The First Trimester
The first three months of pregnancy, or the first trimester, is when basic brain structure begins to form. In the first month, just 16 days after fertilization, an embryo forms the neural tube. The neural tube is the earliest nervous system tissue and eventually develops into the brain and the spinal cord.
During the second month of development, the neural tube begins to differentiate into brain cells and nerve cells. The brain cells transform into recognizable brain structures - most notably, the cerebral cortex is formed. The cerebral cortex is the outer layer of the brain. By the third month, this basic brain development allows the embryo to display reflexes and react to its environment. At the end of the first trimester, hormones are released that will determine whether development will continue to occur as male or female.
The Second Trimester
The second trimester is the fourth, fifth, and sixth months of a pregnancy. During the course of the second trimester, the brain becomes fully developed. Even though the brain has not reached its full size, most of the neurons within the central nervous system are present. A neuron is another name for a nerve cell, or the cells that conduct electrical impulses and make up the brain, spinal column, and nerves.
During the fourth month, the fetus begins to prepare itself for the outside world. The fetus can experience sensory sensations such as sound, taste, and smells. By the fifth month, the fetus is learning to control its reactions to these sensory sensations and to control its movement. The ability to consciously react to sensory sensations becomes even stronger during the sixth month. During the sixth month, another major mark of brain development occurs; the cerebral cortex splits into two separate hemispheres. Some researchers believe that the fetus develops the ability to remember at this stage.
The Third Trimester
The seventh, eighth, and ninth months of pregnancy are the third trimester. This is the last period of prenatal development. During the third trimester, the brain increases in size and begins to form folds. These final stages of prenatal brain development form a brain that is nearly similar in structure to any other human brain.
During the last trimester, the fetus also continues to develop control over movement and stores information that it has gained from sensory sensations. By the time the child is born, it is fully capable of much more than reflexes (such as breathing) or instincts (such as sucking). A newborn can remember the smell and sound of its mother and even recognize familiar tastes.
In the seventh month, brain waves can be detected in the prenatal environment. The eighth month marks the differentiation of major brain areas, such as the visual cortex and auditory cortex that allow the fetus to understand what it sees and hears. By the ninth month of prenatal development, the brain has as many neurons as an adult brain, even though it will be only one-fourth the size of an adult's brain at birth.
Lesson Summary
Brain development occurs at an amazing speed during the prenatal period, and development occurs throughout all three trimesters of pregnancy. Proper prenatal care is essential to prenatal brain development because of the rapid pace at which it occurs.
The neural tube develops in the first month. The neural tube is the earliest nervous system tissue and eventually develops into the brain and spinal cord. The cerebral cortex develops in the second month, and it separates into two different lobes during the sixth month.
At the end of the second trimester, most of the neurons within the central nervous system are present. A neuron is another name for a nerve cell, or the cells that conduct electrical impulses and make up the brain, spinal column, and nerves.
During the eighth month, major brain areas, such as the visual cortex and auditory cortex, are developed. By the time of birth, the brain consists of 100 billion neurons and is one-fourth the size of an adult brain.
Learning Outcomes
Completing this lesson should prepare you to:
- Summarize fetal brain development during the first, second, and third trimesters
- Define neural tube and neuron
