Lecture 9 Flashcards
What animals sleep?
How much of our lives do we spend sleeping?
All multicellular organisms
About 1/3 of our lives we are asleep, different species sleep different amounts due to the variations in their lifestyles and rhythms.
Discuss animals’ rhythms
It used to be thought that the animals’ rhythm was a behavioural response to an external stimulus. However, Richtor since explained that it’s an internal mechanism which spontaneously generates the sleeping rhythm. There are two types of rhythms; the endogenous circadian rhythm, this biological clock lasts 24 hours and occurs regardless of light. There’s also circannual rhythms, these cycles last a year, regardless of the environment, for example migrating birds or hibernating mammals.
Discuss research in relation to the biological clock
Studies have shown that when animals are kept in darkness, they still keep to a 24 hour cycle. Furthermore, when humans are kept in a 28 hour cycle, they still keep to their 24 hour rhythm. Blind and deaf animals have 24 hour cycles still. Richter believes one’s brain generates the cycle. This cycle is robust and still maintains when one has brain damage.
Where is the biological clock found in the brain?
It’s hypothesised to be found in the superchiasmatic nucleus which is in the hypothalamus, just above the optic chiasm. If this is damaged, then the rhythm is also damaged. If the SCN is removed and kept in a petri dish then there is still a 24 hour rhythm of action potentials. If hamsters are implanted with a mutated SCN that last 20 hours then the hamster will live by a 20 hour cycle. The SCN controls the pineal gland which is an endocrine gland posterior to the thalamus. The pineal gland releases melatonin which makes us sleepy.
Discuss environmental interactions with the biologica clock
The clock still responds to the environment, allowing us to adapt to it. Light allows us to periodically reset the clock and the stimulus that changes the clock is called the zeitgeber. This is important for changes in seasons and amount of activity etc. For land mammals, the most crucial zeitgeber is light but other important ones are exercise, noise, temperature etc. Some marine animals respond to the tide. Insomnia rates are higher in scandinavia during the wintdf as they have 2 hours of sunlight. When hamsters lived in constant light, the two SCNs were no longer in sync with each other. However, we aren’t adapted to moving fast, hence why we get jetlag as our clock isn’t synced to the environment, this can raise cortisol levels and repeated jetlag can reduce memory capacity. Phase-delah is easier than phase-advance (going to bed early). When you don’t stick to a normal pattern, even after years, you can feel fatigued and can’t adjust to sleeping in the day.
Why is light so important for the biological clock?
The SCN is next to the visual cortex so light is an important factor. A small branch of the optic nerve connects to the retina and the SCN. Melanopsin is a special photopigment that responds directly to light, it responds slowly so that the SCN gets a general idea of light intensity. This allows the blind mole rat to respondnto light even though it’s blind.
What are the stages of sleep?
The EEG has found that there are 4 stages of sleep that have different levels of activity compared to relaxed wakefulness. Stages 1 and 2: Irregular activity, high activity that’s declining, in stage 2 there’s bursts of activity and the cortex still receives sensory input. Stages 3 and 4: Slow waves of sleep where neuron activity is highly synchronised and sensory input is reduced. As well as these stages, we have REM sleep which is also called paradoxical sleep, it’s when dreams occur supposedly. The characteristics don’t fit light or heavy sleep. A by product of this is eye movement.
Discuss the brain activity during REM
The lateral geniculate nucleus in the limbic syste is active during REM which is where emotion occurs. The pons is also active and it inhibits movement. These two sections work in a PGO wave (pons geniculate occipital). When sleep deprived, these waves pop up whilst awake. When cats received a lesion in the pons, they still have REM sleep but their muscles weren’t relaxed and they moved whilst dreaming.
List some sleep disorders
Insomnia: shifting circadian rhythms
Sleep apnea: inability to breathe whilst sleeping
Narcolepsy: attacks of sleepiness during the day
Periodic limb movement disorder: involuntary movement of legs or arms.
What are the theories about why we sleep?
It could be to conserve energy, like a kind of hibernation and there’s also no advantage of staying awake due to lack of food/light. For example, hibernating hamsters live longer. Without sleep, one also gets dizzy or can hallucinate and their immune system fails. Additionally, sleep enhances memory and allows the brain to forget pointless connections/memories. Sleep as a whole improves memories because when one takes anti depressants, REM is reduced, but this has no effect on memory. Sleep also moistens the eyeballs.
Why do animals have variations in the amount they sleep?
The amount an animal sleeps depends on their safety from predators, how long they need to find food, whether they need to surface for air and so on.
Why do we dream?
Freud believed they were unconscious wishe, however, this has since been discounted.
The activation synthesis hypothesis: Dreams allow us to make sense of distorted information. The PGO waves synthesise a story but this doesn’t always occur during REM.
Clinico anatomical hypothesis: The brain is left to its own devices as there’sno sensory or motor input and working memory is down so the story doesn’t need to be believable.
How do humans regulate temperature?
We shiver, sweat, vasodilate and vasoconstrict. This is controlled by the pre-optic area which responds to skin receptors and the temperature of the pre optic area itself.
How do humans get or retain water?
If the water is scarce then the pituitary gland secretes vasopressin which causes the blood vessels to constrict and therefore raises blood pressure. Vasopressin is also an ADH. Drinking alcohol inhibits the release of vasopressin which makes urine more diluted.
How do humans know what to eat?
How do humans know when to eat?
We know because of learned and unlearned strategies.We learn from peers and our culture and we have innate preferences to sweet food.
This centres around the hypothalamus, it contains neurons sensitive to hunger. This system hasn’t varied much through evolution. The system involves many areas of thd brain.
