Chapter 14: Biological rhythms, sleep, and Dreaming

Question 1

What is a circadian rhythm?

Answer 1

A pattern of behavioral, biochemical, or physiological fluctuation that has a 24-hour period.

Question 2

How is a circadian rhythm measured?

Answer 2

By tracking the running wheel in a hamster’s cage and having it mark it’s duration during the 24 hours of a day

Question 3

What is free-running?

Answer 3

The added activity to maintain a hamster’s cycle because it is a few minutes longer than 24 hours.

Question 4

Define Phase shift:

Answer 4

The shift of activity produced by a synchronizing stimulus.

Question 5

Define entrainment:

Answer 5

The proces of shifting the rhythm

Question 6

Define Zeitgeber

Answer 6

Literally time giver: The outside stimulus that entrains (entrainment) the circadian rhythm.

Question 7

Where is the circadian clock located?

Answer 7

Within the suprachiasmatic nucleus of the hypothalamus (SCN). Located above the optic chiasm

Question 8

How does light biologically affect the SCN?

Answer 8

Photoreceptor cells in the eyes. Certain retinal ganglion cells send their axons along the retinohypothalamic pathway.

Question 9

What is different about the retinal ganglion cells?

Answer 9

These cells contain a photopigment, called melanopsin, that makes them sensitive to light.
They do not rely on rods and cones, even transgenic mice lacking rods and cones, and thusly are blind, entrain their to light.

Question 10

Genes affecting the circadian rhythm

Answer 10

Period: Discovered in experiments with fruit flies whose became arrythmic without the gene. Affects free-running
Genes coding for Clock, Cycle, Bmal1, and cryptochrone(cry)

Question 11

How does the molecular clock function?

Answer 11

5 steps:

1. Clock and Cycle (Bmal1 in mammals) bind forming a “dimer”
2. The dimer binds to DNA, enhancing the transcription of period (per) and cryptochrome (cry) proteins.
3. per and cry bind together and inhibits the production of the clock/cycle dymer.
4. The cry/per dimer eventually degrades, thus no longer inhibiting clock/cycle production
5. Retinal ganglion cells release glutamate which enhances production of the per gene hereby entraining the molecular clock to the day-night cycle.

Question 12

What is an infradian rhythm?

Answer 12

A rythmic biological event whose period is longer than a circadian rhythm - 24hours

Question 13

What is an ultradian rhythm?

Answer 13

A rythimic biological event whose period is shorter than a circadian rhythm -24 hours

Question 14

what is special about the circannual clock?

Answer 14

It is a clock whose cycles does not arise from the circadian clock. They involve a mechanism that is separate from SCN

Question 15

What is the primary method when studying sleep/waking cycles in humans?

Answer 15

EEG measurements coupled with electrooculography (EOG) and Electromyography (EMG).

Question 16

Describe the different classes of sleep

Answer 16

Overall there is two classes of sleep: Slow-wave sleep (SWS) and Rapid-eye-movement sleep (REM).
SWS: Widespread synchronization of cortical activity in slow waves.
REM: Small amplitude, high-frequency activity, similar to an awake individual, coupled with completely relaxed and limp muscles.

Question 17

Describe the different stages of sleep and which EEG patterns characterize them

Answer 17

SWS stage 1 sleep: Closing of eyes, drowsiness, alpha rhythm 8-12 hz, sharp waves called vertex spikes, slowing of heart rate, reduced muscle tension, eyes rolling.
Stage 2 sleep: 12-14 HZ called sleep spindles, K complexes. Not yet aware of sleeping condition.
Stage 3 Sleep: Large amplitude very slow waves called delta waves 1 per second. The old definition of stage 4 is now removed because of similarity with stage 3
REM stage: Small amplitude, high-frequency activity, similar to an awake individual, coupled with completely relaxed and limp muscles. Brainstem regions are inhibiting motoneurons

Question 18

The humans sleep in cycles…

Answer 18

Repeating cycles of 90-110 minutes recurring usually 4-5 times in a night.
Cycles consists of a stage 1 -> 2 -> 3 -> 2 -> REM
Then shifting between REM, stage 2, and stage 3 sleep. With more repeated cycles comes longer REM phases and shorter stage 3 phases.
There are also a few brief awakenings during the cycles.

Question 19

What is the difference between a nightmare and a night terror?

Answer 19

Nightmare is a long frightening dreams which wakes the subject during REM sleep.
Night terror is sudden arousal in stage 3 sleep marked by intese fear and autonomic activation

Question 20

The length of a sleeping cycle is associated with?

Answer 20

Metabolic rate and size of animals.

Small animals with high metabolic rate have short sleeping cycles and vice versa

Question 21

As we grow older we sleep …

Answer 21

Less.

Less overall sleep, less REM sleep, and more brief awakenings

Question 22

What is the importance of Stage 3 sleep?

Answer 22

Secretion of growth hormone.

Lack of stage 3 sleep is associated with coginitive deficits

Question 23

What is the primary feeling and consequence of sleep deprivation?

Answer 23

SURPRISE!

You feel sleepy

Question 24

What are the actual consequences of sleep deprivation?

Answer 24

Irritability, difficulty in concentrating, and episodes of disorientation.
Hallucinations in severe cases

Question 25

Does getting too little sleep for a given amount of time eventually yield the same consequences as total sleep deprivation?

Answer 25

Yes and no, they may yield some similar consequences as this pattern can be sustained longer than total sleep deprivation. Studies of airline employees showed deficits in cognitive tasks and reduced volume of the temporal lobe compared to controls.
Total sleep deprivation in long periods is fatal as it compromises the immune system and yields thalamic degeneration.

Question 26

What are the four major functions of sleep proposed?

Answer 26

Energy conservation, Niche adaptation, body restoration, and memory consolidation.

Question 27

What is meant by Niche adaptation?

Answer 27

The circadian rhythm is adapted to the animals ecological niche. Meaning the unique assortment of environmental opportunities and challenges to which the animals has adapted. Eg. A mouse being nocturnal to hide from diurnal predators.

Question 28

What is associated with body restoration?

Answer 28

Restoration of meterials used during waking, such as proteins. It helps ward against various forms of disease.

Question 29

How was consolidation of memory studied? And what is the general conclusion on the studies?

Answer 29

Various behavioral studies testing declarative memory has been made. In general subjects get taught something before bed time and then the next day they get tested. These are then compared to a group who was taught during the early day and tested later in the afternoon.
Generally the before bedtime groups showed a larger effect suggesting that sleep contributes to stronger memory. In this case it is particularly stage 3 sleep that consolidates memory

Question 30

Which parts of the forebrain are important for what aspects of sleep?

Answer 30

SWS in the cortex for the forebrain is generated by the basal forebrain as shown by electrical stimulation of that area. Gaba-a receptors from tuberomammillary nucleus in posterior hypothalamus seem to induce slow waves in the EEG.

Question 31

Which parts of the brainstem are important for what parts of sleep?

Answer 31

The brainstem generally promotes wakefulness and alertness but also REM sleep.
The reticular formation, specifically the pons, has axons which project towards the brain and activates it. Lesions here will produce constant sleep states.
ventral to the locus coeruleus is an area with axons projecting towards the spinal cord. This area inhibits motoneurons thus promoting the limp muscle state in REM sleep. This is the Pontine REM Sleep Center

Question 32

What is the Hypothalamic sleep center?

Answer 32

A region in the hypothalamus, including neurons that use hypocretin as a neurotransimtter, sends axons to the other three sleep centers and seems to coordinate them, enforcing the patterns of sleep. Loss of hypocretin can lead to disorganized sleep, such as REM-like muscle atonia while still awake (in narcolepsy)

Question 33

What causes narcolepsy?

Answer 33

Malfunctioning of hypocretin receptors. Losing hypocretin neurons seem to cause innapropriate activation of the cataplexy pathway. It keeps sleep at bay and prevents transition from wakefulness directly to REM sleep.