Sleep occurs when the brain activity is below a specified threshold. Science has helped us understand that the brain controls the function of the other organs, so when there’s something that causes a decrease in brain activity, sleep results.
Follow through as we explain the science of sleep and understand how your brain causes you to sleep off.
Short Explanation
Because the brain controls the activities of other organs through nerve cells that transmit sensory signals to and motor (response) signals from them, low motor output results in a decrease in activity in the general body system, manifesting as sleep. An even lower activity manifests as a coma.
Table of Contents
Brain Cells Communicate with Chemicals Called Neurotransmitters
The basic structural and functional unit of life are the cells that make up our tissues and organs. These cells shelter our genes and contain the biochemical processes that fuel our activities. For them to be efficient on a large scale, there has to be a strong connection between the different cells so that the activity of a cell can be synergized by other cells. Such similar cells come together as a tissue, and such similar tissues come together as a system which handles a specific aspect of our lives such as respiration, digestion, reproduction, and nervous coordination.
Cells communicate among themselves using chemicals. Hormones and cytokines are the most common of such chemical agents used in intercellular communication. For example, cells of the pituitary gland release antidiuretic hormone (ADH) so that kidney cells will know it’s time to reabsorb more water into the body because the body needs it. The same thing applies to the nervous system, which uses chemicals called neurotransmitters to transmit neuronal signals from one cell to another.
In the brain, and the rest of the nervous system, nerve cells or neurons have to transmit sensory signals from various parts of the body such as the eyes for visual signals, ears for auditory and skin for touch, and commute the signal to the brain. The brain processes the signal and prepares the right output signal such that if the stimulus is bright light the eyes are shut closed, if the stimulus is a soothing sound one is drawn towards it more, and so on.
This back-and-forth signalling requires transmission by several neurons connecting the brain to the rest of the body. Therefore, from cell A to B, a neurotransmitter is needed, the same as for subsequent transmissions.
Neurotransmitters often stimulate increased activity; such stimulatory transmitters include norepinephrine and dopamine. On the other hand, those that inhibit an action are known to be inhibitory neurotransmitters, such as glutamine and Gamma-aminobutyric acid (GABA). However, some neurotransmitters act as both stimulatory and inhibitory, depending on the location of their action; these include serotonin and acetylcholine, as well as norepinephrine and dopamine, in certain circumstances.
All of these neurotransmitters work together in complex relationship to result in a net effect observed when a neural signal is transmitted.
Activation of the Cerebrum is Mainly Directed at the Reticular Activating System (RAS)
The brain is divided into three main functional parts: cerebrum, cerebellum, and brainstem. The cerebrum is responsible for complex functions of thought, decision, motor impulses, and overall intelligence, while the brain stem connects the cerebrum with the spinal cord which extends downwards the body and distributes nerves across the body. Thus, sensory information from body organs, such as the skin, passes through the brain stem to the cerebrum, where signal processing and final decisions are made.
In this brainstem is a part referred to as the reticular activating system (RAS). The RAS is a group of different nuclei (clusters of nerve cell bodies) relaying activating signals to the cerebrum. It then follows that if the RAS cells are not transmitting sensory signals upwards, the cerebrum will have no input with which it makes motor decisions. Cerebral activities can thus reach a stage of such low activity that culminates in sleep.
RAS and the Onset of Sleep
The RAS, located in the brainstem, is the hotspot of neurotransmitter production. It harbors several neural nuclei, including the locus ceruleus and the raphe nuclei among others.
Most substantially, norepinephrine produced from the locus ceruleus is found to be highly involved in keeping the state of wakefulness, given its natural stimulatory activity. Another hormone, orexin, produced from the hypothalamus in the daytime in response to light, normally maintains a continuous release of norepinephrine by stimulating locus ceruleus. Hence, at night, orexin release ceases and the spontaneous trigger to produce norepinephrine follows suit, thereby reducing cerebral activity and inducing sleep.
In addition to the orexin-norepinephrine pathway, serotonin produced from the raphe nuclei has been found to induce sleep as well. Even though the exact mechanism isn’t fully elucidated, it is found that drugs that block the production of serotonin cause sleep disorders, showing its involvement in sleep initiation.
These two principal hormones, serotonin and norepinephrine, can also be produced as a result of sensory signals from other organs such as the ears and skin so that as long as they receive stimuli, the RAS sends stimulatory signals to the cerebrum. This signal initiates positive feedback, i.e. as the signal reaches the cerebrum, it triggers the RAS to keep firing. The signalling doesn’t stop until after long-hour activity leading to the nerve cells’ fatigue. This naturally leads to sleep during which the cells become replenished and normal activity resumes on wakefulness.
What Now? Your Takeaway
Next time you think of or want to sleep, you can maximize your sleep health by considering the science-backed advice that follows from your understanding of the science of sleep as explained in this post:
- It is best to not miss the night’s sleep because the orexin-norepinephrine pathway isn’t naturally activated and the brain is so meant to rest at that time. As you’d expect, forced wakefulness would thus strain brain cells, increasing the risk of developing neurological disorders, ranging from insomnia to cardiovascular and neurodegenerative diseases.
- To rest better, consider using an earmuff which helps block or, at least, reduce auditory stimuli. Remember that the less the signal the better, as your RAS neurons will have less activity burden on them, leading to sleep, a restful one.
- Talk to your doctor regarding drugs you are taking that may cause sleep irregularities or disorders. Drugs that affect the availability of serotonin, like antidepressants, could lead to irregular sleep habits.
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