The First Two Years: Biosocial Development
The Structure of a Neuron
A typical neuron has four morphologically defined regions: dendrites (receiver)(1) , cell body
(2), axon (3), and presynaptic terminals (transmitter)(5).
Neurons receive nerve signals from axons of other neurons. Most signals are delivered to dendrites (1).
The signals generated by a neuron are carried away from its cell body (2), which contains the nucleus (2a),
the storehouse of genetic information. Axons (3) are the main conducting unit of the neuron. The axon
hillock (2b) is the site at which the cell's signs are initiated. Schwann cells (6), which are not a part of a
nerve cell, but one of the types of glial cells, perform the important function of insulating axons by wrapping
their membranous processes around the axon in a tight spiral, forming a myelin sheath (7), a fatty, white
substance which helps axons transmit messages faster than unmyelinated ones.The myelin is broken at
various points by the nodes of Ranvier (4), so that in cross-section it looks rather like a string of sausages.
Branches of the axon of one neuron (the presynaptic neuron) transmit signals to another neuron
(the postsynaptical cell) at a site called the synapse (5). The branches of a single axon may form synapses
with as many as 1000 other neurons. Axion terminals and dendrites do not actually touch, brain chemicals
called neurotramsmitters carry information across the synaptic gap.
The Brain
Ψ Remember, early brain growth is rapid & widespread, This phenomenal increase is called transient exuberance.
Ψ Experience enhances the brain.
• Experience-expectant brain functions require basic common experiences in order to develop, therefore each person
will be similar to every other person (human).
• Experience-dependent brain functions depend on particular, & variable, events that occur in some families & cultures but
not in others. Infants brains are structured /wired depending on which experiences are present during development,
consequently each person will be unique to a particular family & culture.
Motor Skills
The First Motor Skills are the Reflexes Required for Survival).
- Reflexes that maintain oxygen supply: breathing, hiccups, sneezes, & thrashing
- Reflexes that maintain constant body temperature: crying , shiver, tuck in legs, push away, & drinking
- Reflexes that manage feeding: sucking, rooting, swallowing, crying, & spitting up
Ψ Other reflexes (not necessary for survival) but important signposts of normal development;
• Babinski reflex: occurs when the great toe flexes toward the top of the foot and the other toes fan out after the sole of the
foot has been firmly stroked. This is normal in younger children, but abnormal after the age of 2.
• Stepping reflex: A reflexive movement of the leg seen in newborn infants. This lasts until about two months of age. It can be
demonstrated by holding the baby in an upright position on a flat surface he or she will lift one leg in the air, then step with the
other foot & "walk". Most, but not all babies exhibit this reflex.
• Primary Stepping reflex: weeks - 5 months - If a baby is held upright on a flat surface, she will walk forward while held.
• Swimming reflex: 2 weeks - 5 months - If an infant is placed in water on his tummy, his legs & arms will move in a swimming
motion.
• Palmar grasping reflex: birth - 4 months -If you touch the palm of ha bay's hand, the baby will hold onto your finger.
• Moro reflex: birth - 6 months - If a baby has a sense of falling or not being supported, the arms stretch out to the sides, & the
legs stretch out full length.
• Startle reflex: 6 months - 12 months - Like the Moro Reflex, but occurs later in the baby's development.
- Gross motor skills involve large body movements such as waving the arms, walking, & jumping.
- Fine motor skills involve small body movements, especially with the hands and fingers.
Ψ A detailed list of the norms for movement follows:
Ψ 0-3 months
• Lies on belly & raises head
• Lies on back & moves each arm & leg equally well
• Pushes up on arms from belly & supports self on forearms
• Holds head up when held in a sitting position, with only an occasional bob forward
Ψ 4-6 months
• On belly, lifts head up to 90 degrees
• Holds head steady when upright in caregiver's arms
• On belly, pushes up onto arms, lifting chest up
• Begins to roll belly to back
• Keeps head in line with body when pulled to sitting by holding hands
• Sits with support
• Holds head up
• Sits with straight back
• Briefly sits by leaning on arms for support
Ψ 7-9 months
• Stands when held
• Sits alone
• Works to get an out-of-reach toy
• May begin to pull up on furniture
Ψ 10-12 months
• Stands holding on to someone or something
• Pulls up to standing
• Achieves a standing position
• Turns in a circle when sitting
• Walks around holding onto furniture
• May stand alone momentarily
• Crawls on hands & knees
Ψ 12-18 months
• Walks or stands independently
• Walks upstairs with help
• Throws from standing without falling
• Throws ball towards you
• Attempts to kick a large ball
• Rolls ball to you
Hearing
One-month-old infants have a very keen sense of hearing and can discriminate small sound variations,
such as the difference between bah & pah. By 6 months, infants can make all the sounds necessary to
learn language.
Otitis media is primarily caused by a malfunctioning eustachian tube. The eustachian tube connects the
middle ear to the back of the internal nose structures. The eustachian tube equalizes air pressure between
the middle ear and the environment. If the tubes are blocked (occurs in an infection) these protective
functions cannot occur and bacteria are swept up through the eustachian tube as a result of the pressure
difference.
Public Health Measures
Ψ Immunization is the process by which an individual is exposed to an agent that is designed to fortify his or her
immune system against that agent. When the human immune system is exposed to a disease once, it can develop the
ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled
way, their body will then be able to protect itself from infection later on in life.
Ψ SIDS (Sudden Infant Death Syndrome) is the leading cause of death among infants who are 1 month to 1 year old,
& claims the lives of about 2,500 infants each year in the U.S. It is a frightening prospect because it can strike without
warning, usually in a seemingly healthy infant. Most SIDS deaths are associated with sleep (hence the common reference
to "crib death"), & infants who die of SIDS show no signs of suffering.
• African-American infants are twice as likely & Native American infants are about three times more likely to die of SIDS
than Caucasian infants.
• Most deaths due to SIDS occur between 2 & 4 months of age, & incidence increases during cold weather.
• More boys than girls fall victim to SIDS.
• Potential risk factors for SIDS include:
• Foremost: stomach sleeping. Place healthy infants on their backs to sleep!!
• smoking, drinking, or drug use during pregnancy
• poor prenatal care
• mothers younger than 20
• smoke exposure following birth
• prematurity or low birth-weight
• smoking, drinking, or drug use during pregnancy
• overheating from excessive sleepwear & bedding
Ψ SIDS prevention & Crawling
• In 1994 to prevent SIDS, the Back to Sleep campaign began urging parents to place drowsy infants on their backs
to fall asleep. At that time, 70 percent of babies were tummy sleepers, by 2001 this figure had dropped to 20 percent,
reducing the rate of SIDS significantly.
• But American babies now crawl later than they used to, typically by 2 months. Less stomach time seems to delay a
baby's ability to crawl because there's less opportunity to practice. It should be noted that delayed crawling has not
resulted in delayed walking, with both early & late crawlers taking their first steps close to their first birthdays. The same
goes for the 5 percent of babies who never crawl & who just proceed straight to walking.
Nutrition
Ψ Breast is Best: The World Health Organization (WHO) recommends that infants be fed exclusively
with breast milk for the first four to six months.
Ψ Severe protein-calorie malnutrition: when a person does not consume sufficient food on any kind.
Ψ Marasmus: In the 1st year of life, severe protein-calorie malnutrition leading to death.
Ψ Kwashiorkor: During toddler hood, chronic malnutrition not leading to death in itself but increases risk of death
from diseases such as measles, diarrhea, & influenza.
Key Questions
1. How do the weight, length, & proportions of the infant's body change during the first two years?
2. How does immunizing infants protect the entire community?
3. What specific changes occur in the brain's communication system during infancy?
4. How does experience affect the development of the brain's neural pathways?
5. What reflexes are critical to an infant's survival?
6. What is the general sequence of the development of gross motor skills & fine motor skills?
7. What factors account for individual differences in the timing of motor achievements?
8. How do the sensory capabilities of a newborn infant change over the first year of life?
9. What kinds of sensory experiences do babies typically prefer in early infancy, & why?
10. What are the advantages of breast-feeding?
11. What are some of the consequences of serious long-term malnutrition?
12. What are the major causes of under nutrition?
13. In your experience what are the factors that determine what, & when, a young infant is fed?
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Growth & Development
Robert C. Gates