Question

In a particular mammalian species, certain types of neurons have a neuronal radius of 1.5um, a membrane thickness of 2um, an axoplasmic resistivity paxo= 1.1 Ω-m and a membrane resistivity pmem=1.6x10^7 Ω-m

a) compute decay length, or physiological range, for this type of neuron

b) assuming the ranvier nodes are spaced 1mm apart, how many total ranvier nodes, including the original one, will be activated by a voltage spike? only consider the forward direction, neglect the fact that nodes . behind the spike may also be activated. Hint: using a drawing could make solving this problem easier.

c) is this a myelinated or unmyelenated neuron? explain

Answer 1

Neurons reach out to their targets through an extension of the cellular body called axon. Neurons can have myelinated or unmyelinated axons. The only difference between those two types of neurons is the speed of conduction. The neurons with myelinated axons have faster conduction speed since the myelin sheath acts as insulator that helps propagate the electrical signal faster. Most neurons in the central and peripheral nervous system are myelinated because they require fast conduction speeds such as neuron involved in spinal reflexes. The neurons with unmyelinated axon have much lower conduction of the nerve electrical signal. An example of unmyelinated neurons can be found in both the peripheral and central nervous system in the group c nerve fibers responsible for transmitting secondary pain or itchy.

All myelinated neurons in the central nervous system form the myelin around their axons thanks to glial cells called oligodendrocytes, while all myelinated neurons in the peripheral nervous system form their myelin sheaths thanks to the Schwann cells.