Neuronal Signal Propagation Flashcards
Action potential firing is produced by ________ ion channels.
voltage-gated
The ______property of a neuron describes the likelihood that a neuron will fire an Action Potential depending upon the strength of the input signal
Excitability
________ uses an intracellular electrode to inject current commands across the surface membrane and record the neuronal electrical response (It is like a programmable charge pump)
Current clamp
Rheobase
Minimum current to reach threshold
Chronaxie
Time to fire at a current that is 2x Rheobase
By keeping _____ constant, the ________is kept constant, so all changes in current are due to change in the probability of the channel being open
membrane potential, driving force
Leak current
Linear changes in Current as expected
from Ohm’s Law
How do you isolate a Na+ ion specific component of a current?
Remove K+ from the media or add a drug (TEA) that selectively eliminates the K+ ion dependent current
How do you isolate a K+ ion specific component of a current?
Remove Na+ from the media or add a drug (TTX) that selectively eliminates the Na+ ion dependent current
Name the 3 axonal membrane ionic current components determined through H&H’s experimentation.
- Linear Leak Current (Looks Ohmic)
- A depolarization activated Na+ current that shuts down in a time dependent manner
- A depolarization activated K+ current that remains active
H&H suggested that ____ could be accurately modeled by assuming multiple switches whereas _____ only required a single switch model
activation, inactivation
What positively charged residues are found in transmembrane segment of voltage-gated K+ channel?
Arg, Lys
The ______ structure of Voltage-gated channels suggested that each S4 transmembrane segment was acting like a separate gating switch as predicted by H&H
tetrameric
_____ is a “autoinhibitory” state analogous to receptor desensitization
Inactivation
A ______exists, where the Neuron cannot fire another action potential until the Na+ channels recover from Inactivation
Refractory period
What exists close to the membrane and exists on many lipids proteins, glycosylations? Why can these be problematic?
Fixed charges - ions can bind them, so ion concentration changes can produce surface charge effects that change stability of gating charges - appears as a change in membrane potential
When are surface charge effects particularly large?
With divalent cations like Ca2+
What symptoms result from hypercalcemia?
Decreased excitability of neurons - fatigue, depression, confusion, cardiac arrhythmias, coma
What symptoms result from hypocalcemia? (often due to hypoparathyroidism)
Increased excitability - cardiac arrhythmias, cramps, tingling, bronchospasms, seizures
Higher Ca2+ outside cell (increases/decreases) surface binding, (destabilizing/stabilizing) Na+ channel gating charges in the open state, making it (harder/easier) to fire an action potential.
Increases, destabilizing, harder
Lower Ca2+ outside cell (increases/decreases) surface binding, (destabilizing/stabilizing) Na+ channel gating charges in the open state, making it (harder/easier) to fire an action potential.
Decreases, stabilizing, easier
____ are locations where + charges are entering the cell, driving a depolarization
Sinks
______ are peripheral locations that are being depolarized due to the + charges flowing in at the sink
Sources
A current loop between nearby parts of the same cell that are at different potentials is called a ____
Local circuit current
Action potentials run down the axon from _____depolarized patch of membrane to _____depolarized membranes
More –> Less
Name the current sink and source for a depolarizing synaptic input.
Sink - site of neurotransmitter action, synapse
Source - soma depolarization by dendritic current
Name the current sink and source for a propagating action potential.
Sink - axon hillock
Source - further down the axon, dendrite
How do propagation waves spread in an unmyelinated axon?
Continuously down the axon
If internal resistance increases, what happens to conduction speed
Slows down
Local circuit can extend further if internal resistance is ____ and membrane resistance is ____.
(Low or high?)
Low, high
If membrane resistance increases, what happens to conduction speed?
Accelerates
Myelination is produced by repetitive wrapping of what type of cell around an axons
glial cell
How do myelinated axons reduce amt of current needed to depolarize the membrane?
Reduces the membrane conductance (increasing resistance) and reducing capacitance (greater charge separation)
Does myelin thickness increase or decrease as axon diameter increases?
Increases
T or F. Myelination does not accelerate propagation speed for small axons <1 um
TRUE - but many small CNS axons are myelinated anyway b/c of energy savings
In myelinated axons, propagation waves are only generated where?
Nodes of Ranvier
How do propagation waves spread in a myleinated axon?
Saltatory propagation of action potential down the axon
Name effects of myelination on the following:
- Membrane Resistance
- Membrane Capacitance
- Conduction velocity
- Energy Utilization
- Increases
- Decreases
- Increases
- Decreases - b/c fewer ions need to cross the membrane to propagate the action potential
What is the primary limit to myelination?
Increase in axon caliber
Are myelin sheaths thinner or thicker in brain? Periphery?
Brain - thinner
Periphery - thicker
Is axon density low or high in the periphery? In the brain?
Periphery - low (so diameters are bigger)
Brain - high (to limit diameter so brain doesn’t get too big)
