contd.: Communication Between Neurons

Diagram and mycrography of a synapse of the neuromuscular junction of a fruit fly. 1- Synaptic vesicles; 2- Presynaptic neuron (terminal axon); 3- Synaptic cleft; 4- Postsynaptic neuron. Photo: From Synaptic function, by Kendal Broadie, PhD, Univ. Utah. Reproduced with permission. Diagram: Silvia Helena Cardoso, PhD. Univ. Campinas, Brazil.

The functioning of the brain depends on the flow of information through elaborate circuits consisting of networks of neurons. information is transferred from one cell to another at specialized points of contacts: the synapses.

The sending neuron releases chemicals called neurotransmitters into the synaptic cleft, the space between the two neurons. These chemicals excite receptors on the receiving neuron, causing an impulse to propagate along the second neuron.

When an action potential arrives at a synaptic ending, it causes the release of transmitter which is stored inside tiny vesicles called synaptic vesicles. A subpopulation of these vesicles are concentrated on the inside of the plasma membrane facing the synaptic cleft. The action potential stimulates an influx of Ca++, which causes synaptic vesicles to attach to the release sites, fuse with the plasma membrane and expel their supply of transmitter (fig). The transmitter diffuses to the target cell, where it binds to a receptor protein on the external surface of the cell membrane. The interaction of the transmitter.