Synaptic transmission Flashcards
Reversal potential is reached when Na+ and K+ are moving in and out of the cell simultaneously.
Na+ and K+ concentration force will always be the same. As the membrane potential becomes more depolarized, we see a smaller influx of Na+ and a larger efflux of K+ because the cell becoming more positive. The driving force of Na+ goes down and driving force of K+ goes up.
Describe EPSP.
Start with presynaptic terminal releasing ACh to postsynaptic target. This binds to AChr nicotinic receptors on the end plate or post synaptic target. AChr are permeable to Na+ and K+. Graph shows rapid increase followed by slow decline as ACh disappears by enzyme causing AChr to close.
What kind of states do delayed rectifier K+ (non inactivating) channels have?
Open and close. The start with a positive capacitive current when depolarized step is added followed by a positive leak current.
What kind of states do voltage gated Na+ channels have?
Open, inactivate, and close. Inactivation forces Na+ channels to close. We see positive capacitor leak followed by an inward Na+ negative current when depolarizing voltage is added. This is followed by a positive leak because Na+ leak channels out of the cell (positive leaving).
Describe the locations of the paranode, juxtaparanode, and internode.
Paranode is at the edge where myelin touches the axon. More resistant than inside and current leaks out. Tight adhesion contacts here.
Juxtaparanode is next to the paranode. Between the paranode and internode.
Internode is under the myelin sheath.
Why is the node important?
The current will take the path of least resistance. There are clusters of Na+ channels here meaning the only path of the current to flow is from node to node.
What if the myelin is damaged?
If there is a unmyelinated segment, channels become uniformed (unclustered) and current will move through slower. AP still occurs.
What is an extracellular recording?
Current flows in, propopgate down, and return.
Figure out where the current is coming from extracellularly. Recorded from any two points if there is a current between the points. Has lower resistance.
Ohm’s law: Vex=Iex*Rek
How does current move in extracellular recording?
We take the sum of the voltage. You have a test electrode and reference electrode. Current will move laterally, and then return. At T1, we have the AP with positive current (Na+ entering) and the AP downstream with negative current (K+ leaving).
What happens in the electrocardiogram?
We have synchronous action potentials. There is radiation cloud that travels further the the current is high.
Electrodes in specific positions will pick up different current loops.
Voltage sensitive dyes
Fluorescence changes when Vm change, tracking the AP.
How do other channels affect neuron firings? Like bursting?
Fire spontaneously due to HCN channels. There is an inward current of Ca2++ (small) that is sufficient enough to depolarize Na+ action potentials. Depolarization causes inactivates Ca2++ channels (HCN close). Because hyperpolarization opens these channels, Ca2++ is open and activates initiating the next cycle.
Describe delayed firing.
The cells is held first at hyper-polarization we don’t see the “spike train first” caused by A-type K+ channels. When these channels open, we see a transient outward current that brings the cell away from threshold. Hyperpolarization removes the inactivation.
What are Hyperpolarizing Activated Cation Channels?
An AP without injecting current results in auto-rhythmic firing. Permeable to Na+ and K+. Different because opens at -) potentials and closes at +) potentials. When sensor moves out, they close.
Describe electrical and chemical synapses.
Electrical synapse is bidirectional and has a cytoplasmic bridge that connects the cells together. Sea slug ink. Connected by gap junctions.
Chemical synapses has no continuity. It is activated by the release of NT. In the presynaptic cell, synaptic vesicles are activated by Ca2++ channels, releasing the contents in the vesicles into the synaptic cleft. These molecules bind to the receptor on the postsynaptic cell.
