The human brain can function in a number of ways, some of which are still being studied today. A process that we have studied intensely and have been able to generate a systematic explanation for, is the sleep cycle. The ability of the mind to slip from consciousness, an awareness that makes sense of all the things happening around us at any given time, to unconscious, as sleep following a cycled pattern happens every night and oscillates between states (MyPsychLab). Human survival hinges on sleep as it is a form of relaxation and rejuvenation for the mind and body. The following paper will discuss sleep; including the five stages of the sleep cycle and what is happening in the brain while sleeping.

The Stages of Growth.

Before Birth, Fetal growth and the Behavior of the fetus.

There are several stages that can happen during the growth of the fetal development. The following are the stages of growth from fertilization. Within three weeks of fertilization, the embryo is formed. And the baby’s first nerve cells are created. From the moment of concept to the eighth week of pregnancy the developing baby is called an embryo. After the 8th week the baby is called a fetus, up until the birth of the child. At 4 weeks after fertilization the embryo will resemble a tadpole. With a large head area and tiny balls that will eventually transform into arms and legs. At this stage the parent will not be able to recognize any facial features. At the 9 weeks mark the fetus has lost its tale and the fetus will start looking more like a human body. Arms and legs will begin to grow, and the beginning of fingers and toes will appear. By the 12 weeks range the fetus will have a neck, fingers and toes. The sex of the fetus can be recognized. By the 16 weeks mark the lungs, bones and muscle tissue will have formed. Within two weeks the heartbeat can be heard by using a stethoscope on the abdomen of the mother. Between

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24 and 28 weeks the cerebral cortex has developed. At the 28 to 38 weeks stage the central nervous system has control over bodily functions. At the 39-week stage, the baby continues to grow, their lungs are nearly fully developed. At this stage the babies can blink, close their eyes, turn their head and grasp firmly.

Stimulation from the Outside.

While the baby is in the womb, they have the ability to hear sounds, experience smells, feel pressure, movement and see light through the abdominal wall. At 26 weeks the baby, can hear their mother’s heartbeat. Ears are formed at around the 26th week mark. The baby can respond to sounds by moving. For example, if the baby has a hiccup the mother will notice a jerking motion. By 6 weeks the eyes are formed and the baby is able to detect light at 20 weeks. At the 30 week mark the baby will change positions frequently and will respond to pain, light and sound. At this stage the amniotic fluid begins to diminish, so the baby is able to hear more and see more.

Fetal Movements.

By the 8 to 9-week stage the fetus will start to show small movement as they are growing their limbs, neck and trunk. By 12 weeks the baby will make more movements with their mouths, such as yawning and sucking. The baby will be able to suck on its thumb. Around the 21st week range, the baby’s muscles are developing, and they will be exercising their new muscles. So, the mother will be experiencing much more movement. This type of movement is called quickening. Around the 34 weeks mark the baby will be kicking more. By the 39th week the baby does not move as much, because of the tight space, at this stage the baby will begin to prepare itself for labor and will start moving itself towards the mother’s pelvis. Studies have showed that “working mothers with low levels of serotonin could be less alert to fetal movements. It was demonstrated by Olesen & Svare in their review of fetal movements that busy mothers may not perceive as many fetal movements because they are not concentrating on fetal activity, and they often report an inaccurate reduction of fetal movements.”

Newborn Movements.

The most amazing development happens with in the first few weeks of a baby life. From birth to 3 months, the baby is leaning how to use their motor skills.

Month One- The first few months the baby has limited movements. One of the very first parts of the body that the infant can move are their eyes. The infant will look at familiar sounds that are around them. At this stage the infant is able to move their head from side to side. This action can be seen usually at feeding time, as they are positioning their head towards the mother’s body. Babies will show spontaneous movements within the first few months of birth. They may blink their eyes, open and close their mouths and put a foot in front of the other simulating walking.

Month Two- At this age the baby is improving their muscle control. While laying on their tummy in the superman position they are able to

lift their head. They will also be able to wave their hands and put their hands in their mouths. Their hands will be in a tight fist. They will begin to suck which is a way to calm themselves down. Random facial movements will begin, the mother will begin to see the first smile which shows a sign of affection.

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Month Three- At this stage the baby will be able to become stronger and will coordinate their motions. The baby will be able to close and open their fist, and they will start kicking their legs and straighten out their legs. They will start to roll from tummy to their back. Their grip will improve by grasping at toys and being able to hold and shake hand toys. The baby will discover bouncing. The child would like to be put in a bouncer chair and feel the cyclical movement of rocking.

4 to 7 Months- The child’s next major event will be sitting on their own. Small steps will be taken to strengthen their balance of their trunk, head and neck. They will straighten their body by rocking on their stomach, kicking their legs and swimming with their arms. At first the help of an adult is needed to guide the baby into the sitting position. By putting them in a tripod position they are able to lean over and extend their arms to pick up toys. By the age of 4 months the baby is interested in toys and putting them in their mouths. They will begin to use figures and thumbs to grasp at items. “Between 5 and 7 months of age, infants use a variety of visual depth cues, pictorial depth cues, and kinetic information, to gauge the closer of two objects and to determine whether objects are within arm’s reach.” (Bornstein, Arterberry, & Mash, 2003). The baby will discover how to use their feet and legs to practice walking. They will enjoy jumping up and down and feeling the movement.

8 to 12 Month- The baby will be able to sit by themselves without any support. The baby will began using different movements to prepare themselves to start crawling. One way for them to strengthen their muscles is for them to rock on their hands and knees back and forth. Once the arm muscles are developed, they will use both arms and knees to start crawling. They will dig their feet into the ground to push themselves up to craw. Some babies do not crawl they may use other methods to get around. For example, scooting on their bottoms or slithering on their stomachs. All of these signs are good because the child is building up their muscles to begin walking. “Crawling and walking infants spend an enormous amount of time and energy interacting with the space and objects around them. As infants’ gain experience with self-produced locomotion, their pattern of actions changes when navigating space and pursuing objects.” (Dosso & Boudreau, 2014). The next step is pulling themselves up into a standing position. Once they get comfortable lifting themselves up, they will start to hold on to items and begun to stand on their own. They will begin to start taking a step or two on their own, their balance will be off, and they will fall to the ground a lot. The babies first steps are around their first birthday, but they could start walking earlier than that.

Toddler Stage

12 to 8 months- At one years old the baby is officially a toddler. At this stage the toddler will begin to say words, stand on their own and start walking. Once the toddler can walk, they will enjoy playing with toys. They are able to squat and pick up items on the floor.

Climbing will happen around 12 to 24 months, this is an important milestone because it helps develop coordination that will need to be mastered before they can walk up steps.

Toddlers will be able to climb on to a chair or a bed. Let them explore different objects to climb on, but make sure they are safe. Help the child learn how to climb stairs. Running, can come with some risk, because the toddler will fall a lot. By having the child run on a grassy lawn will help protect them from a fall. By age two the toddler will be, walking, climbing, jumping, running and talking. When the child starts to jump, start off with low structures and gradually move up to higher objects. Jumping requires using bilateral coordination. One way to practice is hopping off a step.  By the age of 3 they will be using a lot of Gross motor skills. The child will be able to walk in a straight line, skip and walk backwards. They will be able to catch a large ball and jump with two feet. As the child grows, they will learn how to control their bodies.


  • Olesen AG, Svare JA: Decreased fetal movements: background, assessment, and clinical management. Acta Obstet Gynecol Scand 2004, 83:818–826.
  • Bornstein, M. H., & Arterberry, M. E. (2003). Recognition, discrimination, and categorization of smiling by 5-month-old infants. Developmental Science, 6, 585–599.
  • Dosso, J. A., & Boudreau, J. P. (2014). Crawling and walking infants encounter objects differently in a multi-target environment. Experimental Brain Research, 232(10), 3047-54. doi:
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To date, there are five different stages of sleep that a person will cycle through in a full night’s sleep. The amount of sleep needed to properly function varies from person to person and the suggested “good night’s sleep” is around seven hours (MyPsychLab). Sleep is initiated by a person experiencing tiredness or exhaustion and will slip into stage one of sleep, the transitional phase. This stage is classified as NREM, non-rapid eye movement, and a person will come in and out of consciousness as they may be partially awake and aware until the mind begins to drift (CrashCourse, 2014). During this transitional phase, the brain wave activity will have both alpha and theta waves. At the beginning of this stage, the waves start as low-frequency alpha waves and eventually will take the form as an even lower frequency theta wave (Advancing Better Sleep T, 2018).

As sleep gets deeper, the body will settle in and relax for the resting period. During this time the heart rate will slow down, the body temperature drops, and muscles will relax as the body prepares for this form of light sleep (CrashCourse, 2014). Still considered an NREM sleep, multiple brain waves happen during this time, but they are interrupted sporadically by an activity known as a sleep spindle. A sleep spindle also referred to as a sigma band or sigma wave is a short burst of a higher frequency brain wave related to memory and learning (Advancing Better Sleep T, 2017). These spindles are generated in the reticular nucleus of the thalamus. There are two types of sleep spindles that can occur, fast spindles that are 13-15 Hz occurring in the centro-parietal part of the brain and slow spindles that are 11-13 Hz that occur in the frontal portion of the brain (Advancing Better Sleep T, 2017). Along with sleep spindles, a K-complex can occur in this second stage of sleep (MyPsychLab). A K-complex is categorized as a brain wave with high amplitude that occurs in a response to a stimulus from the environment. This arousal could be caused simply by a partner shifting in bed, a temperature change that causes the person to shiver, or a noise loud enough to be heard by the sleeping person (Advancing Better Sleep T, 2018).

Stage three or deep sleep is known as slow-wave sleep due to the delta waves that occur during this time. Delta waves are categorized are slow in speed and have large amplitudes. Stage three of the sleep cycle is less likely to be interrupted as it is the deepest form of sleep (Aramli M, 2017). If a person is extremely tired, this stage can be lengthened each cycle of the sleep pattern. The most trouble with sleeping can also occur in this stage, known as parasomnias, which includes sleepwalking, wetting the bed, nightmares, and sleep talking (CrashCourse, 2014).

Deep sleep progresses into stage four of the sleep cycle, another NREM, which also is represented by the slow delta waves. The body truly takes advantage of the deep sleep happening in this stage as the respiratory rate and heart rate drop but increases in the release of growth hormones occur and the immune system restores (Advancing Better Sleep T, 2018). It is not fully studied but it is assumed that during this stage is when the brain performs its reset for the day to begin another. Often stages three and four are referred to together because both are periods of slow wave sleep, SWS. In this slow wave sleep, there is no movement from the body, and it becomes immobile entirely and even the eyes do not move (CrashCourse, 2014).

REM, rapid eye movement, sleep is the fifth and final stage of the sleep cycle and is the brain’s busiest time (MyPsychLab). The eyes are moving and dart in many directions while the body remains immobile and briefly paralyzed. This temporary paralysis is thought to be the body’s way of protecting itself from injury by acting out one’s dreams. A person’s respiration becomes irregular and shallow, while the heart rate and blood pressure rise. During this REM stage is when most dreaming takes place (CrashCourse, 2014). Dreams are caused by the irregular brain waves that occur in this stage that resemble a person being conscious and aware (Aramli, M 2017). A person experiences on average, three to five REM periods in their sleep cycle, with the longest one occurring right before the person wakes up (Advancing Better Sleep T, 2018).

Sleep is vital for human life as it is what restores our energy, bodies, and basic abilities to function. If a person is not regularly experiencing the five stages of sleep, his or her mental function and body could be greatly affected. Sleep and understanding the fluctuation between consciousness and unconsciousness is pertinent to psychology and is very much a part of the framework of the field.

Work Cited

Advancing Better Sleep, T. (2017, April 12). Sleep Spindles and K-Complex Sleep. Retrieved                             July 3, 2019, from

Advancing Better Sleep, T. (2018, December 19). Stages of Sleep – Non-REM and REM Sleep               Cycles. Retrieved July 3, 2019, from

Aramli, M. (2017, February 8). 5 Stages of Sleep: Your Sleep Cycle Explained. Retrieved from     

CrashCourse. (2014, March 31). To Sleep, Perchance to Dream: Crash Course Psychology #9.               Retrieved July 3, 2019, from

MyPsychLab. (n.d.). Episode 6 Consciousness. Retrieved July 3, 2019, from

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