lecture 6 action potential

Question 1

what does oscilliscope do

Answer 1

records membrane potential as a function of time

Question 2

what causes rapid changes in membrane potential during action potential

Answer 2

ions flowing in and out of neuronal cell

Question 3

why do ions flow during action potential

Answer 3

differences between membrane and equilibrium potential

Question 4

at rest in neurons, what is the order of membrane potential in cations

Answer 4

pK>pCl>pNa (membrane potential near Ek)

Question 5

what does nerst equation do

Answer 5

tells us the voltage that will balance the unequal concentration ratio across the membrane for an ion

Question 6

what is ohms law

Answer 6

v=ir (voltage= current times resistance)

Question 7

what is r=i/g

Answer 7

where g is conductance, how much an ion will flow

Question 8

more conductance…. (what’s the inverse)

Answer 8

less resistance

Question 9

what is driving force

Answer 9

(V) the difference between the membrane potential and the ion’s equilibrium potential

Question 10

how do you calculate current with driving force

Answer 10

ionic current = ion conductance * driving force
Gk- absolute value of membrane potential - equilibrium potential

Question 11

what two things affect current

Answer 11

driving force and conductance

Question 12

what is the driving force of Cl at -65mv membrane potential

Answer 12

0 because absolute value of (-65- (-65) is 0

Question 13

how do you calculate driving force

Answer 13

absolute value of membrane potential - equilibrium potential

Question 14

what ions are responsible for the shape of the action potential

Answer 14

na+ and k+

Question 15

what is the refractory period

Answer 15

small time period between action potentials where another action potential cannot be elicited

Question 16

what is rising phase of action potential

Answer 16

rapid
depolarizing stage of the
action potential when the
there is an increase in Na+
current and membrane
potential quickly rises from
around -65 mV (resting
potential) to almost +60 mV

Question 17

what is falling phase of action potential

Answer 17

phase of
action potential after the
peak (Vmax) when the Na+
current decreases and the K+
current increases causing the
membrane potential to
hyperpolarize and fall to or
below the resting potential
(Vrest

Question 18

what are the parts of an action potential

Answer 18

threshold, rising phase, overshoot, falling phase, undershoot

Question 19

what are the three kinds of membrane potential

Answer 19

reception potentials, action potentials, synaptic potentials

Question 20

differences between receptor, synaptic, and action potentials

Answer 20

-action potentials all or none, other two graded
-action potentials propagate with same amplitude and dont decrement with distance, other two do
-local potentials can give rise to action potentials (in same cell), and action potentials can give rise to local potential in different cell

Question 21

if na channels are open where is na going

Answer 21

in (wants to make cell more positive toward its equilibrium potential of +60)

Question 22

if k channels are open where is na going

Answer 22

out (wants to make cell more negative toward its equilibrium potential of -80)

Question 23

if ca channels are open where is na going

Answer 23

in (wants to make cell more positive toward its equilibrium potential of +134)

Question 24

if cl channels are open where is na going

Answer 24

in or out (depends on if membrane potential is hyperpolarized, equal to, or depolarized relative to Ecl)

Question 25

at peak of action potential, cl is flowing...

Answer 25

in

Question 26

at peak of undershoot, cl is flowing

Answer 26

out

Question 27

how is na positive feedback

Answer 27

if na channels open because of depolarization from local potential, na flows down concentration into neuron, causes more depolarization, more na channels open and brings Vm closer to Ena (na channels opening encourages other na channels to open)

Question 28

how is k negative feedback

Answer 28

depolarization with delay opens sluggish k (delayed rectifier) channels during overshoot driving force of k is huge so extra open k channels cause k to leave positively charged interior of neuron loss of k causes inside of neuron to become more negative hyperpolarization closes delayed rectifier channels (k channels opening discourages other k channels opening)

Question 29

difference between bipolar, unipolar, multipolar neurons

Answer 29

amount of processes extending in opposite direction from soma

Question 30

what kind of neuron are motor neurons

Answer 30

multipolar

Question 31

what kind of neuron are sensory neurons

Answer 31

unipolar

Question 32

is the 1a axon neuron efferent or afferent

Answer 32

afferent- it's psuedo unipolar like other sensory neurons

Question 33

what do synapses cause

Answer 33

release of neurotransmitters and opening of chemical gated channels, causing hyperpolarization or depolarization

Question 34

what does conductance facilitate

Answer 34

flow of current (how many ion channels are open)

Question 35

what does driving force facilitate

Answer 35

the propensity of the ion to move across the membrane

Question 36

Overshoot

Answer 36

part of the action potential when the membrane potential is greater than 0 mV

Question 37

Threshold or Threshold Voltage

Answer 37

minimal membrane potential that a neuron must be depolarized to open voltage gated channels and generate an action potential. Typically around -45 mV. Since action potentials are an “all or none” event, if the threshold voltage is reached, an action potential will fire. A subthreshold depolarization is a depolarization that does not reach the threshold voltage, and thus does not trigger an action potential. A local depolarization that is suprathreshold or depolarizes the neuron above the threshold voltage to trigger an action potential is often due to synaptic potentials or a sensory stimulation

Question 38

undershoot

Answer 38

part of the action potential when the membrane potential is below (more hyper polarized than) the resting potential due to the increased K+ current compared to rest. The membrane potential returns to the resting potential as the ionic conductances for all of the ions return to the resting conductance (or resting permeabilities). During the undershoot the membrane potential (Vm) will approach EK. The undershoot is also known as the afterhyper polarization (AHP)

Question 38

Refractory Period

Answer 38

the period of time after an action potential when it is more difficult (i.e. needs more depolarization) to reach threshold. This period is divided into the absolute and relative segments

Question 39

absolute refractory period

Answer 39

when it is impossible to generate another action potential.

Question 40

relative refractory period

Answer 40

when more current, is required to generate another action potential.

Question 41

Conductance

Answer 41

elative ability of charge to move or pass through a material. Conductance is the inverse of resistance (R = 1/g) and can be thought as analogous to permeability in the GHK equation

Question 42

Define driving force, conductance and current and know how they are related by Ohm’s law

Question 43

Diagram an action potential as a function of voltage over time and label the following stages: i. resting potential ii. rising phase iii. falling phase iv. overshoot v. undershoot

Question 44

Which part of most neurons occupies the most volume?

Answer 44

The axon

Question 45

Local potentials (like receptor potentials) vary proportionally to the _______ of the stimulus.

Answer 45

size and duration

Question 46

In the mayotatic stretch reflex, what is the approximate time latency between hitting a tendon and getting a muscle contraction ?

Answer 46

20 milliseconds

Question 47

The ability or ease of an ion to flow is the _____

Answer 47

conductance

Question 48

Of the following options, when is the driving force on K+ the highest (given typical neuronal concentrations)?

Answer 48

At the equilibrium potential for Na+

Question 49

Sensory motor reflex arc

Answer 49

1) Stretch (spindle) 2) Receptor Potential (1a Axon sensory spiral ending) 3) Action potential (starts at 1a axon trigger zone then propagates) 4) Synaptic Potential (motor neuron dendrite) 5) Action potential (starts at motor neuron axon initial segment then propagates) 6) Synaptic potential (extrafusal muscle fiber neuromuscular junction) 7) Action potential (initiated at neuromuscular junction then propagates along muscle fiber) which contracts the muscle relieving the stretch

Question 50

when Na channels are open sodium will flow

Answer 50

in

Question 51

When K channels are open, K current will flow

Answer 51

out

Question 52

Calcium channels open Ca++ will flow

Answer 52

in

Question 53

Feedback: positive

Answer 53

• If some Na channels open because of slight depolarization (from a local potential) then Na flows down its concentration and the electrical gradient INTO the neuron. • The extra positive charge further depolarizes the cell’s membrane potential causing more Na channels to open • This causes more depolarization and more channels to open and brings the cell membrane potential close to Ena • This is POSITIVE feedback because the channel opening encourages more channels to open

Question 54

Feedback: negative

Answer 54

Depolarization with a delay opens the more sluggish K (delayed rectifier) channels • During the overshoot the driving force on K is huge and so the extra open K channels (in addition to the leak channels) cause K to leave the now positively charged interior of the neuron. • The loss of K makes the inside of the neuron progressively more negative (and the Na channels are no longer open) • This hyperpolarization closes the delayed rectifier channels • This is NEGATIVE feedback because the K channel opening discourages more K channels to open

Question 55

During the rising phase of an action potential, is the magnitude of IK (potassium current) or INa (sodium current) larger

Answer 55

Sodium current is larger. During the rising phase, the sodium conductance increases and the driving force (especially at the beginning of the rising phase) on sodium is strong which causes a large sodium current (need to mention both for full credit). Additionally, the neuron keeps depolarizing – more sodium flowing in than potassium flowing out

Question 56

Which ion is primarily responsible for the rising phase of the action potential? Which direction (into or out of the neuron) does that ion flow

Answer 56

Sodium flowing into the cell is primarily responsible for the rising phase.

Question 57

During the undershoot of the action potential, what is the membrane potential “under” (why is it called the undershoot)? Which ion’s equilibrium potential does the membrane potential approach during the undershoot?

Answer 57

During the undershoot the membrane potential is under (more negative) than the resting potential. The membrane potential approaches potassium’s equilibrium potential (EK)