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64 Cards in this Set

  • Front
  • Back
In patients with myasthenic diseases, a ulnar nerve conduction study would reveal what? x2
1. Increased response latency

2. Increased temporal dispersion of compound AP peaks
What are the three types of neuronal signals.
Receptor potential

Synaptic potential
(presynaptic and postsynaptic)

Action potential
Which signals are amplitude modulated?
All of them except AP.
Describe the propagation of neuronal signals.
RP - Passive
SP (presynaptic) - local
SP (postsynaptic) - passive
AP - active
Describe the summation of RP.
Yes in time and space
Describe the summation of SP.
(Presynaptic) - yes in time

(Postsynaptic) - yes in time and space
Describe the summation of AP.
None (all or none)
Describe location and character of the ion channels of RP.
Exist only in sensory neurons because they are the only ones with stimulus sensitive ion channels (Na+, K+, and Ca+)
Describe the location(s) and character of ion channels of SP.
In Presynaptic SP, voltage sensitive calcium channels.

In postsynaptic SP, ligand-sensitive (or 2nd messenger) channels.
Describe the location and character of ion channels of AP.
Voltage sensitive Na+ and K+ channels on unmyelinated axons.
List the four steps/regions of neurons.
1. Input region
2. Integrative/Encoding region
3. Conductive region
4. Output region
What two things may occur in the input region?
1. Transduces a sensory stimulus into a receptor potential (RP)


2. Receives a synapse and generates a post-synaptic potential (EPSP or IPSP)
What kind of modulation occurs in input regions?
Amplitude modulated
What kind of propogation occurs in input regions?
Passively with decrement (loss of amplitude)
What occurs in the integative/encoding regions?
Summations of depolarizing (+) or hyperpolarizing (-) AM signals occur.

If strong enough, a FM AP signal is generated.
What kind of modulation occurs in integrative/encoding regions?
What kind of propagation occurs in the integrative/encoding regions?
Active without decrement
Describe the "trigger zone" of integrative/encoding regions.
Afferent -> Initial segment
Efferent -> Axon hillock
What occurs in the conductive regions?
AP propagates to output region
What kind of propagation occurs in the conductive region?
Active without decrement
Where would you find conductive regions?
Nodes of Ranvier (unmyelinated regions)
What kind of modulation would you expect in the conduction regions?
What occurs in the output region?
Generation of presynaptic signal.

Arriving AP's will depolarize the terminal, thus opening Ca2+ channels. Increased [Ca2+] inside triggers secretion of NT, hormones, etc.
What kind of modulation would you expect at the output region?
What are cable properties and what does it determine.
Passive properties of the membrane which determine how signals propagate.
What are the three cable properties?
Membrane capacitance (Mc)

Membrane resistance (Rc)

Axial resistance (Ra)
Describe membrane capacitance.
Ability to "store" charge based on stable attraction of oppositely charged ions across thin layer of membrane.
Membrane capacitance is determined by what?
Charge separation across membrane. (Transmembrane ionic attraction)
Membrane resistance is determined by what?
Density of permeant ion channels that are open.
Most passive, ion channels are what kind of channels?
K+ channels
Axial resistance is determined by what?
Diameter of the neural process.
Axial resistance is AKA?
Cytoplasmic resistance
Larger processes have what effect on axial resistance and why?
Results in smaller axial resistance b/c lots of cytoplasm to carry signal.

In other words, more ions to carry signal.
Define orthodromic and antidromic.
Orthodromic - towards terminal

Antidromic - towards soma
AP do not normally propagate backwards (though can be made to do so). Why?
Refractory period
Total membrane current has what two components?
1. Capacitance current
2. Ionic current
Local circuit currents propagate signals how?
Local circuit currents initiate what at each new signaling site.
Initiate changes in Vm at each new signaling site.
Whenever there is a signal propagated down an axon, what four things must happen?
1. Capacitance current will discharge the membrane capacitance.
2. Ionic current will change membrane potential.
3. Capacitance current will recharge the membrane capacitance.
4. Ionic current will repolarize the membrane potential.
Before the ionic current flows through Rm and Ra (and Vm begins to depolarize), what must first flow through?
The capacitance current must flow first, reaching a MAX, then fall.
As capacitance current ceases, the charges are restored by what?
Ionic current
Rm (membrane resistance) and Cm (membrane capacitance) determine what?
How fast signals rise and fall PASSIVELY.
Rm (membrane resistance) and Ra (axial resistance) determine what?
How far signals propagate passively
Ra (axial resistance) and Cm (membrane capacitance) determine what?
Conduction velocity of signals.
What does it mean for something to be passive?
Without involvement of voltage sensitive ion channels.
The change in membrane voltage always lag behind what?
Capacitance current.
The capacitance current introduces what in neural signaling?
The importance of time as a variable.
Equation for tau?
Product of Rm(membrane resistance) and Cm (membrane capacitance).
Definition of tau?
Time to decay by 63% to 37% of peak change in Vm
Longer tau increases what?
The probability of effective temporal summpation.

In other words, the higher probability of summing signals that occur at different times.
Longer tau decreases what?
Temporal resolution.
Equation for lambda.
Sqrt (Rm / Ra)
Define lambda
Distance at which signal decays by 63%.
Longer lambda increases what?
Probability of effective spatial summation.
Longer lambda decreases what?
Spatial resolution.
Increase in diameter of axon will also increase what?
Conduction velocity.
In myelinated axons, each MICROmeter of increased diameter, will increase what?
The conduction velocity by 6 meters/sec.
Why does CV increase with diameter? x2
More ions/cytoplasm to to carry current

Less Ra (axial resistance) to current flow.
Increasing diameter of axon, decreases what?
Axial resistance
CV is proportionate with what equation?
1 / (Ra x Cm)
Axial resistance is proportionate to what equation?
1 / (D x D)
Why does CV increase even though increasing the D also increases the membrane capacitance.
Because membrane capacitance is proportional to diameter, thus effect is less.
Myelination increases what? and why? x2
CV b/c it decreases membrane capacitance AND increases membrane resistance
How does myelination decrease membrane capacitance?
By increasing distance between the two capacitor plates.