Conduction velocity of the action potential in myelinated fibers is approximatel
ID: 54237 • Letter: C
Question
Conduction velocity of the action potential in myelinated fibers is approximately proportional (increases or decreases in relation) to the diameter of the axon, while in unmyelinated fibers it is approximately proportional to the square root of the diameter.
A) Using this information, briefly describe the benefit of myelination in terms of the required space when transmitting the action potential at a given speed.
B) As the axon diameter (and distance traveled) decreases, at what point would the benefit of myelination likely not apply?
C) Based on these relationships, why is myelination not useful for axons traveling short distances?
Explanation / Answer
A)
Myelin wrapped around axons allows faster conduction of the electrical signal by forming an electrochemical insulation. Myelinated nerve fibers comprise of gaps known as nodes of Ranvier where depolarization of the membrane takes place. This electrochemical insulation blocks the voltage-gated channels that allow unmyelinated continuous conduction. But it allows an action potential to leap from neurofibril node to another neurofibril node in a saltatory conduction sequence like hopscotch. Thus, myelinated nerve fibers conduct faster than unmyelinated nerve fibers.
B)
The signals are transmitted by means of movement of ions across the membrane. This movement is influenced by the axon diameter. As the axon diameter increases the conduction velocity will also increases for both myelinated and unmyelinated neurons. However, myelinated always have a stable conduction velocity due to proper myelination or saltatory conduction.