1.2 Neurones and Bioelectric Signals

Question 1

Cell Body (Soma)

Answer 1

metabollic centre

Question 2

dendrites

Answer 2

input region

Question 3

axon

Answer 3

signal propagation

Question 4

synaptic terminals

Answer 4

signal transmission

Question 5

Whats in the soma

Answer 5

nucleus, GA and other organelles

Question 6

What does the soma branch out into

Answer 6

into 2 kinds of processes

• several short dendrites
• one long turbular axon

Question 7

What does the soma do

Answer 7

integrates the signals received and may change the activity of the cells causing generation of an AP

Question 8

What are dendrites

Answer 8

branch out in a tree pattern

main apparatus for receiving incoming signal from other nerve cells

Question 9

What does the axon do

Answer 9

typically extends some distance from the soma and carries signals to other neurones

Question 10

What is the initial segment

Answer 10

it is near the beginning of the axon where AP is initiated in a special trigger region

Question 11

What speed does propagation happen

Answer 11

1 to 100 m/s

Question 12

AP voltage?

Answer 12

100mV

Question 13

Information conveyed by AP determined by…

Answer 13

pathway and frequency

Question 14

size of axon

Answer 14

0.1mm to 2m

Question 15

what are large axons wrapped in

Answer 15

myelin sheath interrupted by the nodes of Ranvier

Question 16

What are synapses

Answer 16

near the end of the axon it divides in to fine branches that contact other neurons at specialised zones called synapses

Question 17

presynaptic cell

Answer 17

nerve cell transmitting signal

Question 18

postsynaptic cell

Answer 18

cell receiving the signal

Question 19

presynaptic/nerve terminals

Answer 19

specialised enlarged regions of axons branches that presynaptic cells transmit signals from

Question 20

synaptic cleft

Answer 20

very narrow space separating presynaptic and postsynaptic

Question 21

where do the terminals end

Answer 21

Most presynaptic terminals end on the postsynaptic neuron’s dendrites; but the terminals may also terminate on the cell body or, less often, at the beginning or end of the axon of the receiving cell

Question 22

Examples of transient electrical signals

Answer 22

receptor potentials, synaptic potentials, and action potentials

Question 23

what causes transient electrical signals

Answer 23

temporary changes in the electric current in and out of a cell

Question 24

what do changes in current drive

Answer 24

dives the electrical potential across the cell membrane away from its resting value

Question 25

A rest what is on the extracellular surface of neurons cell membrane

Answer 25

excess of +ve charge

Question 26

A rest what is on the cytoplasmic surface of neurons cell membrane

Answer 26

excess of -ve charge

Question 27

what does the lipid bilayer do

Answer 27

act as a barrier to the diffusion of ions, it acts as a resistor to the flow of ions

Question 28

membrane potential

Answer 28

charge separation gives rise to a voltage across the membrane

Question 29

membrane potential equation (Vm)

Answer 29

𝑉𝑚 = 𝑉𝑖𝑛 − 𝑉𝑜𝑢𝑡

Question 30

resting membrane potential (Vr)

Answer 30

membrane potential at rest
convention 𝑉𝑜𝑢𝑡 = 0 so 𝑉 𝑟 = 𝑉𝑖𝑛
range of -60mV to -70mV

Question 31

what does electrical signalling involve

Answer 31

brief changes to this by electrical currents (of ions) across the membrane

Question 32

direction of current

Answer 32

conventionally defined by net movement of +ve charge

Question 33

cations travel…

Answer 33

in direction of current

Question 34

anions travel…

Answer 34

away from current

Question 35

depolarisation

Answer 35

reduction of charge separation (less –ve 𝑉𝑚)

Question 36

hyperpolarisation

Answer 36

increase in charge separation (more –ve 𝑉𝑚)

Question 37

electrotonic potentials

Answer 37

Changes in 𝑉𝑚 that do not lead to opening of gates ion channels are passive responses
happens for small depolarisation and most hyperpolarisations

Question 38

When depolarisation reaches a threshold

Answer 38

the cell opens voltage gated-ion channels and produces an all-or-none AP

Question 39

Potassium Ion concentrations

Answer 39

is about 20 times higher concentrated within the cell than outside

Question 40

Sodium Ion concentrations

Answer 40

9 times higher outside than inside the cell.

Question 41

how are charges in and out of the cell balanced

Answer 41

due to organic ions

Question 42

What does the concentration gradient create

Answer 42

a chemical driving force

Question 43

What do potassium ions flow through

Answer 43

flow through their specific ion channels in the first place is because there is a massive potassium concentration gradient between the intra- and extracellular space

Question 44

what happens due to potassium ions leaving cell

Answer 44

the spare negative charges incide the cell go to the surface of the inner cell membrane shifting the electrical potential across the membrane towards more negative values

Question 45

electrical driving force

Answer 45

the shift to negative values gives rise to this

Due to the capacitive properties of the membrane at its outer surface the same number of positive charges accumulate

Question 46

what stops the outflow of potassium ions

Answer 46

when the electrical driving force building up in the opposite direction, as potassium ions exit the cell, is equal to the chemical driving force.

Question 47

what does knowing the concentration of potassium ions inside and outside the cell allow us to predict

Answer 47

predict the potential (Ex) across the membrane at which the net flux of potassium ions become zero

Question 48

Equation for chemical driving force

Answer 48

𝑊𝐴 = 𝑅 𝑇ln [𝑋𝑜] [𝑋𝑖]
 𝑅 is the gas constant 8.31 𝐽 𝑚−1𝐾−1
 𝑇 is the absolute temperature in 𝐾

Question 49

Equations for electrical driving force

Answer 49

𝑊𝐵 = 𝐸𝑥 𝑧 𝐹
 𝑧 is valence of ion
 𝐹 is the Faraday constant = 96500 𝐶 𝑚𝑜𝑙−1

Question 50

How to find Nerst equation

Answer 50

equate electrical and driving force equations

Question 51

Equation for The Nerst Equation

Answer 51

𝐸𝑥 =(𝑅𝑇/𝑧𝐹) (ln ([𝑋𝑜] /[𝑋𝑖]))

Question 52

Measurement for potassium cells in Gilal cells

Answer 52

-75mV for 𝐾+ in Glial cells which are only permeable to potassium at rest

Question 53

Nerve cells at rest are permeable to…

Answer 53

Na, Cl, K

Question 54

does K or Na have more channels

Answer 54

There are many more resting 𝐾+ channels than 𝑁𝑎+ channels so 𝑉 𝑟 does not deviate much from 𝐸𝐾 = −75 𝑚𝑉 to the 𝐸𝑁𝑎 = +55 𝑚𝑉

Question 55

what happens when the potential begins to depolarise from the value of K+ equilibrium potential

Answer 55

𝐾+flux is no longer in equilibrium across the membrane.

Question 56

what is reduction

Answer 56

Reduction in the negative electrical force driving 𝐾+into the cell means that there is now a net flow of 𝐾+out of the cell, tending to counteract the 𝑁𝑎+influx.

Question 57

what happens the more the membrane potential is depolarised

Answer 57

the greater is the net electrochemical force driving 𝐾+out of the cell
Consequently the greater the net 𝐾+efflux

Question 58

what happens eventually after the membrane keeps depolarising

Answer 58

the membrane potential reaches a new resting level so the increased outward movement of 𝐾+ just balances the inward movement of 𝑁𝑎+

Question 59

What is the Goldman Equations

Answer 59

𝑉𝑚 = (𝑅𝑇/𝐹)ln((𝑃k[𝐾+]𝑜 + 𝑃na[𝑁𝑎+]𝑜 + 𝑃cl[𝐶𝑙−]𝑜 ) / (𝑃k[𝐾+]i + 𝑃na[𝑁𝑎+]i + 𝑃cl[𝐶𝑙−]i))

Question 60

What is the Goldman Equation for

Answer 60

convenient to describe the membrane potential as it allows for adding other ions species the membrane is also permeable for
the ion species with the highest permeability will dominate Vm

Question 61

lipid bilayer reflects what is an electrical circuitq

Answer 61

capicitance as it has the ability of an insulator to separate electrical charges on either side of it and the presence of thin layer of charge on either side causes a potential difference

Question 62

what kind of capacitor is a membrane

Answer 62

leaky capacitor due to ion-channels that can conduct charge

Question 63

ion channels are highly…

Answer 63

conductive

Question 64

ion equilibrium potentials act as

Answer 64

batteries as can generate emf

Question 65

each K+ channel is represented as…

Answer 65

resistor or conductor of ionic current with single current conductance of 𝛾k

Question 66

what is the sodium - potassium pump

Answer 66

see diagram pg 20 on notes

requires energy to maintain and re-establish the intracellular ionic concentration of a cell at rest

Question 67

Why is the pump needed just because energy is required

Answer 67

More active neurones have a higher demand for ATP so ADP must be phosphorylated more rapidly
The process requires oxygen so clearly neural activity requires oxygen as the resting potential cannot be maintained without the pump

Question 68

what does the pump exchange

Answer 68

3 Na for 2 K

Question 69

what do we assume when calculating membrane potential using equivalent circuits

Answer 69

Initially ignore 𝐶𝑙− channels and begin with only 𝐾+ and 𝑁𝑎+ channels
Also ignore the small influence of the 𝑁𝑎+-𝐾+ pump as it is small
Consider steady-state where 𝑉𝑚 is not changing so ignore membrane capacitance and its delaying effects on changes in 𝑉𝑚

Question 70

which membrane conductance is greater

Answer 70

K is greater than Na

Question 71

total pd across Na potential

Answer 71

𝑉𝑚 = 𝐸𝑁𝑎 + (𝐼𝑁𝑎/ 𝑔𝑁𝑎)

𝐼𝑁𝑎 = 𝑔𝑁𝑎 × (𝑉𝑚 − 𝐸𝑁𝑎)

Question 72

total pd for K potential

Answer 72

𝑉𝑚 = 𝐸𝐾 + (𝐼𝐾/ 𝑔𝐾)

∴ 𝐼𝐾 = 𝑔𝐾 × (𝑉𝑚 − 𝐸𝐾)

Question 73

what happens if Vm is greater than Ek

Answer 73

driving force is positive and current is outwards

Question 74

what happens if Vm is smaller than Ek

Answer 74

driving force is negative and current is inwards