Neuronal Signal Propagation

Question 1

Action potential firing is produced by ________ ion channels.

Answer 1

voltage-gated

Question 2

The ______property of a neuron describes the likelihood that a neuron will fire an Action Potential depending upon the strength of the input signal

Answer 2

Excitability

Question 3

________ 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)

Answer 3

Current clamp

Question 4

Rheobase

Answer 4

Minimum current to reach threshold

Question 5

Chronaxie

Answer 5

Time to fire at a current that is 2x Rheobase

Question 6

By keeping _____ constant, the ________is kept constant, so all changes in current are due to change in the probability of the channel being open

Answer 6

membrane potential, driving force

Question 7

Leak current

Answer 7

Linear changes in Current as expected

from Ohm’s Law

Question 8

How do you isolate a Na+ ion specific component of a current?

Answer 8

Remove K+ from the media or add a drug (TEA) that selectively eliminates the K+ ion dependent current

Question 9

How do you isolate a K+ ion specific component of a current?

Answer 9

Remove Na+ from the media or add a drug (TTX) that selectively eliminates the Na+ ion dependent current

Question 10

Name the 3 axonal membrane ionic current components determined through H&H’s experimentation.

Answer 10

1. Linear Leak Current (Looks Ohmic)
2. A depolarization activated Na+ current that shuts down in a time dependent manner
3. A depolarization activated K+ current that remains active

Question 11

H&H suggested that ____ could be accurately modeled by assuming multiple switches whereas _____ only required a single switch model

Answer 11

activation, inactivation

Question 12

What positively charged residues are found in transmembrane segment of voltage-gated K+ channel?

Answer 12

Arg, Lys

Question 13

The ______ structure of Voltage-gated channels suggested that each S4 transmembrane segment was acting like a separate gating switch as predicted by H&H

Answer 13

tetrameric

Question 14

_____ is a “autoinhibitory” state analogous to receptor desensitization

Answer 14

Inactivation

Question 15

A ______exists, where the Neuron cannot fire another action potential until the Na+ channels recover from Inactivation

Answer 15

Refractory period

Question 16

What exists close to the membrane and exists on many lipids proteins, glycosylations? Why can these be problematic?

Answer 16

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

Question 17

When are surface charge effects particularly large?

Answer 17

With divalent cations like Ca2+

Question 18

What symptoms result from hypercalcemia?

Answer 18

Decreased excitability of neurons - fatigue, depression, confusion, cardiac arrhythmias, coma

Question 19

What symptoms result from hypocalcemia? (often due to hypoparathyroidism)

Answer 19

Increased excitability - cardiac arrhythmias, cramps, tingling, bronchospasms, seizures

Question 20

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.

Answer 20

Increases, destabilizing, harder

Question 21

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.

Answer 21

Decreases, stabilizing, easier

Question 22

____ are locations where + charges are entering the cell, driving a depolarization

Answer 22

Sinks

Question 23

______ are peripheral locations that are being depolarized due to the + charges flowing in at the sink

Answer 23

Sources

Question 24

A current loop between nearby parts of the same cell that are at different potentials is called a ____

Answer 24

Local circuit current

Question 25

Action potentials run down the axon from _____depolarized patch of membrane to _____depolarized membranes

Answer 25

More –> Less

Question 26

Name the current sink and source for a depolarizing synaptic input.

Answer 26

Sink - site of neurotransmitter action, synapse

Source - soma depolarization by dendritic current

Question 27

Name the current sink and source for a propagating action potential.

Answer 27

Sink - axon hillock

Source - further down the axon, dendrite

Question 28

How do propagation waves spread in an unmyelinated axon?

Answer 28

Continuously down the axon

Question 29

If internal resistance increases, what happens to conduction speed

Answer 29

Slows down

Question 30

Local circuit can extend further if internal resistance is ____ and membrane resistance is ____.

(Low or high?)

Answer 30

Low, high

Question 31

If membrane resistance increases, what happens to conduction speed?

Answer 31

Accelerates

Question 32

Myelination is produced by repetitive wrapping of what type of cell around an axons

Answer 32

glial cell

Question 33

How do myelinated axons reduce amt of current needed to depolarize the membrane?

Answer 33

Reduces the membrane conductance (increasing resistance) and reducing capacitance (greater charge separation)

Question 34

Does myelin thickness increase or decrease as axon diameter increases?

Answer 34

Increases

Question 35

T or F. Myelination does not accelerate propagation speed for small axons <1 um

Answer 35

TRUE - but many small CNS axons are myelinated anyway b/c of energy savings

Question 36

In myelinated axons, propagation waves are only generated where?

Answer 36

Nodes of Ranvier

Question 37

How do propagation waves spread in a myleinated axon?

Answer 37

Saltatory propagation of action potential down the axon

Question 38

Name effects of myelination on the following:

• Membrane Resistance
• Membrane Capacitance
• Conduction velocity
• Energy Utilization

Answer 38

• Increases
• Decreases
• Increases
• Decreases - b/c fewer ions need to cross the membrane to propagate the action potential

Question 39

What is the primary limit to myelination?

Answer 39

Increase in axon caliber

Question 40

Are myelin sheaths thinner or thicker in brain? Periphery?

Answer 40

Brain - thinner

Periphery - thicker

Question 41

Is axon density low or high in the periphery? In the brain?

Answer 41

Periphery - low (so diameters are bigger)

Brain - high (to limit diameter so brain doesn’t get too big)