Electric Signalling

Question 1

charge

Answer 1

• Movement of charge is the currenty of neuronal signalling
• Charge (Q) is a quantity of electricity due to net + or net – measured in Coulombs (C)
• In neurones charge is in the form of ions in aqueous solution

Question 2

ions

Answer 2

• Ions are atoms or molecules which have gained or lost electrons and have a net charge
• Cations +ve, and flow towards the -vely charged cathode
• Anions have net -ve charge and attracted to the anode
• Monovalent ion has lost/gained one electron
• One elementary charge=1.6x10^-19C

Question 3

current ( I )

Answer 3

flow of charge from one point to another over time, in ampere 1A=1C/S

Question 4

conductance

Answer 4

• How much current flows for a given potential difference in Siemens

Question 5

resistance

Answer 5

the reciprocal of conductance in Ohm

Question 6

voltage

Answer 6

•also called potential difference
Voltage arises when unequal charge is separated by a barrier like the PM, when charged ions move across neuronal PM, V changes

• Value of V reflects the density of unbalanced charge
• Measure in volts

Question 7

Ohms Law

Answer 7

describe relationship between V, I, R and G: V=I/R

Question 8

neurons excitability determined by two forces

Answer 8

movement of ions in solution depends on charge and concentration

Question 9

concentration

Answer 9

ions are chemical as well as electrical entities

Question 10

ion flux balanced

Answer 10

at equilibrium ( no net flow )

Question 11

nerst equation

Answer 11

• equlibrium potential

net flux continues until a potential difference is achieved where the concentration drive is balanced by the counteracting electrical force
• can calculate this potential for a given concentration difference using the Nernst equation

-Ex=RT/zF.ln(Xout/Xin)

Question 12

ions flow

Answer 12

down their concentration gradient

Question 13

water analogy

Answer 13

water through a system of pipes is driven by a pump (battery) that creates a pressure difference (voltage) across it, water (charge) flows from a region of high pressure to lower pressure, and pressure drops along the flow-resistance (electrical resistance) of the pipes

Question 14

resting membrane potential

Answer 14

potential difference across plasma membrane in resting state

Question 15

driving force

Answer 15

=difference between membrane pot. And Nernst potential for the ion

Question 16

Goldman-Hodgkin-Katz equation

Answer 16

• Goldman-Hodgkin-Katz equation takes into acc. Permeabilities of all main permeant ions

use if membrane permeable to more than one neuron

Question 17

cell membrane made up of

Answer 17

phospholipid bilayer structure

Question 18

phospholipid bilayer

Answer 18

non-conducting, high resistance to ionic current

Question 19

• 3 core electrical properties of the membrane:

Answer 19

• 1. Acts as battery, cause of potential diff inside rel. to outside
• 2. Acts as variable resistor/conductor, dep on number of ion channels present and open
• 3. Acts as capacitor, this arises from non-conducting bilayer combined w/ a conducting medium (electrolyte) either side, as a capacitor membrane can store charge

Question 20

what does capacitance do in cells

Answer 20

slows everything down

Question 21

capacitance

Answer 21

• =storage of charge at an insulating gap between two conductors at different potentials

Question 22

pumps and transporters

Answer 22

• Move ions against their electrochemical gradients using energy eg NA/K/ATPase (3NA out 2K in for each ATP)

Question 23

ion channels

Answer 23

• Membrane-spanning glycoprotein molecules w/ aqueous solution through a central pore
• Gating (opening and closing) by conformational changes

Question 24

length constant

Answer 24

• λ=distance over which the voltage decays to 37% of its initial value

Question 25

why are neurons poor conductors?

Answer 25

high internal resistance low resistance to outward flow passive conductance properties

Question 26

lenght constant determined by

Answer 26

- membrane resistance Rm - internal resistance Ri - resistance of extracellular fluid Ro

Question 27

how are the problems of passive conductance properties mediated

Answer 27

voltage gated ion channels that boost signals before they decay

Question 28

active signal

Answer 28

action potential

Question 29

larger axon diameter

Answer 29

longer lenght constant

Question 30

time constant

Answer 30

time for V to reach 37% of its final value

Question 31

myelin

Answer 31

many layers of the glial cell membrane wrapped round axon to make a fatty, low conducting sheath

Question 32

after-hyperpolarisation

Answer 32

undershoot after an A.P occured

Question 33

size amplitude of axon

Answer 33

does not encode much

Question 34

how is information encoded in AP

Answer 34

rate and pattern of firing