Electrical signalling Flashcards
Graded vs action potentials?
Charges in charge of dendrite/soma are variable in amount.
However, changes in charge of axon are always identical
- all or nothin…
How does patch clamping work?
Patch clamping allows measurement of channel activity.
Voltage = Current * Resistance.
Open channels reduce resistance.
Voltage clamping = keep voltage constant to record changes in current, or current clamping = keep current constant to record voltage (APs)
Fill micropipette with electroltye solution and place in contact with membrane of isolated cell…. Then another electro in bath surrounding cell or ttissue = reference ground electrode.
= Setting up a circuit!
Outside-out is best as it can isolate single ion channels and involves forming convex membrane at end of micropipette…
How do electrical synapses work?
Use gap junctions = direct linkage between cells so ions flow directlybetween.
= Faster, but can introduce bidirectional flow.
= Found in the olfactory bulb!
What surrounds the somatic motor neurone at the NMJ?
Schwann cells surround somatic motor neurone.
Fast vs slow chemical synapses?
Fast = NT activates ligand-gated ion channels - e.g nACh receptors in autonomic ganglia.
Slow = large vesicles release NT… NT activates GPCR’s e.g. M3 ACh receptors in Ciliary ganglion
What is the Nernst equation?
Assuming a membrane is selectively permeable to 1 type of ion only and there is a difference in conc. across the membrane.
Nernst equation calculates the equilibrum potential = the voltage required to oppose the flow of a given ion across the membrane.
What is the reversal potential?
Reversal potential = membrane potential where there is NO ionic current.
= dependent on conc. + permeability of ALL ions involved in genereating current.
Used to indicate which ion is responsible for stimulating AP…
What is the Goldman equation?
equation which takes into account the permeability for the three main ions = K+, Na+ and Cl-
58log (sum of permeability * ion conc… Outside/inside.)
EPSP vs IPSP?
Increasing the likelihood an AP will be initiated in post-synaptic cell = NA+ influx.
Decreasing likelihood an AP will be initiated in post-synaptic cell = Cl- influx/ K+ efflux.
What are the equilibrium potentials for Na+ and K+?
-75mV for K+
+65mV for Na+
Equilibrum potential is the voltage required to oppose the flow of the ion across the membrane.
at -75mV, K+ flow is opposed… at +65mV Na+ flow is opposed…
Spatial vs Temporal summation?
Simultaneous stimulation from 2 or more nearby synapses…
Multiple stimulations at 1 synapse in short period of time!!!
What is the role of the soma?
Integration = simultaneous stimulation at many synapses is evaluated…
Absolute vs Relative refractory periods?
VA Na+ channels are all inactivated and cannot reopen… (Na+ channels go from closed, open to inactivated…)
Relative = some Na+ channels may be available to open if stimulation is strong enough to activate depleted population of Na+ channels. (they are in closed state)
Why is myelin sheath so important?
Increased conduction velocity reduces the requirement for thicker axons…
Reduced energetic expenditure = only Na+/K+ ATPase required at Nodes of Ranvier as opposed to along the entire axon.
Unmyelinated neurones would need to be 83 times larger than myelinated neurone to achieve the same conduction speed.
Where are the different Ca+ channels found?
L-type = Skeletal muscle, cortex, vascular SM…
N-Type = CNS/PNS.
P-type = Cerebellum.
