Question

Describe how an action potential propagates along a myelinated and an unmyelinated axon, including how the potential is spread along the membrane. How are these two processes similar and how are they different? What two benefits do myelinated axons have over unmyelinated ones? Provide one way in which a myelinated axon is similar to an electrical wire and one way in which an axon is different than a wire. Why does multiple sclerosis (MS) prevent transmission in myelinated axons (that is, why can’t these axons just propagate the action potential in the same way that an unmyelinated axon does)? Finally, what if a drug 3 was developed that allowed M.S. patients to use continuous propagation for all of their neurons all the time; what would be the impact of such a drug?

Answer 1

First part

The propagation of action potential along both the unmyelinated axon and myelinated axons require the activation of voltage gated sodium channel. This is the similarity.

Dissimilarity is that In myelinated axons,the voltage gated sodium channel is present only in the nodal spaces called nodes of ranvir where as in unmyelinated axon the voltage gated sodium channel is present along the entire axon. Thus the action potential propagation in unmyelinated axon require the activation of sodium channel present throughout the axon where as in myelinated fibres activation of sodium channel only in nodes of ranvir is required. So the action potential propagation in myelinated nerve fibre is very fast compared to unmyelinated fibres.

Second part

Due to presence of myelin the speed of propagation of nerve impulse in myelinated fibres are 10 times more faster than unmyelinated axon.

The response to stimuli is very prompt in myelinated fibres compared to unmyelinated fibres.

Temporal precision and synchronization of spatially distributed targets is more in myelinated fibres compared to unmyelinated fibres.

Third part

An electric wire is insulated out side and current flows only through the metallic string inside. Like wise myelin sheath insulate the axon .

In electric wire electric conduction happens along the entire wire where as in myelinated axons it happens only along the nodes of ranvir, that is jumping of nerve impulses or saltatory nerve conduction is happening.

Fourth part

In myelinated axons nerve conduction or propagation happens only in nodes of ranvir and fast saltatory conduction happens . In multiple sclerosis , the autoimmune cells destructs this myelin sheath and the fast rhythmic conduction of impulse is lost. Group A and B fibres are myelinated nerve fibres and they are meant for fast synaptic conduction where as Group c fibres for pain sensation are non myelinated and are meant for slow conduction. When myelinated fibre become unmyelinated as in multiple sclerosis,the normal speed of impulse propagation is affected. Type c fibres are inherently meant for slow conduction for normal communication.

Fifth part

As mentioned above, there are three types of axons

Group A and B which are myelinated

Group C which are non myelinated

As mentioned earlier, myelinated fibres are meant for fast conduction and non myelinated fibres are meant for slow conduction. If the drug cause continuous conduction,the saltatory conduction meant to happen in myelinated fibres will be lost. The continuous nerve conduction will make the nerve impulse propagation in myelinated nerve fibres to be slow. So the normal nervous system communication process in the body effected.