Neuronal conduction and myelin

Question 1

Identify factors that influence how fast signals propagate along neuronal processes

Answer 1

-How fast the next segment of membrane is depolarised to threshold
-Speed/length constant = how far can a current spread passively along axon
-Myelin speeds up conduction of AP
-Thicker axon, faster AP conduction speed as wider diameter = less resistance
-Internode distance

Question 2

Explain why these factors influence neuronal conduction speed: Axon diameter, Myelination, Temperature, Distance

Answer 2

Axon diameter
-Axons with larger diameters offer less resistance to ion flow, which allows for faster depolarization and repolarization. This leads to faster signal propagation along the axon

Myelination
-Myelin is an insulating layer that allows for saltatory conduction, where the signal jumps from node to node, bypassing the myelinated segments. This increases the speed of propagation

Temperature
-Higher temperatures increase the speed of ion flow and chemical reactions, which can increase the speed of signal propagation. Conversely, lower temperatures can decrease the speed of propagation.

Distance
-The longer the distance that the signal has to travel, the more time it takes to propagate. This is because the signal can weaken over longer distances, leading to slower conduction.

Question 3

Compare these factors across species and different kinds of neurons and relate this comparison to neuronal conduction speed and energy efficiency

Answer 3

-The giant squid has axons that are much larger in diameter than those of other species, which allows for faster conduction speeds. The myelin sheath that surrounds axons in many species also greatly increases the speed of conduction by reducing the amount of current that is lost to the surrounding environment.
-However, the thickness of the myelin sheath can vary across different types of neurons and across species. Thicker myelin sheaths generally lead to faster conduction speeds, but also require more energy to maintain

Question 4

Describe saltatory conduction and nodes of Ranvier

Answer 4

-Nodes of ranvier are parts of axon without myelin sheath
-Saltatory conduction is the way an electrical impulse skips from node to node down the full length of an axon
-Saltatory = jumping
-Sodium channels at the nodes of ranvier, saving energy
-The influx of positive sodium ions flowing into the axon recharges the action potential
-Consecutive nodes of ranvier reach threshold quicker and, therefore, the conduction velocity is increased