membrane potential and neuronal action potentials

Question 1

electrical signals necessary for neural function are mediated by the flow of ions through:

Answer 1

aqueous pores in the nerve cell membrane

Question 2

what are one of the principle theraputic targets of drugs

Answer 2

ion channels

Question 3

what is membrane potential

Answer 3

charge difference across the plasma membrane

Question 4

the plasma membrane acts as a:

Answer 4

capacitor

Question 5

what is a capacitor

Answer 5

two conductive surfaces (ions in solution) separated by a non-conductive surface (lipid bilayer)

Question 6

when ion channels open, current is allowed:

Answer 6

to flow across the plasma mebrane potential

Question 7

what is the resting membrane potential of a neuron

Answer 7

-70mV

Question 8

what is depolarization

Answer 8

• any positive change in the membrane potential
• inside of the cell becomes more positive

Question 9

what is hyperpolarization

Answer 9

• any negative change in the membrane potential
• inside of the cell becomes more negative

Question 10

what is hyperpolarization

Answer 10

• any negative change in the membrane potential
• inside of the cell becomes more negative

Question 11

is a chloride channel (Cl- flows into neuron) depolarization or hyperpolarization

Answer 11

hyperpolarization

Question 12

what is Ohm’s law

Answer 12

• describes the relationship between ion flow (current) and membrane voltage
• voltage (V) = current (I) x resistance (R)

Question 13

the amount of current is ____ ____ to the voltage across the membrane

Answer 13

directly proportional

Question 14

what dictates the amplitude of ion flux

Answer 14

Vm (membrane potential)

Question 15

what is the membrane potential

Answer 15

cell interior is electrically negative relative to the exterior

Question 16

what are the two forces that determine the asymmetric equilibrium distribution of ions across the plasma membrane

Answer 16

electrical (membrane potential) and chemical (concentration gradient) forces = electrochemical gradient

Question 17

how is equillibrium achieved

Answer 17

when the tendency of an ion to move down its concentration gradient is exactly counter-balanced by an opposing electrical gradient, resulting in no net ion flux

Question 18

what is electrical gradient

Answer 18

ion diffusion is affected by electrical charge differences and they tend to move toward opposite charge

Question 19

what is chemical gradient

Answer 19

ions move by diffusion from high to low concentration

Question 20

what is the main determinants of the resting membrane potential

Answer 20

the differential distribution of ions across the plasma membrane

Question 21

Na+/K+ ATPase

Answer 21

contributes only a small amount of the resting membrane potential

Question 22

K+ leak channels

Answer 22

relatively selective permeability of the plasma membrane to K+ contributes most of the resting membrane potential

Question 23

what is the equilibrium (reversal) potential , Eion

Answer 23

• defined as the membrane potential at which the direction of ion flow through a particular channel reverses direction
• enables one to predict which direction ions will flow
• determined by the intracellular and extracellular concentration of each ion

Question 24

what is the nerst equation used for

Answer 24

to calculate the equilibrium potential for a given set of ionic conditions

Question 25

what is needed to pull K+ into the cell against outward concentration gradient

Answer 25

very negative cell interior

Question 26

what is needed to push Na+ out of the cell against inward concentration gradient

Answer 26

very positive cell interior

Question 27

what is an action potential

Answer 27

* rapid change in membrane potential * occurs when a "stimulation" of the nerve cell membrane depolarizes the membrane enough to allow Na+ channels to to open **(threshold ~ -50mV)**

Question 28

what are voltage-gated NA+ channels responsible for

Answer 28

depolarizing membrane and (inward current) conduction of action potential

Question 29

what are the voltage-gated K+ channels responsible for

Answer 29

repolarization following action (outward currents) potential (returning towards resting potential)

Question 30

what are Na+/K+ ATPase and K+ leak channels responsible for

Answer 30

sets resting potential and returns membrane potential back to resting during refractory period

Question 31

when does depolarization occur

Answer 31

when ligand-gated nonselective cation channels at the post-synaptic membrane generate small excitatory depolarizing stimuli

Question 32

what does the small excitatory depolarization stimuli allow

Answer 32

Na+ to begin to pass into the cell and the depolarization spreads to the **axon hillock and initital segment**

Question 33

why does the AP start at the axon hillock and initial segment

Answer 33

the **initital segment** contains high conc. of voltage-gated sodium channels

Question 34

what are EPSP (excitatory post-synaptic potentials)

Answer 34

* positive charges into the cell; graded potential * **depolarizations are excitatory**

Question 35

what are IPSP (inhibitory post-synaptic potentials)

Answer 35

* negative charges into the cell; graded potential * **hyperpolarizations are inhibitory**

Question 36

what is the threshold

Answer 36

depolarizations to approx. -55 to -50 mV is required for action potential

Question 37

what is sodium channel inactivation important for

Answer 37

unidirectional AP conductance

Question 38

what are the 6 phases of the action potential

Answer 38

1. threshold 2. rising phase (depolarization) 3. peak (Na+ channels inactivate) 4. falling phase (hyperpolarization) 5. undershoot 6. recovery

Question 39

what is the absolute refractory period

Answer 39

time immediately after action potential which another AP cannot occur (due to Na+v channel inactivation and delay in K+v channel closing)

Question 40

what is the relative refractory period

Answer 40

time after AP during which greater stimulation is necessary to cause another AP

Question 41

how does the AP travel down the axon | one spot

Answer 41

* some Na+ ions flow in * membrane potential rises to ~50 mv * reaches threshold for voltage-gated Na+ channels * voltage gated Na+ channels activated * Na+ flowing in - membrane potential continutes to rise rapidly * reaches threshold for voltage-gated K+ channels - they open * Na+ channels inactivate and close * K+ flowing out rapidly - membrane potential drops (repolarization) * membrane potential drops below -70mV * K+ channels inactivate * Na+ channels reset * K+ channels reset

Question 42

what happens along the whole axon during the depolarization phase

Answer 42

as the membrane potential rises in this spot, the membrane potential directly next to it is also affected

Question 43

what happens along the whole axon along the repolarization phase

Answer 43

as the membrane potential falls in this spot, the membrane potential directly next to it is also affected and follows

Question 44

what factors will improve axon potential conduction velocity and distance

Answer 44

* increase the density of Na+v channels * increase the diameter of the axon * insulation (myelin)

Question 45

what is myelin

Answer 45

* schwann cells (glia) wrap around the axon and acts as insulation * conduction jumps from node to node **(saltatory conduction)**

Question 46

what is saltatory conduction

Answer 46

* metabollically efficient - ion movements limited to nodal regions * 100x faster conduction velocities

Question 47

what are the consequences/benefits of axon myelination

Answer 47

* less "leaky" = more downstream * lower capacitance = more downstream current * have highly increased concentration of Na+ channels at the nodes

Question 48

summation - spatial vs temporal

Answer 48

* spatial - E1 and E1 occur at different spots one right after the other * temporal - E1 and E2 ontop of each other