#568 Why don’t we move when we’re dreaming?

Why don’t we move when we’re dreaming? Chemicals in the brain inhibit the motor neurons and stop them from triggering the muscles. As well as this, the membrane potential in the motor neurons decreases, meaning the nerves need more voltage to trigger them.

We dream when we are in REM sleep, which is one of the four stages of sleep. We go through cycles of sleep, usually about 3 to 5 a night, with each cycle taking about 90 minutes. The first stage is called N1 and is very light sleep. Stage two is N2, which is deeper sleep. Your heart rate and body temperature both drop. This is the longest part of the sleep cycle, about 45%, and it is thought to be the part of sleep where the brain processes and integrates things learned and new memories. The third stage is N3, which is the deepest part of sleep. The heartbeat and breathing rate are very low. There are no eye movements and the brain produces delta waves, which are a high amplitude wave. This is the part of sleep where the body repairs itself and strengthens its immune system. It regenerates cells and repairs tissue. The fourth stage is REM sleep, which stands for Rapid Eye Movement. This is the dreaming stage of sleep. The heart rate and the breathing rate increase. Brain activity and eye movement increase. And this is the part of sleep where the brain needs to paralyze the body.

We need to dream. There is no definitive reason why, but it is thought to be used for memory consolidation, emotional processing, brain development, and preparation to wake up. In order to do all of these things, the brain acts out different scenarios that are our dreams. Obviously, our bodies can’t move while our brain is acting out these scenarios. If it did, we wouldn’t be able to stay in bed.

Two things happen to keep our muscles from moving. The first is by shutting down the motor neurons. When you want to move your hand, electrical signals go from the motor neurons in the brain, down the spinal cord, along all the nerves until they reach the hand and makes the muscles contract. The motor neurons have receptors through which they receive the signals to start transmitting to the muscles. To stop this, in REM sleep, a neurotransmitter called gamma-aminobutyric acid (GABA) and a neurotransmitter called glycine are released. They connect to the receptors on the motor neurons and switch them off. The brain thinks about moving, but the signal doesn’t get transmitted. These neurotransmitters only attach to the motor neurons that activate skeletal muscles. That means they don’t paralyze the eyes and they don’t stop the involuntary muscle movements, such as the heart and the diaphragm. The second is the depolarization of the motor neurons. When they do this, they require more voltage to be triggered and they inhibit wakefulness.

We stay in REM sleep for about 10 minutes for the first cycle, then it increases in length with each cycle. The final REM cycle could be as long as one hour before you wake up. At the end of the REM cycle, your brain starts to release serotonin to wake you up. If you wake up naturally, that is.

Some people suffer from sleep disorders that stop their body from releasing the neurotransmitters that block the motor neurons, which means their bodies aren’t paralyzed when they sleep. These people can sleepwalk, fight in their sleep, and one person was even known to ride a motorbike while asleep. Another sleep disorder that can happen is the opposite. Your brain paralyzes your body, but you are conscious. This is known as sleep paralysis, and it can be terrifying. People who suffer from this say that it feels like a very heavy weight is pressing down on their chest, holding them down. People can hallucinate as well, making the situation even scarier. Many sufferers say that it feels like they are being held down by a demon or a monster. Interestingly, when people who suffer from this are hallucinating, their cerebellum, the part of the brain that is responsible for letting you know where your body is, tells them that they are floating upwards. This can explain why people believe they are having out of body experiences or being abducted by aliens. And this is what I learned today.

Sources