Lecture 10

Question 1

Do all multicellular organisms sleep

Answer 1

Yes - so this is shared by many creatures on the planet

Question 2

How does sleep work?

Answer 2

Animals have rhythms that correspond to the functional activity of the animal

Question 3

What is the biological clock

Answer 3

Animals have an internal mechanism that spontaneously generates a rhythm.

Question 4

Define Endogenous circadian rhythms

Answer 4

Internally controlled cycles that last about a day

Question 5

How do we know our biological clock (rhythm) is internally generated

Answer 5

If you stay up all night, you feel sleepier as it gets later but then perk up in the morning. Animals kept in total darkness still keep to a 24 hour cycle (DeCoursey, 1960). Humans kept in an environment with a 28 hour cycle cannot synchronise - they slip back to a 24 hour cycle. Blind and deaf animals generate nearly normal circadian rhythms. Circadian rhythms are maintained despite most types of brain damage, anaesthesia, and food deprivation.

Question 6

What generates this sleeping rhythm

Answer 6

The biological clock

Question 7

What is the biological clock

Answer 7

A mechanism in our brain that generates the sleeping cycle.

Question 8

Where is the biological clock

Answer 8

Suprachiasmatic nucleus (SCN). Which is part of the hypothalamus, above the optic chiasm

Question 9

What happens when the suprachiasmatic nucleus is damaged

Answer 9

It causes damage to the circadian rhythms

Question 10

How do we know the suprachiasmatic nucleus generates a rhythm automatically

Answer 10

Remove the SCN and keep it is a tissue culture - it continues to prodce a 24 hour rhythm of action potentials. Hamsters with a mutant gene coding a 20 hour rhythm, SCN removed and implanted in normal hamsters, they start to live a 20 hour cycle.

Question 11

How does the biological clock work

Answer 11

Controls the pineal gland = an endocrine glad posterior the thalamus. Releases melatonin - Hormone that makes us sleepy

Question 12

What happens when yo upset the biological clock

Answer 12

The clock is internal, but it still responds to the environment. Feedback system between our clock and the world to allow us to adapt to change. So although circadian rhythms can exist without light, light is crucial for periodically resetting them. The stimulus that changes the clock is called zeitgeber. Good for changes in seasons, activity levels; after a weekend of late drinking and late morning 8 am Monday feels like 5 am.

Question 13

What is zeitgeber

Answer 13

Time-giver: for most land mammals the dominant zeitgeber is light, but we also respond to exercise, noise, temperature and meals. Some marine mammals respond to tides. People in Scandinavian countries become insomniac during the winter - where there’s only 2 hours of sunlight a day. Hamsters living in constant light have no coordination and two sleep and two wake cycles when the SCN in one hemispheres is out of the phase with the right

Question 14

How does jet lag implicate the biological clock

Answer 14

Disrupting rhythms by crossing time zones. Sleeping at the wrong times = depression, lack of concentrations and nausea. Mismatch between biological clock and external stimuli - we are not adapted to moving so fast. Can be stressful and raise cortisol levels - damaging in the long term! Delaying your sleep is easier than having to sleep earlier. Travelling east to west is easier - you just stay up later, but west to east is hard and your night has been shortened, so you need to catch up in the following days

Question 15

How does shift work impact the biological clock

Answer 15

Even years after working shifts people can have disruptive sleep patterns and feel fatigued, can’t sleep well during the day, don’t adjust when working at night, as well as the light levels aren’t high enough in artificial conditions - need to have complete reversal to fully change that biological clock

Question 16

Why is light so important to the biological clock

Answer 16

Optic chiasm and suprachiasmatic nucleus are close to eachother. Small branch of the optic nerve goes directly from the retina to the SCN and not the visual cortex. Input to this pathway comes from special type of retinal ganglion cells - special photopigment, melanopsin, responds directly to light with no input from rods and cones, respond slowly and turn off slowly, so the SCN gets an idea of general light intensity - perfect to gauge the time of the day

Question 17

Can a blind mole rat respond to light

Answer 17

YES

Question 18

How many stages of sleep are there and what to they do

Answer 18

4. Stage 1 and 2 = irregular activity, high but declining, bursts of activity in stage 2, cortex still receiving sensory input. Stage 3 and 4 = slow wave sleep = neuronal activity is highly synchronised, sensory input is reduced

Question 19

How can we detect different stages of sleep

Answer 19

With EEG’s, can be used to detect electrical signals of spontaneous brain activity OR in response to a stimuli

Question 20

In addition to the 4 stages what other stage is there

Answer 20

REM sleep - Rapid Eye Movement sleep - also called paradoxical sleep. Neither light nor deep sleep - light because lots of brain activity but deep because muscles are relaxed

Question 21

What does REM stand for and what does it mean

Answer 21

Rapid Eye Movement, where you are in neither a light sleep or deep sleep because there is lots of brain activity going on but muscles are relaxed

Question 22

What is the brain doing during REM sleep

Answer 22

Lateral geniculate nucleus in the thalamus - limbic system - emotion. Pons = bridge, axons from cortex cross here to spinal cord - for movement. PGO waves (pons-geniculate-occipital)

Question 23

What happens when you lesion the pons

Answer 23

In cats, they still have REM sleep but muscles are not relaxed - chases prey, jumps and pounces

Question 24

Name 4 sleep disorders and what they are

Answer 24

Insomnia: Stress, anxiety, depression, shifting circadian rhythms and dependent on sleeping pills. Sleep Apnea: Inability to breathe while sleeping - obesity/old age? Narcolepsy: Attacks of sleepiness during the day, REM during the day? Periodic Limb Movement Disorder: Involuntary movement of the legs/arms, maybe something to do with the pons?

Question 25

What is the function of sleep

Answer 25

As all animals sleep, we need to consider function in all species; a form of hibernation - conserving energy when you can’t get much done- when food is scarce, light is too high or too low, hibernating hamsters live longer than other hamsters.

Question 26

What does sleep depend on

Answer 26

Safety from predators, how much time they need to find food, whether they need to surface for air

Question 27

Is there more to sleep than just energy conservation?

Answer 27

Sleep deprivation causes dizziness & hallucinations, eventually the immune system fails in animals severely deprived, sleep enhances memory!

Question 28

Discuss how deprivation of REM effects life

Answer 28

We spend 1/5 of sleep in REM and if deprived, the brain attempts to REM during waking hours, babies have more REM than adults - so it must have some biological function

Question 29

Why do we need to sleep

Answer 29

To strengthen memories, and weed out the pointless connections - but sleep on the whole seems to improve memories and anti-depressant drugs reduce REM sleep and people have no memory problems. Moistening the eyeballs - but if deprived of REM sleep via drugs, corneas aren’t damaged

Question 30

Why do we dream

Answer 30

Freud thought they were unconscious wishes. 1. The activation-synthesis hypothesis - effort to make sense of distorted info, PGO waves from pons activate parts of the cortex, which synthesises a story, but not always in REM. 2. The clinico-anatomical hypothesis - dreaming is thinking, senses are suppressed, so brain left to its own devices, motor cortex suppressed, so no action, pre-frontal cortex suppressed, so no working memory to link a believable story together

Question 31

Discuss temperature regulation in animals and humans

Answer 31

Animals have evolved different mechanisms to cope with temperature change, the wood frog can survive in freezing cold because of physiological mechanisms. Birds keep legs warm through behaviour mechanisms like standing on one leg. Humans shiver, sweat have blood vessel constriction and dilation. These are because of the pre-optic area near the hypothalamus and responds to changes in its own temperature and also temperature receptors in the skin

Question 32

Discuss thirst in animals and humans

Answer 32

Animals have evolved different mechanisms to get/retain water. Beavers drink lots and urinate lots and Gerbils may never drink and have dry faeces. Humans have flexible strategies depending on the circumstances, if water is scarce the pituitary gland secretes vasopressin and blood vessels constrict and raises blood pressure and compensates for the low fluid volume. Vasopressin in also an antidiuretic hormone makes urine more concentrated by causing the kidneys to reabsorb fluid from urine. Drinking alcohol blocks the production of vasopressin by the pituitary gland and prevents the kidneys from absorbing water and makes urine more diluted - so the morning after we experience massive widespread dehydration - hence very thirsty

Question 33

Discuss hunger in humans and how we know what and when to eat

Answer 33

We eat a combination of learned and unlearned strategies because we have learned from peers and culture but innate tastes are essential and likeliness of sweet food, disgust for bitter/sour. We know when to eat because of the way the brain processes information and decides whether to eat is complication, BUT it centres around the hypothalamus which has neurons sensitive to hunger and feeling full, these feeding mechanisms seem to have changed very little during mammalian evolution but many areas are involved which means it can make many errors, although other areas can compensate

Question 34

Discuss eating disorders

Answer 34

Obesity is a big problem in industrialised countries, excessive eating due to huge availability of food. Anorexia and Bulimia nervosa are poorly understood but biological issues are associated with it, but culture and individual issues are more likely to be the cause

Question 35

Discuss obesity

Answer 35

Excessive eating due to availability of food. There is a huge cultural influence and social aspect. Still rooted in our biology, propensity to like fatty foods. Fat and sugar was scarce pre-industrialisation. Native populations adapted to a specific diet, now exposed to new foods

Question 36

Discuss Anorexia Nervosa

Answer 36

Have an unwillingless to eat and is in 0.3% of young women. Perception of fatness even when they are thin even cause death! Unlikely to have a specific genetic basis, serious condition but not as widespread or culturally problematic as obesity

Question 37

Discuss Bulimia Nervosa

Answer 37

Extreme dieting mized with binge eating, vomit after mealtimes and have an imbalance of hormones associated with feeding but may be result of erratic eating rather than cause. It may be similar to drug addictions, as rats deprived of food for 12 hour periods and drank increasing amounts of sugar solution in the feeding periods and drinking during these periods released dopamine and opiate like compounds in the brain

Question 38

Discuss reproductive behaviours - how does our sex affect our behaviour

Answer 38

Evolutionary theory = we are the product of successful strategies, so we should have inherited successful strategies, men and women were subject to different selection pressures in evolutionary history therefore exhibit different traits. But there are two main ways how men and women differ: sexual strategies = hormones (androgens produced in the testes and the adrenal gland, and sensitive regions of the brain underlying sexual motivation in men, and in women oestrogens are produced by the ovaries and androgens produced by the adrenal gland which is associated with sex drive, post-menopausal women can still have high sex drive due to androgen production) mate choice, attitudes to sexual behaviour, and cognition = cognitive skills rooted in different reproductive and survival strategies