NSCI 201 Circadian rhythms and sleep

what is considered endogenous circadian rhythms?

• sleep cycle

• frequency of drinking and eating

• body temp

• secretion of hormones

• urination

• sensitivity to drugs

Why do we have circadian rhythms?

• To keep our internal workings in phase with the outside world

• if there were no external cues, the human circadian rhythm would be slightly longer than 24 hours

What are Zeitgebers?

• time giver

• stimulus that resets circadian rhythm

Examples of Zeitgebers

• sunlight

• exercise

• meals

• arousal

• temp of environment (colder room = early wake up)

• tides

travelling west

phase-delays our circadian rhythms

travelling east

phase-advances our circadian rhythms

SCN (suprachiasmatic nucleus)

• main control center of circadian rhythms of sleep and temp

• located above the optic chiasm and part of the hypothalamus

• damage to SCN = less consistent body rhythms: animals still fall asleep and wake up but would do so at very random times of the day

• SCN very active during the day, not as much at night

• single cell extracted from SCN and raised in tissue culture continues to produce action potential in a rhythmic pattern

retinohypothalamic path

• small branch of optic nerve

• travels directly from retina to SCN

• NOT A VISUAL PATHWAY - used to synchronize daily cycle

• sensitive to light but not used for seeing

• comes from ganglion cells that have melanopsin (photosensitive)

• when light hits ganglion cells = SCN activated

slave oscillators

• sub-systems of the brain that uses info from SCN to determine when to execute a behaviour

• controls the rhythmic occurrence of a behaviour

• hunger, physical activity

• driven by SCN via hormones, proteins or neurotransmitters

what is responsible for generating the circadian rhythm?

• proteins

• PER and TIM

How does PER and TIM control the circadian rhythm?

• increase the activity of certain kinds of SCN neurons that regulate sleep and waking

• higher levels of PER and TIM = lower activity of circadian rhythm, hence lower cellular firing in SCN

Effects of external stimuli on PER and TIM

• daylight degrades PER and TIM, so SCN cells are working overtime to make

• reaches a substantial amount at night, SCN cells can relax now since there is enough PER and TIM

SCN and other parts of the brain

• inhibits pineal gland = less melatonin during the day bc that’s when SCN is active

• at night, retinohypothalamic path is not activated, so SCN is deactivated, which activates the pineal gland = increase melatonin

Coma

• extended period of unconsciousness

• low brain activity

• little response to stimuli

• result of brain injury

vegetative state

• alternates between sleep and arousal but no awareness of surrounding

• some autonomic (involuntary) arousal to painful stimulus

minimally conscious state

• a stage higher than a vegetative state

• occasional brief periods of purposeful action and limited speech comprehension

Brain death

• no sign of brain activity

• no response to any stimulus

• legally dead

what was used to discover various stages of sleep?

EEG - allows bulk cortical activity to be recorded at diff phases of sleep

polysomnograph

• combination of EEG and eye-movement records

• electrodes places around the eye

electromyogram

• measures muscle movement and tone

• electrodes placed on the jaw

beta waves

• high freq (12-30 Hz)

• most common in frontal lobe - in memory and visual areas

alpha waves

• not-intellectually engaged like doomscrolling

• lower frequency (8-12 Hz)

• higher amplitude and more synchronized than beta

theta waves

• 4-8 Hz

• S1/non-REM stage of sleep

• can still respond but is considered asleep (are you asleep? No…)

Delta waves

• 1-4 Hz

• slow brain activity

• high amplitude

Stage 1 sleep

• start of sleep

• most of the neurons are firing equally

• slowly go from alpha → theta

Stage 2 sleep

• slower theta waves

• sleep spindles - 12-14 Hz, lasts at least half a second, very high freq - MEMORY consolidation

• K-complex - sharp wave, temporarily inhibits neuronal firing, high amplitude, very brief

Slow wave sleep: stage 3 and 4

• delta waves

• slowing of heart rate, breathing rate, and brain activity

• highly synchronized neuronal activity

• important for protein synthesis (good memory) and release of growth hormones (build muscle mass)

• if interrupted = fatigue

• length decreases as the night progresses

• early parts of sleep

REM sleep

• rapid eye movement

• theta and alpha waves

• muscle atonia

• vivid dreams

• after an hour of sleep = first REM

• length increases as the night progresses

• more REM sleep in early stages of life

NREM sleep

• throughout the night we alternate between NREM and REM randomly

• nightmares

The reticular formation

• part of the midbrain

• extends from medulla to forebrain

• responsible for arousal

• receives input from eyes and ears

pontomesencephalon

• part of RF

• releases acetylcholine and glutamate, which contributes to cortical arousal

Locus coeruleus

• small structure in the pons

• LC axons release norepinephrine - increase wakefulness and important for fight/flight

• shuts down when asleep

• arouses various areas of the cortex

Hypothalamus

• has neurons that release histamine - excitatory

• antihistamines = sleepiness and shuts down the hypothalamus

Hypothalamus and orexin

• oexin released by lateral and posterior nuclei of hypothalamus

• orexin = neurotransmitter

• needed to STAY awake

• if someone lacked orexin = people would alternate in between brief periods of waking and sleeping

Basal forebrain and arousal

• orexin is also released by cells in the basal forebrain → wakefulness and arousal

• basal forebrain is anterior and dorsal to hypothalamus

• cells in BF also release GABA (inhibitory) - important for sleep, decreasing temp and metabolic rate, hyperpolarizing the thalamus and cortex

• other axons release ach = excitatory and increases arousal when awake but shifts sleep from NREM to REM

brain activity in REM

• activity increases in the pons, limbic system (feeling emotions during sleep), and visual cortex

• activity decreases in motor cortex, and the dorsolateral prefrontal cortex

• associated with PGO waves originate in the pons - high amplitude

• REM deprivation = high density of PGO waves

• serotonin and nonadrenaline interrupts REM

sleepwalkers

• awake in motor cortex, pons and medulla

• occurs in stage 3 or 4

lucid dreaming

high activity in frontal and temporal cortex (important for awareness)

sleep paralysis

pons in REM = loss of muscle tone, but the rest are awake

sleep apnea

• inability to breathe while sleeping for a long period of time (few seconds to a few minutes)

• consequences: sleepiness during the day, impaired attention, depression

• causes: genetics, old age, obesity

• effects: cognitive impairment

• treatment; breathing device

Narcolepsy

• frequent attacks (gradual or sudden) of sleepiness

• occasional cataplexy: muscle atonia triggered by strong emotions

• sleep paralysis

• hypnagogic hallucinations

• seems to run in families, but no identified gene

• caused by lack of hypothalamic cells that produce and release orexin (important to stay awake)

• treatment: stimulant drugs like Ritalin = increase wakefulness by increasing dopamine and norepinephrine activity. -activates LC

Periodic limb movement disorder

• repeated involuntary jerking of arms and legs

• occurs during NREM

• treatment: sleeping pills = inhibit motor neurons and sleeping with a weighted blanket

REM behaviour disorder

• acting out dreams in REM sleep

• inadequate GABA and other inhibitory neurotransmitters

all animal with SC _____

sleep

all warm-blooded animals _____

dream