Introduction

• Synapses: junctions between neurons and between neurons and receptor or effector cells

• Nerves transmit electrical impulses by changing the ionic distribution across the neuronal membrane (membrane potential)

• Therefore, electrical signals are not able to be conducted when a semipermeable membrane is absent

• Neurons transmit information across synapses by converting the electrical signal into a chemical signal

Chemical Transfer Across Synapses

• When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels

• Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane

• The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft

• Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels

• The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal

• The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity)