Question

Compare the distribution of ion channels along unmyelinated versus myelinated axons and explain how this accounts for the difference in conduction velocity between these two types of axons. Predict the effects on action potential propagation of demyelinating diseases, such as multiple sclerosis.

Answer 1

Explanation:

The Myelinated neuron are covered with myelin sheath(which are  deposits of water, lipds,protein wrapped in concentric rings around axon by process of myelination ) . These deposits are interrupted at intervals by gaps called nodes of Ranvier. The latter  are the sites of  high number of voltage gated channels, of sodium and potassium ions and therefore determines  the conducting velocity of the  a neuron.  

When  action potential (AP) reached  the  nodes,  the  sodium channels opens (depolarization) and the AP jumps across  the myelinted neuron to the next nodes. This is called saltatory conduction.Thus myelin ensures  energy efficiency  and increases conduction velocity of AP

Unmyelinated neurons lack myelin deposits, and the Nodes of Ranvier.  Therefore transmission of  action potential along the axon is stopped leading to Conduction block. If the demyeliantion is partial, conduction velocity is slow down, or the axon failed to conduct fast AP .

Relatively MS; is an autoimmune, environment and genetic- mediated diseases in which immune systems destroy the myelin deposits  around axon of the brain and spinal cord.That is( demyelination of the axon).

Thus the action potential transmission function of the myelin sheath is lost.Therefore  depending on the site of neuron where this occurs, Conduction block occurs thus  no AP is propagated, the speed of  transmission of AP in the subject is  slowdown , and  can not transfer fast AP.

Consequently  sensory inputs  or motor outputs  to and fro  the brain and spinal cord is affected and this results in mutiple neuro -degenerated  symptoms of MS.

Explanation:

Answer 2

Answer:

Myelinated Axons; leak channels are insulated by myelin leading to less loss of current flow and better conduction velocity. Ion channels omly located at nodes of ranvier; thus signal has sultatory conduction along myelin sheaths and jumps and move much quicker

Demyelinating diseases; along locations where myelin sheaths once was current links occur and conduction slows, the signal cannot make it very far because it looses energy as it travels through the axon

Unmyelinated axon; Ion channels are sequentially placed all along axons; thus it takes longer to send signal down axon. the energy isn't leaked out, it still contains the same signal but it is simply slower. distance between voltage gated channels needs to be small enough so local current flow can depolarize the membrane.

N/B; Harder to generate action potential in demyelinating disease

axon diameter( bigger diameter= less resistance= faster current).