slow waves (1 Hz)
Delta Waves
Widespread synchronized activity across the cortex