2
HEAD HEAD
1. SHORTEST
LONGEST-SLEEPING MAMMALS
Giraffe
2. AVERAGE
Human
Giraffes require less sleep than any other mammal, typically getting 20-30 minutes per day for five minutes at a time.
3. LONGEST
The amount of sleep we need varies from person to person, but we typically require about eight hours per night.
Koala Koalas are some of the heaviest sleepers, clocking up approximately 15 hours of snoozing per day.
DID YOU KNOW? Light affects the sleeping pattern of blind people, as ganglion cells are different from those that allow us to see
The science of insomnia Why checking your phone before bed could be spoiling your sleep Light sensitivity
How light affects your ability to sleep
The ganglion layer The retina of the eye contains a layer of photosensitive ganglion cells, which contain a photopigment melanopsin, called the ganglion layer.
Pineal gland The suprachiasmatic nucleus sends information from the photosensitive ganglion cells to the pineal gland, located in the epithalamus section of the brain.
Light sensitivity Unlike the other photoreceptors in the eye, photosensitive ganglion cells contribute little to vision, but they are sensitive to light.
Suprachiasmatic nucleus
Optic nerve
The suprachiasmatic nucleus is a tiny area of neurons, located in the hypothalamus area of the brain, which controls circadian rhythms.
The photosensitive ganglion cells have long fibres that connect to the optic nerve and eventually reach the suprachiasmatic nucleus.
Melatonin When the photosensitive ganglion cells detect darkness, a message is sent to the pineal gland to produce melatonin, a hormone that causes drowsiness. ©Art Agency
Most of us experience insomnia at some point in our lives, finding it difficult to drift off and stay asleep despite having plenty of opportunity to. Typical causes of insomnia include stress and anxiety, but did you know that your gadgets could be to blame, too? Our sleepiness and wakefulness throughout the day and night is regulated by our circadian rhythm. This is essentially our body clock, creating physical, mental and behavioural changes that occur in our bodies over a roughly 24-hour cycle. Circadian rhythms are found in most living things, including animals, plants and many tiny microbes, and are created by natural factors in the body. However, they also respond to signals from the environment, such as light, so that we remain in sync with the Earth’s rotation. All forms of light, both natural and artificial, affect our body clock, as when the photosensitive retinal ganglion cells in our eyes detect light, they send this information to the suprachiasmatic nucleus (SCN) – the group of nerves in the brain that controls circadian rhythms. When light is detected, the SCN will delay the production of melatonin, a hormone that sends us to sleep. However, the retinal ganglion cells have been found to be particularly sensitive to the blue light with a short wavelength of 480 nanometres emitted by most computer, smartphone and tablet screens. Exposure to a lot of this type of light in the hours before we go to bed has been proven to suppress melatonin levels, making it difficult for us to get to sleep.
Blocking blue light The best way to reduce your exposure to blue light is to avoid staring at a screen in the two hours before you go to bed. Instead illuminate the room with the warmer longer-wavelength light from regular incandescent bulbs or even candles. However, if you just can’t resist staring at your computer or phone
WWW.HOWITWORKSDAILY.COM
before bed, then there are ways that you can do so and still get a good night’s sleep. Wearing special glasses with amber-coloured lenses will filter out blue, low-wavelength light, allowing you to stare at your screen for as long as you like. Companies such as Uvex (uvex-safety.co.uk) make blue-blocking glasses and
goggles in a range of st Alternatively, you could computer software suc (justgetflux.com) and s apps such as Twilight (p com) that automatically screen to filter out blue sunset and sunrise, rep softer red light.
Filter out blue light with a pair of amber-tinted glasses or by using smartphone apps
