84 Human Body Facts - Brain, Senses & Health

Brain

Your brain uses about 20% of your body's total energy even though it only makes up about 2% of your body weight.
During sleep, your brain organises memories and removes toxins, effectively performing a nightly cleaning process.
Neurons in the brain communicate through electrical impulses that travel up to 400 kilometres per hour.
The brain has no pain receptors, which is why brain surgery can be performed on conscious patients.
The average adult brain weighs about 1.4 kilograms and contains roughly 86 billion neurons.
Each neuron can form thousands of synaptic connections, resulting in trillions of possible neural pathways.
The human brain generates enough electricity to power a small light bulb.
Your brain’s structure changes throughout life in response to experience, a phenomenon called neuroplasticity.
When you imagine an action, your brain activates many of the same areas as when you actually perform it.

See also: Animal & Nature Facts - Wildlife, Plants & Ecosystems

Senses

Your sense of smell is directly linked to the limbic system, the part of the brain responsible for emotion and memory.
Humans can distinguish more than one trillion different scents, though most people are aware of only a small fraction.
The human eye can detect a candle flame from nearly 50 kilometres away under perfect conditions.
Your taste buds regenerate roughly every 10 to 14 days, although this ability declines with age.
The brain processes sound faster than sight, allowing you to react to noises before identifying visual cues.
Human eyes can perceive only a tiny fraction of the electromagnetic spectrum, known as visible light.
The skin is the body’s largest sensory organ, containing about 4 million sensory receptors.
People who lose one sense often experience enhanced performance in others due to neural adaptation.

See also: Science Facts - Physics, Chemistry, Biology & Astronomy

Sleep

Dreams help consolidate memory, strengthen emotional resilience, and boost creativity.
The world record for staying awake is 11 days, but long-term sleep deprivation can cause severe cognitive and immune damage.
Humans spend about one-third of their lives asleep, which adds up to around 25 years for an average lifespan.
REM sleep, the stage when most dreaming occurs, accounts for about 20% of total sleep time.
Your brain is more active at night than during some parts of the day, particularly during dreaming.
Lack of sleep for just 24 hours can impair coordination as much as being legally drunk.
Sleep strengthens neural connections related to recently learned tasks.
Your body temperature drops slightly during sleep to help conserve energy and promote rest.

Health

Laughter reduces stress hormones and boosts immune function by increasing antibody production.
Your heart beats over 100,000 times a day, pumping about 7,500 litres of blood through your body.
The liver can regenerate itself from as little as 25% of its original tissue, making it unique among human organs.
Regular exercise increases the size of the hippocampus, the brain region linked to memory and learning.
A sneeze can travel at speeds up to 160 kilometres per hour, expelling thousands of droplets.
Blood makes up about 8% of your total body weight.
The stomach’s lining renews itself every few days to protect against its own acid.
Your gut microbiome contains more bacterial cells than your body has human cells.
About 70% of the immune system is housed in the gut.

Emotions

Tears from sadness, joy, and irritation have different chemical compositions, reflecting distinct emotional states.
When you blush, the lining of your stomach blushes too, as both are controlled by the same nervous response.
Humans are capable of feeling secondary emotions such as embarrassment and pride that few other species exhibit.
Smiling, even when forced, can trigger a small increase in happiness due to feedback from facial muscles.
Fear can enhance memory formation, helping you remember details of threatening situations.
The amygdala, a small almond-shaped structure, plays a key role in processing fear and pleasure.
Emotional tears contain more stress hormones than reflex tears, helping to relieve tension.
People subconsciously mimic others’ expressions, a behaviour known as emotional contagion.

Memory

Every time you recall a memory, your brain slightly rewrites it, meaning memories subtly change over time.
Short-term memory can hold about seven pieces of information for roughly 20 to 30 seconds before fading.
Long-term memories are stored by strengthening the synapses between neurons.
The hippocampus acts as a hub that transfers short-term memories into long-term storage.
Your brain begins storing memories before you are even born, responding to sounds in the womb.
Sleep deprivation greatly reduces the ability to form new memories.
People remember emotional experiences more vividly than neutral ones due to amygdala involvement.
Smell is the sense most strongly linked to memory because of its direct connection to the limbic system.

Language

The human brain processes metaphors using the same regions that handle physical sensations.
Bilingual people often unconsciously change personality traits slightly when switching languages.
Learning a new language can physically increase grey matter density in the brain.
Infants can distinguish sounds from all world languages, but lose this ability around 10 months of age.
The left hemisphere controls language in about 95% of right-handed people and 70% of left-handed ones.
Sign languages activate the same brain regions as spoken languages.
Humans are the only species known to use recursive grammar, allowing infinite combinations of ideas.
Reading silently activates inner speech mechanisms, causing tiny muscular movements in the throat.

Genetics

Humans share about 60% of their genes with bananas and about 98% with chimpanzees.
Most of your DNA does not code for proteins but regulates when and how genes are expressed.
Every person has about 20,000 protein-coding genes, fewer than some plants and worms.
Identical twins have almost the same DNA but different epigenetic markers that influence how genes are expressed.
Your genetic makeup is 99.9% identical to every other human being on Earth.
Mitochondrial DNA is passed almost exclusively from mothers to their children.
A single mutation in one gene can sometimes cause dramatic physical or behavioural differences.
Humans have around 200 genes that appear to have originated from ancient viruses.

Ageing

After age 30, you begin to lose about 1% of your muscle mass each year if you do not exercise.
Telomeres, the protective caps at the ends of chromosomes, shorten with age and influence cellular ageing.
Regular exercise and meditation have been shown to slow telomere shortening.
Your skin starts producing less collagen in your twenties, contributing to wrinkles over time.
The sense of smell is one of the first senses to decline noticeably with age.
Cognitive decline is not inevitable; lifelong learning can build a ‘cognitive reserve’ that delays its effects.
Some species, such as certain jellyfish, can biologically reverse ageing, though humans cannot.
Older adults often need less sleep but more recovery time after physical exertion.

Oddities

Some people can hear their own eyeballs move due to a rare condition affecting the inner ear.
About 1 in 50 people have an extra rib, a harmless genetic variation known as a cervical rib.
Your stomach gets a new lining every few days to protect against its own acid.
The acid in your stomach is strong enough to dissolve razor blades, though the stomach wall renews constantly.
You shed around 500 million skin cells every day, forming much of the dust in your home.
Goosebumps are a vestigial reflex inherited from our hairy ancestors who used it to appear larger when threatened.
A small percentage of people can wiggle their ears due to ancient muscles humans no longer use.
The human body glows faintly in the dark from bioluminescent metabolic reactions, but the light is too weak to see.
Some people have a condition called synaesthesia, where senses blend, such as seeing colours when hearing music.
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