Forensic crime drama CSI will be celebrating its 18th birthday this year and it appears our fascination with crime TV has not quit since the show made its debut in 2000. But have you ever wondered what actually happens to the body and brain right after we die?
We have enlisted the help of Professor Jens Dreier from the Center for Stroke Research at the Charité University Medicine Berlin and Dr Stuart Hamilton, Home Office pathologist, to find out.
So here it is, a step-by-step breakdown of everything that happens to the brain and body once the heart stops beating and the blood stops circulating – no gory deets left out.
Ready?
The immediate aftermath…
Chemical substances called neurotransmitters flood the brain, causing brain activity to spike for 30 seconds or so before crashing. It is not good news: normal brain activity has now ceased.
Minutes after cardiac arrest…
One to five minutes after death, the brain is hit by a process called terminal spreading depolarization (SD) – or, in less scientific terms, a “brain tsunami”. In its most basic form, this is a wave of neuron activity that starts in the deeper brain structures and radiates outwards, unlike the previous burst of neuron activity, which hits all areas of the brain simultaneously. Importantly, it signifies the breakdown of the brain’s electrochemicals (the substances responsible for keeping our neurons alive and functioning) and marks the point at which the capacity for brain function and awareness are lost. Oh dear.
“Until then, there is the possibility for evoked or spontaneous activity, even if the brain is silent,” Dreier told IFLScience. “Terminal spreading depolarization marks the onset of the toxic cellular changes that eventually lead to death, but is not a marker of death per se, since depolarization is reversible – up to a point – with restoration of the circulation.”
Meanwhile, because blood is no longer circulating the body, the skin develops a pale, vampire-like complexion – a phenomenon called pallor mortis, Latin for “the pallor of death”. The lack of fresh blood also causes the body’s internal temperature to drop in a second process, algor mortis (“the chill of death”). This usually occurs at a rate of 1°C (or 1.8°F) every hour until the body reaches room temperature, though it can vary depending on the body’s size.
Hours after cardiac arrest…
Now, the body may be starting to develop some attractive reddish blotches. This is because of a process known as livor mortis (“the wound of death”), also called hypostasis or lividity, which essentially refers to the discoloration of the skin that occurs when the blood gathers at the parts of the body closest to the ground. You can thank gravity for that.
The pools of blood “will initially move if the body is moved, but as the blood cells break down, they will stain the skin permanently,” explained Hamilton.
Interestingly, the cause of death and surrounding environment can affect the skin's coloring. Carbon monoxide poisoning, for example, produces cherry red splotches, extreme cold can result in a pinkish discoloration, and in other instances, the skin can adopt a blue or brown tinge.
At this point, the muscles are also starting to stiffen. Rigor mortis, which literally translates to “the stiffness of death”, takes place when there is a build-up of calcium and a depletion of adenosine triphosphate (ATP), a situation that causes the fibers of the muscles to bind together and solidify. The first muscles to be affected are the smaller ones (like the jaw), but by hour 12, complete rigor mortis has taken hold and the body remains frozen in position. This state is only temporary – 24 to 36 hours later, the muscles start to relax again and, yes in case you’re wondering, this can lead to defecation.
Then there is autolysis (aka self-digestion), a process whereby cells are destroyed by their own enzymes. Gruesome. The speed of autolysis depends on the type of tissue and is usually first noticed in the pancreas. It then sets off another process called putrefaction (or rotting in regular English speak), which ramps up as the hours, days, and weeks go by. Collectively, autolysis and putrefaction are known as decomposition.
All the while, the skin is shrinking, which, bizarrely, has the effect of making it look as though your hair and nails are growing despite the fact you are dead. Spooky.
Days after cardiac arrest...
Things aren’t looking pretty (think: bloating, blistering, and oozing fluids) and they have started to smell bad, too. The body is releasing nasty-smelling chemicals called putrescine and cadaverine, which are produced when the body’s amino acids breakdown. Hence, there is a lovely rotting corpse aroma. If you want to try and “picture” this smell, it has been compared to “a garbage can left to ferment in high heat for an extended period of time” and “a rotting piece of meat with a couple drops of cheap perfume.”
Meanwhile, the blood forms clots, the fat liquefies, and the corpse turns a lovely green color. All the while, the body’s enzymes continue to digest its own organs. Those without much fibrous content (such as the brain) will be the first to go. Those with more fiber (like the heart and uterus) will stick around longer.
Weeks after cardiac arrest...
The rotting body is becoming a sweet home for flies, maggots, and other creepy crawlies. “Almost from the moment of death, or even before in some cases, flies will lay eggs on the body – usually around the nose, mouth, and eyes, and maggots will hatch and begin to consume the body,” Hamilton told IFLScience. By day seven, the greedy grubs are able to consume up to 60 percent of the corpse.
At this point, the hair is also starting to fall out, leaving bald patches, and what’s left of the body turns purple and then black as it continues to decay.
Months after cardiac arrest...
The body has cooled down and temperatures are hovering around the 10°C (50°F) mark – so things are feeling fairly nippy. But the body hasn’t finished decomposing just yet. In fact, it will take roughly four months depending on the surrounding environment for the soft tissue to fully decompose.
“[The length of time it takes for the body to decompose is] incredibly variable and dependent on conditions of the place you are, how you died – people with infections tend to decompose more quickly, as they already have excess bacteria in the body, and are often warmer when they die,” said Hamilton.
Despite what you may assume, larger bodies actually decompose faster than thinner bodies because they retain heat for longer.
Years after cardiac arrest...
The final stage of decomposition is called skeletonization. The soft tissues are now gone, leaving the bones fully exposed. The skeleton gets lighter, drier, and more brittle. Eventually, it will disappear completely, but that can take thousands of years and all depends, once again, on the surrounding environment.
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