Elecrophyaiologoy 1 Flashcards
Describe the various techniques for electrophysiological recording
EEG’s & ECG’s
distinguish extracellular from intracellular recording
Extracellular:
Microelectrode needle placed outside the neurones capturing spikes of multiple neurones within the same region of the brain
Detects small transient voltage change
Cannot measure the voltage difference between inside and outside of a cell
Non invasive
Intracellular:
Micro-electrode needle placed inside the neurone such that it’s more invasive but can detect the voltage different across the cell
Describe the intracellular recording of Vm
2 microelectrodes are needed:
recording: this one records the vm
stimulating: this one one injects the current
inward current causes a depolarisation
outward current causes a hyperpolarisation.
one current is injected the change in voltage is not seen immediately (slight delay) due to the capacitance property of the membrane. this means that a proportion of the current is used to charge the capacitor and then the rest of the current flows across the membrane reflecting the new voltage level.
what are the electrical properties of the neuron
-voltage
-resistance
-capacitance
Relate the electrical properties of the neuron to the neuronal
membrane
-voltage - refers to the RMP
this is around -70mv where there is excess negative charge on the inside of the membrane compared to the outside (more na ions outside, more k ion inside, more cl outside)
resistance - depends on the number of available ion channels across the neuronal membrane. this regulates the concentration gradient and electrical gradient across the neuronal membrane.
capacitance - is the ability to store and separate charge across the neuronal membrane.
Explain the difference between action potentials and graded potentials
APs are generated when once the threshold is reached, which propagates along the whole length of the axon, carrying electrical impulses to the subsequent neurone/cell. it is an all-or-nothing event, it is sufficient enough that the signal does not decay. APs cannot summate and they are large and fast.
GPs are the input signals for the neurones that can summate together to determine the Vm of the postsynaptic neurone. They occur prior to the AP in the cell body and AP occurs/generates at the axon hillock. GPs are slower and smaller and can decay, their signal decays along the length/disappates.
Explain synaptic integration in terms of temporal and spatial
summation of postsynaptic potentials.
Temporal summation: occurs when signals arrive in rapid succession from one presynaptic neurone. 2nd AP arises before the 1st AP falls below baseline which allows for summation to occur. if the summation is greater enough (above threshold), AP can be generated.
Spatial summation: occurs when a postsynaptic neurone synapses with multiple presynaptic neurones receiving signal/PSPs simultaneously in close proximity. if the summed signal is sufficient enough to reach threshold, AP can be generated.
Explain the effect of membrane space and time constants on synaptic
integration
Space/length constant: the amount of decay of voltage across the length of the neuronal membrane.
(short space constant- greater decrement in voltage amplitude which means signals do not propagate along the whole length of the neurone, and so summation cannot occur. long space constant- smaller decrement in voltage amplitude which means signal does propagate along the length of the neurone and so summation can occur.
Time constant: the rate at which the neuronal MP changes in response to current stimulation. it describes the speed by which the neurone can recover from alterations and return to resting state.
(long time constant- voltage rises and falls more slowly, allowing for summation to occur. short time constant- voltage rises and falls more quickly, does not allow for summation.)
What space/time constant is required for summation
-long space constant and long time constant.
what type of summation does the space constant and time constant affect
-space/length constant affects spatial summation
-time constant affects temporal summation
what is synaptic integration
Synaptic integration: is the sum of the PSPs either spatial or temporal summation that is sufficient enough to generate AP if threshold level is surpassed.
