Sleep is a fundamental part of a human’s daily life. We spend approximately 1/3 of our 24 hours sleeping. However, no two people sleep the same; sleep quality is different from one person to another.
Sleeping has become a topic of great interest in recent years, so much so that the traditional ideology of 8 hours sleep has come into question. If you’d like to keep a note of your sleep cycle, try out this sleep calculator.
The Anatomy Involved in Sleep
Sleep is essential in the formation and maintenance of learned pathways in our brain. The whole process is controlled by major regions of our brain, which includes the:
- Hypothalamus: The suprachiasmatic nucleus (SCN) is located within the hypothalamus. It has a significant impact on the regulation of the circadian rhythms with the light-dark cycle. The purpose of the suprachiasmatic nucleus is to process information regarding light exposure. Injury to this area can cause one to sleep erratically during the daytime to the loss of appreciation of light perception.
- Brain stem: The brain stem is a bridge between the brain and the spinal cord located at the brain’s base. The parts of the brain stem, namely the pons and medulla, are of great importance to the sleep-wake cycle. The hypothalamus communicates to these centers within the brain stem using the neurotransmitter GABA. GABA plays its part by causing the muscle to relax, providing an appropriate tone for the body to rest.
- Thalamus: Thalamus is essentially the relay center for a large deal of sensory information prior to its entry into the cerebral cortex. During your resting phase, the thalamus no longer plays a role, blocking out any external stimulus from interrupting sleep. This does not mean that the thalamus isn’t active at all; we feel and sense changes around us, but only when the stimulus is large enough to evoke a response.
- Pineal gland: The pineal gland makes a small part of the endocrine system responsible for melatonin production. Melatonin is a hormone that aids in the initiation of the sleep cycle when the light is dimmed. Those people who can no longer appreciate when it’s dark or bright outside can intake melatonin through exogenous sources to help induce sleep.
- Amygdala: The Amygdala is the most active part of the human nervous system during the REM (Rapid eye movement) cycle of sleep. It is a collection of cells present at the base of the brain and is a part of the limbic system.
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How Does a Person Sleep?
The sleep cycle is regulated by two internal mechanisms, namely homeostasis, and the circadian rhythm. The body’s circadian rhythm is the pattern of physiological effects within the body in an organized manner. The whole process is highly specific and detailed. Hence functions like the body’s metabolism, sleep-wake cycle, temperature, and hormone release are controlled. To put it simply, the body’s 24 hours clockwork is the circadian rhythm.
The external stimulus (temperature, light, etc.) plays a major role in regulating your circadian rhythm. Night shift workers often have a hard time sleeping in the day and staying awake during working hours because their circadian rhythm is disturbed.
On the other hand, we have the body’s sleep homeostasis. Homeostasis is described as the regulation of the internal body environment close to a constant. The role of homeostasis in sleep is to remind the body when to rest and wake up. The more tired you are, the deeper your sleep will be.
However, the sleep cycles can be disturbed by a plethora of medical conditions, some of which include Insomnia, stress, and medication. Other than health-related concerns, what you eat and the environment you sleep in also play a major role.
The Stages of the Sleep Cycle
The sleep cycle is classified into two different stages: the REM (rapid eye movement) cycle and the non-REM cycle. The non-REM part is effectively further classified into three more categories. During a typical night’s sleep, a person will alternate between REM and non-REM parts of the cycle. However, the REM part of the cycle occurs more frequently during the morning hours. Now we will discuss the 4 stages of the sleep cycle in greater detail.
Stage 1: known as non-REM or N1, lasts for a total of 1-5 minutes. This part of the cycle serves as a bridge between the waking period and the transition to sleep. During this phase, your breathing rate becomes slower, muscles relax, and eye movements began to slow down.
Stage 2: also known as the non-REM or N2, lasts for 10-60 minutes; this stage of the cycle is longer than any other stage. During this part of the cycle, your heart rate and breathing slow down even further, and your muscles relax to a greater extent. Moreover, your body temperature drops, and your eye movements halt. You can also expect your brain waves to begin slowing down and with a brief burst of electrical activity.
Stage 3: This phase of the cycle has many names other than non-REM. This includes the following variations:
- Slow-Wave Sleep (SWS)
- Delta Sleep
- Deep Sleep
The third stage of the cycle lasts for 20-40 minutes which is an essential stage as it plays an important role in making you feel refreshed once you wake up. In this stage of sleep, the muscles are completely relaxed, and waking a person becomes a difficult task.
Stage 4: The last and final stage of the sleep cycle is the REM. This phase of the cycle lasts for 10-60 minutes and first occurs approximately 90 minutes into your sleep cycle. As the name indicates, a person’s eye moves rapidly from side to side behind closed eyelids during their sleep. Here the brain waves show frequencies similar to those seen when a person is awake. This is because the person’s breathing rate and heart rate increase and become irregular.
Most people start dreaming during this stage. However, one can dream during the non-REM stages as well. Additionally, the body’s limb muscles relax enough to not allow any frantic movements to occur during the dreaming period.