Neurons

• The infant brain grows and develops through the continual interaction of biological forces and environmental influences.

• Communication within the central nervous system (CNS), which consists of the brain and spinal cord, begins with nerve cells called neurons.

• Scientists estimate that the average human brain has 86 million neurons

• Neurons transmit and receive information. They connect to one another via networks of nerve fibers called axons and dendrites.

• Each neuron typically has a single axon and numerous dendrites which are spread out like branches of a tree

• Electrical impulses in the axons cause the release of chemicals called neurotransmitters

• Neurotransmitters: chemicals that carry information from the axon of the sending neuron to the dendrites of the receiving neuron.

• Information passes from neuron to neuron via chemical interactions in the gap known as a synapse.

Brain Development

• Neurons change in two significant ways during the first years of life.

  1. Connectivity among neurons increases, creating new neural pathways.

  2. Myelination, the process of encasing axons with fat cells, continues into adolescence and emerging adulthood.

• Nearly twice as many connections are made as will ever be used; used connections “bloom” (grow stronger and survive), while unused connections are “pruned.”

Neurons - Myelination

• When babies are born, the myelin sheath does not yet cover all the neurons in the nervous system.

• There are imaging techniques that can trace the developmental pattern of myelination in the human brain as it proceeds from the lower centers at the base of the brain through the higher centers of the cerebral cortex.

• Experience also affects the development of myelination.

• The process of producing synaptic connections, pruning away those that are not being used, and myelinating the connections that are left—begin in infancy but continue throughout childhood and adolescence

Plasticity

• Plasticity: the ability of the infant brain to change in form and function

• Early experiences can have lasting effects on the capacity of the brain.

• Positive experiences can spur brain development and even make up for past deprivation.

• Conversely, the lack of enriching experiences and exposures to hazards may inhibit the normal process of brain development and growth