Neuron Signal Generation and Propogation Flashcards Preview

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Flashcards in Neuron Signal Generation and Propogation Deck (19):

What decides whether or not to fire an AP?

voltage gated channels



the likelihood that a neuron will fire an AP depending on the strength of the signal


What method is used to analyze a neuron's excitability?

Current clamp - uses an intracellular electrode to inject current commands across the surface membrane and record the neuronal electrical response. Used to determine minimal signal to fire APs


Threshold voltage

Point at which voltage-gated channels trigger a switch to accelerated voltage change. (Fire AP!)


What two parameters are used to measure excitability?

Rheobase - minimum current needed to reach threshold

Chronaxie - time needed to fire at a current that is 2x Rheobase


Voltage clamp

Way to study proteins involved in making cell membrane user more control over membrane potential. Provides direct control of channel gating stimulus, allowing the sensitivity of the voltage-dependence to be studied in great detail


Total conductance for a channel type =?

Conductance of a single channel of that type times the number of channels of that type in the membrane times the probability that the channels are in open state and thus able to conduct ions


How is voltage gated channel function determined?

- number of gating charges
- intrinsic stability of closed and open in the absence of membrane potential
- kinetics that determine how rapidly the transitions between these states occur
- selectivity properties that determine which ions can pass through open channel
- inactivation will occur in many channels during sustained depolarization


Describe AP sequence

1. Depolarization cause voltage gated Na channels to open
2. Further depolarization
3. THRESHOLD! = positive feedback to open more Na channels = more depolarization
4. short delay, K channels start to open and Na channels inactivate
5. Cell returned to negative potential
6. Refractory period (cannot fire another AP)


Why does great care need to be taken particularly when changing extracellular Ca2+ levels?

Surface charge.

Close to membrane, fixed charges exist on lipids/proteins/glycosylations and ions can bind to these charges which would seem like you have made a change in membrane potential, alltering how a channel responds to environment/stability of the channel. This effect is especially apparent with divalent ions (i.e. Ca2+)


High serum Ca2+ levels (hypercalcemia) = ?

symptoms resulting from DECREASED excitability of neurons: fatigue, depression, confusion, and cardiac arrhythmias


Low serum Ca2+ (hypocalcemia) = ?

symptoms resulting from INCREASED excitability: arrhythmias, cramps, tingling in the extremities, interruption of breathing


What wraps around myelinated axons?

oligodendrocytes or Schwann cells (repetitive wrapping of a glial cell around axon)


What does the myelinated wrap do?

Reduces amount of current needed to depolarize the membrane by reducing the membrane conductance (increasing resistance) and reducing capacitance (greater charge separation) --> allows conduction velocity to increase linearly with diameter (also increases thickness of axon)


What are the effects of axon diameter on propagation speed?


when axon becomes more narrow:
- internal resistance goes up (slows conduction)
- membrane resistance goes up (accelerates conduction)

balancing effects mean that conduction velocity increases as the square root of diameter


If myelination doesn't accelerate propagation speed for small axons, why bother with them?

they save energy!


saltatory conduction

in myelinated axons, propagation waves are only generated at nodes of Ranvier as AP propagates down axon


Myelination improves....

- increases membrane resistance and decreases membrane capacitance (improve conduction velocity)
- also decreases energy utilization because fewer ions need to cross membrane to propogate AP


Limits to myelination

- increasing axon diameter = needs more space (PRIMARY LIMIT)
big deal in brain (since brain can't get too big), but not so big deal in periphery