# Developmental psychology/Chapter 3/Infant Growth

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It is crucial for the newborn to be in a position where they are closely monitored, including their organs and physicality (height, weight).

## Weight

Weight gain is fast-paced.
* Lose weight in the first 3 days
* Gains an ounce a day for a few months
* Doubles by 4 months
* Triples every year
An avg. 7 pound baby will be 21 pounds in a year. By the next year, the child will be nearly 30 pounds (a slower rate, but still dramatic). They've also gone from 20in to 34in by the age of 2. They are already half their adult height and only 3/4th their adult weight! If a baby's percentile dramatically changes, this may result from an error in care (for example, overfeeding or underfeeding).

## Sleep

Sleep is where most of the changes take place in the baby. Newborns start off at 15-17hrs.
* First 2 months: 14 1/4 hours of sleep
* Next 3 months: 13 1/4 hours of sleep
* Next year: 12 3/4 hours of sleep
Individual babies vary, but these are the norms of the population. Infants also vary in how much they sleep at given intervals. Brest-fed infants wake up often while many babies (at 3 months) sleep from midnight to 5am, much to the dismay of the parents.
About 1/2 of the sleep of newborns is REM sleep, where dreaming takes place. At 3/4 months, quiet sleeping (slow-wave sleeping) takes over.
Placing the baby during their sleep is a matter of what the parents decide. Some parents decide to bed-share with the baby (in the parent's bed) while others co-sleep with the baby (in the parent's room). As long as the parent can hear the baby cry, all goes well. Statistically, breast-fed babies are usually bed-sharing with their parents (easier for mother to feed it). The disruption a newborn causes for their parent's sleep can cause them to fall into dysfunctionality or maternal depression. Many solutions are there, but conflicting opinions make the situation hard to tackle.

## Brain Development

The brain is the most important organ of the infant's body. The brain is 25% of the adult size and is 3/4 of the adult weight by age 2! Over the same time interval, the brain grows from 14in to 19in. During this period, babies learn patterns and specific events that've taken place. For example, babies are learning what to expect from their caregiver (parents) and respond to them.

### Early Dendrite Growth

The rapid formation of dendrites that develop in an infant's brain is known as transient exuberance. Some of these dendrites are temporary since some of the unused brain atrophy is cut away to make way for new dendrite connections. This action, known as pruning, is actually beneficial to the infant. For example, infants with fragile X syndrome are unable to cut away brain atrophy, making thinking hard.

### Expected/Dependent?

In order for the infant to develop normally, there are normal things that an infant must have (and is expected to have) in order for their dendrites and neurons to develop. These are called experience-expected experiences (examples being people to love, objects to interpret). Experience-dependant experiences are situations which may or may not occur, therefore those brain functions may/may not fully develop (examples being language, type of people they see). Plasticity, as explained in Chapter 1, are showcased here as babys' brains are molded to their specific culture.

### Stress' Impact on the Brain

A baby's emotions can be severely altered if they produce too many cortisol (stress hormone) during their infant period. Comforting a crying baby is a must rather than forcibly yelling and shaking the baby (this may lead to shaken baby syndrome). Death could occur from this.

## The 5 Senses

Infants use all of their senses:
* Wondering eyes
* Sensitive ears
* Responsive noses
* Responsive tongues
* Soft skin

### Sensation to Perception

* Sensation - When a stimulus is presented, such as a pupil intercepting light, a sensory organ (look back at the 5 senses) responds. Attached with a sensation must be a set of emotions or experiences. For example, a baby is not going to respond to a bottle unless its been bottle-fed several times
* Perception - Mental processing of sensory messages.

### Hearing

The ability for a fetus to hear is developed in the last trisemester, it being the most matured sense at birth. The areas of the brain dealing with hearing (the cortex related to language) rapidly matures. Babies soon start interpreting "random" sounds into distinctive sylabuses. This is why if a baby has an ear infection, it must be treated as soon as possible!

### Eyesight

In comparison to hearing, eyesight matures very slowly and isn't acute at birth since they've nothing to see in the womb. By 2 months, an infant can smile based on the faces they are looking at with the maturation of the visual cortex and as well as experiences. Originally, infants use their individual eye to interpret the world rather than focus both eyes on a single image (binocular vision). Experience plays a role here, with infants developing binocular vision about 2-4 months after birth. Visual scanning abilities are also increased as time passes, as by 3 months most infants can look more to a face (including their eyes and mouth) and smile if its a happy face in front of them.

### Taste and Smell

Taste and smell are senses which are developed during the infant period. The taste sense is seen when babies try new foods and react to it based on the taste (for example, a baby eating a lime). These experience-dependent experiences (eating their cultural food) may explain why immigrants spend a lot of money buying their original foods. The smell sense is shown when babies are more comforted when their parents join them in the bath as their smells and senses alleviate the shock of a new environment.

### Touch and Pain

Cuddling a newborn is comforting, showcasing that their touch sense is acute. Pain is still a topic of obscurity. Are pain receptors sensitive at birth? If not, how can a baby handle the pain of birth (being transferred from the womb to the real world)? Obviously so, a baby can experience pain. An example being a baby crying while being changed (cold wind hitting baby's sensitive skin). Proper cuddling and care results in improved social and neurological developments. Digestive pain, or colic, [due to their gut microbiome] may be the reason why infants cry constantly for the first 3 months after birth.

## Motor Skills

Motor skills are defined as any learned ability to move a part of the body. Every motor skill is developed within the first 2 years. Reflexes convert into skill if encouraged too. Large body motor skills are known as gross motor skills, such as walking and jogging. These skills come right from reflexes and go through in a cephalocaudal (head-down) and proximodistal (center-out) direction. An example of a cephalocaudal motor skill is an infant lifting their head up to scan their surroundings. Then the infant's control of their body goes from the head down to the toes.
Half of infants master walking and running in a year and 18 months, respectively. Most infants are able to walk well by 14.4 months and running by 20 months. The ability to jump up is a difficult task that only most babies learn by 29 months (this is on average and it depends on the certain infant because as the infanct grows, nurture and nature impact the baby more). On the other hand, most babies can sit up supported by someone's lap by 3 months. 3 months later, babies can sit unsupported.
Also, walking children trigger more language than crawling babies do. So its actually a better estimate to figure out the walking age vs. a norm for babies to start talking. Walkers also see their caregivers more than crawling babies, so they talk more.
Crawling Process
Crawling is a good example of a cephalocaudal and proximodistal direction skill. The ability to crawl is NOT necessary for a child's development.
* Initially: When placed on their stomach, they immediately start lifting their heads and moving their arms out (as if they were swimming)
* Then: As they naturally gain muscle strength, they "resist" the floor by pushing against it.
* 5 months: Infants start using their legs to "resist" the floor. The 'when?" depends on how much time they spend on their tummy and this depends on the culture they're in. This is also the period where infants can coordinate two hands at a given time, accomadating them in the "crawling" process.
* 8-10 months: "Crawling" usually begins here. This depends on the culture as some babies never crawl (babies in extremely cold environments may never crawl).
Although failing many times in the process, they begin to start mastering the process of walking. Babies realize that they get to places faster by walking so they prefer walking, once mastered, to crawling.

### Fine Motor Skills

Fine motor skills are minor body movements. Finger movements are the most crucial fine motor skills, as this enables the ability to write. Movement of the tongue is also a fine motor skills, enabling the ability to speak in cohorent sentences. Mouth skills take place way before finger skills (newborns start suckling almost immediatly).
Caregivers must pay extra attention to infants by 9-12 months of age since this is the time when infants can put small objects in their mouths (for example, they're able to put a bottlecap in their mouths). By the infant's first birthday, they are able to feed themselves ableit messily.
Fine motor skills actually take longer to master than gross motor skills since these skills require precision.
Basic Hand Skills
* First 2 Months: Infants wave their arms at objects
* 3 Months: Touch objects, but cannot grasp them.
* 4 Months: Infants attempt to grab but timing is poor.
* 6 Months: The ability to grab has been mastered!