The stages of life from fertilization to death are as following: 1) the germinal period – fertilization to 14 days; 2) the embryo – 14 to 60 days after fertilization; 3) the fetus – 60 days after fertilization to birth; 4) neonate – birth to 1 month after birth; 5) infant – 1 month to 1 or 2 years; 6) child – 1 or 2 years to puberty; 7) adolescent – puberty (age 11 to 14) to 20 years; 8) adult – age 20 to death.

A great number of changes occur in the life of the newborn from the time of birth until 1 year of age. The time when these changes occur may vary from child to child. The brain is still developing at this time, and much of what the neonate can accomplish depends on the amount of brain development achieved. It is estimated that the total adult number of neurons is present in the central nervous system at birth, but subsequent growth and maturation of the brain involve the addition of new neurological cells, some of which form new myelin sheaths, and addition of new connections between neurons, which may continue throughout life.

By 6 weeks the infant is usually able to hold up its head when placed in a prone position and begins to smile in response to people or object. At 3 months of age the infant’s limbs are exercised aimlessly. However, the arms and hands are in enough control that voluntary thumb sucking can occur. The infant can follow a moving person with eyes. At 4 months the infant begins to do push-ups (i.e., raises itself by its arms). It can begin to grasp things placed in its hand, roll from its back to its side, listen quietly when hearing a person’s voice or music, hold its head erect, and play with its hands. At 5 months the infant can usually laugh out loud, reach for objects, turn its head to follow an object, lift its head and shoulders, sit with support, and roll over. At 8 months the infant can recognize familiar people, sit up without support, and reach for specific objects that it sees. At 12 months the infant may pull itself to a standing position and may be able to walk without support. The infant can pick up objects in its hands and examine them carefully. It can understand much of what is said to it and may say several words of its own.

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