15.3 Passage Of An Action Potential Flashcards
How does an action potential move along an axon, and what happens to its size during this process?
- moves rapidly without any decrease in size.
- remains the same from one end of the axon to the other.
- It is a travelling wave of depolarisation, where each region of the axon membrane generates an action potential, causing depolarisation of the next region.
- The previously depolarised region undergoes repolarisation and returns to resting potential.
Describe the ion concentration and charge difference across the membrane of an unmyelinated axon at resting potential.
At resting potential:
- The concentration of sodium ions is higher outside the axon membrane than inside.
- The concentration of potassium ions is higher inside the axon membrane than outside.
- The overall concentration of positive ions is greater outside, making the outside positive relative to the inside. The axon membrane is polarised.
How is an action potential propagated along an unmyelinated axon?
- The localised electrical currents cause the influx of sodium ions by opening voltage-gated sodium channels further along the axon.
- Sodium ions enter, causing depolarisation in this region.
- Behind this region, potassium voltage-gated channels open, and potassium ions leave the axon, repolarising the previous region.
- The depolarisation moves along the axon, and this process continues until the action potential reaches the end of the axon.
How does the passage of an action potential differ in a myelinated axon compared to an unmyelinated axon?
- In a myelinated axon, the myelin sheath acts as an electrical insulator, preventing the formation of action potentials along the length of the axon.
- Instead, action potentials occur only at the nodes of Ranvier, where the myelin is absent.
- The action potential jumps from one node to the next in a process called saltatory conduction, which allows the action potential to travel faster than in unmyelinated axons of the same diameter.
Why is saltatory conduction faster than continuous conduction in unmyelinated axons?
1) action potential jumps from node to node, rather than being propagated along the entire axon membrane.
2) reduces time needed for depolarisation and repolarisation to occur at every point along the axon, speeding up the overall transmission of the nerve impulse.
What is the role of the nodes of Ranvier in the passage of an action potential in a myelinated axon?
- The nodes of Ranvier are gaps in the myelin sheath where action potentials can form.
- They allow the action potential to jump from one node to the next via saltatory conduction, significantly increasing the speed of transmission along myelinated axons.
Where are the voltage-gated sodium channels found on myelinated axons vs. Un myelinated axons
Myelinated = only found in the nodal spaces
Unmyelinated = along the entire length of the membrane
