Lecture 26 Flashcards
Are circadian rhythms endogenous or exogenous?
Endogenous and persist without environmental cues
However they are modulated by external cues
What is an example of external cues?
Zeitgebers e.g. sun
They adapt the rhythm to the environment
What is the major internal clock?
Suprachiasmatic nucleus of anterior hypothalamus
- regulates TIMING of sleep but not sleep itself
What is the neurotransmitter that stimultates the syprachiasmatic nucleus?
glutamate (passes retinohypothalamic tract)
What happens when the suprachiasmatic nucleus has lesions?
Dampens down the circadian rhythm of sleep
How does the suprachiasmatic nucleus regulate the timing of sleep?
Nucleus tells you timing of waking up and falling asleep
Melatonin naturally accumulates until reaches a point where it sends a cue to fall asleep - used in sleeping medicine
How is sleep defined behaviorally?
Reduced motor activity
Reduced response to stimulation
Stereotypic postures (eye closed in humans)
Relatively easy reversibility
How can physiological activity be measured?
electrical readings
Muscle movements with electromyography
Eye movements with electro-oculography
Brain activity with electroencephalography
What does the electroencephalogram measure?
Synchronous, electrical activity from large populations of neurons in the brain
Caused by cellular, ionic movement, which creates an electrical field
Many millions of neurons, all of a similar “spatial orientation”
How is the electroencephalogram used?
Electrodes placed on the surface of the scalp detect these electric fields
Linked to an electrical amplifier (they are tiny electric fields) and to a motor
What are advantages of electroencephalogram?
Non invasive
Easy to administer
Data easily gathered
What are features of electroencephalogram?
High temporal resolution (milliseconds!)
“Event generated potential”
Low spatial resolution
Electric fields follow an inverse square law so only cortical activity detectable
Is the neuronal activity high or low during non-REM sleep?
Low - not much action potential firing between neurons
Is the metabolic rate and brain temperature high or low during non-REM sleep?
Lowest
Does heart rate and blood pressure increase or decrease?
decrease (decreased sympathetic nervous system outflow)
Increase in parasympathetic outflow dominates non-REM sleep - constricted pupils
How does non-REM sleep affect muscle tone and reflexes?
intact
What is the first stage of non-REM sleep?
Drowsiness
Awakened easily
Eyes move slowly and muscle activity slows
During this stage, many people experience sudden muscle contractions preceded by a sensation of falling
Transition from wakefulness to onset of sleep
- lasts several minutes
Awake people show low voltage EEG activity
(10-30 micro volts at 16-25 Hz)
As they relax - sinusoidal (alpha) activity 20-40 micro volts at 10 Hz
What shows in EOG during the first stage of non-REM sleep?
Eyes show slow, rolling movements
What shows in the EMG during the first stage of non-REM sleep?
During stage 1, and all non-REM, some muscular activity
What shows in EEG during the first stage of non-REM sleep?
Characterized by low-voltage activity if mixed frequencies
What is the second stage of non-REM sleep?
Light sleep
Eye movements stop and brain waves become slower with only an occasional burst of rapid brain waves
The body begins to prepare for deep sleep
Body temperature drops, heart rates slows
Characterized by bursts of sinusoidal waves called “sleep spindles” (12-14Hz) and biphasic waves called K complexes
What are K complexes?
Occur episodically against background of continuing low-voltage EEG activity
What is the third stage of non-REM sleep?
Deep sleep
Extremely slow delta waves are interspersed with smaller, faster waves
Sleepwalking, nigh terrors, talking during one’s sleep, and bedwetting, “parasomnia”
Occur during the transitions between non-REM and REM sleep
What is the last stage of non-REM sleep?
Very deep sleep
Brain produces delta waves almost exclusively
Disorientation for several minutes following arousal from stage 4
Slow wave activity increases and dominates the EEG record
What are stages 3 and 4 in humans called?
Slow wave sleep
Do all animals have fast wave and slow wave sleep?
no: for some animals all non-REM sleep is slow wave
What is the final stage of sleep?
REM sleep
What does EEG mimic during REM sleep?
Wakefulness! - low voltage mixed frequency
What can be observed during REM sleep?
Closed eyes move rapidly from side-to-side
Perhaps related to the intense dream and brain activity
How is REM sleep paradoxical?
REM - neuronal firing very like in wakefulness! Neurons in pons, lateral geniculate nucleus and occipital cortex fire in more intense bursts during REM than in wakefulness
Generates high-voltage spike potentials in EEG trace called ponto-geniculo-occipital spikes or PGO spikes
Where do PGO spikes originate from?
In the pontine reticular formation
Propagate through the lateral geniculate nucleus and on to the occipital lobe
How can PGO-type spikes be produced?
In alert subjects by startling them with an abrupt stimuli like a loud noise
What does the induction of PGO-type spike imply?
PGO of REM sleep may be activated by the same neural circuits that initiate the “startle response”
PGOs are also correlated with bursts of eye movements in REM sleep
- involves Superior colliculus to control eye movement
How does brain temperature and metabolic rate change during REM sleep?
Rises
Consistent with increased neural activity
In some areas - greater than in waking
How are the muscles in REM sleep?
Skeletal muscles are atonic (flaccid and paralyzed)
Muscles controlling movements of the eyes, middle ear ossicles, and diaphram remain active
Can breathe and hear an impending changes
Penile erections/Clitoral engorgement
Pupils highly constricted (miosis)
- parasympathetic system
Respiration is unresponsive to changes on blood pCO2
Responses to heat and cold reduced or even absent
- body temperature drifts toward ambient
Does sleep fit into a conitnuum from light to deep?
no
How can REM sleep be lighter sleep?
Arousal is easier than in Stage 3 or 4
How can non-REM sleep be lighter sleep?
Body temperature, muscle tone and reflexes are all maintained
After stage 4…
After 70-80 minutes, returns to stage 3 or 2 before entering first REM phase of the night which lasts 8-10 minutes
How long is one cycle from stage 1 to end of REM?
90-110 minutes
How many times is the sleep cycle repeated at night?
4 or 5 times
- during each repetition, stages 3 and 4 decrease in duration and REM increases
In young adults, how much of sleep time is spent in stage 1?
5%
What is the largest amount of sleep time?
Stage 2: 50-60%
How much does stage 3 or 4 constitute?
15-20%
How much does REM constitute?
20-25%
What are the functions of dreaming?
unknown
What are some theories regarding dreaming?
Occurred only in REM (from waking studies)
As high as 70% occur in non-REM sleep
Strange imagery: brain not fully functioning
Exercises synapses when no external activity
“circuit testing” “memory consolidation”
