Jenna Beam
Happy Halloween Science-verse! Sorry to disappoint you, but this article is not about Rick and Morty. Instead, in celebration of the spooky season, I thought we’d talk about dead people. Unfortunately (or fortunately?), the Walking Dead-esque “undead” (read: zombies) don’t exist…at least not to our knowledge (bum bum bum). But what does exist is the series of processes that a body goes through after death. Let’s dive right in.
If you’ve watched half as many crime dramas as I have, you’re pretty familiar with the term rigor mortis. Rigor mortis derives from the Latin for “stiffness” (rigor) and “death” (moors), and literally refers to the stiffening of the body a few hours after death. Rigor mortis broadly occurs because, as a person stops breathing and blood stops circulating, their cells lose the ability to respire. How does this lead to muscle stiffening? I’m glad you asked! Let’s go for a quick dive into cellular respiration and muscle contraction.
The muscles that control movement of the skeletal system are known as skeletal muscles. These muscle cells are long and tubular and made up of thick and thin filaments. The thick filaments are mostly made of a protein called myosin, while the thin filaments are made of actin. When your muscle cells get a signal to contract, the myosin protein attaches to the actin protein and pulls, as you can see in the GIF (or by clicking here). This process of muscle contraction requires energy in the form of a molecule called ATP. ATP is generated using oxygen and glucose in processes known as glycolysis and the Krebs cycle. 
Muscles will stay in the contracted state until ATP binds to myosin, allowing myosin to release from actin. When a person dies and stops breathing, their cells run out of oxygen. And when they run out of oxygen, they stop producing ATP. Without ATP, myosin maintains its death grip (pun very much intended) on actin, locking muscles in the contracted state.
Eventually rigor mortis ends. And contrary to what you might see out there on the interwebs, it doesn’t end because your muscles suddenly relax. Instead, during rigor mortis, a process known as autolysis also begins. During autolysis, all the cells in the body begin to lyse, or burst. As the cells burst, the muscles break down and soften as decomposition progresses. This process is generally followed by putrefaction, but we’ll save that barrel of fun for another time.
Forensic scientists can use rigor mortis to roughly approximate time of death. “Roughly” is the operative word there since everything from how someone died to the outside temperature to the amount of fat on someone’s body can affect how and when rigor mortis sets in.
Rigor mortis is just the tip of the freaky iceberg when it comes to what happens to a body after death. Stay in the spooky spirit and check out this cool video from the American Chemical Society to learn more about the whole process!
Peer edited by Kayla Goforth