Chapter 13 Flashcards
1
Q
Biological rhythms
A
Biological basis of daily activities
- Many animals show daily rhythms (24-hour)
- Controlled by the CIRCADIAN CLOCK, an internal clock housed in the HYPOTHALAMUS which regulates the daily cycle
2
Q
Circadian rhythms - General
A
- definition: functions of a living organism (animal and plants) that display a rhythm of about 24 hours
+ 24 hours is a universal pattern because the Earth takes 24 hours to rotate around the sun -> experience only a specific amount of sunlight
+ enables animals to anticipate an event + help with survival, especially in new or unpredictable environment - rhythms may be:
+ behavioral: wake up in the morning, sleep at night
+ physiological: hormone release (cortisol, testosterone, melatonin)
+ PINEAL GLAND: single gland on top of brainstem, secretes an amine hormone, MELATONIN, almost exclusively at night (start: 6PM, peak: 12AM, end: 6AM) -> genetically predisposed procedure
+ Melatonin provides a signal that tracks day length
+ Seasonal change can bring melatonin imbalance -> sleep disorder
+ biochemical: cellular, nucleus, DNA, and protein levels - types:
+ DIURNAL: active during the light (e.g. humans)
+ NOCTURNAL: active during the dark (e.g. owls)
3
Q
Mechanism of circadian rhythms
A
- circadian rhythms are generated by an endogenous (internal) clock
- FREE-RUNNING: maintaining one’s own cycle with NO external cues (e.g. light) -> innate program tells when to rest or be active, cycle is ~24 hours but there are some errors
- PERIOD: time between successive cycles
- PHASE SHIFT: shift in activity in response to a synchronizing stimulus (e.g. light, food)
+ example: traveling overseas -> night/day cycle is flipped -> body adjusts to local time (jet lag)
4
Q
Example: Measuring circadian rhythms
A
- mice, which are highly domesticated lab animals, are put in a cage with a wheel
- mice = nocturnal -> become active at night -> run on wheels, rest in the morning
- experimenters track running activity
- experiment: keep lights on and turn them off on different cycle (e.g. 3 hours later than usual)
- mice experience phase shift under manipulation of constant daylight
+ disconnect: external stimuli vs. internal clock
+ internal = more important -> no longer go by a 24-hour cycle, won’t correspond to external environment
5
Q
Hypothalamus and the circadian clock
A
- biological clock is in SUPRACHIASMATIC NUCLEUS (SCN), which is located above the optic chiasm in the hypothalamus
- lesions in SCN -> disrupted circadian rhythms
- isolated SCN neurons can maintain electrical activity synchronized to the previous light cycle
- TRANSPLANT studies prove that endogenous period is generated in SCN -> SCN = internal clock
+ hamsters with SCN lesions (aka abolished circadian rhythms) receive SCN TISSUE TRANSPLANT from tau hamsters, mutated hamsters with a very short 20-hour period
+ hamsters now restore the circadian rhythms but match the shorter period of the donor
6
Q
Entrainment
A
- definition: process of shifting the rhythm
- circadian rhythms entrain to light/dark cycles using different pathways, some outside the eye
+ in mammals: light info goes from the eye to SCN via the RETINOHYPOTHALAMIC PATHWAY, which consists of retinal ganglion cells that project to SCN
+ ganglion cells do not rely on rods + cones but contain MELANOPSIN, a special photopigment that makes them sensitive to light, especially blue light
+ blue light triggers action potential -> sends signal to retinohypothalamic pathway -> stimulates + modulates circadian rhythms
+ axons of ganglion cells in the retinohypothalamic tract release GLUTAMATE, an excitatory neurotransmitter, onto neurons in SCN -> trigger modulation of circadian rhythm
7
Q
Molecular circadian clock
A
- SCN cells in mammals make 2 proteins: CLOCK and CYCLE
- CLOCK and CYCLE proteins bind -> form DIMER
- CLOCK/CYCLE DIMER promotes transcription of 2 genes: PERIOD (PER) and CRYPTOCHROME (CRY)
+ bind with transcription factors in non-coding region -> enhance transcription - Proteins arise from PER and CRY bind to each other
- The PER/CRY protein complex enters the nucleus and inhibits the transcription of PER and CRY genes
- No new proteins are made until the first set degrades; cycle begins approximately every 24 hours -> negative feedback
8
Q
Sleep - General
A
- different animals have different sleep periods (e.g. horses: 2 hours, humans: 8 hours, little brown bats: 20 hours)
+ plant-eaters: small animals sleep more than large ones in correlation with their normal high metabolic rate (bigger surface ratio)
+ predators: no difference between sizes, all tend to sleep much more than prey species
+ EXCEPTION: existence of people who hardly sleep at all but function normally + healthily
+ replace sleep = brief nap -> more EFFICIENT sleeper who demonstrate less STAGE 1 + 2 sleep -> lots of SWS (STAGE 3) + REM - REM sleep evolves in some vertebrates
+ most mammals and birds display REM + SWS -> evolutionary development?
+ UNILATERAL SLEEP in PARIETAL CORTEX: alternate cycle, 1 hemisphere = awake, 1 hemisphere = asleep (marine mammals - e.g. dolphins) - sleep = synchronized to external events, including light + dark
+ stimuli like light, food, job, and alarm clocks entrain us to be awake or to sleep
+ absence of cues -> free-running period of approximately 25 hours, vary with age
+ gradual shift after loss of cues, but go back immediately upon seeing stimulus again
9
Q
Measures for human sleep
A
- electrical brain potentials = used to classify levels of arousal and states of sleep
+ ELECTROENCEPHALOGRAPHY (EEG) records electrical activity in the brain
+ EEG can tell activity but NOT location (which specific region is active) - ELECTRO-OCULOGRAPHY (EOG) records eye movements
+ certain stage of sleep can be tracked by eye movements - ELECTROMYOGRAPHY (EMG) tracks muscle activity
+ muscle = relaxed during sleep
+ procedure:
+ insert fine needle into muscle to be tested
+ muscle fiber that contracts will produce an action potential
+ presence, size, and shape of the wave form of the action potential are recorded
+ recordings are made while muscle = at rest, then during contraction
10
Q
2 classes of sleep
A
- SLOW WAVE SLEEP (SWS): can be divided into 4 stages and is characterized by slow-wave EEG activity
- RAPID-EYE-MOVEMENT (REM) SLEEP: characterized by small amplitude, fast-EEG waves, no postural tension (body = relaxed), and rapid eye movements (eyes = closed, move under lids)
11
Q
Awake state
A
- pattern of activity in an AWAKE person contains many frequencies:
+ dominated by waves of FAST FREQUENCY and LOW AMPLITUDE (15 - 20 Hz)
+ known as BETA ACTIVITY or DESYNCHRONIZED EEG
+ ALPHA RHYTHMS occur in relaxation, regular oscillation: 8 - 12 Hz - prominent EEG bands:
+ DELTA (0.5 - 4 Hz)
+ THETA (5 - 7 Hz)
+ ALPHA (8 - 12 Hz)
+ BETA (18 - 30 Hz)
+ GAMMA (30 - 50 Hz)
12
Q
Sleep stages
A
- WAKING: high frequency + low intensity waves
- STAGE 1 SLEEP: between awake and asleep
+ events of irregular frequency + amplitudes + sharp waves called VERTEX SPIKES
+ slow heart rate, reduced muscle tension, eye movement for several minutes - STAGE 2 SLEEP:
+ waves of 12 - 14 Hz occurring in bursts -> SLEEP SPINDLES - STAGE 3 SLEEP:
+ appearance of large amplitude, very slow waves -> DELTA WAVES, occur once/second - LATE STAGE 3/STAGE 4: DELTA waves dominate
- REM:
+ active EEG with small amplitude, high frequency waves like awake
+ muscles = relaxed, flaccid, and unresponsive
13
Q
REM sleep (Paradoxical sleep)
A
- sleep period during which brain activity resembles that of an awake person
+ mismatch conflict: sleep but brain is active
+ characteristics:
+ random movement of eyes
+ low muscle tone throughout the body
+ propensity of sleeper to dream vividly
-> PARADOXICAL SLEEP (PS) or DESYNCHRONIZED SLEEP: physiological similarities to waking states - rapid, low voltage DESYNCHRONIZED brain waves -> higher use of neurotransmitter ACETYLCHOLINE -> very important for learning + memory
14
Q
Sleep processes
A
- typical night for young adult:
+ time: 7 to 8 hours
+ 45 - 50% = STAGE 2 sleep, 20% = REM (vary w/ age -> older = less REM)
+ Cycle = 90 - 110 minutes BUT cycles EARLY in the night have MORE STAGE 3 SWS, LATER have more REM
+ REM increases as the night goes on
+ no identified reasons for why we need so many cycles - puberty: most people shift circadian rhythm so they get up later in the day
+ most high schools require adolescents to arrive earlier -> conflict -> later starts improve attendance + enrollment and reduce depression + in-class sleeping - sex difference: sleep is regulated by testosterone -> MALES have trouble waking up
+ however, sex difference goes away as we get older
15
Q
Dream
A
- vivid dreams occur during REM -> visual imagery, sense that dreamer = there
- NIGHTMARE: frightening dream that awakens the sleeper from REM, may lead to sleep walk
+ unclear reason BUT you’re conscious!
+ SLEEPWALK: reason = unknown, possible causes: stress, genetics (50% chance), addiction - NIGHT TERROR: sudden arousal from STAGE 3 SWS (DELTA WAVE SLEEP)
+ marks: fear + autonomic activity (scream, rapid heart rate, sweat) - BOTH may be stress (and therefore cortisol?) related
- REHEARSAL:
+ patterns of neuronal activity while task is being learned during wakefulness are RE-CREATED during subsequent SWS
+ use cue to REACTIVATE learning during SWS
-> learn during night -> sleep + dream about what you learned during the day - example: songbirds
+ experiment: track activity of individual neurons while zebra finches are both awake + sleeping
+ birds learn how to sing from tutors
+ electrodes are installed to record neural activity
+ birds learn song during sleep -> disrupt sleep = disrupt learning
+ neurons fire at precise time in HVC (RA) aka Broca’s area’s equivalent -> encode songs
+ brain cells of zebra finches fire in very similar pattern while sleeping and singing - example: rats running maze - groups of neurons in rats fire the same patterns while they try to learn to run a maze awake vs. asleep
16
Q
Sleep and age
A
- sleep patterns change across lifespan
+ mammals sleep more during infancy than in adulthood
+ infant sleep: shorter cycles, no clear circadian rhythms until 16+ weeks, more REM (50%) -> essential stimulation to develop nervous system, move directly from awake to REM
+ stable pattern does not consolidate until ~16 weeks because neurons are still developing - people age -> total sleep time declines, # of awakenings (conscious or unconscious) increases
+ most dramatic decline: LOSS OF TIME SPENT IN STAGE 3, deep sleep (important for learning + memory)
+ 60: half as much time spent in stage 3 as at 20, 90: none
+ less REM -> strongly correlated with brain development (cortex, synapse growth) -> needs more when you’re younger and growing
17
Q
Functions of sleep (1): REMOVE METABOLIC WASTE
A
- brain uses lots of energy -> produces CO2 -> gets rid of ~1.5 kg of waste/year
+ CO2 react with H2O -> turn into CO3 -> diffuse in blood
+ waste goes through circulatory system - Central nervous system (CNS) lacks lymphatic system:
+ LYMPHATIC SYSTEM: immune function, but also waste removal - available through out body but not at brain
+ solution: CIRCULATORY SYSTEM -> takes care of 70% waste, 30% to lymphatic
+ ELEPHANTIASIS: weak immune system from weak lymphatic system -> infection -> accumulation of metabolic waste in a body part -> “swollen” appearance - Cerebrospinal fluid (CSF) = waste removal sink, plumbing system
+ GLYMPHATIC system: functional waste clearance pathway for vertebrate CNS, traffics brain’s waste removal
+ ventricles = suspended with CSF -> soak brain
+ CSF has lots of MICROGLIA -> protect brain from pathogens, viruses, etc.
+ CSF surrounds and flushes through tissue + blood vessel during deep sleep -> clear out brain
+ amyloid b accumulates a lot -> affect brain health if not cleaned
+ when brain’s awake + busy -> delay waste clearance
18
Q
Functions of sleep (2): CONSERVE ENERGY
A
- sleep reduces: muscular tension, heart rate, blood pressure, temperature, and rate of respiration -> save energy
+ meat eaters use a lot of energy
+ small animals = very high metabolic rates -> when food = scarce, reduced activity = valuable - SLEEP DEPRIVATION: partial or total prevention of sleep
+ symptoms: increased irritability, difficulty in concentrating, episodes of disorientation
+ cannot remove metabolic waste
+ total deprivation: compromises immune system -> possible death
+ FATAL FAMILIAL INSOMNIA - inherited, midlife: stop sleeping and die 7 - 24 months after onset, autopsy: degeneration in cortex + thalamus (neuronal death)
+ effects of deprivation vary with age and other factors
19
Q
Functions of sleep (3): RESTORE BODY
A
- tired -> sleep -> restores body: replenishes METABOLIC REQUIREMENTS, materials used during waking (e.g. proteins)
- most growth hormones = released during SWS
- sleep helps resist illness
+ too little or too much -> affect health (disrupt circadian rhythm)
+ irregular sleep -> irregular hormonal release -> risk for different diseases, higher risk for cancer
20
Q
Functions of sleep (4): LEARNING + MEMORY
A
- sleep helps consolidate memory:
+ sleep during interval between learning and recall may reduce interfering stimuli (e.g. outside activities)
+ CANNOT learn new material while sleeping
+ SWS helps consolidate DECLARATIVE memory (can be stated or described - e.g. verbal learning)
+ REM helps consolidate NON-DECLARATIVE memory (e.g. motor processes - e.g. riding a bike, playing a piano) - example: memory consolidation in SWS:
+ subjects learn location of various objects on a computer screen while EXPOSED to odor
+ night: exposed to same odor during sleep (SWS or REM)
+ test next morning to see how much is memorized -> odor triggers stimuli
+ exposed to odor during SWS -> improved memory - example: learning + dreaming
+ people learn how to play computer game
+ go to bed -> awaken throughout the night and ask to reveal dream
+ dream = about computer game
+ lots of neural activity during sleep -> rehearsing daily life
+ forget dreams by morning
21
Q
Neural systems underlying sleep
A
- sleep = active state mediated by:
+ FOREBRAIN system: displays SWS
+ BRAINSTEM system: activates forebrain into wakefulness
+ PONTINE system: triggers REM sleep
+ HYPOTHALAMIC system: affects other 3 - GENERAL ANESTHETICS: cause unconsciousness by producing slow waves in EEG that resembles SWS
+ these are AGONISTS of GABA(A) receptors -> enhance opening of GABA receptors -> more Cl- ions out of cell -> cell = more positive -> inhibit neural firing + depolarization -> no action potential fired, gain sleep state
-> GABA promotes SWS?
22
Q
Transection experiments
A
- showcase that different sleep systems originate in different parts of brain
- ISOLATED BRAIN, or ENCEPHALE ISOLE: made by incision between medulla and spinal cord
+ uses razor blade to cut brain to see if animals can still function
+ monitor with electrode + EEG
+ cut central command -> cannot move -> animals die soon
+ animals show signs of wakefulness and sleep -> networks reside in brain -> sleep = controlled by brain - ISOLATED FOREBRAIN, or CERVEAU ISOLE: made by incision in midbrain
+ use razor to cut off communication between midbrain
+ electrical activity: constant SWS, not REM -> generated by BASAL FOREBRAIN which releases GABA and onsets sleep
+ animals are hardly wakeful -> forebrain alone can generate SWS
23
Q
Brain mechanisms underlying sleep
A
FOREBRAIN + RETICULAR FORMATION guide brain between SWS and wakefulness
1. BASAL FOREBRAIN: promotes SWS by releasing GABA into TUBEROMAMMILARY NUCLEUS in HYPOTHALAMUS
+ electrical stimulation -> animals = sleepy; lesions -> induce insomnia
2. BRAINSTEM has RETICULAR FORMATION: projects axons to the brain that activate it
+ electrical stimulation: promotes wakefulness + alertness; lesions -> produce constant sleep state
3. Near LOCUS COERULEUS -> REGION: sends widespread projections via axons that promote REM: to SPINAL CORD -> inhibit motoneuron firing -> no muscle contraction AND to BRAIN - activate other regions
+ lesions -> prevent loss of muscle tone during REM -> cats with lesions act out dreams/sleepwalk
4. REGION IN HYPOTHALAMUS: uses HYPOCRETIN = neurotransmitter and sends axons to other 3 sleep centers -> coordinate + enforce sleep pattern
+ loss of HYPOCRETIN -> disorganized sleep (e.g. REM-like muscle atonia while still awake)
24
Q
Narcolepsy
A
- hypothalamic sleep center disorder triggered by excitement
- symptoms:
+ frequent sleep attacks + excessive daytime sleepiness
+ do not go through SWS before REM
+ may show CATAPLEXY, sudden loss of muscle tone -> collapse - narcoleptic dogs: have mutant gene for HYPOCRETIN receptor
+ HYPOCRETIN regulates different SLEEP 3 stages, prevents transition from wakefulness directly into REM
+ interfering with hypocretin signaling -> narcolepsy - narcoleptic humans lose about 90% of their hypocretin neurons
+ neural degeneration -> loss of hypocretin-containing neurons in LATERAL HYPOTHALAMUS
+ hypocretin neurons in hypothalamus project to other sleep system centers (BASAL FOREBRAIN, RETICULAR FORMATION, LOCUS COERULEUS)
+ axons go to TUBEROMAMILLARY NUCLEUS inhibited by BASAL FOREBRAIN to induce SWS
+ hypothalamus contains hypocretin-based sleep center -> controls when we are awake, in SWS, or in REM sleep
