A drawing after the 2008 map of Lee, McPhee and Stringer and standard landmarks. Real borders overlap.
Anatomy you can check on yourself
Your skin has stripes. You can’t see them
Every strip of your skin reports to one nerve of your spine. On an adult the strips look scrambled; on the embryo you were at five weeks they formed one neat stack. That old order is why an irritated diaphragm can hurt at the tip of the shoulder.
Tap any strip on the figure, or any block in the coloured column beside it, which stands for the spine, to see which nerve it reports to. Then scroll.
31 pairs of nerves leave your spine: eight in the neck, twelve in the chest, five in the lower back, five in the sacrum, one at the tailbone. Each carries touch, warmth and pain from one strip of skin on its own side of the body. Anatomists call such a strip a dermatome.
The strip lit on the figure runs through the navel. It belongs to the tenth nerve of the chest, T10 for short.
The page lists 29 strips on each side. The first nerve of the neck usually has no skin of its own, and the last strip, at the tip of the tailbone, is left out.
Try it. Put a finger on your navel and slide it sideways around your waist, rising a little, until it reaches the spine. That was one nerve’s territory.
From the collarbone to the groin the strips lie like hoops on a barrel, each sloping down a little toward the front. Doctors use them as a ruler: T4 at the nipples, T6 at the lower end of the breastbone, T10 at the navel, L1 at the groin.
When an injury to the spinal cord takes away feeling, the level on the skin where feeling stops tells the doctor roughly where the damage is.
Count down from the neck: C2, C3, then C4 over the shoulder and the top of the chest. The next hoop is T2. Five nerves, C5 to T1, are almost absent from the front of the trunk.
They are in the arm. C5 covers the outside of the shoulder, C6 runs down to the thumb, C7 reaches the middle finger, C8 the little finger, and T1 comes back up the inside of the forearm.
Try it. Touch your thumb, then your little finger. They are a hand’s width apart and they report to different nerves: the sixth and the eighth of the neck.
Pose the figure the way an embryo holds its limbs: straight out from the trunk, thumbs and big toes toward the head. The strips of the arm now run in order from top to bottom, C5 to T1, and fit between C4 above and T2 below.
Nothing was missing. The middle of the stack was drawn out sideways into a limb.
Try it. Hold your arms straight out with your thumbs up. The thumb side of each arm is the head end of the old stack; the little-finger side is the tailbone end.
Early in the second month after conception, the back of an embryo a few millimetres long is a row of paired blocks of tissue called somites. Each block gives rise to one vertebra’s worth of muscle and skin, and that skin keeps the block’s own nerve for life.
Near the end of the fourth week, around day 26, the arm buds appear beside the lower neck. The leg buds follow beside the lower back. Each bud grows outward and takes the nerves of its own blocks with it.
Look at where the heart is: just under the head. It will matter further down.
In the seventh week each limb turns a quarter of a circle. The arm turns outward, so the palm faces forward and the thumb points away from the body. The leg turns inward, so the big toe ends up on the inside.
That is why your arm folds forward at the elbow and your leg folds backward at the knee. The strips were carried round with the limbs, and those of the leg now run aslant across the thigh and shin.
Try it. Stand with your palms facing forward. Thumbs point outward, big toes inward: the two ends that once pointed the same way.
The chickenpox virus never leaves the body. It stays dormant in the clusters of nerve cells beside the spine, one cluster for each nerve, and in those of the nerves of the head. If it wakes, decades later, it travels down that nerve to the skin.
The rash then shows the strip: one, sometimes two neighbouring ones, on one side of the body, and it usually stops at the midline. The Greek name, zoster, means a belt. “Shingles” comes from the medieval Latin for a belt, cingulus.
In the United States about 1 person in 3 gets shingles in a lifetime, by the estimate of the US Centers for Disease Control and Prevention. The first maps, drawn by Henry Head in the 1890s, used such rashes, together with the patches of skin that turn tender when an organ is diseased.
Three classic maps exist. Henry Head, later with a co-author, Campbell, drew his from shingles rashes. Otfrid Foerster, in Breslau, cut the nerve roots around a single root in patients and mapped the skin that still felt. Keegan and Garrett, in 1948, mapped the numb skin of people with slipped discs. The three disagree, and textbooks reprint different ones.
In 2008 three anatomists, Lee, McPhee and Stringer, reviewed the evidence and concluded that the maps in use were “inaccurate and based on flawed studies”. They drew a new one from the best data, and asked for more weight on overlap and on differences between people. The figure on this page follows their map; its sharp edges are a drawing convention.
A teaching file hosted by the American Association for Anatomy adds something the maps leave out: Foerster’s patients most likely came from a psychiatric unit, and it is highly unlikely that they were asked for consent.
The diaphragm, the muscle you breathe with, lies under the lungs. Its muscle cells came from blocks in the neck, probably the third to the fifth, and moved down as the embryo grew. Its nerve, the phrenic, went with it: it still leaves the spine in the neck and runs down past the heart.
The skin over the top of the shoulder reports to the same part of the neck. So irritation under the diaphragm is often felt at the tip of the shoulder. Doctors know the left-shoulder version as Kehr’s sign, an uncommon clue to bleeding under the diaphragm, classically from the spleen.
After keyhole surgery the same pain is common: up to 80% of women have shoulder-tip pain after a gynaecological laparoscopy, a figure cited by a Cochrane review. The leading explanation is that the gas used to lift the abdominal wall irritates the diaphragm; the exact cause remains unknown.
A nerve that reaches the voice box by way of the chest §
In the embryo the heart sits just under the head, and the nerve of the voice box reaches it by passing just below the great arteries. Then the neck forms, and the heart and its arteries move down into the chest. The nerve is hooked under them and dragged along.
In an adult, the left nerve of the voice box still leaves the skull, travels down into the chest, loops under the arch of the body’s main artery and climbs back up the neck. Every living animal descended from the first four-limbed vertebrates has the same loop. In the largest giraffes the whole route approaches 5 metres, calculated from a neck 2.4 metres long.
Try it. Hum. The signal that brought your left vocal cord to the middle went down to your chest first.
The heart’s pain fibres enter the spinal cord around the top of the chest. Those segments also own the skin of the chest and of the inner arm. That is the usual explanation for the textbook pattern: pressure in the middle of the chest that may spread to the arm.
Pain in the neck and jaw probably takes another route, along the vagus nerve to the very top of the spinal cord. The researchers who study it say much remains to be worked out.
The pattern is far from universal. In a US registry of 1,143,513 people admitted with a heart attack, 42% of the women and 31% of the men had no pain recorded in the chest, arm, neck or jaw on arrival. If it could be a heart attack, call the emergency number at once: what the health services say.
The appendix lies in the lower right of the abdomen, but its nerve fibres enter the spine with those of the middle of the gut, at T8 to T10, the strips around the navel. Early appendicitis is typically a vague ache there.
Hours later the pain usually moves to the lower right and sharpens. That second pain is no longer referred: the inflamed appendix is now touching the lining of the abdominal wall, which has precise nerves of its own, like skin. A review in the BMJ notes that the full classic sequence may be present in only half of patients.
The tube from kidney to bladder, the ureter, reports to T12 to L2. As a stone moves down it, the pain typically starts in the flank and travels to the lower abdomen, the groin or the genitals, along the skin of those segments.
The testes began beside the kidneys and descended before birth; their arteries still leave the body’s main artery just below those of the kidneys. In one hospital series of 76 cases of a twisted testis, nine patients (12%), boys of 10 to 17, arrived complaining of abdominal pain. A twisted testis is an emergency: the usual window for saving it by surgery is about six hours from the start of the pain.
The explanation most researchers accept is called convergence. Pain fibres from an organ and pain fibres from a patch of skin enter the spinal cord at the same level and meet on the same relay cells. One cell, two sources.
Fibres from organs are few: less than 10% of those entering the cord. That scarcity may be why a signal on the shared line is read as coming from the usual sender, the body wall. Where exactly the mix-up happens is still unknown.
The embryo explains part of the rest. For the diaphragm and the gut, the organ and its patch of skin were neighbours in the stack. The heart’s wiring is less tidy, and the sources do not agree on its segments.
Five connections between parts of the body that seem to have nothing to do with each other. Some are in everyone, some in a minority. Answer all five and the page puts your set into one sentence you can send.
None of the five is, on its own, a reason to see a doctor.
Do you sneeze when you step into bright sunlight?
It is called the photic sneeze reflex. Studies have found it in anything from 3.2% of people (a Japanese web survey) to 57% (patients of a German ear, nose and throat clinic, counting occasional sneezers). A pooled estimate from 2026, not yet peer reviewed, is 22%.
It is more common within some families. The usual guess is cross-talk between the nerve of the eye and the nerve of the nose and face. Nobody has shown it.
Does something in your ear canal make you cough?
A branch of the vagus nerve, the nerve of the throat and airways, supplies part of the ear canal. In a few people, touching the canal sets off a cough: 2% of healthy volunteers in one study, and 25.5% of adults with a chronic cough.
Think of the last time a doctor looked into your ear or you cleaned it. Do not push anything into the canal to find out.
Knock your funny bone. Does your little finger tingle?
The ulnar nerve passes just under the skin behind the inner knob of the elbow, on its way to the little finger and the near half of the ring finger. Struck at the elbow, it reports from the place it normally serves.
A light tap in the groove behind the inner elbow is enough. The brain reads the line, not the place where it was hit.
With your middle finger folded under, can your ring finger lift?
Lay your hand flat on a table, fold the middle finger under the palm and try to raise each of the others. Bands of tendon tie the ring finger’s tendon to its neighbours on both sides, and the fingers also share muscle and control.
Hand researchers disagree on how much of this is tendon and how much is control.
Has ice cream ever hurt in your forehead?
The cold is on the palate; the pain arrives in the forehead. In a trial with 145 schoolchildren, 20 of the 73 told to finish their ice cream in under five seconds reported the headache (27.4%), against 9 of the 72 told to take more than thirty (12.5%).
Read this table from left to right only. It says where an organ’s pain tends to appear. It does not work backwards: a pain in one of these places has many possible causes, and no table can tell them apart.
Organ
Where its pain is usually felt
The shared wiring
Diaphragm
The tip of the shoulder on the same side.
Its nerve leaves the spine in the neck (C3 to C5); the skin over the shoulder reports to C3 and, mostly, C4.
Heart
The middle of the chest. It may spread to either arm, the neck, the jaw, the upper back or the upper belly.
Pain fibres enter around the top of the chest (one reference work gives C7 to T4). Neck and jaw: probably along the vagus nerve.
Stomach and lower gullet
The upper middle of the abdomen.
The first stretch of the embryo’s gut.
Appendix and small intestine
Around the navel. In appendicitis the pain usually moves to the lower right within hours.
The middle stretch of the gut, T8 to T10. The later pain is direct, not referred.
Gallbladder
Under the right ribs or in the upper middle of the abdomen. It may reach the back, the right shoulder blade or the right shoulder.
The shoulder pain goes by way of the diaphragm’s nerve on the right.
Ureter, with a stone in it
The flank, moving to the lower abdomen, the groin or the genitals.
T12 to L2.
Testis
The scrotum; sometimes the lower abdomen first.
It formed beside the kidney and descended. Why its pain can start in the abdomen is not established.
If it could be a heart attack
Call 999 in the United Kingdom, 112 anywhere in the European Union, 911 in the United States. Do not drive yourself to hospital.
The NHS lists these signs: chest pain that may feel like crushing or squeezing and may spread to the arm, neck and jaw; shortness of breath; feeling or being sick; a feeling like indigestion; sweating; pale, blue or grey skin. The British Heart Foundation adds pain that spreads to either arm, the upper back or the stomach, and feeling light-headed, and notes that you may not have all of these.
Chest pain is the most frequent symptom in women and in men. It is not always there: in the US registry of 1,143,513 patients (1994 to 2006), 42% of the women and 31% of the men arrived at hospital with no pain recorded in the chest, arm, neck or jaw. Such heart attacks were more common in older patients.
This page explains anatomy. It cannot tell you what a pain means. The wording above was checked against the NHS and British Heart Foundation pages on 10 October 2026.
The strip of skin whose feeling is carried by one spinal nerve. Each side of the body has its own set, so a strip stops at the midline.
How many dermatomes does a person have?
There are 31 pairs of spinal nerves. The first one in the neck frequently has no sensory root, so it usually has no strip of its own; that leaves about thirty on each side. The page lists 29, from C2 to S5; four of them, S2 to S5, lie on the back and underside of the body and are not visible on the figure. The last strip, at the tip of the tailbone, is not listed.
Are dermatome maps exact?
No. The classic maps were made by different methods and disagree, each strip overlaps its neighbours, and people differ. The 2008 map of Lee, McPhee and Stringer, as reproduced, leaves parts of the body unshaded.
Why does the shoulder hurt after keyhole surgery?
The usual explanation is that the gas used during the operation irritates the diaphragm. The diaphragm’s nerve comes from the neck, like the nerves of the skin over the shoulder, so the pain is felt at the shoulder tip. A review of the studies says the exact cause remains unknown.
Why can a heart attack be felt in the arm or jaw?
The heart’s pain fibres enter the spinal cord at the top of the chest, at segments that also serve the skin of the chest and the inner arm. Neck and jaw pain probably travels along the vagus nerve. A large minority of heart attacks cause no pain in the chest or arm at all.
Does shingles really follow one strip?
Usually one or two neighbouring strips on one side of the body, most often on the trunk, and the rash usually does not cross the midline (US Centers for Disease Control and Prevention).
The figure. A drawing made for this page, front view only. The layout of the strips follows the evidence-based map of Lee, McPhee and Stringer (2008), as reproduced by Bernhoff and others (2016), and the landmark list in StatPearls (thumb C6, middle finger C7, little finger C8, nipples T4, navel T10, big toe L5). Where that map leaves skin blank, the drawing extends the nearest strip. At the knee the tap texts follow the StatPearls landmarks. Borders are drawn sharp; in a body they overlap.
The embryo. A schematic of an embryo of about five weeks, one block per future vertebra, coloured with the same key as the adult. Sources date the limb buds differently: the third week in Gray’s Anatomy of 1918, the end of the fourth week in a current textbook, about day 26 and “around the fifth week” in two StatPearls chapters. The page uses the current textbook’s dating. The arm bud’s nerves are given as C5 to T1; the range drawn for the leg, L2 to S2, is this page’s simplification. The 1918 textbooks give wider ranges (Gray: C4 to T2 and T12 to S4). The drawing has 37 blocks; counts for a real embryo of this age run from about 30 to 44 pairs. The quarter-turn is dated to the seventh week in the current textbook and to the third month in Cunningham’s of 1918; the folding of elbow and knee is described in Gray’s.
The old maps. How Head, Foerster, and Keegan and Garrett worked is described after a 2025 guide for hospital residents and a teaching file hosted by the American Association for Anatomy.
Organs. Where each organ’s pain is felt comes from StatPearls chapters, NHS pages and the reviews listed below. Sources disagree on the heart’s segments (C7 to T4 in one, the upper chest and lower neck without C7 and C8 in another), so the page names no exact range in the story. The ranges for the appendix and the ureter each come from one StatPearls chapter. The explanation by convergence is the one most reviews accept; one of them states that the place and the mechanism of the mix-up are still unknown.
The five tests. The share of people who sneeze at the sun depends heavily on how the question is asked; nearly all studies in the pooled estimate were judged at high risk of bias. The ear-cough figures come from 100 healthy adults, 100 healthy children, 200 adults and 100 children with chronic cough; another study found the reflex in none of 55 healthy people. The ice-cream percentages are computed from the trial’s counts; the paper prints them rounded, as 27% and 13%.
Health. This page was written by a journalist, not a doctor. Its health wording was checked on 10 October 2026 and will be checked again before 27 March 2029, when the first of the NHS and British Heart Foundation pages is due for review.