Neuronal Signal Propagation Flashcards Preview

Term IV: Neuro > Neuronal Signal Propagation > Flashcards

Flashcards in Neuronal Signal Propagation Deck (41):
1

Action potential firing is produced by ________ ion channels.

voltage-gated

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

Excitability

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)

Current clamp

4

Rheobase

Minimum current to reach threshold

5

Chronaxie

Time to fire at a current that is 2x Rheobase

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

membrane potential, driving force

7

Leak current

Linear changes in Current as expected
from Ohm’s Law

8

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

9

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

10

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

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

11

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

activation, inactivation

12

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

Arg, Lys

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

tetrameric

14

_____ is a “autoinhibitory” state analogous to receptor desensitization

Inactivation

15

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

Refractory period

16

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

17

When are surface charge effects particularly large?

With divalent cations like Ca2+

18

What symptoms result from hypercalcemia?

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

19

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

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

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.

Increases, destabilizing, harder

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.

Decreases, stabilizing, easier

22

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

Sinks

23

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

Sources

24

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

Local circuit current

25

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

More --> Less

26

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

Sink - site of neurotransmitter action, synapse

Source - soma depolarization by dendritic current

27

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

Sink - axon hillock
Source - further down the axon, dendrite

28

How do propagation waves spread in an unmyelinated axon?

Continuously down the axon

29

If internal resistance increases, what happens to conduction speed

Slows down

30

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

(Low or high?)

Low, high

31

If membrane resistance increases, what happens to conduction speed?

Accelerates

32

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

glial cell

33

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)

34

Does myelin thickness increase or decrease as axon diameter increases?

Increases

35

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

36

In myelinated axons, propagation waves are only generated where?

Nodes of Ranvier

37

How do propagation waves spread in a myleinated axon?

Saltatory propagation of action potential down the axon

38

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

39

What is the primary limit to myelination?

Increase in axon caliber

40

Are myelin sheaths thinner or thicker in brain? Periphery?

Brain - thinner
Periphery - thicker

41

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)