Class Notes (810,512)
Canada (494,140)
NESC 2570 (6)

March 29th 2012.docx

4 Pages
Unlock Document

Dalhousie University
NESC 2570
Stefan Kreuger

March 29th 2012 March-29-12 11:33 AM Neural Plasticity Ch. 8, 24, 25  Under low frequency stimulation, responses of neurons tend to be stable  However under non-stable conditions, the way we respond to stimulation can change  How we respond to a new stimulus different than how we would when it gets customary, or "boring"  Nervous system has evolved in a way that allows this adaptation to occur o Adapt themselves based on prior inputs, shape responses based on past experience Short-term plasticity changes  Change in the behaviour of synapses that occurs in a time frame of milliseconds to tenths of seconds  Presynaptic membrane potential spike often causes a response in the post-synaptic membrane potential o However sometimes the size of the postsynaptic potential can change if the two occur in a very short time frame  Two occur very close together as a way of ensuring that the firing is not random noise, which is more likely to occur with just one firing than it is with two successive firings Paired-pulse facilitation  The phenomenon when the second postsynaptic potential is larger than the first  If the subsequent potentials are smaller than the first, it is called depression as opposed to facilitation  The closer the two potential changes are together, the more facilitation occurs, farther apart, less facilitation o However they can't get too close together because of the absolute refractory period  First observed in neuromuscular junction o Because these were the easiest to measure from, to they were observed here first because with the older crude pipette technology, it was easier to measure from here Katz and associates 2+  Observed that the postsynaptic response was very dependent on the extracellular Ca levels  Under low calcium conditions, the amplitude of response is much lower o But as stimulation continued, the response became facilitated  So amount of calcium influx important in facilitation The degree of facilitation or depression depended largely on the amount of transmitter release  More transmitter release corresponds with higher amount of depression These phenomenon have to do with two competing processes  Calcium influx, causing vesicles to fuse, releasing transmitter  Also has to do with the release probability o How many calcium channels are near release facility o How long they stay open o What voltage they open at  So if you have a finite potential of release, you can have failure o Another action potential coming quickly after that, there could be residual calcium remaining after the first  The residual calcium ions will sum with the next lot of influxed calcium to reach higher levels, making release of vesicular content more likely the second time than first What mechanism controls depression then?  There is a bit of time between when the first vesicles are released from the active site, and when the second set of vesicles can be docked and primed before then can be released.  First stimulation releases some of the vesicles, and then there are not as many available for release when a subsequent action potential fires shortly after o May take many 10s of milliseconds before next pool of vesicles are biochemically ready for release When a high frequency train of stimulatory pulses are fired  Facilitation can occur first  But once it depletes the pool of readily releasable vesicles, depression will then begin to occur  After pausing from the train of pulses, and the pool of readily releasable vesicles is re-stocked, the amplitude of the postsynaptic potential returns to a very normal level o Called post-tetanic potentiation  High frequency trains like the one in the slide are not unnatural, many neurons communicate with each other using a burst of potentials  Short-lived enzyme activation in the pre-synaptic membrane (calcium dependent enzymes, all have different affinity for, therefore activated at different levels) can cause changes in the behaviour of the cell o For example, the brief higher calcium levels can activate some of these enzymes (typically protein kinases), phosphorylate some things that promote transmitter release, so even once the calcium is gone, the release probability will remain increased until the things have phosphorylation removed  Can be what cause the longer term facilitation These processes are pretty much ubiquitous in chemical synapses throughout the animal kingdom  Regardless of where in the nervous system it is Marine invertebrates tend to have very large cells  And less complex nervous systems  Makes it easier to recognize cells from organism to organism, making it easier to experiment on the same cells between organisms, and obtain more accurate experimental data  Often used the ganglion of these animals o Very small number of very large cells in these, easily identifiable between organisms Sea hair aplysia  Kandell did experiments on  Mantle used to protect gills, retracts to expose, can cover them up to protect o Has very very large cells up to a couple hundred microns across in size o Same pattern of cells between individuals  Kandell and his students were able to
More Less

Related notes for NESC 2570

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.