Function
Features of the ribbon synapse enable it to process information extremely quickly. Bipolar neurons present a good model for how ribbon synapses function.
In photoreceptor and bipolar cells information is transferred via the release of the neurotransmitter glutamate at the ribbon synapse. Conventional neurons encode information by changes in the rate of action potentials, but for complex senses like vision, this is not sufficient. Ribbon synapses enable neurons to transmit light signals over a dynamic range of several orders of magnitude in intensity. This is achieved by encoding changes in tonic rate of transmitter release which requires the release of several hundred to several thousand synaptic vesicles per second.
To accomplish this level of performance, the sensory neurons of the eye maintain large pools of fast releasable vesicles that are equipped with ribbon synapses. This enables the cell to exocytose hundreds of vesicles per second, greatly exceeding the rate of normal neurons without the specialized ribbon synapse.
The current hypothesis of calcium-dependent exocytosis at retinal ribbon synapses suggests that the ribbon accommodates a reservoir of primed releasable vesicles. The vesicles that are in closest contact with the presynaptic plasma membrane at the ribbon base constitute the small, rapidly releasable pool of vesicles, whereas the remaining vesicles tethered to the ribbon constitute the large, readily (slower) releasable pool. These regularly aligned rows of synaptic vesicles tethered to either side of the ribbon along with the expression of the kinesin motor protein KIF3A at retinal ribbon synapses can move vesicles like a conveyor belt to the docking/release site at the ribbon base.
Read more about this topic: Ribbon Synapse
Famous quotes containing the word function:
“To look backward for a while is to refresh the eye, to restore it, and to render it the more fit for its prime function of looking forward.”
—Margaret Fairless Barber (1869–1901)
“Think of the tools in a tool-box: there is a hammer, pliers, a saw, a screwdriver, a rule, a glue-pot, nails and screws.—The function of words are as diverse as the functions of these objects.”
—Ludwig Wittgenstein (1889–1951)
“The fact remains that the human being in early childhood learns to consider one or the other aspect of bodily function as evil, shameful, or unsafe. There is not a culture which does not use a combination of these devils to develop, by way of counterpoint, its own style of faith, pride, certainty, and initiative.”
—Erik H. Erikson (1904–1994)