The lecture this week started with a quick quiz of 5 minutes containing only multiple choice questions. What made it difficult for us was that some of the questions were about the classification of neurons (spinous or not, Golgi Type I or II, motor/sensory/interneuron), which was discussed in a very specific paragraph of the chapter we had to read. In addition, there was a question about Alzheimer’s disease, which was unexpected because of the fact that we haven’t spent much time discussing the biology behind Alzheimer’s disease yet.
The lecture was about action potentials (4th chapter of the course book) and synaptic communication (5th chapter of the book). We clarified the process of action potential propagation as well as the mechanisms of depolarization. In the picture below we can see the typical three phases of an action potential: the depolarization due to the Na+ influx, the re-polarization caused by the K+ efflux and the hyper polarization phase, which causes a “refractory period” making Vm more negative than the normal. The picture also depicts failed initiations, which indicate that to form an action potential the initial signal has to be strong enough to overcome the threshold.
We also learnt a lot about synapses and how they work. The main classification that must be done is between electrical and chemical synapses. The difference between them is in the way the signal is propagated: for electrical synapses there are the so-called gap junctions which allow an almost immediate propagation, chemical synapses on the other hand work by releasing some specific neurotransmitter molecules into the synaptic cleft. These will then bind to the receptors of the post-synaptic cell and induce the propagation of the signal. This difference is also the explanation of why the synaptic delay is present in the chemical synapses but not in the electric ones (there was a question in the exercises about the synaptic delay).
During the exercise session we went through few questions of the quiz. The assistants explained to us that all the possible choices we had in the question about Alzheimer’s disease were related to other neurological diseases (Parkinson, Multiple sclerosis, etc…). The other questions of this week were about the synaptic delay (as mentioned above), the action potential, glial cells and the Nernst equation. The latter was the most challenging, since we were asked to obtain the Nernst equation from the Boltzmann’s distribution.
See you next week,
Laura, Hugues and Leonardo