Brent Cornell

    
A synapse is a junction at which a neuron transmits a signal to another cell (relay neuron or effector)

• Most synapses transmit chemical signals, although electrical synapses also exist

A developing neuron will form multiple synapses, creating a vast array of permutable communication pathways

• Within the CNS, a neuron may form a synapse with another axon, dendrite or cell body (soma)
• Within the PNS, a neuron may form a synapse with a muscle fibre (neuromuscular) or gland (neuroglandular)
• Some neurons may form a synapse with capillaries and secrete chemicals directly into the bloodstream (neurosecretory)

Types of Synapses within the Central Nervous System 

    
During embryonic and early post-natal development, neurons will form multiple synapses to maximise available connections

• As an organism matures, some synapses are used more frequently and these connections are consequently strengthened
• Other synapses are not used as often and these connections are weakened and do not persist
• This strengthening and weakening of certain neural pathways is central to the concept of how organisms learn

Neural pruning involves the loss of unused neurons (by removing excess axons and eliminating their synaptic connections)

• Infant and adult brains typically have the same total number of neurons (roughly 100 billion neurons in total)
• However infant brains form vastly more synaptic connections (approximately twice the number found in adult brains)

The purpose of neural pruning seems to be to reinforce complex wiring patterns associated with learned behaviour

• Pruning is influenced by environmental factors and is mediated by the release of chemical signals from glial cells

Synaptic Formation and Neural Pruning