Questions about Lecture 6: Generation of action potential

Lecture 6: Generation of Action Potential

On Page 2 Third slide, the notes says that ligand-gated channel open or close in response to a specific chemical stimulus (neurotransmitter, hormones, ions) directly or indirectly (second messenger system). The example given is Na+ inward, Ca2+ inward and K+ outward. I know that the ACh can bind to the receptor at post-synaptic membrane and causes influx of sodium. But i dunno what condition can cause the influx of calcium ions and efflux of potassium ions. Do you know the examples?

On Page 5 Third slide, it is stated that overshoots means exceeding the isopotential. Initially I was confused by this term, but later on I find out that it simply means same charges at both side of the axolemma. In another words, isopotential means 0mV. Overshoot means exceeding 0mV.

On Page 8 Second slide, the examples of synapses given are axodendritic (between axon and dendrite), axosomatic (between axon and soma/cell body) and axoaxonic (between 2 axons). I also learned that there is synapses that is called dendrodendritic (between 2 dendrites). I am wondering how come the AP can pass from axon to axon or from dendrite to dendrite? Isn't the AP only travel in one direction?

On Page 9 First slide, one-way conduction include orthodromic conduction (conducting impulse in the normal direction) and antidromic conduction (conducting impulse in a direction opposite to the normal). What is the example of antidromic conduction? How can the AP be conducted in the opposite way? Is it possible for AP to travel in both directions in an axon or dendrite?

On Page 9 second slide, the notes discuss about excitatory post-synaptic potential (EPSP) and implies that depolarisation occurs when sodium ions that enter the cell exceed the amount of calcium influx or potassium ion efflux. I dun quite understand about the role of calcium ion and potassium ions in the EPST. Isn't influx of calcium ions will help depolarise the membrane better? On the other hand, I learned that Inhibitory post-synaptic potential will open the cloride ions channel and the influx of it will hyperpolarise the cell membrane.

On Page 10 first slide, it is stated that examples of inhibitory system organization includes the negative feedback of Renshaw cell and spinal motor neurone. Can you explain more about this?

Thank you.