Synapses
edyong | April 12, 2009
Sponges are among the most primitive of all animals. They are immobile, and live by filtering detritus from the water. They have no brains or, for that matter, any neurons, organs or even tissues. If you were looking for the evolutionary origins of animal intelligence, you couldn't really pick a less likely subject to study.
So it was with great surprise that Onur Sakarya from the University of California, Santa Barbara found that sponges carry the beginnings of a nervous system.
With no neurons to speak of, these animals still have the genetic components of synapses, one of the most…
purepedantry | October 29, 2007
One of the mechanisms -- perhaps even the primary mechanism -- by which synapses in the brain are potentiated -- made more sensitive to activation -- is the insertion of more AMPA receptors (AMPA-R) into the synapse. AMPA-R are glutamate-activated, cation (Na and Ca) channels that are really the business end of creating the electrical activity in the post-synaptic cell. Their insertion is activated by the Ca admitted by another cation channel, the NMDA receptor. Basically long-term potentiation (LTP) -- which we believe is the primary storage form of memories on a cellular level -- of…
purepedantry | September 20, 2007Synaptic transmission is incredibly fast. For example at the neuromuscular junction, the minimum time between the appearance of the electrical activity in the axon terminal and the appearance of electrical activity in the muscle as little as .4-.5 ms.
How is this managed?
One of the ways is that the vesicles that contain neurotransmitters are docked very close to the membrane. I talked about this is an earlier article where reconstruction of electron micrographs showed that synaptic vesicles are hemifused to the membrane.
Here is another article in this vein. Siksou et al. in the…
purepedantry | December 14, 2006There has always been a bit of a debate as to whether the vesicles in the presynaptic nerve terminal that contain transmitter are just near the presynaptic membrane or are in fact hemifused with it.
At the presynapse, vesicles containing neurotransmitter are prepared and aligned by the presynaptic membrane -- the process of synaptic release needs to be very rapid. When an action potential travels down the axon, calcium flows into the presynaptic terminal. This calcium activates SNARE proteins that are involved both in docking the vesicles near the membrane and fusing them with the membrane…