Excitable Cells

Question 1

____, ____, and most ____ are often referred to as “excitable cells” bc their physiologic functions rely critically on electrical events in their plasma (i.e. surface) membrane

Answer 1

neurons (single nerve cells)
sensory cells
muscle cells

Question 2

3 mechanisms of electrical events

Answer 2

• cell to cell (intercellular) communication
• sensing environmental changes (light, sound, temp, etc.)
• triggering intracellular events

Question 3

three components of cell excitation

Answer 3

extracellular fluid (ECF) or interstitial fluid
intracellular fluid (cytosol)
membrane

Question 4

extracellular fluid has a high ____ concentration

Answer 4

NaCl

Question 5

intracellular fluid is predominantly _____

Answer 5

KCl

Question 6

cell membrane made up of ____ and ____

Answer 6

phospholipid bilayer ; proteins

Question 7

a characteristic of cell membranes, essential to excitation, is _____

Answer 7

permeability

Question 8

changes in permeability, that are ____ and ____, are essential to excitation in cells

Answer 8

ion-specific; exquisitely timed

Question 9

random diffusion down an electrical or concentration gradient; done by organic molecules or ions

Answer 9

simple diffusion

Question 10

examples of non-polar substances

Answer 10

O2, CO2, fatty acids, and steroid hormones

Question 11

amount of a substance crossing a surface per unit of time

Answer 11

flux

Question 12

diffusion between 2 compartments is always _____

Answer 12

bi-directional

Question 13

the difference between the two unidirectional fluxes

Answer 13

net flux

Question 14

when net flux=0, the system is referred to as being in a state of ______

Answer 14

diffusion equilibrium

Question 15

two types of mediated transport

Answer 15

facilitated diffusion and active transport

Question 16

primary active transport

Answer 16

energy source is hydrolysis of ATP > transporter becomes phosphorylated > changes affinity for solute (ligand) > increases transport rate

Question 17

examples of primary active transport

Answer 17

1. transport of Na ions out of cells

2. transport of K ions into cells

Question 18

secondary active transport uses energy in ____ across membrane; transporter has ____ binding sites

Answer 18

ion concentration gradient; two

Question 19

example of secondary active transport

Answer 19

transport of amino acids, uses [Na] gradient

Question 20

3 steps in mediated transport

Answer 20

1. ligand binds to transporter
2. transporter undergoes conformation change
3. ligand is released on other side of membrane

Question 21

types of channels

Answer 21

ligand-sensitive
voltage-sensitive
mechanosensitive

Question 22

water is polar and diffuses through channels called ____; water diffuses ____ its concentration gradient

Answer 22

aquaporins; down

Question 23

the total solute concentration in a solution

Answer 23

osmolarity

Question 24

engulfment of fluid and particles from the extracellular space

Answer 24

endocytosis

Question 25

engulfment of small particles with or without small volume of ECF; performed by all cell types

Answer 25

pinocytosis

Question 26

engulfment of large particles or cellular debris; performed by specialized cells

Answer 26

phagocytosis

Question 27

electrical charge difference between the inside and outside of a cell

Answer 27

voltage (V)

Question 28

voltage (V) in a resting cell is ____. therefore, plasma membrane must have a ____

Answer 28

steady; resistance (R)

Question 29

when resistance changes, ions cross the plasma membrane, and this ion movement is a ____

Answer 29

current (I)

Question 30

conductance (g) is the ____ of resistance

Answer 30

reciprocal

Question 31

Ohm's law

Answer 31

V = IR

Question 32

____ and ____ are both membrane properties

Answer 32

conductance; resistance

Question 33

the nernst equation yields the ____ of a single ionic species

Answer 33

equilibrium potential (or equilibrium voltage)

Question 34

the equilibrium potential is the voltage across a cell membrane that exactly balances the force in the ____ of a ____ ion

Answer 34

concentration gradient; permeable

Question 35

diffusion potentials can be ____; they are due to an ____ ion flow- an imbalance in the flow of an ion or several ions between two compartments

Answer 35

transient (disappear over time); asymmetric

Question 36

a diffusion potential can also be ____ at a ____ level over time

Answer 36

maintained; steady

Question 37

toward 0 mV

Answer 37

depolarization (hypopolarization)

Question 38

toward resting potential

Answer 38

repolarization

Question 39

increase in membrane potential (i.e. more negative)

Answer 39

hyperpolarization

Question 40

equilibrium is reached when the force in the ____ for K+ ions to move out of the cell is balanced by opposing force in the ____ which favors keeping K+ ions inside the cell

Answer 40

concentration gradient; electrical gradient

Question 41

membrane potential at equilibrium

Answer 41

-70-90 mV

Question 42

equilibrium potential for K+

Answer 42

-100 mV