sexta-feira, 10 de setembro de 2010

What does a synapse have to do with education?

The Synapse

Neurons have specialized projections called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body.

Information from one neuron flows to another neuron across a synapse. The synapse contains a small gap separating neurons. The synapse consists of:

1.  a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles

2.  a postsynaptic ending that contains receptor sites for neurotransmitters

3.  a synaptic cleft or space between the presynaptic and postsynaptic endings.

Electrical Trigger for Neurotransmission

For communication between neurons to occur, an electrical impulse must travel down an axon to the synaptic terminal.


Neurotransmitter Mobilization and Release

At the synaptic terminal (the presynaptic ending), an electrical impulse will trigger the migration of vesicles (the red dots in the figure to the left) containing neurotransmitters toward the presynaptic membrane. The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft. Until recently, it was thought that a neuron produced and released only one type of neurotransmitter. This was called "Dale's Law." However, there is now evidence that neurons can contain and release more than one kind of neurotransmitter.

What does this have to do with Language Acquisition?

At birth, human brains and chimpanzee brains are about the same size. The chimp's brain expands about 28% by adulthood, while a human brain expands 300%.

This means that most of our brain develops after birth and is influenced by the environment. Almost all the neurons (nerve cells) in the brain are formed before birth, but until age one there are rapid increases in the overall size of the brain, and of the grey matter, where the synapses needed for higher mental function are found.

A two year old child has 50% more synapses than an adult, and brain metabolic activity peaks at age four. The eccentric manner in which brain development occurs is totally unlike the way that computer programs are developed. The multitude of extra pathways in the child's brain may either be used and therefore reinforced, or may atrophy and disappear due to disuse. That's why synapses wither and metabolic rate slows inexorably as we approach adulthood.


These changes probably correlate with the child's amazing ability to absorb languages, and with the difficulty we have with new languages as we get older. Children's brains also have more plasticity and redundancy than adults’ brains, so they can master both language itself and a perfect accent, and even if brain damage occurs, can relearn far more than an adult would.

What are we doing to exercise our children's brain? A topic for the next post!


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