PS231 Ch 10: Biological Rhythms and Sleep

What is an example of a biological rhythm?

The sleep/wake cycle

What drives biological rhythms?

Most rhythms follow a 24-hr cycle as the sun rises and sets on a 24-hr basis.

What happens when daily cues are removed?

Cycles of activity will drift (free-run) according to an endogenous circadian rhythm.

what does endogenous mean?

originating from within the body

What is entrainment?

If a 24 hr cycle is reintroduced, our biological clock synchronizes to the new cycle.

What allows entrainment to occur?

zeitgebers

What are zeitgebers?

Environmental cues that help biological clocks become entrained to the day-night cycle and the 24-hour day.

ex. light

What creates internal rhythms?

the suprachiasmatic nucleus (SCN) in the hypothalamus is responsible for organizing many of the body's circadian rhythms.

Where is the SCN?

above the optic chiasm in the hypothalamus.

What is the evidence that the SCN are the site of the "biological clock"?

- Hormone release from the SCN (vasopressin) occurs cyclically even after the SCN are removed from brain.

- Removal/lesion disrupts cycles of activity

How does the SCN coordinate entrainment to light?

There is a specialized pathway to the SCN from the retina, called the retinohypothalamic tract (RHT).

The Retinohypothalamic Tract (RHT)

Specialized photosensitive ganglion cells in the retina send projections directly to the SCN. GCs contain the photopigment melanopsin.

What rhythms does the SCN control?

- the SCN is the master oscillator that controls other rhythms (peripheral oscillators)

What are the peripheral oscillators?

Numerous circadian rhythms in many organs and cells of the body such as the heart, pineal gland, liver, adrenal gland.

What is the role of melatonin?

- It is a hormone produced by the pineal gland located deep in the brain that is released under control of SCN input.

- Helps coordinate the circadian responses throughout the body.

- Used as a sleep aid

How does the SCN keep time?

Uses a gene-protein negative feedback loop (Per, Cry, Clock, Cycle) that naturally cycles every ~24 hours, and light input fine-tunes it to match the solar day.

What do Clock/Cycle (Cl/Cy) proteins do in SCN neurons?

They turn on the Per and Cry genes.

What do Per/Cry proteins do after they are produced?

They inhibit Clock/Cycle (Cl/Cy) proteins and stop Per/Cry gene activation.

What happens when Per/Cry proteins degrade?

Inhibition lifts and Cl/Cy becomes active again, restarting the cycle.

When do rhythms become disrupted and proper sleep is affected?

- Natural zeitbergers are unchanged, but the sleep-wake cycle is altered.

- Jet lag: the sleep urge is out of sync with the new time zone.

Time zones effects

People on the west coast receive an extra hour or more of natural light in the evening which is not good for sleep.

What are the three standard measures of sleep?

1) Electroencephalogram (EEG) = brain waves

2) Electrooculogram (EOG) = eye movements

3) Electromyogram (EMG) = muscle tension

There are four major EEG waveforms?

1) Beta 15-30 Hz = Awake

2) Alpha 9-14 Hz = Relaxed, calm

3) Theta 4-8 Hz = Deep relaxation

4) Delta 1-3 Hz - Deep, dreamless sleep

Stage 1 of Sleep

The state of transition between wakefulness and sleep, characterized by relatively rapid, low-amplitude brain waves. (Theta waves)

Stage 2 of Sleep

the body goes into deep relaxation; characterized by the appearance of sleep spindles and K complexes.

Stage 3/4 of Sleep

slow wave sleep, delta waves

What does REM stand for in sleep terminology?

Rapid Eye Movement

What is a common characteristic of REM sleep?

Vivid dreams commonly occur.

What is another name for REM sleep?

Paradoxical sleep

What happens to the muscles during REM sleep?

The muscles are relaxed.

Are other body systems active during REM sleep?

Yes, other body systems are active.

When does SWS (Slow Wave Sleep) typically occur during the night?

SWS appears mostly early

What is the typical duration of REM sleep bouts?

Bouts of REM sleep are usually less than 30 minutes

How many series of sleep stages occur in a typical night?

4-5 series per night

What are the features of SWS?

- cerebral metabolism decreases by 75%

- brain areas active while awake show highest levels of delta waves during sleep.

- parasympathetic system dominance

- increased release of growth hormone

What are the features of REM sleep?

- darting eyes, fluctuations in heart and breathing rates

- increased cerebral blood flow and oxygen use

- subjects easily awakened

- PGO waves: electrical activity from pons to geniculate to occipital regions prior and during REM

- Dreaming

What is the Freudian dream theory?

Dreams represent the expression of unconscious wishes or desires

What is the activation-synthesis theory?

the belief that dreams are the product of the brain trying to make sense of random neural activity

What is the neurocognitive theory?

dreams are a meaningful product of our cognitive capacities, which shape what we dream about

What happens if there is complete sleep deprivation (animals)?

- Rat: sickness and death will occur after several weeks

- Pigeon: no effect on health after several weeks

Complete sleep deprivation (humans)

- Will experience numerous physiological and cognitive deficits

What is rebound sleep?

sleep after periods of deprivation, which recovers some sleep mostly SWS and REM.

What stages of sleep are important to memory?

SWS and REM sleep

Why do we sleep?

cognitive function, energy conservation, memory, and restoration/repair.

Adaptive theory?

theory of sleep proposing that animals and humans evolved sleep patterns to avoid predators by sleeping when predators are most active

Is sleep required in humans?

Yes an example is fatal familial insomnia which is a degenerative brain disorder that includes a complete loss of NREM sleep.

What is narcolepsy?

A sleep disorder characterized by uncontrollable sleep attacks. The sufferer may lapse directly into REM sleep, often at inopportune times.

- cataplexy: paralysis while awake

- loss of orexinergic cells in the hypothalamus

What are some disorders of sleep?

insomnia, sleep apnea, sleepwalking, and REM behavior disorder (dreams being acted out)

What are the two types of theories of the neurobiology of sleeping and waking?

Passive and Active

What controls wakefulness according to Passive Theories?

An adequate level of sensory input.

When does sleep occur according to Passive Theories?

When you turn out the lights and stop the influx of sensation.

What does EEG during sleep indicate about brain activity according to Active Theories?

The brain is not inactive while sleeping.

What is the name of the arousal center in the brainstem that keeps us awake according to Active Theories?

Ascending Reticular Activating System (ARAS)

How does caffeine prevent sleep?

It is an adenosine receptor antagonist which prevents adenosine which builds up during the day which then triggers sleep.