Body Atlas

How your body works, one honest answer at a time

Plain-language explanations from the Body Atlas courses — every one of them interactive in the app.

Heart · Meet Your Heart

• Why does the body need a heart?
• Why do we feel the heartbeat on the left if the heart is central?
• Does the heart ever rest?
• How long does one lap of the circulation take?
• What's the difference between an artery and a vein?

Heart · The Four Chambers

• Why is returning blood called 'used'?
• Does the right ventricle pump the same amount as the left?
• Aren't veins supposed to carry oxygen-poor blood?
• Why is the left ventricle so much stronger?
• Why does the heart need four chambers instead of two?
• What is a 'hole in the heart'?

Heart · The Four Valves

• What happens if a valve leaks?
• Are 'heart strings' a real thing?
• How can a valve work without muscles?
• What is a heart murmur?
• Which organ gets fresh blood first?
• What makes a valve open at the right moment?

Heart · Follow the Blood

• How does blood in my feet get back up against gravity?
• Why is it called an artery if the blood is oxygen-poor?
• Is blood ever actually blue?
• How does blood 'know' which branch to take?
• Why does the lung loop need to be gentle?
• How far does blood travel in the body loop?
• Why is blood in my veins darker?

Heart · The Heart's Own Blood Supply

• Why can't the heart use the blood inside its own chambers?
• Does the heart have its own mini-circulation?
• Why doesn't the heart get tired like other muscles?

Heart · How the Heart Beats

• What happens first in a heartbeat?
• Why do the atria go first?
• Do both ventricles fire together?
• Does the heart ever truly rest?
• Can the heart beat without the brain?
• Why does the signal need to pause?
• What is an ECG actually measuring?
• What is a doctor listening for with a stethoscope?

Heart · Heart and the Body

• What's a normal resting heart rate?
• Why do heart rate and breathing rise together?
• What do the two numbers in a blood-pressure reading mean?
• Why do athletes have such low resting heart rates?
• Why does my heart race before a presentation?

Heart · Healthy Heart Habits

• How does exercise change the heart?
• Why is salt bad for the heart?
• Why is smoking bad for the heart?
• How does sleep affect the heart?
• What does 120/80 mean?
• Why do healthy habits matter for the heart?

Heart · Put It All Together

• What should I learn next after the heart?

Lungs · Meet Your Lungs

• What do the lungs actually do?
• How much of my chest is lung?
• Why do the two lungs have different numbers of lobes?
• What counts as part of the respiratory system?
• Why can't we hold our breath for hours?

Lungs · The Airway

• Is it better to breathe through the nose or the mouth?
• What happens when food 'goes down the wrong way'?
• Why does the windpipe have rings?
• Why do inhaled objects usually go into the right lung?
• What happens to the airways during asthma?
• Where does all the dust I breathe in go?

Lungs · The Alveoli

• Where exactly does oxygen enter the blood?
• Why do lungs need so much surface area?
• How thin is the wall gas has to cross?
• Why don't the tiny air sacs just collapse?
• How long does blood spend in the lungs?

Lungs · The Great Gas Swap

• Do oxygen and carbon dioxide swap places?
• Does the body spend energy moving oxygen into the blood?
• Is the blood coming back from the body empty of oxygen?
• How does carbon dioxide travel in the blood?
• Why does blood need hemoglobin at all?
• Is blood ever actually blue?

Lungs · How You Breathe In

• Which muscle does most of the breathing?
• What are the muscles between the ribs for?
• If the lungs have no muscle, what moves them?
• Do lungs suck air in?
• Why is breathing so effortless most of the time?

Lungs · How You Breathe Out

• Do you use muscles to breathe out?
• What actually pushes the air back out?
• How much more air can you move when exercising?
• How much air do the lungs hold?
• Can you empty your lungs completely?

Lungs · Who Controls Your Breathing

• Why don't I stop breathing when I fall asleep?
• Why do I feel the urge to breathe?
• Why is it dangerous to hyperventilate before swimming underwater?
• Why do I start breathing hard the moment I start running?
• Do singers have bigger lungs?

Lungs · Healthy Lung Habits

• What does smoking actually do to the lungs?
• Why is haze actually dangerous?
• What's the difference between a cold and pneumonia?
• Does exercise make your lungs bigger?
• What does a lung function test measure?

Lungs · Put It All Together

• How do the heart and lungs work together?

Muscles · Meet Your Muscles

• What does a muscle actually do?
• If muscles only pull, how do I push a door?
• How many muscles does the body have?
• What makes up the muscular system?
• Why do I shiver when I'm cold?

Muscles · Three Kinds of Muscle

• Why is skeletal muscle striped?
• Why doesn't the heart get tired?
• Can you swallow upside down?
• Which muscles can I control?
• Do all muscles work the same way inside?
• Why is it called the biceps?

Muscles · Inside a Muscle

• Is a muscle fibre one cell?
• What causes the stripes in muscle?
• What is the smallest part of a muscle that can contract?
• What actually pulls inside a muscle?
• How does a muscle's pull reach the bone?
• Why can't I hold a maximum grip for long?

Muscles · How a Muscle Contracts

• Do the parts inside a muscle get shorter?
• What starts a contraction inside the fibre?
• What fuels muscle contraction?
• What causes rigor mortis?
• How do I control how hard I grip something?

Muscles · From Thought to Movement

• How fast does a nerve signal travel?
• How does a nerve tell a muscle to contract?
• Why are eye movements so precise?
• How does my body decide how much muscle to use?
• Why do I pull my hand back before I feel the pain?

Muscles · Muscles and Bones

• What's the difference between a tendon and a ligament?
• Why does the same muscle do different things in different exercises?
• Why do muscles come in pairs?
• Why does lifting a small weight need so much muscle force?
• Which muscles work when I'm doing nothing?
• What is that silvery film on meat?

Muscles · Fuel, Fatigue and Fibre Types

• Are some people born to be sprinters?
• Why can't I sprint for more than a minute?
• Why do I keep panting after I stop running?
• Is lactic acid what makes muscles burn?
• Why can I suddenly run faster when being chased?

Muscles · Healthy Muscle Habits

• How does muscle get bigger?
• Does eating protein build muscle?
• Why am I sore two days after exercise?
• How fast do muscles waste away?
• When do muscles actually tear?

Muscles · Put It All Together

• What happens between deciding to move and moving?

Brain · Meet Your Brain

• How many cells are in the brain?
• Does thinking hard burn more calories?
• What is cerebrospinal fluid for?
• What's the difference between the central and peripheral nervous systems?
• Do we really only use 10% of our brain?

Brain · Neurons and Signals

• What does a neuron look like?
• How does a neuron signal a strong sensation?
• Do neurons touch each other?
• Is dopamine the pleasure chemical?
• Why are nerve signals so fast?
• Are all brain cells neurons?

Brain · The Big Three

• Which part of the brain does the thinking?
• What does the cerebellum do?
• Which part of the brain keeps me breathing?
• Why is the brain wrinkled?
• What's the difference between grey and white matter?

Brain · The Four Lobes

• Which part of the brain controls self-control?
• How do I know where my limbs are without looking?
• Where are memories formed?
• Why is the vision centre at the back of the brain?
• Why does the left brain control the right hand?
• Why does a paper cut on a finger hurt so much?

Brain · Building Reality

• How does the brain tell sight from sound?
• Why do optical illusions still work when I know the answer?
• Why can't I see my blind spot?
• Can humans really multitask?
• Why does the same injury hurt more some days?

Brain · Memory and Learning

• Why do I forget a phone number so quickly?
• Why is eyewitness testimony unreliable?
• Where are memories stored?
• Can adults still rewire their brains?
• Why do we forget?
• Does sleep really help memory?

Brain · Emotion, Drive and Control

• Why do I jump before I know what scared me?
• Why is checking my phone so compelling?
• Why is self-control harder when I'm tired?
• Why does stress affect the body so much?
• What controls body temperature?

Brain · Healthy Brain Habits

• How much sleep does the brain need?
• Does exercise really help the brain?
• Do brain training games work?
• Does loneliness affect the brain?
• What actually happens in a concussion?

Brain · Put It All Together

• How do all the brain's parts work together?

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Body Atlas is an educational product. It does not provide diagnosis, treatment, or personal medical advice. · Privacy