Electrical Properties of Neurons Flashcards
what are the two forces responsible for the membrane potential?
ionic disequilibrium- uneven distribution of ion species on the inside vs outside of the cell
selective permeability- the membrane is permeable to some ions (K), and impermeable
what is ion that the membrane is permeable to? what is the concentration gradient that it creates?
K
145 mM inside the cell
4mM outside the cell
provides a chemical driving force for K to move into the extracellular space, and is primarily responsible for the existence of a membrane potential
describe the net ion flow of ions at steady state
no net flow
how is ionic disequilibrium maintained?
Na/K ATPase
transports 3 Na out and 2 K into the cells per ATP
does the Na/K ATPase generate the resting membrane potential?
no
ouabain
poisons that block the Na pump, which destroys the membrane potential
cardiac glycosides
an Na pump blocker. can be used at low levels to promote heart performance. blocking the pump increases the intracellular [Na], which stimulates the Na/Ca exchanger, and the Ca influx promotes a stronger myocyte contraction
nernst equation
allows us to calculate the equilibrium potential of any ion species
it accounts for temp and ion valence
equilibrium potential
the potential at which there is no net ion flow b/c the chemical and electrical gradients are in perfect balance
goldman-hodgkin-katz equation
an equation that describes the actual membrane potential
creates an average of all ions respective equilibrium potentials weighted by their ion permeabilities
why is the resting potential so close to Ks equilibrium potential
b/c it is much more permeable than other ions, so it exerts more influence on the total equilibrium potential
however, as the permeability of the membrane changes to other ions, the equilibrium potential will change as well
what are the two intrinsic properties of membranes?
capacitance- a non-conducting surface dividing two conductive elements
conductance- potential for ions to move from one side of the membrane to the other
the total charge on either side of the membrane is equal. only the membrane feels the difference in voltage
ok
voltage
electrical potential energy
current
rate of flow of electrical charge
resistance
the difficulty of current to flow along a given path
why is capacitance important?
selective capacitance (permeability) shapes electrical responses in time by acting as a low pass filter
the membrane is a biological capacitor. as the permeability changes, it releases charge, but the process of releasing its charge takes time
why is conductance important?
this is the opportunity of ions to flow across the membrane, and changing the meb
why are muscle cells different w/ regards to resting membrane potential?
like neurons, they have excitable membranes. however, unlike neurons, they are also permeable to Cl in addition to K
repeated APs w/ just a K permeability result in the buildup of K in the t-tubules and the inability to fire muscles
Cl does not participate in the AP and thus there is no buildup. this allows it to maintain a potential even with repeated APs
myotonia congenita
a mutation in the CLCN1 that encode the Cl channel which results in a delayed relaxation of skeletal muscles after voluntary movements. this manifests itself in stiffness or waerkness
the CLCN1 channels opens at very poorly and only at very positive voltages
are ion channels passive or active transport?
passive
leak channels
high probability of being open in the absence of any stimulus
K leak channels are crucial for generating the resting membrane potential
voltage gated
the channels are opened by a change in the membrane potential
what causes the membrane potential?
selective permeability of K
ligand gated ion channels
channels opened when bound to a specific ligand. important in synapses
mechanosensory channels
opened in result to mechanical stimulation, such as pacinian corpuscles
