Lesson 13: The Membrane Potential

Question 1

what is the electrical potential?

Answer 1

the difference in concentration of charged particles between one point and another

(a type of potential energy (V))

Question 2

what is a current?

Answer 2

the flow of a charged particle from one point to another

Question 3

what is the resting membrane potential (RMP)?

Answer 3

the charge difference across the plasma membrane

Question 4

what does a negative value for the resting membrane potential mean?

Answer 4

theres more negatively charged particles on the inside of the plasma membrane compared to outside

Question 5

how are electrical currents in the body created?

Answer 5

they are created by the flow of ions through gated channels in the membrane

Question 6

what is the difference between a leak/passive channel and a gated channel?

Answer 6

leak/passive channel: channels that are always open

gated channel: channels that are normally closed but can be stimulated to open

BOTH are specific for its specific ion

Question 7

what are the 3 types of gated channels and what are their stimuli?

Answer 7

1. chemically gated channel: binding of chemical (found on neuron cell body, dendrites)
2. voltage gated channel: change in the membrane potential (found on neuron axon, skeletal and cardiac muscle membrane)
3. mechanically gated channel: physical stress/deformation on cell plasma membrane (found on sensory receptors; touch, pressure, vibration)

Question 8

what are the 3 states of gated channels?

Answer 8

1. closed
2. open
3. inactivated: ions cant pass through the channel but not considered closed, inactivation gate blocks the channel

Question 9

how are ions distributed between extracellular fluid and intracellular fluid?

Answer 9

the ions are unequally distributed

Question 10

what occurs for the presence of a resting membrane potential?

Answer 10

THE COMBINED EFFECT OF
1. the diffusion of ions down their concentration gradients through the membrane
2. selective permeability of the membrane, allowing some ions to pass more easily than others
3. the electrical attraction of cations and anions to each other

Question 11

which ion has the greatest influence on the RMP and why?

Answer 11

potassium (K+) because it is much more abundant in the ICF than the ECF. the cell membrane is more permeable to K+ than Na+ since there are more K+ leak channels

Question 12

how does sodium (Na+) influence the RMP?

Answer 12

Na+ is more abundant in the ECf than the ICF but the membrane is not as permeable to Na+ as K+. since the inside of the cell is negative, Na+ enters down its concentration gradient causing some of the negative charge to be cancelled out by the influx of sodium (only by a little bit though)

Question 13

what compensates for the Na+ leakage in and the K+ leakage out?

Answer 13

the sodium-potassium pump uses ATP to move 3 Na+ out and 2 K+ in, concentrating Na+ outside and K+ inside.

Question 14

what is a local potential and how does it occur?

Answer 14

an electrical signal that occurs when a physical stimulus acted on a sensory neuron triggers a local, temporary change in the membrane potential

Question 15

what are some characteristics of local potentials?

Answer 15

graded - vary in magnitude with stimulus strength (stronger stimuli will cause gated channels to remain open longer causing a larger depolarization for Na+ influx or hyperpolarization for K+ efflux

decremental - get weaker the farther they spread from the point of stimulation

reversible - if stimulation ceases, membrane voltage quickly returns to normal resting potential

can be excitatory or inhibitory (either promoting the generation of an electrical signal or inhibiting it)

Question 16

what is depolarization?

Answer 16

when the cell’s internal charge becomes less negative (more positive)

Question 17

depolarization & hyperpolarization. which is inhibitory and which is excitatory?

Answer 17

depolarization -> excitatory (makes a neuron more likely to fire an action potential)

hyperpolarization (membrane more negative)-> inhibitory (makes a neuron less likely to produce an action potential)

Question 18

what is an action potential?

Answer 18

a rapid up & down change in voltage proceeded by the coordinated opening and closing of voltage-gated ion channels

Question 19

where do action potentials occur and how does it occur?

Answer 19

where there is a high enough density of voltage-gated ion channels (trigger zone of axon)

if excitatory local potential reaches trigger zone and is still strong enough, it opens enough voltage gated Na+ channels to generate an action potential

Question 20

name the steps of an action potential

Answer 20

1. local potential spreads to axon hillock
2. voltage at axon hillock must reach threshold (minimum voltage to open voltage gated channels)
3. voltage gated Na+ channels open quickly
4. Na+ enters the cell, depolarizing it past 0 mV
5. when voltage reaches +35mV, Na+ voltage gated channels inactivate (different than closed)
6. voltage gated K+ on membrane are stimulated to fully open at +35 mV, K+ flows out of the cell and repolarizes membrane (inside of cell is negative again)
7. membrane potential returns back to RMP as Na+ leaks into cell raising the voltage inside

Question 21

true of false: the concentration of Na+ and K+ on either side of the membrane change significantly during an action potential.

Answer 21

FALSE

Question 22

name some characteristics of action potentials

Answer 22

all or none law - if threshold reached (-55mV), neuron fires up/depolarizes to the maximum voltage (+35 mV); if threshold not reached, it does not fire an action potential

non decremental - does not get weaker with distance. action potential is “regenerated” as it travels along the axon

irreversible - once started, an action potential travels all the way down the axon and cannot be stopped by normal means

Question 23

what is the refractory period?

Answer 23

period of resistance to stimulation

Question 24

what are the 2 phases in the refractory period?

Answer 24

1. absolute refractory period - no stimulus of any strength will trigger another AP
   (caused by inactivation of voltage gated Na+ channels)
2. relative refractory period - an unusually strong stimulus is needed to trigger a new AP
   (during hyperpolarization, a larger depolarization (local potential) is required to reach threshold since it has to overcome the hyperpolarization)

Question 25

how are the absolute and relative refractory periods related to the action potential?

Answer 25

during the absolute refractory period, the voltage gated Na+ channel is inactivated. during the relative refractory period, the channel is now back to its resting state, which is closed.

Question 26

why do unmyelinated axons have continuous conduction?