Sleeping and Biological Rhythms Flashcards
What happens electrically when a neuron fires?
Positive current flows into the dendrite leaving the extracellular fluid around dendrite slightly negative. The positive current then escapes at deeper parts of the neuron leading to slightly positive extracellular fluid there.
What do EEGs measure?
EEGs measure the change in voltage through thick layers of tissue
What role does synchronization play in EEG signals?
When neuron responses are synchronized, the EEG signals are much larger than if unsynchronized.
Beta activity
High frequencies with low amplitudes
EEG characteristics of a waking state
EEGs are desynchronized, with beta activity
What frequency are alpha rhythms?
8-13 Hz
EEG characteristics of Stage 1 sleep
Alpha rhythms appear during relaxation and sharp waves called vertex spikes appear during stage 1.
What frequency are sleep spindles?
12-14 Hz
K-complexes
Sharp negative EEG potential
EEG characteristics of Stage 2 sleep
Brief periods of sleep spindles and K complexes
Delta waves
The slowest type of EEG waves, with a frequency of 1 Hz
EEG characteristics of Stage 3 Sleep
Also know as slow wave sleep (SWS), it’s characterized by long and slow delta waves
EEG characteristics of REM sleep
EEG activity resembles waking activity despite deep muscle relaxation
What happens to REM sleep as the night goes on? (in a young adult)
REM sleep gets longer
What happens to SWS as the night goes on? (in a young adult)
We lose stage 3 sleep
Name two things that occur in the body during non-REM sleep
- Heart rate and respiration have a slow decline
- Brain temperature is decreased
- Cerebral blood flow is reduced
- Knee jerk reflex is normal
- Eye movements are infrequent, slow, and uncoordinated
- Thoughts are mostly vague with occasional dreams
- High growth hormone secretion
Name two things that occur during REM sleep.
- Heart rate and respiration are variable with high bursts
- Brain temperature is increased
- Cerebral blood flow is high
- Knee jerk reflex is suppressed
- Eye movements are rapid and coordinated
- Vivid dreams
- Low growth hormone secretion
How is sleep different in marine mammals?
One hemisphere is used for slow wave sleep and the other is used for REM sleep
How do sleep time and body size correlate?
In herbivores, the larger animals such as elephants sleep less while smaller ones like voles sleep more.
Carnivores sleep on average the same amount regardless of size
What does human sleep look like early in life?
We spend almost all the day sleeping, with half of it in REM sleep.
What does human sleep look like later in life?
We sleep about 8 hours a night with 20% of that spent in REM.
What does sleep look like in elderly people?
They wake up frequently, and have a severe reduction in slow wave sleep.
How did people perform on a memory retrieval test when exposed to an odor during SWS and testing?
People who did the test while re-exposed to the odor did better at recalling object locations.
What effects do anesthetics have on GABA receptors?
All anesthetics are some degree of agonist for GABA
What effects do anesthetics have on glutamate receptors?
Anesthetics antagonize glutamate receptors
What effect on sleep is seen when the brain is cut at the level of the lower brainstem?
Normal sleep patterns with wakefulness, SWS, and REM are seen. This means systems controlling sleep are found in the brain.
What effect on sleep is seen when the brain is cut at the level of the midbrain?
A constant SWS is exhibited, showing that the forebrain system promotes SWS while the brainstem facilitates REM and wakefulness.
What role does the basal forebrain play in sleep
It releases GABA onto the hypothalamus to promote SWS
What role does the brainstem play in sleep
The brainstem contains the reticular formation which is an arousal system
What role does the subcoeruleus play in sleep
The subcoerulus sends projections to promote REM sleep
What role does the medulla play in sleep
Medullary axons projecting to the spinal cord inhibit motor neurons which causes muscle atonia in sleep
What role does the hypothalamus play in sleep
Sends axon to other sleep centers to enforce patterns of sleep using the neurotransmitter hypocretin
Diurnal
Active during the light
What pattern of activity do hamsters usually have?
Active during the night; nocturnal
What happens to a hamster’s activity when a phase shift occurs?
The hamster showed a phase shift of activity, becoming active later as the lights turned off later.
What happens to a hamster’s activity when it’s placed in constant dim light?
The hamster becomes active a few minutes later in the day, indicating an endogenous clock with a period slightly longer than 24 hours.
Where is the suprachiasmatic nucleus located?
In the hypothalamus, above the optic chiasm and next to the 3rd ventricle
What happens when SCN cells are isolated?
The cells show an activity with a ~24 hour rhythmicity
What happened in hamsters when the SCN was lesioned in light/dark conditions?
The hamster still was more active when the lights weren’t on
What happened in hamsters when the SCN was lesioned in continuous dim light?
The hamster had a completely random activity, indicating the elimination of the endogenous rhythm.
Zeitgeber
A stimulus that entrains circadian rhythms
What happens when you transplant SCN cells with a different circadian rhythm into a lesioned SCN?
The hamster with a lesioned SCN will adopt the circadian rhythm of the transplanted SCN.
Pineal gland
The source of melatonin release, and a structure sensitive to light in some animals
Melanopsin
A photopigment that causes retinal ganglion cells to be sensitive to light
What type of light are retinal ganglion cells most sensitive to
Blue light
Which two proteins bind together to form a dimer
Clock and Cycle
Where are the Clock and Cycle proteins made
SCN
What does the Clock/Cycle dimer bind to
It binds to DNA and enhances the transcription of Period (per) and Cryptochrome (Cry) genes
When per and cry bind together, what do they inhibit?
The Clock/Cycle dimer
What is the result of inhibiting the Clock/Cycle dimer?
Transcription of the per/cry genes are slowed, which slows production of the Per and Cry proteins
What happens when Per/Cry protein production is slowed
The Per/Cry proteins start to break down
What role does glutamate play in the molecular clock
Glutamate is released onto neurons in the SCN which amplifies transcription of per/cry proteins and entrains us to a 24 hour clock instead of our endogenous one
Infradian
A biological rhythm with a period longer than a day, such as the menstrual cycle
Circannual
A biological rhythm that runs on a yearly basis, with a mechanism separate from the SCN
Ultradian
A biological rhythm with a period shorter than a day
EOG
Electrical recording of eye movements
EMG
Electrical recording of muscle activity
What is the circadian rhythm of cortisol?
Higher in the morning and higher when you go to sleep
Explain how a two neuron oscillator works
The first neuron excites an inhibitory second neuron which acts on the first neuron
What causes the rhythm in a two neuron oscillator
Excitation of the inhibitory neuron leads the first neuron to stop firing, which stops the inhibition. The first neuron then fires again until the excitation on the inhibitory neuron stops the first neuron again
What is observed in voltage recordings of neuron oscillators during sleep
Even when a short (>0.1 second) pulse of a stimulus current is fired, the neuron responded with 2 seconds of rhythmic firing
