138 Fun Facts About Human Anatomy

How many bones are typically found in the adult human body?

206 is the usual adult count, but none of it is inert: bone is living tissue that the body keeps breaking down and rebuilding throughout life.

What is the folded outer layer of grey matter covering the brain called?

The cerebral cortex is only 2 to 4 mm thick, so its folds are what let such a large sheet of it fit inside the skull.

Which is the thickest and strongest tendon in the human body?

The Achilles tendon ties the calf muscles to the heel bone and is named after the Greek hero Achilles, who in legend could be wounded only in the heel.

Which organ in the throat is commonly known as the voice box?

The larynx houses the vocal cords; at puberty its front wall grows more prominent in boys, forming the bump known as the Adam's apple.

Which blood type is the 'universal recipient', able to receive red cells from every ABO and Rh group?

AB positive red cells already carry the A, B and Rh antigens, so nothing in a donor's red cells looks foreign to the immune system; O negative is the reverse, the universal donor.

Which gland is often referred to as the 'master gland' of the endocrine system?

The pituitary gland is only pea-sized, and the 'master' has a master of its own: it releases its hormones on orders from the hypothalamus, the brain region just above it.

What is the collective name for the three membranes, the dura, arachnoid and pia mater, that wrap the brain?

The meninges are what meningitis inflames, which is why a stiff neck is one of its warning signs.

Which artery carries oxygen-poor blood away from the heart?

The pulmonary artery runs from the right ventricle to the lungs for a refill; the real rule is that arteries carry blood away from the heart, not that they carry oxygen.

Which butterfly-shaped gland at the front of the throat sets the pace of the body's metabolism?

The thyroid cannot make its hormones without iodine, which is why table salt is iodised: where diets lack iodine, the gland swells into a goitre.

Which heart chamber has the thickest muscular wall?

The left ventricle has the thickest wall because it must drive blood round the whole body, while the right ventricle only has to reach the lungs next door.

A newborn has dozens more bones than an adult because many of them later do what?

They fuse together: a baby's skull, for one, starts as separate plates joined by soft gaps, the fontanelles, which let the head flex during birth before the bones knit.

The skull, spine and rib cage together make up which part of the skeleton?

The axial division's 80 bones form the body's central column and guard the brain, spinal cord, heart and lungs; the limbs and their girdles hang from it.

What name is shared by the bones of the fingers and the bones of the toes?

Phalanges share their name with soldiers: the Greeks used one word, phalanx, for a line of battle and for these bones, which sit in rows like ranks; thumbs and big toes have two each, other digits three.

In adults, where are almost all new blood cells made?

The bone marrow is the body's blood-cell factory; donors give theirs through a needle into the hip bone, one of the main sites where adults keep active marrow.

Vesalius corrected Galen's claim that which body part was made of two bones rather than one?

Galen, who dissected animals, described a two-part lower jaw; Vesalius showed in De humani corporis fabrica (1543) that the human mandible is a single bone.

The stapes, the smallest bone in the body, is named after its resemblance to what?

A stirrup: 'stapes' is a medieval Latin coinage, because stirrups reached Europe only centuries after ancient Rome and classical Latin had no word for one.

The topmost vertebra, which carries the skull, is named after which figure of Greek myth?

Atlas, the Titan condemned to hold up the heavens, gave his name to the bone that holds up the head; the joint it forms with the skull is what lets you nod.

Forensic scientists often estimate a person's height from which bone, the longest in the body?

The femur makes up about a quarter of a person's height in both sexes, so a single thigh bone is enough to estimate how tall its owner stood.

Which skull bone houses the inner ear within its dense petrous part?

The temporal bone's petrous part is so dense that ancient DNA survives in it far better than elsewhere in a skeleton, which makes it the first bone geneticists reach for.

What name is given to the waves of muscle contraction that push food along the digestive tract?

Peristalsis is strong enough to work against gravity: food and drink you swallow will still reach your stomach if you are standing on your head.

Which is the shortest of the three regions of the small intestine?

The duodenum is only about 25 cm long, and its name says so: it comes from the Latin for 'twelve each', after its length of about twelve finger-widths.

Which finger-like projections lining the small intestine are named from the Latin for 'shaggy hair'?

Villi, Latin for 'shaggy hairs', carpet the gut wall so thickly that it looks like velvet, a word that grew from the same Latin root.

Roughly how many neurons does the human brain contain?

About 86 billion, by a 2009 count that broke brain tissue down and tallied its cells directly; textbooks had long quoted a round 100 billion.

The brain is only about 2% of body weight, yet it uses roughly what share of the body's oxygen?

It also takes 15% of cardiac output and a quarter of the body's glucose.

What is the largest of the nerve tracts connecting the brain's two hemispheres?

The corpus callosum bundles at least 200 million nerve fibres between the hemispheres; severing it to treat epilepsy produced the famous 'split-brain' patients.

Which lobe at the back of the brain is devoted mainly to processing vision?

The occipital lobe does the actual seeing: damage to it can leave a person blind even though both eyes are perfectly healthy.

Which layer of the body's outer covering contains no blood vessels at all?

The epidermis has no blood vessels at all, and its outer cells do not need them for oxygen: they take it straight from the surrounding air.

The stratum lucidum, a clear extra layer found only in the body's 'thick skin', occurs where?

The palms and soles alone have this layer, whose dead, flattened cells are packed with a clear protein that makes them look see-through under the microscope, hence 'lucidum'.

Which protein in the dermis lets skin stretch and then snap back into shape?

Elastin fibres in the dermis give skin its recoil; as they dwindle with age and are damaged by years of sun, skin sags and wrinkles.

Which part of the eye does most of its focusing, more than the lens itself?

The cornea does most of the eye's focusing and the lens only fine-tunes it, which is why laser surgery corrects sight by reshaping the cornea.

Which retinal cells handle dim light and give you grey night vision, outnumbering their colour-sensing partners about twenty to one?

Rods need time to reach full power: after about half an hour in darkness the eye is thousands of times more sensitive, which is why night vision arrives slowly.

Which type of tooth is missing from a child's 20 milk teeth?

Premolars exist only in the adult set, where they grow into the gaps left when the milk molars fall out.

Wisdom teeth are formally known as what?

Third molars are called wisdom teeth because they arrive last, usually between 17 and 25, an age at which people were supposed to be growing wise.

What is the hardest substance in the human body, and one it can never regrow once damaged?

Tooth enamel is almost entirely mineral, and the body cannot make any more once a tooth has formed, which is why a cavity never heals on its own.

On an abdominal ultrasound, the portal vein, hepatic artery and bile duct form a pattern named after whom?

Radiologists call it the 'Mickey Mouse sign': on a transverse view of the porta hepatis the portal vein forms the head and the hepatic artery and bile duct the ears.

Each kidney contains about a million of which microscopic filtering units?

Nephrons work in two steps: a tiny filter strains fluid from the blood, then a long tubule returns what the body still needs and sends the rest on as urine.

The right kidney sits slightly lower than the left because which large organ lies above it?

The liver, the body's largest internal organ, pushes the right kidney down; it is also one of the very few organs that can regrow after part of it is removed.

The windpipe divides into two branches, one for each lung, called what?

Bronchi are not mirror images: the right one is wider and steeper, so an object that is accidentally inhaled is more likely to end up in the right lung.

Oxygen enters the blood through hundreds of millions of tiny air sacs in the lungs called what?

Alveoli would collapse without surfactant, a film that lowers the surface tension of their wet walls; premature babies who have not yet made enough struggle to breathe.

Which bone is commonly known as the shoulder blade?

The scapula carries the shallow socket for the upper arm bone; that loose fit is what makes the shoulder the most mobile joint in the body.

Which bone cells, named from the Greek for 'broken', dissolve old bone so it can be rebuilt?

Osteoclasts dissolve old bone and osteoblasts build new; when the dissolvers outpace the builders, as often happens after the menopause, bones thin into osteoporosis.

What is the name for the study of tissues, usually done under a microscope?

Histology depends on dyes: the standard pair, haematoxylin and eosin, stains a thin slice of tissue in purples and pinks so that its cells stand out under the microscope.

The sinoatrial node, a cluster of cells in the wall of the right atrium, is known as the heart's natural what?

Pacemaker is the usual name, because the node fires on its own and each heartbeat spreads from that spark; when it falters, an implanted electronic pacemaker can take over.

Which structure do human red blood cells push out as they mature, leaving more room to carry oxygen?

The nucleus is pushed out as the cell matures, which leaves a flexible disc that can fold to squeeze through the narrowest capillaries.

Roughly how much fluid do the kidneys filter out of the blood each day?

About 170 litres are filtered, yet only one or two leave as urine: the kidney's tubules hand almost all of it straight back to the blood.

Roughly how many cells make up an adult human body?

About 30 trillion human cells, most of them red blood cells, and roughly as many bacteria again: a 2016 recount retired the old claim that microbes outnumber our cells ten to one.

Which large veins carry blood from the head back down towards the heart?

Jugular veins drain the brain and face, and a wound to one is so dangerous that 'the jugular' has come to mean anyone's most vital or vulnerable point.

Which coloured ring of muscle widens and narrows the pupil to control how much light enters the eye?

The iris takes its name from the Greek word for rainbow; its pattern is unique to each person, which is why scanners can use it to check identity.

Which protein gives bone the flexibility to bend slightly without snapping?

Collagen is what goes wrong in brittle bone disease: a fault in the genes for it leaves bones that can break at the slightest knock.

Which is the longest and widest single nerve in the human body?

The sciatic nerve, formed from spinal roots L4 to S3, runs from the lower back down the back of each leg; irritating it produces the shooting pain of sciatica.

The stapedius, the smallest skeletal muscle in the human body, is found where?

In the middle ear, where it steadies the tiny stapes bone to damp loud sounds; if the muscle is paralysed, ordinary noises can seem uncomfortably loud.

Which individual muscle is the largest in the human body?

The gluteus maximus is far bigger in humans than in other apes, yet it barely works when we walk; it fires hard when we run, steadying the trunk at each stride.

Which horseshoe-shaped bone is the only one in the body that does not touch any other bone?

The hyoid hangs in the throat from muscles and ligaments alone and anchors the tongue; because little else breaks it, a fractured hyoid is a classic forensic sign of strangulation.

The seven cervical vertebrae make up which part of the spine?

The neck has seven vertebrae in almost every mammal, a giraffe included, whose neck bones are simply much longer; sloths are among the very few exceptions.

The upper seven of the 12 pairs of ribs attach directly to which bone?

The sternum shields the heart behind it, so in open-heart surgery the surgeon cuts the bone down the middle to reach it.

The olfactory nerve, first of the twelve cranial nerves, carries which sense to the brain?

Smell is the one sense whose signals skip the brain's central relay station and go straight to its higher centres, alongside the regions that handle emotion.

Which fatty sheath wraps many nerve fibres, insulating them and speeding up their signals?

Myelin lets a nerve signal leap from gap to gap along a fibre instead of crawling; in multiple sclerosis the immune system attacks it, and the messages slow or fail.

The kneecap sits inside the tendon of which muscle group?

The quadriceps tendon holds the kneecap, the body's largest sesamoid bone, and the bone repays the favour: it gives that tendon extra leverage for straightening the knee.

Where are over half the body's bones?

The hands and feet hold 106 of the adult skeleton's bones, 27 in each hand and 26 in each foot, where they form the springy arches that absorb the shock of every step.

Which part of the adrenal gland produces the body's steroid hormones?

The cortex makes cortisol and its fellow steroids, hormones so necessary for life that people whose adrenal cortex fails must take replacements every day.

The insulin-producing islets of the pancreas are named after which anatomist?

Paul Langerhans first described the islets in 1869 while working towards his doctorate in Berlin; he noticed the odd clusters of cells but could not say what they did.

Which clear fluid, made inside the brain's ventricles, cushions the brain within the skull?

Cerebrospinal fluid floats the brain so effectively that an organ of about 1.4 kg presses on the base of the skull with the weight of only 25 to 50 g.

Which tiny gland produces melatonin, the hormone that helps set the body's sleep cycle?

The pineal gland, named from the Latin for 'pine cone' after its shape, releases melatonin as darkness falls, which is how the body's clock learns that it is night.

The hippocampus takes its name from its resemblance to which animal?

A seahorse: the name is Greek for 'horse sea-monster', and a rival name, the 'horn of Ammon', survives in the labels CA1 to CA4 for its subfields.

Which brain region, a tenth of its volume, holds most of its neurons?

The cerebellum, Latin for 'little brain', is packed with tiny granule cells; it does not start movements but fine-tunes their timing, so damage to it leaves a person clumsy and unsteady.

Breathing, heart-rate and vomiting centres sit in which part of the brainstem?

The medulla oblongata runs breathing and heartbeat without a thought, which is why opioid overdoses kill: the drugs quiet the brainstem's breathing centres.

Roughly how long does a red blood cell circulate before it is broken down and recycled?

About 4 months, or roughly 120 days; to keep pace with the losses, the body has to make more than two million new red cells every second.

Which blood component consists of tiny cell fragments rather than whole cells?

Platelets are fragments that pinch off giant cells called megakaryocytes; where a blood vessel is damaged they turn sticky and clump together to start a clot.

Which pale yellow liquid makes up a little over half of the blood's volume?

Plasma from donors is frozen soon after collection to keep its clotting factors working, then thawed when a patient needs it.

The phrenic nerves, from spinal segments C3 to C5, drive which of the breathing muscles?

The diaphragm depends on them entirely, hence the students' rhyme 'C3, 4, 5 keep the diaphragm alive': damage to those nerves can paralyse it.

Which of these joints is a ball-and-socket joint, able to swing in every direction?

The hip's ball sits deep in its socket, trading some mobility for the stability needed to bear weight; the shoulder, the other big ball-and-socket joint, makes the opposite trade.

Which valve lets blood pass from the right atrium into the right ventricle?

The tricuspid valve's three flaps are tethered by fine cords, the chordae tendineae or 'heart strings', which stop them being blown back into the atrium when the ventricle contracts.

The heart's mitral valve is named after the ceremonial headdress worn by whom?

Bishops wear the mitre, a tall hat that closes in two peaked halves; the valve earned the name because it is the heart's only valve with two flaps rather than three.

Waldeyer's ring, an immune barrier around the throat, consists of which structures?

Tonsils ring the throat because that is where germs arrive: the adenoid and the tonsils at the back of the tongue join the familiar pair to meet whatever is breathed in or swallowed.

The windpipe is held open by 16 to 20 C-shaped rings made of which tissue?

Cartilage keeps the windpipe from collapsing when you breathe in; each ring is open at the back, where a band of muscle completes the tube and lets it flex.

Which leaf-shaped flap folds over the airway during swallowing?

The epiglottis covers the airway only while you swallow, but if an infection makes it swell it can block the airway completely, which is a medical emergency.

Which 25 cm muscular tube carries swallowed food from the throat to the stomach?

The oesophagus ends in a ring of muscle that closes once food has passed; when it leaks, stomach acid splashes back up, and that burning is heartburn.

Which strong acid do cells in the stomach lining secrete to help break down food?

Hydrochloric acid would attack the stomach itself but for a coat of alkaline mucus and a surface lining that is completely renewed every few days.

The appendix dangles from which pouch at the start of the large intestine, just past where the small intestine ends?

The cecum, Latin for 'blind', is the pouch; the appendix is now thought to shelter helpful gut bacteria rather than being a useless leftover.

The large intestine, about 1.5 metres long, mainly absorbs what from the remains of digestion?

Water is drawn out there, turning liquid waste into solid stool; the 'large' refers to its width, since it is far shorter than the small intestine.

Which pear-shaped organ stores and concentrates bile, releasing it when a fatty meal arrives?

The gallbladder is not essential: people live normally without one, since bile can flow straight from where it is made into the intestine instead of waiting in storage.

Which organ in the upper left of the abdomen filters the blood and breaks down worn-out red cells?

The spleen can be removed after an injury and life goes on, though its loss leaves a person more prone to certain infections.

T cells mature inside which organ behind the breastbone, which shrinks after puberty?

The thymus gives T cells their name, T for thymus; it is busiest in childhood, and from the early teens its tissue is slowly replaced by fat.

Urine travels from each kidney to the bladder through which narrow tube?

The ureter squeezes urine along in waves of muscle contraction; a kidney stone that blocks one causes the sharp, severe pain known as renal colic.

Which coiled part of the inner ear is named from the Latin for 'snail shell'?

The cochlea is where sound finally becomes nerve signals: vibrations ripple through its fluid and bend rows of tiny hair cells, which fire in response.

The Eustachian tube, which lets your ears 'pop', opens into which space?

The nasopharynx, the space behind the nose, is where the tube opens; swallowing or yawning pulls it open and lets air through, which is how the pressure on each side of the eardrum evens out.

The eye's blind spot is where which structure leaves the retina?

The optic nerve leaves through the optic disc, a patch with no light receptors at all; you never notice the hole because the brain fills it in from the surroundings and the other eye.

Which tiny retinal pit, made entirely of cones, gives the sharpest vision?

The fovea is about 1.5 mm wide and its centre has no blood vessels at all, so light reaches its tightly packed cones without scattering.

Which cranial nerve's Latin name means 'wandering', fitting its route down to the gut?

The vagus, Latin for 'wandering', also acts as a brake on the heart, which is why doctors use manoeuvres that stimulate it, such as bearing down, to slow a racing pulse.

The small bumps visible on the tongue, which house its taste buds, are called what?

Papillae are the bumps you can see, while the taste buds themselves are microscopic; the thread-like papillae that cover most of the tongue carry no taste buds at all.

What is the pale crescent at the base of a fingernail called?

The lunula, from the Latin for 'little moon', is named for its crescent shape; it marks the visible edge of the root from which the whole nail grows.

Hair, nails and the outer layer of skin are built mainly from which protein?

Keratin also builds claws, hooves and feathers, and even a rhino's horn is made of it: the same material as your hair and fingernails.

Which cells produce the pigment that colours skin and hair?

Melanocytes hand their pigment to the surrounding skin cells, where it shields them from ultraviolet light; sunshine makes them produce more, and that extra pigment is a tan.

Which bone is named from the Greek for 'cuckoo', because it resembles the bird's curved beak?

The coccyx, usually four small vertebrae joined into one at the foot of the spine, is better known as the tailbone: it is what remains of a tail.

Which long, thin thigh muscle, the body's longest, is named from the Latin for 'tailor'?

The sartorius runs from the hip to the inner knee; it is said to be named for tailors because it pulls the leg into the cross-legged position in which they once sat to work.

Which is the only long bone that lies horizontally in the human body?

The clavicle, from the Latin for 'little key', props the shoulder out from the chest like a strut, so the force of a fall onto an outstretched arm runs straight into it and often breaks it.

Hitting your 'funny bone' actually strikes which nerve against the elbow?

The ulnar nerve runs just under the skin behind the inner elbow, so a knock sends a jolt down to the little finger; the 'funny' may be a pun on 'humerus' or simply describe the odd tingle.

Carpal tunnel syndrome comes from pressure on which structure at the wrist?

The median nerve shares the carpal tunnel with nine flexor tendons; pressure on it there numbs the thumb, index and middle fingers, the classic pattern of carpal tunnel syndrome.

Which tough bands of fibrous tissue tie one bone to another and are overstretched in a sprained ankle?

Ligaments vary from person to person: people described as double-jointed simply have more elastic ones, which let their joints bend further than usual.

Lack of which nutrient stops the body making stable collagen, so that gums bleed and wounds heal poorly?

Vitamin C is needed to stabilise collagen, and going without it causes scurvy, a disease estimated to have killed at least two million sailors between 1500 and 1800.

Which type of body fat burns energy to make heat and is especially plentiful in newborn babies?

Brown fat owes its colour to iron-rich mitochondria that turn fuel into heat without any shivering. Adults keep small deposits above the collarbones and along the spine.

Which type of muscle tissue pushes food through the intestines in waves, without any conscious control?

Smooth muscle is named for lacking the stripes other muscle shows under a microscope. It also lines blood vessels, the bladder and the stomach.

What name is given to the tiny junction where one nerve cell passes its signal on to the next?

Synapse was coined in 1897, more than fifty years before electron microscopes could show the gap itself, which is only about 20 nanometres wide.

Which tiny beating projections on airway lining cells sweep mucus and trapped dust away from the lungs?

Cilia beat in coordinated waves, with around 200 on every airway lining cell, carrying mucus and the debris stuck in it away from the lungs.

What is the name for removing a small sample of living tissue so it can be examined for disease?

A biopsy takes its name from Greek words for 'life' and 'sight'. The French dermatologist Ernest Besnier introduced the term to medicine in 1879.

What do surgeons call healthy tissue moved from one part of the body to repair another, as in burns treatment?

A graft arrives without a blood supply of its own, so it survives only if new vessels grow into it from the tissue around it.

Which fatty insulating layer wraps around nerve fibres and greatly speeds up their electrical signals?

Myelin works like the insulation around an electrical wire, and when it is damaged, as in multiple sclerosis, signals slow down or fail to arrive.

What forms when fibrous tissue takes the place of normal tissue after a deep wound has healed?

A scar is made of the same collagen as the tissue it replaces, but its fibres all line up in one direction instead of a basket-weave, which leaves it of poorer quality.

In nervous tissue, what feeds, protects and holds in place the neurons that carry the signals?

Glial cells were long said to outnumber neurons ten to one, but newer counting methods put the overall ratio at less than one to one.

Which long, slender fibre carries electrical impulses away from the body of a nerve cell towards other cells?

Axon fibres are typically about a thousandth of a millimetre across, yet a single one can run for a metre or more through the body.

What is the medical term for the premature death of cells in living tissue, as seen in gangrene?

Necrosis is uncontrolled and harmful, the opposite of apoptosis, the programmed cell death that happens naturally in a healthy body.

What name is given to the material that fills the space between the cells of a connective tissue such as bone?

Matrix can be rock-hard or runny: in bone it is collagen fibres stiffened with mineral, while in blood it is the liquid plasma.

Histamine, released during an allergic reaction, is stored in the granules of which residents of connective tissue?

Mast cells got their German name from a word for fattening: Paul Ehrlich called them Mastzellen for the large granules that pack each cell.

Which type of cartilage, the most common in the body, coats the ends of bones inside joints?

Hyaline means glass-like, a nod to its translucent look, and when this coating wears away inside a joint the result is osteoarthritis.

Which type of epithelium lines the bladder and ureters, flattening out so that they can stretch as they fill?

Transitional epithelium looks cube-shaped when relaxed and flat when stretched, and it is the most impermeable membrane in a mammal's body.

Skeletal muscle looks striped under a microscope because of which tiny repeating units that shorten as it contracts?

Sarcomeres sit end to end along each fibre, and the alternating dark and light bands they create were first described by Antonie van Leeuwenhoek.

Which connective tissue, known to most people simply as body fat, stores energy and cushions the organs?

Adipose tissue is more than padding: its cells release hormones such as leptin, which signals to the brain how much energy the body has in reserve.

Which junctions link heart muscle cells end to end, letting each beat sweep through the tissue as one wave?

Intercalated discs let heart cells work as a single unit, and skeletal muscle has none, which is one way to tell the two tissues apart on a slide.

Which muscle, forming the rounded contour of the shoulder, is the usual upper-arm site for vaccine injections?

Deltoid comes from the triangular Greek capital letter delta. The muscle suits only small injections, usually a millilitre or less.

Which large muscle spanning the back of the neck and upper back lifts the shoulder blades when you shrug?

Trapezius is named for its trapezium-like outline, and it works against itself: its upper fibres hoist the shoulder blades while its lowest fibres pull them down.

Which large, flat back muscle, trained by pull-ups and chin-ups, draws a raised arm down towards the body?

Latissimus dorsi is Latin for 'broadest of the back', and the muscle fans out wide along the spine before narrowing to its attachment on the arm.

Serratus anterior, which pulls the shoulder blade forward around the ribs, is nicknamed after which sport?

Boxing gives it the name 'boxer's muscle', because it drives the shoulder blade forward as a punch is thrown. It is also called the big swing muscle.

The muscles of the rotator cuff all run from the shoulder blade to attach around the head of which bone?

Humerus is the upper arm bone, and its head sits on a socket so shallow that the joint is likened to a golf ball on a tee, which is why the cuff has to hold it in place.

Which thick, fan-shaped muscle makes up the bulk of the chest and pulls the arm in towards the body?

Pectoralis major takes its name from the Latin for breast, and its job of drawing the arm inward is the motion of flapping the arms like wings.

A tear in which muscle's long head at the shoulder leaves an upper-arm bulge called the Popeye sign?

Biceps has a long head that runs straight through the shoulder joint, and when it snaps the muscle bunches up like the cartoon sailor's famous arm.

Which rotator cuff muscle, the one that starts lifting the arm out sideways, is torn more often than the others?

Supraspinatus begins the lift, then the larger muscle capping the shoulder takes over as the main mover beyond about 15 degrees.

What is a shoulder blade called when it sticks out from the back because serratus anterior is paralysed?

Winged scapula usually follows damage to the long thoracic nerve, because the muscle that nerve serves normally anchors the blade flat against the ribcage.

Which term describes raising the arm out sideways from the body, the main job of the muscle capping the shoulder?

Abduction is any movement away from the body's midline, and a tightrope walker's outstretched arms are the textbook example. Adduction brings the limb back in.

Which muscles of the upper back, a major and a minor on each side, pull the shoulder blades in towards the spine?

Rhomboids are named after the slanted, diamond-like rhombus, and they also keep the shoulder blades pressed against the wall of the chest.

Infraspinatus and teres minor, on the back of the shoulder blade, team up to produce which movement of the arm?

External rotation swings the arm outward, and infraspinatus is the shoulder's main muscle for it, with teres minor helping from just below.

Which nerve, often injured when the shoulder dislocates, powers the muscle that gives the shoulder its rounded shape?

Axillary nerve injury flattens the shoulder's outline and numbs a patch on the outer upper arm that doctors call the regimental badge area.

Which cranial nerve, the eleventh of the twelve pairs, powers the muscle that shrugs the shoulders?

Accessory nerve fibres take an odd route: it is the only cranial nerve to both enter and exit the skull, climbing from the neck before heading back down.

Which bony tip of the shoulder blade forms the summit of the shoulder and meets the outer end of the collarbone?

Acromion joins Greek words for 'highest' and 'shoulder', and its shape matters: some forms of it are linked to a greater risk of rotator cuff tears.

Which kind of slippery, fluid-filled sac lets the rotator cuff glide freely beneath the bony arch of the shoulder?

A bursa is lined with a membrane that makes a fluid as thick as raw egg white, and the body keeps these cushions around most of its major joints.

Which hook-like knob of the shoulder blade do surgeons call the 'lighthouse of the shoulder' when finding their way?

Coracoid process means 'like a raven's beak' in Greek, and it earns the lighthouse nickname by marking where major nerves and blood vessels bundle together.

Which shoulder condition produces a 'painful arc' when the arm is lifted between about 60 and 120 degrees?

Impingement syndrome hurts in that range because lifting the arm narrows the gap beneath the shoulder's bony roof, squeezing the rotator cuff as it passes through.

Serratus anterior, a muscle anchored by separate slips to the upper ribs, is named after the Latin for which tool?

A saw is what its jagged outline suggested to anatomists: the muscle starts as a row of separate slips, giving it a toothed edge along the side of the chest.

Which birth injury to the arm's upper nerve roots weakens the shoulder and leaves a 'waiter's tip' posture?

Erb's palsy is named after Wilhelm Erb, who showed in 1874 that this pattern of paralysed muscles traced back to just two nerve roots in the neck.