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