Nerve Cells & Neural Signaling pt 1

Question 1

define resting membrane potential; what variable is used to denote this?

Answer 1

electrical potential (voltage) of a cell across the membrane (inside vs. outside); Vm

Question 2

what is the resting membrane potential range for all cells; neurons; what does negative indicate?

Answer 2

• -5 to -100mV
• -70mV

the negative indicates that the inside of the cell is negatively charged compared to the outside

Question 3

how do neurons communicate

Answer 3

generation of electrical signals, which shows in the form of changes in membrane potentials; some of these changes trigger release of neurotransmitters that carry the signal to the other cell

Question 4

what is the reason(s) for difference in charge on each side of plasma membrane

Answer 4

• membrane permeability
• action of Na+/K+ pumps
• negatively charged molecules inside the cell

Question 5

what terms can we use for “the difference in charge”

Answer 5

• potential difference
• membrane potential

Question 6

how does the sodium/potassium pump work

Answer 6

creates concentration gradients for Na+ and K+ ions by moving 3 Na+ out and 2 K+ in for every 1 ATP molecule hydrolyzed

(Nah nah nah, kk) –> Net +1 out

Question 7

What is the concentration for the inside and outside of cell for Na+

Answer 7

high outside, low inside (chemical driving force pushes Na+ into cell)

Question 8

What is the concentration for the inside and outside of cell for K+

Answer 8

low outside, high inside (chemical driving force pushes K+ out of cell)

Question 9

fixed anions are negatively charged at cytoplasmic pH. what are examples of these?

Answer 9

• cellular proteins
• phosphate groups of ATP and other organic molecules

Question 10

what is the effect of fixed anions on distribution of cations

Answer 10

• unequal distribution of charges
• negative charge inside cell attracts cations
• as cations increase (to a limit) the concentration gradient favours their diffusion out of the cell

Question 11

define equilibrium potential

Answer 11

membrane potential that would stabilize ions at their concentrations

Question 12

What is the Nernst equation

Answer 12

Ex = (61/z)log(x0/x1)

• Ex = equilibrium potential in mV for ion X
• x0 = concentration of ion outside cell
• x1 = concentration of ion inside cell
• z = valence of ion (+1 for sodium or potassium)

Question 13

in neurons (and other cells) at rest, neither sodium nor potassium is at equilibrium. why is this?

Answer 13

electrochemical forces act on both ions
- Na+ leak ins and K+ leak outs
- leaks create membrane potential but also slowly change concentrations in cell
- sodium/potassium pump returns ions to maintain gradients and also contributes to negative intracellular environment

Question 14

what are the types of electrical signals

Answer 14

graded and action potentials

Question 15

what are the types of gated channels

Answer 15

• voltage
• ligand (chemically)
• mechanically

Question 16

why does membrane potential change due to gated channels

Answer 16

• open or close in response to stimuli
• affect movement of ions
• ion movement leads to electrical signal

Question 17

how can we describe changes in membrane potential

Answer 17

• resting potential (reference point)
• depolarization
• repolarization
• hyperpolarization

Question 18

define graded potentials

Answer 18

• small
• communicate over short distances
• initiated by a stimulus (stronger = larger change in Vm)
• small change in membrane potential
• decremental
• short distance travel

Question 19

define action potentials by size and how they communicate

Answer 19

• large
• communicate over long distances

Question 20

what stimuli produce graded potentials

Answer 20

• chemicals like neurotransmitters
• sensory stimuli like touch and light

Question 21

how do graded potentials spread

Answer 21

electrotonic conduction (spread of voltage by passive charge movement)

Question 22

what is the purpose of graded potentials

Answer 22

• determines whether action potential will occur
• action potential will generate if neuron is depolarized to threshold

Question 23

what is threshold

Answer 23

level of depolarization needed to elicit action potential

Question 24

what does excitatory depolarization do

Answer 24

bring Vm closer to threshold

Question 25

what does inhibitory hyperpolarization do

Answer 25

take Vm away from threshold

Question 26

what does the direction of change in potential depend on

Answer 26

• neuron
• stimulus
• specific ion channels that open/close in response to stimulus

Question 27

define temporal summation

Answer 27

describes how graded potentials can sum
- same stimulus
- repeated close together in time

Question 28

define spatial summation

Answer 28

describes how graded potentials can sum
- different stimuli
- overlap in time