IMAT 2011 Q56 [Neurons]

Which adaptation cannot help increase the speed of transmission in a motor neurone?

A. long axon

B. nodes of Ranvier

C. synapse

D. presence of an insulating myelin sheath

E. greater axon diameter

We are asked what CAN NOT help speed up the transmission in a motor neuron (or any other neuron for that matter).

A long axon – The longer the axon, the faster the transmission will go, imagine it like a waterfall, if the top of the waterfall is higher, the water that falls will have a much quicker velocity with the help of the acceleration, so this one does help the speed of transmission.

Nodes of Ranvier – the whole point of the nodes is to speed up the process by limiting and separating the places of membrane potential and action potential to take place. This one must speed up the process, so it is not what we are looking for

Presence of an insulating myelin sheath – similar to the nodes of Ranvier, the myelin sheath around the axon is meant to limit the membrane potential to particular places, therefore, forcing the action potential to move faster.

Greater axon diameter – the greater the width of the axon, the faster a transmission will go through it.

Synapse – The synapse is just the place of transmitting the neurotransmitters to the next neuron cell; it does not increase the speed of transmission in any way.

Therefore, the answer must be C