The Seven Ages of the Brain

Innate Human Reflexes (02:45)
An infant human demonstrates a reflex similar to walking, a toe-flexing response, and a grasping reflex.

Adult Human Reflexes (02:20)

Adult human reflexes include rapid pulse rate in response to an unexpected event.

Fertilization of Human Egg (01:53)

In fertilization, egg and sperm each contribute 23 chromosomes for a total of 46 chromosomes that determine one's genetic fate.

Embryonic Development of Nervous System (03:21)

Within 30 hours after fertilization of a human egg, the zygote begins to divide. Within about 21 days, the future nervous system forms a neural tube from which the spinal cord and brain will grow.

Growth of the Human Brain: Cell Migration (03:26)

Two important things happen in the development of the human brain: migration and aggregation. The host explains the function of glial cells and neurons.

Growth of the Human Brain: Cell Aggregation (04:37)

Neurons "team up" or aggregate according to specific functional markers. A colorful brain model shows how aggregated cells form all the parts of the brain and spinal cord. Magnification shows perkinje cells of the cerebellum that have mutated into an organized pattern.

Human Brain at Birth (01:40)

At birth, the brain of a human infant is growing at a rapid rate--the same brain as Cro Magnon 30,000 years ago. The brain is capable of adapting to the environment into which it is born.

Human Brain: Communication Among Neurons (02:59)

High-speed video shows a neuron growing and sending out axons for communication with its target.

Neuronal Adaptation (02:34)

When something goes wrong with connectivity between the neuron and its target, other neurons may "step in" to make the best of a bad situation. With the help of a model, the host demonstrates the neuronal workings of a frog's eye.

Neuronal Malfunction and Adaptation (03:01)

The whiskers of a mouse serve a vital function. When the normal pattern of whiskers on a mouse are damaged, the neurons adapt to make up for the differences.

Abnormality in Neuron Function (02:14)

An Italian boy who is blind in one eye only presents a puzzle to doctors. The reasons behind the blindness reveal that the "good" eye had taken up the "territory" of the other eye when it was bandaged briefly in the child's infancy.

Normal Neuron Function in a Child (02:35)

A normally developing one-year-old child demonstrates voluntary skills such as grasping, hand-eye coordination, fine motor skills, and "pincer" movement between thumb and forefinger.

Functions of the Autonomic Nervous System (05:15)

Neuronal feedback controls basic processes in the human brain. For example, a human does not have to consciously regulate the heart rates of the size of the pupils. This nervous system controls the "flight or fight" response.

Gender Differences in the Human Brain (03:13)

Nine weeks into gestation, gender hormones begin to work on the brain. Gender differences have physical manifestations in the human brain, particularly in the corpus callosum.

Gender Differences in Skills (04:42)

To measure gender differences in dexterity, four twelve-year-olds participate in an experiment. Though the test subjects are small, there appear to be demonstrable differences between genders.

Brain Development and Environment (03:56)

The human brain is mature by age 16, yet by age 2, brain cells have already begun dying. How is brain circuitry maintained? An experiment with rats demonstrates the value of environmental stimulation to brain development.

Reaction Time and the Aging Brain (03:33)

In a test of reaction times, a younger woman performs more successfully than an older woman.

Learning and the Aging Brain (02:59)

Learning new skills such as driving takes significantly longer as people age. On the other hand, age is not a determiner in all areas of life skills. Longevity data reveals that more people are now living longer.