The Beginnings of Behavior
At the moment of conception a tiny sperm cell successfully penetrates a much larger egg cell. The fertilized egg begins to divide and divide according to the strict patterns set down by its genetic structure. The process of division produces a mass of cells. Some of these cells grow more rapidly than others and move to the top of the sphere. A cavity appears in the middle of the cell mass. The body begins to take on shape, its heart begins to beat, and by the seventh or eighth week after conception the unborn baby (or fetus) can make its first response to a stimulus, to move its head away from a tickle near the mouth region. Behavior has begun.
During the gestation period, which in human beings is about 280 days, the fetus is surrounded and cushioned by amniotic fluid within the uterus. Nutrients enter its bloodstream, wastes are removed, and oxygen is supplied through the umbilical cord, which links the infant's circulatory system. Thus the fetus is protected, fed, and its wastes are removed without any effort.
The mother first notices movements during the fifth month of pregnancy. The baby tends to be active when the mother is resting and to rest when the mother is active. By the 28th week after conception, the fetus can make weak muscular movements, can avoid light or sound by turning its head, can grasp weakly, and can cry, should it be born prematurely. There is a good chance of survival if the baby is born any time after the beginning of the sixth month.
Normal birth occurs at approximately the 40th week after conception, when the fetus is expelled through the cervix out the birth canal. The newborn baby, now called a neonate by students of child development, must make five major adjustments at birth. (1 ) Removed from the aquatic environment of the uterus, he must adjust to the world of air. The first breath begins even before the umbilical cord is cut. (2) The circulatory relationship between mother and child ceases when the umbilical cord is severed so the neonate must now eat and digest his own food. is) He must also now excrete his own wastes, and (4) maintain his own body temperature. (5) Finally food is now only available at certain intervals, so the neonate must also adjust to intermittent feeding.
Unlearned reflexes are essential for an infant's survival immediately after birth.
To help make these adjustments, the infant has quite a large number of inborn behavioral patterns, called reflexes or reflex actions. Sucking, swallowing, hiccuping, blinking, urinating, and defecating are all present in the baby's behavioral repertoire at birth. These reflex behaviors are unlearned and are necessary for survival.
Other interesting unlearned behavior patterns are illustrated in Figure 8. If the neonate is placed on his back, he will respond to a noise or a slap on the mattress by bringing his legs and arms forward as if to embrace someone or something. This is the Moro (or startle) reflex. A gentle tickling or striking of the sole of the foot produces a fanning of the toes, called the Babinski reflex. Perhaps the most dramatic neonatal reflex action is the Darwinian reflex, in which the infant grasps hard when anything touches his palms. Most infants have such a strong Darwinian reflex that they can hold their own weight up if allowed to clutch a rod. All three reflexes disappear in the first few months of life. In fact, if the Babinski is observed in an adult it is considered a sign of neurological problems.
Neural and physical differences at birth influence the rate and direction of an infant's development
Are babies little individuals at birth, or are they, as some philosophers have suggested, like a tabula rosa (a blank tablet) upon which the experiences of life have yet to make their impression? We have seen that each baby has a unique genetic makeup that will ultimately determine stature, hair, eye and skin color, and possibly even intellectual potential. There is also some behavioral evidence for individual differences at birth. Neonates differ in their general level of activity, their responsiveness to light and sound, and the quality and intensity of their bodily reactions. For example, when in pain, some babies react with changes in heart or breathing rate, others with skin rash, and still others by vomiting (Grossman, 1967).
The baby's inherited bodily structure determines his initial behavioral patterns to a considerable degree. All babies have mouths and stomachs, but those with larger stomachs can retain more food and can go without food for longer periods. Such babies will naturally cry less between feedings. All babies have eyes and ears, but those with more completely developed nervous systems will be able to perceive and respond to their environment earlier. These babies will be able to start learning sooner, as well.
The way an infant reacts to the world affects the way he is treated. The active and alert baby may get more attention than the quiet, placid baby. The fretful infant may be held more than the quiet infant. In this way, each infant begins to develop a personal history that may influence the course of his entire life.
You might recall touching a baby's "soft spot" or fontanel. The fontanel is an opening where the bones of the skull are still growing together. The neonate's skeleton is mostly soft and pliable cartilage which eventually hardens into bone.The bones lengthen and become heavier as the child matures.
At birth, the average infant weighs about seven pounds and is about 20 inches long. He will measure 24 inches three months later. By his first birthday he will typically be 30 inches in height, and by age two, 35 inches. An average girl will attain half her adult height before her second birthday, while the average boy will attain half his eventual height just after his second birthday.
As a child develops we can see that the body is changing and growing, but it is interesting that some parts of the body grow faster than others. Consider a baby's eyes. The beauty and fascination are due not only to the color and the steady gaze, but to the size. A child's eyes, in comparison with an adult's,are proportionally much larger than the rest of his body. On observing closely,it is apparent that a child's entire skeletal structure is proportionally different from that of an adult. Other fundamental differences in a child are the nervous system and the hormonal and biochemical make-up A child s bodily development and growth rate can be partly understood simply by observing changes in his form and proportions.
In Figure 9, notice that a child's head is larger in proportion to his body than an adult. The different parts ol the body do not grow at the same rate, or at the same time. Instead, the head develops first, the torso next, and the limbs last. At birth a baby's head is about 25% of of the total body length, or about 60% of its adult size An adults head is normally less than 15% of the total body length. Many medieval painters were apparently not aware of this difference. Often paintings of the young Christ done at this time make him appear to be a miniature adult.
Figure 9Changes in bodily proportions with age
The torso develops next and is about one-half of its total length by the end of the second year. The legs and arms grow rapidly from the second year to the fourth year, at which time they are about one-halt their adult see. This progressive growth rate (head, trunk. legs) is called cephalocaudal development.
A baby is born with nearly all the muscle fiber he will ever need, but the muscle fiber is not very well developed. In fact, each fiber will grow until it weighs more than 40 times what it weighed at birth its growth rate will be determined in part by its location in the body.
An infant's behavior, as well as body proportion reflects a cephalocaudal, head-to-trunk, direction of development. An infant's earliest and best organized behavior is the nursing or sucking response, which is a behavioral illustration of the fact that the head has the earliest growth increase . However, the sucking response is instinctive. The child s first purposeful behavior stems from the shoulder and pelvic girdles. The infant controls his head before his neck, his neck before his shoulders, and his shoulders before his trunk it is later in infancy that effective movements appear at the elbows, wrists, knees, and ankles.
While the body has been growing in length it has also been growing from central to peripheral parts, which is termed the proximodistal direction. Again, your observation may show you that the trunk and torso develop first. The growth sequence in an arm goes from shoulder to arm to wrist to fingers in a leg, from thigh to ankle to toes.
Different organs grow at different rates and the parts of each particular organ grow at different rates. For an example, let us look at the brain. Even though the rate of change for parts of the bran varies, it contains at birth all the neural cells it will ever have. As the body grows, the size and chemical composition of the nerve cells and the length and state of development of nerve fibers change. The pyramidal Beta cells, which are important for motor control, are more developed at six months than any other type of cell in the cortex. During the first six months of life the circumference, length, structural compactness, and protective covering of the nerve fibers in the parts of the brain that control motor and sensory activity are far more advanced than those of the fibers in the rest of the brain.
Motor development depends on the maturation of muscles, bones, and the nervous system. It follows the same pattern in almost every child. Each skill appears in order, with simple skills setting the stage for more complex skills. The child moves from lying to lifting his head to sitting to standing then to walking. Many investigators have studied the progression of motor development, and a great deal of information exists on the subject. Approximate age ranges for each motor skill have been determined. The skill which appears the most often within a particular age range is called the norm for that age.
Figure 10 shows the progression of motor behavior from birth to the first step.
The neonate often assumes a position much like that of the fetus, with knees drawn up toward the chest and arms flexed close to the body. A six-month old infant can lift her head and roll over. By the seventh month the typical infant sits unsupported, and by the eighth month she can move about by creeping or crawling. A ten-month-old infant can pull herself up and stand holding on. From her new upright position she can eventually walk, first with support and later, at about the thirteenth month, entirely on her own.
The development of motor skills follows a cephalocaudal pattern -- from head to shoulder movements, then to movements of the trunk and legs. The other direction of development is the proximodistal
direction of growth and can be seen in the progression of arm, wrist, hand, and
finger skills, which are illustrated in Figure 11. As we saw in the last module,
the newborn infant can grasp hard in a reflexive response to stimulation on
the palms (the Darwinian reflex). During the first month of life the Darwinian
reflex weakens. Although the two-month-old infant can hold an object put into
his hand, he cannot reach out and grasp an object until the fifth month. The
first movements toward an object involve the shoulder and arm more than the
hand, in a side-to-side scooping motion. At eight months the child is
beginning to oppose the thumb to the rest of the hand in order to grasp
objects. By the ninth month he can pick a small object up with accuracy, using
the fingers alone. Fine muscle coordination continues to improve during
childhood as the child progresses from large-scale scribbling to more and
more controlled drawing and lettering
PROGRESS CHECK 1
Now test yourself without looking back.
1. What are the two major directions of growth in the human body?__________________
2. The progression of hand and arm coordination follows which order
a. Shoulder, wrist, hand, arm, fingers
b. Fingers, hand, wrist, arm, shoulder
c. Shoulder, arm, wrist, hand, fingers
d. Any of the above may be seen in normal infants.
3. List three adjustments the infant must make at birth.
NOW DO PROGRESS CHECK 2
PROGRESS CHECK 2
1. The two major directions of growth in the development of a human baby are_______________________________________ and _____________________________
2. The sequential order of control in leg and foot coordination is:
a. toes, ankle, calf, knee, thigh.
b. thigh, knee, calf, ankle, toes.
c. ankle, toes, knee, calf, thigh.
d. none of these.
3. Which of the following refers to the reflex action(s) that weaken(s) during the first months of life?
a. Darwinian reflex
b. Babinski reflex
4. The infant must make several adjustments at birth. In which of the areas below must the neonate adjust?
b. Excretion of waste
c. Self-regulation of body temperature
d. Intermittent feeding
5. An unlearned response pattern largely under the control of a specific stimulus is called____________________________
6. Three neonatal reflex actions are the Moro reflex, the Darwinian reflex, and the Babinski reflex. Write the name of the reflex in the space provided.
a. The reflex in which the infant's toes fan out in response to tickling the sole of his foot is called the________________________ reflex.
b. The reflex in which the infant responds to noise or other startling stimulation by bringing his arms and legs forward as if to embrace someone or something is called the _______________________________________reflex.
c.The reflex in which the infant grasps hard when his palms are touched is called the ______________________reflex.
ANSWER KEY .
5 OR MORE CORRECT -- Go to Module 5
FEWER THAN 5 CORRECT INSTRUCTOR CONFERENCE
August 5, 2001