What Is Sleeping and How Does It Happen?

Photo by Andrea Piacquadio Credit

Have you ever wondered what is sleeping and why we need it so much?

It's something all living things do. Basically, when we sleep, we're kind of taking a break from everything. Our bodies slow down, and we go into this temporary stare of unconsciousness where we're not really aware of what's happening around us. It’s like giving our bodies a chance to rest and recharge.                                                            

Why Do We Sleep? 

There is no doubt that sleeping is important. If you ask any person why do you sleep? The answer would be self-evident; we sleep because we are tired. The answer is that simple yes. I cannot give you a definitive answer to why we sleep but I can tell you what would happen if we did not.

Sleep is important in many functions in the body such as temperature regulation, cognitive and memory functions, and homeostasis which is (preserving the internal conditions of the body as they are for survival). This is basically what we know so far.

Sleep Physiology

To understand how sleep works, we need to learn more about the brain's anatomy:

Illustration by Author

In your brain, two teams are working against each other.

One team, The Arousal-Promoting System, keeps you awake, while the other team, The Sleep-Promoting System, wants you to doze off.

The Arousal-Promoting System

As you can see in the above illustration, the green dots represent the subcortical regions or nuclei that constitute the “Ascending” arousal system. It is called ascending because it begins from the brainstem and then goes all the way up to the cortex.

This system, also known as the Reticular Activating System (RAS), is made up of different parts that work together to keep you alert and ready to go. They release all sorts of chemicals, like norepinephrine, serotonin, histamine, dopamine, acetylcholine, and orexin, to help keep your brain buzzing with activity. The Sleep-Promoting System

On the other hand, the Sleep-Promoting system, represented by the red dots in the illustration is all about encouraging you to fall asleep.

It is centered around a part of your brain called the VLPO (Ventrolateral preoptic nucleus) in the hypothalamus. It releases calming chemicals like GABA and Galanin, which help dial down brain activity and encourage sleepiness.

These two systems work together in an unbelievable harmony, balancing each other out. It is like a delicate seesaw, ensuring your brain knows exactly when it is time to rest. 

What Triggers The Systems?

Now that we have a general idea about the structures involved in the wakefulness-sleep process, the question still stands; how does it get triggered? How does our brain wake us up? How is this process triggered and maintained?

Illustration by author

When the sun rises and light hits our eyes in the morning, it kickstarts our brain into action. This info goes to a special part of our brain called the Suprachiasmatic Nucleus (SCN), which acts like our bodies' internal alarm. The SCN then talks to the Reticular Activating System (RAS), our wakefulness center, waking us up and getting our brain going.

This whole process—Sunlight + SCN + RAS + Cortex Activation—gets us ready for the day. But the SCN's work doesn't stop there; it also controls our body's internal clock, known as the circadian rhythm. This rhythm controls when we release hormones like Melatonin and Cortisol, affecting when we feel sleepy or awake.

As the day winds down and it gets darker, the SCN slows down. This leads to less activity in the RAS and more in the other opposing part of the brain. Can you name it?

That's right, it is the Sleep-Promoting System (VLPO). This shift makes us feel sleepy by releasing calming chemicals.

Throughout the day, our cells keep busy, breaking down food and making energy. This creates by-products like Adenosine, which build up in our body. When Adenosine levels rise, they influence the VLPO as well and increase its activity. They tell the brain it's time to rest and sleep.

Interestingly, caffeine in coffee blocks Adenosine, keeping us alert. But once its effects wear off, Adenosine kicks back in, making us feel sleepy.

So, as night falls, the SCN and RAS take a back seat, letting the VLPO lead us into a good night's sleep.

What are Sleep Waves?

Sleep waves, also known as brain waves, are patterns of neuronal activity in the brain that can be measured using an electroencephalogram (EEG). These waves vary in frequency and amplitude, reflecting different stages of wakefulness and sleep.

Types of Sleep Waves

There are four primary types of sleep waves: alpha, beta, delta, and theta waves.

Alpha Waves	Beta Waves	Delta Waves	Theta Waves
Relaxed & Awake	High frequency, low amplitude	The slowest and highest amplitude	Slower than Alpha and Beta but faster than Delta
Present during alert wakefulness	Present during awake and active engagement, problem-solving, or decision-making	Most prominent during deep, restorative sleep	Associated with light sleep and REM (rapid eye movement) sleep, the stage of sleep where most dreaming occurs

Sleep Cycles and Sleep Waves

A typical night’s sleep consists of multiple sleep cycles, each lasting about 90 minutes. Each sleep cycle includes stages of non-REM sleep (characterized by alpha, theta, and delta waves) and a period of REM sleep (associated with theta waves).

Non-REM			REM
N1	N2	N3	Rapid Eye Movement
The transition from wakefulness to sleep	Light sleep	Deep sleep	Vivid Dreaming Muscle Paralysis
Theta Waves	Theta Waves	Delta Waves	Theta Waves

In summary, understanding how we sleep is a fascinating area that researchers and sleep fans find intriguing 

Whether it's the complex actions of brain chemicals or the regular patterns of deep and dream sleep, each part of sleep is crucial for our health 

Exploring sleep physiology helps us appreciate just how important a good night's sleep is for our bodies and minds during the day