Thoughts on week 2
This week we talked about membrane proteins, membrane potential and action potential. For me of special interest was how ionic currents spread inside the neuron. The currents that result in thousands of synapses exciting and inhibiting the dendrites are integrated and if the total change in membrane potential is high enough at the axon hillock near the soma, the action potential is triggered. Before the positive current reaches the axon hillock it is diminished by the leaking of current through K+ channels and possibly by inhibition. In dendrites the current can move to any direction, but in axons it moves only towards the axon terminal because the voltage gated Na+ channels are in inactive state after opening. Also axon’s shape and myelin sheath surrounding it facilitates the movement of the current in one direction
Since the positive current can spread in any direction in the dendrites there exists a phenomenon called neural backpropagation. It means that after an action potential has been fired down along the axon, the depolarization spreads back from the soma to the dendrites where it started from. The function of the backpropagation is not known but it has been suggested that it might facilitate LTP in hippocampal neurons, maybe by letting the presynaptic neuron know that the postsynaptic neuron has fired. The backprogating action potential can also have LTP related function in activating NMDA receptors and the release of BDNF and retrograde neurotransmitters. Since endocannabinoids are retrograde neurotransmitters, it would be interesting to know if they have something to with LTP.