Excitable Membranes

Question 1

what is an excitable cell or membrane?

Answer 1

any membrane that can hold a charge or propagate and electrical signal

Question 2

2 types of excitable tissues and what they do?

Answer 2

1. neurons: transmit electrical impulses

2. muscles: contract to produce a pulling force

Question 3

diffusion

Answer 3

net movement of molecules from an area of high concentration to an area of low concentration

Question 4

osmotic gradient

Answer 4

the difference in concentration b/w 2 solutions on either side of a semi-permeable membrane and is used to tell the difference in percentages of the concentration of a specific particle dissolved in a solution

Question 5

what is a gradient?

Answer 5

difference in concentration of any parameter across a distance

Question 6

what are the 4 types of gradients?

Answer 6

1. ion gradient (osmotic gradient)
2. energy gradient
3. temperature gradient
4. pressure gradient

Question 7

what is net flux and what equation do we use?

Answer 7

(Jnet) occurs from high concentration to low concentration until the gradient disappears; Fick’s law of diffusion

Question 8

when does diffusion work best?

Answer 8

over small areas

Question 9

what do we mean by resting membrane potential?

Answer 9

all excitable cells maintain a non-zero membrane potential; the cell is inactive but ions are still diffusing/maintaining a negative voltage

Question 10

what is the resting membrane potential for neurons?

Answer 10

-70 mV

Question 11

what is the resting membrane potential for muscles?

Answer 11

-85 mV

Question 12

what kinds of ions are inside/outside the cell during resting membrane potential?

Answer 12

1. high concentration of K+ and proteins inside (low concentrations outside cell)
2. high concentration of Cl- and Na+ outside (low concentrations inside cell)

Question 13

what is the Nernst Equation used for?

Answer 13

calculate electrical potential from concentration gradients but dose NOT consider permeability of the membrane

Question 14

what affects membrane permeability?

Answer 14

membrane channels

Question 15

what 3 things are happening at resting membrane potential?

Answer 15

1. lots of K+ leaking out of cell through leak channels
2. little Na+ leaking in cell through membrane
3. Cl- leaking through leak channels

Question 16

membrane potential only exists because?

Answer 16

ions are flowing through the membrane

Question 17

What does the Goldman-Hodgkin-Katz Equation tell us?

Answer 17

it determines the reversal potential across a cell’s membrane, taking into account all of the ions that are permeant through that membrane

Question 18

what prevents the concentration gradient from approaching zero?

Answer 18

maintenance of gradients requires an active process which require ATP to pump ions against their concentration gradient (Na+K+ATPase pump)

Question 19

for every 1 ATP hydrolyed–>

Answer 19

3 Na+ move OUT

2 K+ move in

Question 20

is the Na+K+ pump working while the cell is at rest?/why?

Answer 20

YES; the pump maintains the resting membrane potential

Question 21

3 parts of an action potential

Answer 21

1. depolarization
2. repolarization
3. hyperpolarization

Question 22

what happens during depolarization?

Answer 22

there is a positive change in voltage due to activation of voltage-gated channels

Question 23

voltage-gated channels control permeability of what ion?

Answer 23

Na+ and K+

Question 24

when does Na+ flow into the cell?

Answer 24

only when both the activation gate and inactivation gates are open

Question 25

when the cell is at rest, the activation/inactivation gates are open/closed?

Answer 25

activation gate is closed and inactivation gate is open

Question 26

at depolarization, which gates open/close? what happens?

Answer 26

activation gate opens, inactivation gate is open, Na+ flows into cell

Question 27

what occurs when the cell is at rest?

Answer 27

threshold has not been met. RMP is still at -70 mV. K+ flows out of cell through leak channels, activation gate of Na+ channel is closed so Na+ doesn’t flow in, voltage-gated K+ channels are closed

Question 28

what occurs during depolarization?

Answer 28

threshold stimulus is met and cell becomes more positive and approaches zero. K+ leaking out of cell through leak channels, activation gate for Na+ channels opens and Na+ flows in to cell, activation gate of K+ channels opens slowly

Question 29

what occurs at the peak of an AP?

Answer 29

the AP reaches its highest point and becomes the most positive. K+ leaking out of cell through leak channels, inactivation gate of Na+ channels is closing, activation gate of K+ channels continues to open and more K+ flows out of cell

Question 30

what occurs during repolarization?

Answer 30

cell becomes more negative again.K+ leaking out of cell through leak channels, inactivation gate is closed for Na+ channels, activation gate of K+ channels is fully open and more K+ flows out of cell

Question 31

what occurs during hyperpolarization?

Answer 31

cell undershoots -70 mV. K+ still leaking out through leak channels, inactivation gate reopens and activation gate closes of Na+ channels. activation gate of K+ closes slowly

Question 32

what is the refractory phase?

Answer 32

period of time where we cannot re-stimulate the membrane

Question 33

what is the absolute refractory period?

Answer 33

activation gate of Na+ channels is open and insensitive to any additional voltage, inactivation gate is closed and insensitive to any voltage altogether

Question 34

what is the relative refractory period?

Answer 34

voltage-gated Na+ channels activation gate closes and inactivation gate reopens and both gates can be re-stimulated, need a supra-threshold stimulus

Question 35

what happens when 1 voltage-gated Na+ channel opens?

Answer 35

it creates a cascade of continuous conduction, voltage-gated Na+ channels open in sequences along the length of the cell

Question 36

structure of neurons?

Answer 36

1. dendrites- receiving end
2. axon- AP travels down it
3. cell body w/ soma- houses nucleus
4. terminal- sends out signal to postsynaptic cell

Question 37

what is continuous conduction?

Answer 37

voltage-gated Na+ channels open in sequences along the length of the cell, propagates AP at ~2 m/s; very slow

Question 38

what is saltatory conduction?

Answer 38

requires myelin sheath that insulates the axon: oligodendrocytes in CNS and schwann cells in PNS, rich in cholesterol, insulates axon from ion leakage, voltage-gated Na+ and K+ channels are located in nodes b/w myelinated regions of axon, propagates AP at ~ 100 m/s; very fast

Question 39

what are the steps that occur at the end of an A.P.?

Answer 39

1. AP propagates down axon
2. AP stimulates voltage-gated Ca2+ channels to open
3. Influx of Ca2+
4. Ca2+ signals vesicles to fuse with membrane and exocytose their neurotransmitter contents into synapse (transduce electrical signal into a chemical signal
5. neurotransmitters bind to ligand-gated channels on postsynaptic cell

Question 40

what are ligand-gated channels?

Answer 40

chemically-gated channels on the postsynaptic cell that receive the neurotransmitter from the presynaptic cell

Question 41

what is the effect of Na+ ligand-gated channels?

Answer 41

make the cell more positive

Question 42

what is the effect of K+ ligand-gated channels?

Answer 42

make the cell more negative

Question 43

what is the effect of Cl- ligand-gated channels?

Answer 43

make the cell more negative