Electrophysiology intro Flashcards
define electrophysiology:
- branch of physiology that deals with measurement of electrical activity of living cells/ tissues
where are graded potentials generated in neuron?
in dendrites when neurotransmitter binds to receptors
where are action potentials generated in neuron?
at axon hillock (initial segment) and transmitted along axon
define biopotentials:
- changes in Vm in response to stimulus
define: polarisation
any time Vm not at 0mV
- charge separation exists
define: depolarisation
- change in Vm makes membrane less polarised (less -ve) that at RMP
define: repolarisation:
- Vm returns to RMP after being depolarisad
define: hyperpolarisation
- change in Vm that makes membrane more polarised (more -ve) that at RMP
list types of electrophysiological recording:
- intracellular
- patch clamp
- extracellular
intracellular single cell?
yes
patch clamp single cell?
yes
extracellular single cell?
yes
intracellular multiple cell?
no
patch clamp multiple cell?
no
extracellular multiple cell?
yes
intracellular recording: at rest membrane has what excess charge
excess negative charge relative to outside cell
intracellular recording: tip of electrode -ve or +ve relative to outside cell
- tip is negative
= location of reference electrode
intracellular recording: what causes inside membrane become briefly more positive
localised influx of +ve Na ions
- electrode records +ve voltage
intracellular recording: what causes inside of membrane to become more negative again
localised efflux of +ve K ions
- electrodes records this
intraceullar vs extracullular recordings of nerve impulses:
differ in:
- amplitude (extracellular smaller V)
- shape (incl. polarity)
patch clamp: features
- glass micropipette (electrode) filled w physiological saline solution
- forms high-resistance (giga) seal w plasma membrane
patch clamp: different configurations
- cell-attached
- whole-cell
- excise patch
patch clamp: cell-attached configuration
- record activity of single ion channels
- monitor spiking activity of whole cell
patch clamp: whole-cell configuration
- pipette bore and cytoplasms contiguous (share common border)
- measure currents produced by stimuli/ synaptic activity
patch clamp: excised patch (inside-out/ outside-out)
- record activity of single channels and manipulate composition of fluid on cytoplasmic face of membrane
- useful for study (neurotransmitters)
define local field potential:
- when 1+ neuron is active, recorded summed voltage
LFP voltage includes what
impulse sum of extracellular potentials generated and:
- action potentials
- graded potentials
- ‘global’ field potentials
contribution of neuron to LFP depends on:
- neuron type and anatomy
- distance from electrode
- other factors (degree of myelination)
recording biopotentials: pathway instruments
amplifier - filter - digitiser - storage
recording biopotentials: signal of amplifier
analog signal
recording biopotentials: signal of filter
analog
recording biopotentials: signal of digitiser
analog to digital converter
recording biopotentials: signal of storage
digital signal
recording biopotentials: amplifiers features
- biopotentials are small (µV or mV) analog signals
- signals must be amplified to record w sufficient resolution
- typically x1000 x10 000 or x100 000
recording biopotentials: amplifiers types
- AC coupled
- DC coupled
recording biopotentials: amplifiers AC
preserves changing signals, signores steady state (stable) voltages
- best for v small or noising machines (ECG)
recording biopotentials: amplifiers DC
- preserves both steady state and changing voltage signals
- when absolute voltage is important (intracellular measurement of membrane potential (Vm) of neuron)
recording biopotentials: signal conditioning
- 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
recording biopotentials: sampling/ digitasation
- amplifier gives analog ver of signal
- will convert into digitalusing ADC
- need to choose sampling rate (temporal resolution in Hz) high enough
recording biopotentials: minimalist sampling rate
Nyquist-Shannon Sampling Theorem
- min sampling rate frequency at least 2x frequency of highest frequency (100Hz for 50Hz signal)
recording biopotentials: if too slow sampling rate
- aliasing where false signals appear in data
- general rule: sampling rate x10 to x100 faster
recording biopotentials: voltage resolution
- typical ADC resolution is 16 bit
