lecture 25 - anya hurlbert Flashcards
what is sleep
readily reversible state of diminished responsiveness to and interaction with the environment
how is it different to coma or general anaesthesia
coma or general anaesthesia are not readily reversible
the drive to sleep is governed by…
circadian rhythm
sleep pressure
circadian drive is high in the morning and starts to fall towards evening (the drive to stay awake) whereas…
the sleep drive builds up during the day and becomes higher and higher
what is building up during the day
adenosine
adenosine is part of…
ATP
adaptational purposes of sleep
hides organism when vulnerable
conserves energy
regulatory purposes of sleep
thermoregulation (cooling of the brain)
metabolism regulation
restorative purposes of sleep
emotions
mental health
growth (increased protein and RNA synthesis)
immune system
cognition
consolidation of learning and memory
consolidation of learning and memory
- slow wave sleep transfers learning from hippocampus to cortex
- REM sleep consolidated memories in cortex
medial temporal cortex neurons in rats fire most actively at night
this is involved in…
consolidation of memories
during sleep protein synthesis increases
this strengthens synapses
as proteins are being made that make synaptic changes permanent
behavioural evidence
learning occurs more effectively after a good nights sleep
stages of sleep
REM sleep:
- rapid eye movement (25% of total sleep time)
- duration increases through night
non REM sleep
- 75% of total sleep time
- stage 1 (few minutes, lightest sleep)
- stage 2 (5-15 minutes, deeper)
- stage 3 (up to 30 mins, absent towards morning)
- stage 4 (up to 40 mins, deepest sleep)
measuring brain rhythms with EEG (electroencephalography)
EEG measures synchronised electrical activity of neurones in the brain (primarily pyramidal cell neurones)
EEG record is characterised by amplitude and frequency
recorded from scalp electrodes, only thing that gets up to the electrodes that are sitting on the brain is activity that’s strong enough to make it through different media (that will be activity that represents synchronised activity of many thousands of neurones)
in the awake state what is observed on an EEG
brain waves of very small amplitude and mostly irregular high frequency (called beta rhythms)
when are alpha rhythms seen
when you’re awake but your eyes are closed and you’re relaxing
they are more regular and have higher amplitude
awake, eyes closed
alpha, 8-12 Hz, low voltage
REM sleep
beta, 14-150 Hz, low voltage
stage 1: falling asleep, lightest sleep
theta, 4-7 Hz, high voltage
stage 2: deeper sleep
theta, K complexes (high amplitude, sharp from cortex) and spindles (bursts of 8-14Hz oscillations, from thalamus)
stage 3 and 4: deepest sleep
delta, 1-4 Hz, high voltage
EOG (eye movement)
non-REM:
no eye movements at all
REM:
look like eye movements in awake state
sensations
awake - vivid, externally generated
non-REM - dull, absent
REM - vivid, internally generated (dreams)
thoughts
awake - logical, progressive
non-REM - logical, perseverative (round and round)
REM - illogical, bizarre
movement
awake - continuous, voluntary
non-REM - episodic, involuntary
REM - inhibited: none except eye movements
alternation between what two different neurotransmitter systems governs the change in brain rhythms
ascending reticular activating systems (RAS) and the pontine reticular formation (PRF)
RAS
set of noradrenergic neurons in the locus coeruleus
and serotonergic neurons in the raphe nucleus
alternate in activity with
cholinergic neurones in the pons and the basal forebrain
these two different NT systems project to the…
thalamus (gateway to the cortex)
neuromodulatory systems
core system consists of small number of neurons each contacting more that 100,000 neurons spread widely across the brain
most neurones arise from the central core of the brain
synapses release neurotransmitter into extracellular fluid so that transmitter can diffuse to many neurons not just across synaptic cleft
systems use NE, 5HT, ACh, DA (all activate metabotropic receptors)
modular activity of neurons making them more or less excitable or synchronous
the NE diffuse modulatory system.
arises from locus coeruleus cluster of cells in the pons
send outputs to multiple areas in the brain
regulates attention, arousal, sleep-wake cycle
the 5HT diffuse modulatory system
arises from raphe nuclei (various clusters running down the brainstem)
projects all around the brain
regulates attention, arousal, sleep-wake cycle
the ACh diffuse modulatory system
regulate wakefulness
arises from the pontomesencephalotegmental complex (dont need to remember) in the brainstem
the activity of the neurones in the clusters in the pons oscillates at the same time as…
REM and non-REM stages
as REM sleep end, activity ________ in NE neurones and 5HT neurones and then ______ as non REM sleep begins
increases
decreases
as REM sleep enters, activity _____ in ACh neurones in the pons
increases
the cholinergic neurones block…
the thalamus from setting up slow wave sleep
by blocking burst mode of thalamic relay cells
when signals come through the thalamus, the thalamus can either be in transmission mode where a the signal is passed to the cortex (awake or REM).
or can be in burst mode and sends little bursts of AP separated by long interval which creates a low frequency brain wave.
the ACh will block that burst mode and enable it to be in transmission mode and makes the brain look like its awake, any signal that comes up from the thalamus to the brain are perceived as real stimuli even if they’re internally generated
the biological clock is located in the…
suprachiasmatic nucleus of the hypothalamus (SCN)
receives direct input from retina for adapting to dark/light cycles
this then regulates the timing of which hormone
melatonin released from the pineal gland which in turn feeds back to SCN to reduce its activity
melanopsin containing intrinsically photosensitive retinal ganglion cells (ipRGCs)
they respond directly to light through their pigments in their membranes
the pigments are most sensitive to short wavelength light (blue light, 480nm)
project to SCN
exposure to 2 hours of 480nm light (blue) at night time suppresses melatonin and sleepiness more than exposure to 550 light (green) or darkness
the SCN is periodic in its firing
it contains clock genes that determines its periodicity
during sleep the hippocampus and the cortex replay events that happened during the day.
hippocampus generates sharp waves and ripples, similar to cortical K complexes
the active system consolidation hypothesis
during non REM reactivation and redistribution of hippocampus dependent memories to neocortical sites (coordinated by slow oscillations, spindles and ripples)
synaptic consolidation of memories in cortex, via local increases in plasticity related immediate early gene activity, during REM
