electrical signaling Flashcards
The brain
lots of neurons and even more synapses, 2% of body mass but 20% ATP use
ATP use drives massive and rapid signaling
Electrical within the neuron, chemical communication between neurons
Electrical potential
much harder to move electrical signals through aqua than electric wires
Neuron plasma membrane has an electric potential gradient: lipid bilayer is a diffusion barrier, impermeable to most molecules therefore charge builds up on each side
Resting membrane potential (Vm): (-) charge builds up on inside, (+) charge builds on outside the separation of the + and - and creates a membrane potential difference of -70mV
The membrane lipid bilayer is a conduit
Ion channels are special proteins embedded in plasma membrane
made of several subunits, allow ions to flow down their concentration gradient
Selective for specific ions based on ion size and charge
Some are very specific Na is much more specific than K due to pore sizes
Others are minimally selective
Flip between open and closed states, depending on coltage ligants temp and mechanics
what creates the resting membrane potential
impermeable plasma membrane will not alow ions to flow down their concentration gradient.
K ions are high on the inside and move out leaving behind a negative charge
the negative charge attracts some K back in the point atwhich the flow in and out is the equilibrium potential, the number of actual ions moved is tiny
The resting membrane potential is determined almost solely by K gradient, but a few Na channels are open letting in some Na inside so its -65mV
concentration gradients are maintained by ion pumps
Concentrations of ions are maintained by ATP driven pumps ATP provides energy tp push ions against concentration gradient, pumps 3 Na out and 2 K in for 1 ATP
maintains high K inside and low NA out
Passive (generator) potentials
synaptic potentials, receptor potentials potentials, end plate potentials, located graded potentials
amplitude is small and proportional to stimulus strength
Cable properties: the amp of the potentials change decays exponentially as you move away from its source
The change in Vm passively spreads in both directions along the axon/dendrite
length constant is the is the distance over which the amp of potential decays by 63% of original value
depolarizing or hyper (EPSP or IPSP): can be summed over time and space and can actually lead to AP
Active (action potentials) impulses spikes
triggered by passive/synaptic/generator potentials
signal does not decay, AP actively propagates over long distances, depolarization of membrane and reversal of membrane potential
Large amp, short duration, no summation
all or non with w/ a refractory period, prop in uni direction
AP
when enough passive EPSP summate, the Na channels open leading to a flux of Na in, and after a short period the positive voltage striggers the inactivation
while sodium is fludding in this treggers the K channels to also open, allowing the Vm to go down back to normal or even hyperpolarize bc the K leaves
Refractory periods
Due to inactivation gate in Na channel
limit the repitition rate, determine the frequency (encodes information)
Ensure that the AP travels in only 1 direction
Absolute followed by relative
Channelopathies
Hyperkalemic periodic paralysis: muscle weakness and decreased muscle tone (Krich foods)
unable to fire APs bc the neurons are already depolarized
Mutation of voltage gated Na channels
myotonic congenita: Cl channel disease fainting goats
Tetrodotoxin: hydrated Na mimic binds in pore shuts down
