Study Notes on Action Potential Propagation and Synapse Actions
Propagation of Action Potential
Action potential travels along an axon to the axon terminal.
Na+ influx repels nearby Na+ ions, causing a change in membrane voltage.
Action potentials propagate as Na+ and K+ channels open sequentially.
Voltage Gated Channels (VGCs)
Na+ VGC opening leads to depolarization, followed by K+ VGC opening for repolarization.
Na+ VGCs propagate the action potential in one direction due to channel characteristics.
Myelinated vs Unmyelinated Axons
Unmyelinated axons: Continuous conduction, slower.
Myelinated axons: Saltatory conduction, impulse jumps between nodes of Ranvier, faster transmission.
VGCs are dense at nodes in myelinated axons.
Refractory Periods
Absolute refractory period: No new action potential, regardless of stimulus.
Relative refractory period: Stronger stimulus needed for subsequent action potential.
Occurs due to inactivation of Na+ channels and K+ outflow.
Synapses
Action potential triggers release of neurotransmitters into synaptic cleft upon reaching axon terminal.
Neurotransmitters bind to postsynaptic receptors to open ion channels.
One-directional transmission: Presynaptic neurons send impulses, postsynaptic receive and propagate them.
Types of Synapses
Axodentritic, Axosomatic, Axoaxonic.
Configurations: Converging, Diverging, Reverberating circuits, and Parallel after-discharge circuits.
Key Concepts
Action potentials are one-directional due to channel mechanisms and refractory periods.
Saltatory conduction is faster than continuous due to myelination effects.
Synapses mediate communication between neurons and effectors.
How Your Body's Wires Talk
Imagine your body has tiny electrical wires everywhere! When these wires want to send a message, it’s like a tiny electric spark, called an "action potential," zipping down the wire.
This spark moves along because little "go" chemicals (Na+) rush into the wire, pushing other "go" chemicals along, like a domino effect!
Special Doors on the Wires
These wires have special little doors. First, a "Na+" door opens, letting "go" chemicals rush in, making that spot in the wire more positive. This is like turning a light on.
Then, a "K+" door opens, letting "stop" chemicals out, turning the light off and getting ready for the next signal.
These doors make sure the electric spark only goes in one direction, like a one-way street!
Fast Wires vs. Slow Wires
Some wires are like regular bare wires; the spark has to crawl along every tiny bit. This is a bit slow.
Other wires are super special! They're wrapped in fatty tape (called myelin), which makes the spark jump really fast from one unwrapped spot to the next, like a super-fast skipped hop! These are much quicker.
Wire's Recharge Time
After a part of the wire sends a spark, it needs a tiny break to recharge, like when you flush a toilet and have to wait for the tank to fill up.
For a very short time, it can't send another spark at all, no matter how hard you try.
After that, it can send another spark, but you have to give it a really big push!
How Wires Hand Off Messages
When the spark reaches the very end of one wire, it doesn't touch the next wire directly.
Instead, it squirts out tiny chemical messengers (neurotransmitters) into a tiny gap. These messengers are like little notes telling the next wire to start its own spark!
This message always goes from the "sender" wire to the "receiver" wire, always in one direction.
Different Ways Wires Connect
Wires can connect in different ways: some talk to the "branches" of another wire, some to its "body," and some even to its "end."
Sometimes many wires all talk to one wire, or one wire talks to many other wires, like a big telephone network!
Important Ideas
The electric sparks in your body only go in one direction because of the special doors and the wire's short recharge time.
Wires wrapped in fatty tape send messages much faster than bare wires.
The connections between wires (synapses) are super important for all your body parts to talk to each other and tell your body what to do!