Question

If myelin sheath is continued in myelinated nerve fiber then what will happen in a neuronal conduction?
A. Velocity will be increased.
B. Conduction will be slow.
C. Conduction will be stopped.
D. No effect is seen.

Answer 1

Hint: Myelin sheath is a thick layer that is wrapped around all the nerves present in the brain and spinal cord. It allows electrical impulses to pass through nerve cells. The node of Ranvier helps the electrical pulses to move faster.

Complete answer:
Myelin sheath contains fat and protein and it is wrapped around the axon to insulate them. It keeps the axon separated from the external environment and also decreases the rate of conduction. The nodes of Ranvier which are aperiodic gaps in between myelin sheath helps pulses to move faster. The myelin sheath prevents the local current to flow through the membrane which leads to the current to travel down to the nodes of Ranvier. These nodes of Ranvier are rich in ion channels which trigger the conduction to the next node slowed by a myelin sheath. We can see jumping of the action potential in nerve fiber as it is regenerated at every node. The nerve with an unmyelinated axon will have action potential in the entire membrane and it will fade and defuse back to the original depolarized region.

So, coming back to our question, if the entire axon is myelinated without nodes, it will bring down the action potential and the conduction will be slowed down.

The correct answer is B which is conduction will be slow.

Note:
The myelin sheath helps the action potential to pass through the axon efficiently and quickly. The damage in myelin causes the impulses to slow down which leads to the disease such as multiple sclerosis. This disease is not curable but can be managed with proper symptoms relieving treatment.