Neurons and Neuronal Excitability (Both Parts)

Question 1

Functional Unit of Nervous Sytem

Answer 1

Neuron

Question 2

How many Neurons in a Body?

Answer 2

100 Billion

Question 3

What part receives signals?

Answer 3

Dendrites

Question 4

What part transmit signals?

Answer 4

Axons

Question 5

Types of Transport (3)

Answer 5

Fast
Slow
Fast Retrograde

Question 6

What does Fast Transport use?

Answer 6

Protein Kinesin

Question 7

What does Fast Retrograde Transport use?

Answer 7

Protein Dynein

Question 8

Functional Areas: What are their characteristics?

Receptor Zone
Initial Segment
Axon
Nerve Endings

Answer 8

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

Question 9

Receptor Zones are composed of?

Answer 9

Somas and Dendrites

Question 10

Resting Membrane Potential Value

Answer 10

-70mV

Question 11

Is the whole cell actually charged negatively?

Answer 11

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

Overall it is neutral

Question 12

3 Mechanisms Generating RMP

Answer 12

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

Question 13

What happens to K at RMP?
Na?
Cl?

Answer 13

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

Question 14

What is mainly responsible for the RMP?

Answer 14

Potassium because it can freely diffuse due to potassium leak channels

Question 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]

Answer 15

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

Question 16

[Goldman Constant Field Equation]

Na

Driving Force?
Permeability?
Net Flux?

Answer 16

Very high driving force
Very low permeability
Small net flux

Question 17

[Goldman Constant Field Equation]

K

Driving Force?
Permeability?
Net Flux?

Answer 17

Small driving force
Very high permeability
High net flux

Question 18

[Goldman Constant Field Equation]

Cl

Driving Force?
Permeability?
Net Flux?

Answer 18

Least flux

Question 19

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

Answer 19

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

Question 20

What happens to the RMP without ATP?

Answer 20

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

Question 21

Function: Na-K ATPase Pump

Answer 21

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

Question 22

Define: Local Potential

Answer 22

Shift of membrane potential in a localized cell area

Question 23

Characteristics of Local Potential (5)

Answer 23

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)

Question 24

Formula for Time Constant

Answer 24

T = RC

τ = Time constant R = Resistance
C = Capacitance

Question 25

Formula for Space Constant

Answer 25

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)

Question 26

Define: Space Constant

Answer 26

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

Question 27

Result of Higher Rm?

Answer 27

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

Question 28

Result of Greater Diameter of Axon?

Answer 28

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

Question 29

Result of Smaller Diameter of Axon?

Answer 29

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

Question 30

Define: Spatial Summation

Answer 30

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

Question 31

Define: Temporal Summation

Answer 31

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

Question 32

Define: Action Potential

Answer 32

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

Question 33

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

Answer 33

No it is not, it renews itself along the neuron

Question 34

Impulses passing in one direction only is called?

What if it’s in the opposite direction?

Answer 34

Orthodromic Conduction

Antidromic Conduction

Question 35

What would increase the speed of propagation of an AP?

Answer 35

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

Question 36

Define: Saltatory Conduction

Answer 36

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

Question 37

Function: Myelin

Answer 37

Insulator that keeps electrical signals within the axon

Question 38

Function: Oligodendrocytes

Answer 38

CNS Version of Myelin (Many Axons)

Question 39

Function: Schwann Cells

Answer 39

PNS Version of Myelin (One Axon)

Question 40

Presence of Myelin leads to? (5)

Answer 40

• 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