Electrical Properties of Neurons

Question 1

what are the two forces responsible for the membrane potential?

Answer 1

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

Question 2

what is ion that the membrane is permeable to? what is the concentration gradient that it creates?

Answer 2

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

Question 3

describe the net ion flow of ions at steady state

Answer 3

no net flow

Question 4

how is ionic disequilibrium maintained?

Answer 4

Na/K ATPase

transports 3 Na out and 2 K into the cells per ATP

Question 5

does the Na/K ATPase generate the resting membrane potential?

Answer 5

no

Question 6

ouabain

Answer 6

poisons that block the Na pump, which destroys the membrane potential

Question 7

cardiac glycosides

Answer 7

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

Question 8

nernst equation

Answer 8

allows us to calculate the equilibrium potential of any ion species

it accounts for temp and ion valence

Question 9

equilibrium potential

Answer 9

the potential at which there is no net ion flow b/c the chemical and electrical gradients are in perfect balance

Question 10

goldman-hodgkin-katz equation

Answer 10

an equation that describes the actual membrane potential

creates an average of all ions respective equilibrium potentials weighted by their ion permeabilities

Question 11

why is the resting potential so close to Ks equilibrium potential

Answer 11

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

Question 12

what are the two intrinsic properties of membranes?

Answer 12

capacitance- a non-conducting surface dividing two conductive elements

conductance- potential for ions to move from one side of the membrane to the other

Question 13

the total charge on either side of the membrane is equal. only the membrane feels the difference in voltage

Answer 13

ok

Question 14

voltage

Answer 14

electrical potential energy

Question 15

current

Answer 15

rate of flow of electrical charge

Question 16

resistance

Answer 16

the difficulty of current to flow along a given path

Question 17

why is capacitance important?

Answer 17

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

Question 18

why is conductance important?

Answer 18

this is the opportunity of ions to flow across the membrane, and changing the meb

Question 19

why are muscle cells different w/ regards to resting membrane potential?

Answer 19

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

Question 20

myotonia congenita

Answer 20

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

Question 21

are ion channels passive or active transport?

Answer 21

passive

Question 22

leak channels

Answer 22

high probability of being open in the absence of any stimulus

K leak channels are crucial for generating the resting membrane potential

Question 23

voltage gated

Answer 23

the channels are opened by a change in the membrane potential

Question 24

what causes the membrane potential?

Answer 24

selective permeability of K

Question 25

ligand gated ion channels

Answer 25

channels opened when bound to a specific ligand. important in synapses

Question 26

mechanosensory channels

Answer 26

opened in result to mechanical stimulation, such as pacinian corpuscles