Electrophysiology intro

Question 1

define electrophysiology:

Answer 1

• branch of physiology that deals with measurement of electrical activity of living cells/ tissues

Question 2

where are graded potentials generated in neuron?

Answer 2

in dendrites when neurotransmitter binds to receptors

Question 3

where are action potentials generated in neuron?

Answer 3

at axon hillock (initial segment) and transmitted along axon

Question 4

define biopotentials:

Answer 4

• changes in Vm in response to stimulus

Question 5

define: polarisation

Answer 5

any time Vm not at 0mV

- charge separation exists

Question 6

define: depolarisation

Answer 6

• change in Vm makes membrane less polarised (less -ve) that at RMP

Question 7

define: repolarisation:

Answer 7

• Vm returns to RMP after being depolarisad

Question 8

define: hyperpolarisation

Answer 8

• change in Vm that makes membrane more polarised (more -ve) that at RMP

Question 9

list types of electrophysiological recording:

Answer 9

• intracellular
• patch clamp
• extracellular

Question 10

intracellular single cell?

Answer 10

yes

Question 11

patch clamp single cell?

Answer 11

yes

Question 12

extracellular single cell?

Answer 12

yes

Question 13

intracellular multiple cell?

Answer 13

no

Question 14

patch clamp multiple cell?

Answer 14

no

Question 15

extracellular multiple cell?

Answer 15

yes

Question 16

intracellular recording: at rest membrane has what excess charge

Answer 16

excess negative charge relative to outside cell

Question 17

intracellular recording: tip of electrode -ve or +ve relative to outside cell

Answer 17

• tip is negative

= location of reference electrode

Question 18

intracellular recording: what causes inside membrane become briefly more positive

Answer 18

localised influx of +ve Na ions

- electrode records +ve voltage

Question 19

intracellular recording: what causes inside of membrane to become more negative again

Answer 19

localised efflux of +ve K ions

- electrodes records this

Question 20

intraceullar vs extracullular recordings of nerve impulses:

Answer 20

differ in:

• amplitude (extracellular smaller V)
• shape (incl. polarity)

Question 21

patch clamp: features

Answer 21

• glass micropipette (electrode) filled w physiological saline solution
• forms high-resistance (giga) seal w plasma membrane

Question 22

patch clamp: different configurations

Answer 22

• cell-attached
• whole-cell
• excise patch

Question 23

patch clamp: cell-attached configuration

Answer 23

• record activity of single ion channels

- monitor spiking activity of whole cell

Question 24

patch clamp: whole-cell configuration

Answer 24

• pipette bore and cytoplasms contiguous (share common border)
• measure currents produced by stimuli/ synaptic activity

Question 25

patch clamp: excised patch (inside-out/ outside-out)

Answer 25

• record activity of single channels and manipulate composition of fluid on cytoplasmic face of membrane
• useful for study (neurotransmitters)

Question 26

define local field potential:

Answer 26

• when 1+ neuron is active, recorded summed voltage

Question 27

LFP voltage includes what

Answer 27

impulse sum of extracellular potentials generated and:

• action potentials
• graded potentials
• ‘global’ field potentials

Question 28

contribution of neuron to LFP depends on:

Answer 28

• neuron type and anatomy
• distance from electrode
• other factors (degree of myelination)

Question 29

recording biopotentials: pathway instruments

Answer 29

amplifier - filter - digitiser - storage

Question 30

recording biopotentials: signal of amplifier

Answer 30

analog signal

Question 31

recording biopotentials: signal of filter

Answer 31

analog

Question 32

recording biopotentials: signal of digitiser

Answer 32

analog to digital converter

Question 33

recording biopotentials: signal of storage

Answer 33

digital signal

Question 34

recording biopotentials: amplifiers features

Answer 34

• biopotentials are small (µV or mV) analog signals
• signals must be amplified to record w sufficient resolution
• typically x1000 x10 000 or x100 000

Question 35

recording biopotentials: amplifiers types

Answer 35

• AC coupled

- DC coupled

Question 36

recording biopotentials: amplifiers AC

Answer 36

preserves changing signals, signores steady state (stable) voltages
- best for v small or noising machines (ECG)

Question 37

recording biopotentials: amplifiers DC

Answer 37

• preserves both steady state and changing voltage signals

- when absolute voltage is important (intracellular measurement of membrane potential (Vm) of neuron)

Question 38

recording biopotentials: signal conditioning

Answer 38

• recordings are noisy from random noise, mains etc.
• raw recordings need to be filtered
• for graded (DC or 0.1Hz to 300 Hz)
• action potentials: 100Hz - 5kHz

Question 39

recording biopotentials: sampling/ digitasation

Answer 39

• amplifier gives analog ver of signal
• will convert into digitalusing ADC
• need to choose sampling rate (temporal resolution in Hz) high enough

Question 40

recording biopotentials: minimalist sampling rate

Answer 40

Nyquist-Shannon Sampling Theorem

- min sampling rate frequency at least 2x frequency of highest frequency (100Hz for 50Hz signal)

Question 41

recording biopotentials: if too slow sampling rate

Answer 41

• aliasing where false signals appear in data

- general rule: sampling rate x10 to x100 faster

Question 42

recording biopotentials: voltage resolution

Answer 42

• typical ADC resolution is 16 bit