Neurons and Neuronal Excitability (Both Parts) Flashcards Preview

[OS 202] Lecture Exam A > Neurons and Neuronal Excitability (Both Parts) > Flashcards

Flashcards in Neurons and Neuronal Excitability (Both Parts) Deck (40):
1

Functional Unit of Nervous Sytem

Neuron

2

How many Neurons in a Body?

100 Billion

3

What part receives signals?

Dendrites

4

What part transmit signals?

Axons

5

Types of Transport (3)

Fast
Slow
Fast Retrograde

6

What does Fast Transport use?

Protein Kinesin

7

What does Fast Retrograde Transport use?

Protein Dynein

8

Functional Areas: What are their characteristics?

Receptor Zone
Initial Segment
Axon
Nerve Endings

RZ: Graded Electrogenesis
IS: Site of Origin of Conducted Impulse
Axon: All or None Transmission
Nerve Endings: Secretion of Synaptic Transmitter

9

Receptor Zones are composed of?

Somas and Dendrites

10

Resting Membrane Potential Value

-70mV

11

Is the whole cell actually charged negatively?

No, only the area just inside is negative and the area just outside is positive

Overall it is neutral

12

3 Mechanisms Generating RMP

1. Transmembrane K+ Gradient Through Non-gated K+ Leak Channels
2. Donnan Effect
3. Na-K ATPase Pump

13

What happens to K at RMP?
Na?
Cl?

K: Tends to move out
Na: Tends to move in
Cl: Doesn't do anything

14

What is mainly responsible for the RMP?

Potassium because it can freely diffuse due to potassium leak channels

15

Why is RMP different from the potential for K, if K's movement is the one responsible for the RMP? [He "might" ask this]

Not a perfect system, some sodium is still able to leak in and contribute a positive charge

16

[Goldman Constant Field Equation]

Na

Driving Force?
Permeability?
Net Flux?

Very high driving force
Very low permeability
Small net flux

17

[Goldman Constant Field Equation]

K

Driving Force?
Permeability?
Net Flux?

Small driving force
Very high permeability
High net flux

18

[Goldman Constant Field Equation]

Cl

Driving Force?
Permeability?
Net Flux?

Least flux

19

How come the Nernst Equation approximates the Goldman Constant Field Equation?

Concentration and contribution of K is so high that the other factors in the equation are negligible

20

What happens to the RMP without ATP?

It will dissipate because it is not in a true equilibrium, it is in a steady state equilibrium

21

Function: Na-K ATPase Pump

Hydrolysis of ATP results in 3 Na being brought out and 2 K brought in

22

Define: Local Potential

Shift of membrane potential in a localized cell area

23

Characteristics of Local Potential (5)

1. Localized within an area
2. Graded Response
3. Decrementally Transmitted (Magnitude decreases the further it travels)
4. Potential for Summation
5. Very Rapid (Faster than AP)

24

Formula for Time Constant

T = RC

τ = Time constant R = Resistance
C = Capacitance

25

Formula for Space Constant

λ=√(Rm /Ra)

No need to memorize the equation, just remember
the relationships.
• Directly related to transmembrane resistance (Rm)
• Inversely related to internal axoplasmic resistance (Ra)

26

Define: Space Constant

Distance at which initial transmembrane voltage change has fallen to 37% of its peak value

27

Result of Higher Rm?

Lower Leakage -> More Ions Travel Down Axon -> Higher Space Constant

28

Result of Greater Diameter of Axon?

Lower Ra -> Greater Current Will Flow Farther Down Cell -> Greater Space Constant -> AP is Faster

29

Result of Smaller Diameter of Axon?

Does not need speed -> Lower Space Constant -> AP is slower

30

Define: Spatial Summation

Separate sites fire and while each firing cannot depolarize the cell, the combination of them can

31

Define: Temporal Summation

Firing in rapid succession can cause summation of charges causing an AP

32

Define: Action Potential

Fleeting, self-renewing wave of depolarization that propagates without decrement along the entire length of a nerve axon at high speed

33

Is the AP generated at the beginning the same as the end AP?

No it is not, it renews itself along the neuron

34

Impulses passing in one direction only is called?
What if it's in the opposite direction?

Orthodromic Conduction
Antidromic Conduction

35

What would increase the speed of propagation of an AP?

An increase in diameter of the axon
Decrease cytoplasmic resistance
Increase flow of ions
Increase length of axon depolarized (increase space constant)
Decrease time needed for AP to travel along axon

36

Define: Saltatory Conduction

Phenomenon that occurs at the Nodes of Ranvier where the signals jump from one node to the next

37

Function: Myelin

Insulator that keeps electrical signals within the axon

38

Function: Oligodendrocytes

CNS Version of Myelin (Many Axons)

39

Function: Schwann Cells

PNS Version of Myelin (One Axon)

40

Presence of Myelin leads to? (5)

• Increase in effective resistance of axonal membrane (Rm): ions must flow through myelin before reaching the ECF
• Decrease in effective capacitance of axonal
resistance (Ra): greater distance between ICF and ECF
• Lowers time constant
• Increases space constant
• Increases conduction velocity
o Myelinated conduction velocity = 3- 120 m/sec