A) In the mechanism of action potential, wheninput is present, neurons have a membrane potential which is around -70millivolts and without input, the resting potential will remain the same. However,excitatory or inhibitory inputs, which can come into the soma or the axon, butare more likely to enter through the dendrites, will cause changes to theresting potential, also known as the graded potential. Graded potentials can beboth depolarizing, also known as excitatory potential, and hyperpolarizing,also known as inhibitory potential. Action potentials on the other hand, alwayscause depolarization and reversal of the membrane potential. Whether an excitatoryor inhibitory potential, movement to the membrane potential is involved.
Meaning, they can be closer to or farther away from the threshold potential, whichlands at around -50 millivolts. As polarization from both excitatory and inhibitoryinput spreads along the membrane, the size of the graded potential gets smaller.Spreading action potentials down the axons of neurons is what makes neurons capableof transmitting information over a wide range of distances.
Amplitude isall-or-none when it comes to action potential. Another big difference betweengraded and action potentials is that action potentials do not decay withdistance. Action potentials down an axon are unchanged no matter how long theaxon is and are usually very fast. Large-diameter axons lead to action potentialsbeing very fast. Axons that have a myelin sheath, known as myelinated axons, alsolead to action potentials being faster than axons that don’t have a myelinsheath. This makes sense because myelin sheaths are usually on larger-diameteraxons.
Action potentials run slower through the gaps between the myelinatedsegments, known as the nodes of Ranvier than through the myelinated segment. Thisoccurrence is called saltatory conduction. The word “saltatory” comes froma Latin word for jumping. When defining jumping in action potential, you are explainingthat action potential jumps from node to node rather than having a steady,regular conduction along the axon.