Action potentials are the main means of communication between neurons, and their exact timing can be
really important. But the specific timing of action potentials is
really important in the auditory system, because the auditory system encodes (among other things) information about sound wave frequency.
I've previously written about auditory processing with regards to
the wonder that is the chicken brain, but today we will focus on timing-specificity in the mammalian brainstem. Specifically, some weird channels in the Medial Nucleus of the Trapezoid Body (the MNTB).
 |
| Mammalian Auditory Brainstem (source) |
At the
Society for Neuroscience meeting, I learned about the sodium-activated potassium channels which help the electric fish fire
super-fast super-large action potentials. I was suprised to learn that sodium-activated potassium channels are located in many parts of the mammalian brain.
A paper from the Kaczmarek lab at Yale explains that these sodium-activated potassium channel (SLICK and SLACK) are present in the mouse auditory brainstem and contribute to the 'temporal accuracy' of the MNTB neurons.
Yang et al. (2007) record the action potentials from these neurons at a range of frequencies and show that the neuron can 'keep' up with the frequencies better when more sodium is present.
In the figure above, the 'flatter' the line, the better the 'temporal accuracy.' They also made a
computational model of this neuron and ran simulations altering the sodium values and reversal potential.
 |
| Yang et al., 2007 Figure 9D |
Their model simulations are similar to their experimental recordings, in that more sodium results in more temporal accuary of the action potential. They confirmed that this was dues to a sodium-activated potassium channel by
directly activating SLACK and seeing a similar improvement in temporal accuracy.
The SLACK channel still blows my mind, but its role in helping the auditory system fire with the utmost precision actually makes a lot of sense.
©
TheCellularScale
Yang B, Desai R, & Kaczmarek LK (2007). Slack and Slick K(Na) channels regulate the accuracy of timing of auditory neurons. The Journal of neuroscience : the official journal of the Society for Neuroscience, 27 (10), 2617-27 PMID: 17344399
IIRC, the auditory system also has some special fast motor proteins in the cochlea, and some special fast synapses (also in the MNTB, I think). That's all cool for the temporal processing of sound. What I've always wondered, though, is why these fancy things aren't just everywhere? Why can't I just be built out of those extra fast motor proteins and have super reflexes? Okay, it probably wouldn't work like that, but I wonder what the benefit of some things being SLOWER is.
ReplyDeleteIn this post, you described comprehensively about the action potentials as the main means of communication between neurons, and their exact timing is very important. Thank you so much for your good work. traumatic brain injury
ReplyDelete