Neurobiology of Sleep & Rhythms Flashcards
(41 cards)
1
Q
Endogenous circannual rhythm
A
-Self-generated rhythm that lasts about a year
2
Q
Endogenous circadian rhythm
A
-Self-generated rhythm that lasts about a day
3
Q
Zeitgeber
A
- Stimulus that resets the circadian rhythm
- Zetigeber means “time giver”
- Light is by far the most dominant zeitgeber for land animals, and tides for marine animals
- Other zeitgebers include exercise, arousal of any kind, meals, and the temperature of the environment
4
Q
Jet lag
A
- A disruption of circadian rhythms due to crossing time zones
- Travelers complain of sleepiness during the day, sleeplessness at night, depression, and impaired concentration
- All these problems stem from the mismatch between internal circadian clock and external time
5
Q
Phase-delay vs phase-advance
A
- Phase-delay refers to jet lag, when we go from east to west. We stay awake later at night at night and then awaken late the next morning, already partly adjusted to the new schedule (most people find this easier)
- Going from west to east, we phase-advance to sleep earlier and awaken earlier. Most people find it difficult to go to sleep before their body’s usual time and difficult to wake up early the next day
6
Q
Suprachiasmatic nucleus (SCN)
A
- Although cells throughout the body generate circadian rhythms, the main driver of rhythms for sleep and body temperature is the suprachiastmatic nucleus (SCN)
- The SCN generates circadian rhythms itself in a genetically controlled manner. If SCN neurons are disconnected from the rest of the brain or removed from the body and maintained in tissue culture, they continue to produce a circadian rhythm of action potentials
- The SCN is between the optic chiasm (above it) and the hypothalamus
- The SCN is a part of the hypothalamus
7
Q
Retinohypothalamic path
A
- A small branch of the optic nerve, from the retina to the SCN, alters the SCN’s settings
- Most of the input to this path, however, does not come from normal retinal receptors
- The retinohypothalamic path to the SCN comes from a special population of retinal ganglion cells that have their own photopigment, called “melanopsin”, unlike the ones found in rods and cones
- They respond to light slowly and turn off slowly when the light ceases, therefore they respond to the overall average amount of light, not to instantaneous changes in light
- The average intensity over a period of time is exactly the info the SCN needs to gauge the time of day
- These ganglion cells respond mainly to short-wavelength (blue) light, which is why exposure to tv, phones, and compute screens tends to phase-delay the circadian rhythm and make it difficult to fall asleep at the usual time
8
Q
How does light reset the biological clock?
A
-A branch of the optic nerve, the retinohypothalamic path, conveys information about light to the SCN. The axons comprising that path originate from special ganglion cells that respond to light by themselves, even if they do not receive input from rods and cones
9
Q
The biochemistry of the circadian rhythm
A
- Mammals have 3 version of the PER protein (period protein) and several proteins closely related to TIM (timeless protein) and others found in flies
- The concentrations of these two proteins, which promote sleep and inactivity, oscillates over a day, based on feedback interactions among neurons
- In the morning, the messenger RNA levels responsible for producing PER and TIM start at low concentrations
- As they increase during the day, they increase synthesis of the proteins, but the process takes time, and so the protein concentrations lag hours behind
- As the PER and TIM protein concentrations increase, they feed back to inhibit the genes that produce the mRNA molecules
- Thus, during the night, the PER and TIM concentrations are high, but the mRNA concentrations are declining
- By the next morning, PER and TIM protein concentration levels are low, the flies awaken, and the cycle is ready to start again
10
Q
How do the proteins TIM and PER relate to sleepiness in Drosophila?
A
- The proteins TIM and PER remain low during most of the day and begin to increase toward the evening
- They reach high levels at night, promoting sleep
- They also feed back to inhibit the genes that produce them, so that their level declines toward morning
11
Q
Melatonin
A
- The SCN regulates waking and sleeping by controlling activity levels in other brain areas, including the pineal gland, an endocrine gland located just posterior to the thalamus
- Melatonin is released by the pineal gland, mostly at night
- In diurnal animals like humans, it increases sleepiness
- In nocturnal animals, it increases wakefulness
- In addition to regulating sleep and wakefulness, melatonin also helps control the onset of puberty and bodily adjustments to changes of season (such as hibernation)
12
Q
Electroencephalograph (EEG)
A
-Records electrical activity of the brain through electrodes attached to the scalp, ranging from just a few to more than a hundred
13
Q
Sleep vs coma
A
- Sleep is a state that the brain actively produces, characterized by decreased activity and decreased response to stimuli
- In contrast, coma is an extended period of unconsciousness caused by head trauma, stroke, or disease
- Someone in a coma has a low level of brain activity and little or no response to stimuli
14
Q
Vegetative state
A
-Someone in a vegetative state alternates between periods of sleep and moderate arousal, although even during the more aroused state, the person shows no awareness of surroundings and no purposeful behaviour
15
Q
Minimally conscious state
A
-Is one state higher than a vegetative state, with brief periods of purposeful actions and a limited amount of speech comprehension. A vegetative or minimally conscious state can last for months or years
16
Q
Brain death
A
-Is a condition with no sign of brain activity and no response to stimulus
17
Q
Polysomnograph
A
-A combination of EEG and eye-movement records
18
Q
Alpha waves
A
-A steady series of brain waves at a frequency of 8-12 per second that are characteristic of relaxation, not necessarily of all wakefulness
19
Q
Stages of sleep
A
Stage 1 sleep
- Jagged, low voltage waves
- Brain activity is less than in relaxed wakefulness, but higher than in other sleep stages
Stage 2 sleep
-Prominent characteristics of stage 2 are K-complexes and sleep spindles
Stage 3 and 4 sleep
- AKA slow-wave sleep (slow waves indicate that neuronal activity is highly synchronized)
- Heart rate, breathing, and brain activity decrease
- Slow, large amplitude waves become more common
- Difference is that stage 3 has fewer slow waves and stage 4 has more of them
- When you fall asleep you start in stage 1 and slowly progress to stage 2 and then into slow-wave sleep. After about an hour of sleep, you begin to cycle from slow-wave sleep back to stage 2 and then REM
- The sequence repeats, with each cycle lasting about 90 minutes
-Early in the night, slow-wave sleep predominates. As time passes, REM occupies an increasing percentage of the time
20
Q
K-complexes
A
-Is a sharp wave associated with temporary inhibition of neuronal firing
21
Q
Sleep spindle
A
- Is a burst of 12-14 Hz waves for at least half a second
- Sleep spindles result from oscillating interactions between cells in the thalamus and the cortex
- Sleep spindles increase in number after new learning, and the number of sleep spindles correlates positively with improvements in certain types of memory
- Sleep spindles represent activity related to the consolidation of memory
22
Q
What do large, slow waves on an EEG indicate?
A
-Large, slow waves indicate low levels of activity, with much synchrony of response among neurons
23
Q
Paradoxical sleep
A
-Sleep that is deep in some ways and light in others
24
Q
Rapid eye movement sleep (REM)
A
- Synonymous with “paradoxical sleep”
- During REM, the EEG shows irregular, low-voltage fast waves that indicate increased neuronal activity. In this regard, REM sleep is LIGHT, and similar to stage 1 except for the eye movements
-However, the postural muscles of the body, including those that support the head, are more relaxed during REM than other stages. In this regard, REM is DEEP SLEEP
- REM is also associated with erections in males and vaginal moistening in females
- Heart rate, blood pressure, breathing rate, and facial twitches fluctuate during REM more than in other stages
-The amount of REM depends on time of day more than how long you have been asleep. That is, if you go to sleep later than usual, you still increase your REM at about the same time that you would have ordinarily
25
Non-REM (NREM) sleep
-The stages other than REM
26
Reticular formation
-A cut through the midbrain decreases arousal by damaging the reticular formation, a structure that extends from the medulla into the forebrain
27
Pontomesencephalon
- One part of the reticular formation that contributes to cortical arousal
- These neurons receive input from many sensory systems and also generate activity of their won, varying with circadian rhythms
- Their axons extend into the forebrain
- Axons from some of the cells release GABA, which inhibits or interrupts behaviour and promotes slow-wave sleep
-Axons from other cells release acetylcholine, glutamate, or dopamine, producing arousal in the hypothalamus, thalamus, and basal forebrain
28
Locus coeruleus
- A small structure in the pons, is usually inactive, especially during sleep, but it emits bursts of impulses in response to meaningful events, especially those that produce emotional arousal
- Axons from the locus coeruleus release norepinephrine widely throughout the cortex, so this tiny area has a huge influence
- Output from the locus coeruleus increases what engineers call "gain" --> That is, it increases activity of the most active neurons and decreases the activity of the less active neurons --> The result is enhanced attention and memory
29
Orexin or hypocretin
- Orexin is released from a pathway from the lateral and posterior nuclei of the hypothalamus
- The axons releasing orexin extend from the hypothalamus to the basal forebrain and many other areas, enhancing wakefulness and activity
- Orexin is not necessary for waking up, but it is for STAYING awake
30
Basal forebrain
- Area anterior and dorsal to the hypothalamus
| - Includes cell clusters that promote wakefulness and sleep
31
How do we remain unconscious during sleep in spite of sustained neuronal activity?
- The answer is inhibition
- During sleep, axons that release the inhibitory neurotransmitter GABA increase their activity, interfering with the spread of information from one neuron to another
- Connections from one brain area to another become weaker
32
PGO waves
- Pons-geniculate-occipital waves
- A distinctive pattern of high-amplitude electrical potentials that occur first in the pons, then in the lateral geniculate nucleus of the thalamus, and then in the occipital cortex
- Each PGO wave is synchronized with an eye movement in REM sleep
- REM sleep is associated with these
33
Sleep apnea
- Is one type of insomnia, which is impaired ability to breathe while sleeping
- People with sleep apnea have breathless periods of a minute or so from which they awaken gasping for breath
34
What kinds of people are most likely to develop sleep apnea?
-Is most common among people with a genetic predisposition, old people, and overweight middle-aged men
35
Narcolepsy
- A condition characterized by frequent periods of sleepiness during the day
- People with narcolepsy lack the hypothalamic cells that produce and release orexin
Has 4 main symptoms:
1. Attacks of sleepiness during the day
2. Occasional cataplexy - an attack of muscle weakness while the person remains awake. Cataplexy is often triggered by strong emotions
3. Sleep paralysis - an inability to move while falling asleep or waking up
4. Hypnagogic hallucinations - dreamlike experiences that the person has trouble distinguishing from reality, often occurring at the onset of sleep
36
Periodic limb movement disorder
- Another sleep disorder characterized by repeated movement of the legs and sometimes the arms during sleep
- With this disorder, the legs kick once every 20-30 seconds for minutes or hours, mostly during NREM sleep
37
REM behaviour disorder
-A sleep disorder where people move around vigorously during their REM periods, apparently acting out their dreams
38
What are some functions of sleep?
- We rest our muscles
- Decrease metabolism
- Perform cellular maintenance in neurons
- Reorganize synapses
- Strengthen memories
39
How does weakening synapses during sleep improve memory?
-Weakening the less active synapses enables the strengthened ones to stand out by contrast
40
Activation-synthesis hypothesis
- According to this activation-synthesis hypothesis, a dream represents the brain's efforts to make sense of sparse and distorted information
- Dreams begin with periodic bursts of spontaneous activity in the pons - the PGO waves previously described - that activate some parts of the cortex but not others
- The cortex combines this haphazard input with whatever other activity was already occurring and does its best to synthesize a story that makes sense of the information
41
Neurocognitive hypothesis
- The neurocognitive hypothesis regards dreams as thinking that takes place under unusual conditions
- It emphasizes that dreams begin with spontaneous brain activity related to recent memories
-According to this hypothesis, dreams originate mostly from the brain's own motivations, memories, and arousal. This stimulation often produces peculiar results because it does not have to compete with normal visual input and does not get organized by the prefrontal cortex
