Plan
► Concept of synapse. Historical aspect of concepts of synaptic transmission.
► Classification of synapses.
► Modern concept of structure of chemical synapse and mechanisms of signal transmission at chemical synapse.
► Concept of substances of synaptic action.
► Structure and properties of electrical synapse.
Concept of synapse. Historical Aspect of Concepts of Synaptic Transmission
A synapse is a formation that provides transmission of excitation from one structure to another. The term "synapse" (from Greek "synapsis" meaning clasp) was proposed by famous English neurophysiologist Charles Sherrington (1897) to denote a hypothetical formation or region specializing in cell-to-cell transmission of signals.
It should be noted that at that time information was believed to be transmitted by bioelectrical impulses, and Sherrington introduced this concept to denote a site of contact between cells for transmission of electrical impulses.
First ideas about a probable chemical mechanism of transmission of excitation from nerve to muscle were put forward by French physiologist Claude Bernard (1850, 1856).
C. Bernard studied action of curare poison used by American Indians and found that in animals paralyzed by this poison, both excitability of muscles and conductance of nerves supplying these muscles, were significantly decreased.
Resting himself on these data, Bernard suggested that curare acted on nerve endings inside muscles. However, investigations of Bernard did not lead to the idea of a chemical way of transmission of excitation through a neuromuscular junction. This idea was first formulated by English physiologist T. Elliott (1904). He based his hypotheses on the similarity between
action of epinephrine on an isolated heart and the effect produced by stimulation of sympathetic nerves, but, however, this theory was not adopted by the contemporaries.