Excitable Cells

Question 1

________, ________ and most ________ are often referred to as “excitable cells.”

Answer 1

Neurons, sensory cells, and most muscle cells…

Question 2

What is the definition of an excitable cell?

Answer 2

It’s physiologic functions relies critically on electrical events in their plasma membrane.

Question 3

Electrical events in cells can cause three different actions. What are they?

Answer 3

1. Communication
2. Sensing environmental changes
3. Triggering intracellular events

Question 4

What are the three environments involved in cell excitation?

Answer 4

1. ECF
2. Membrane
3. Intracellular fluid

Question 5

____ has a high concentration of NaCl.

Answer 5

ECF

Question 6

____ has a high concentration of KCl.

Answer 6

Intracellular fluid

Question 7

Changes in permeability that are ______ and ________, are essential to excitation in cells.

Answer 7

ion-specific; exquisitely timed

Question 8

The amount of a substance crossing a surface per unit of time is ____.

Answer 8

flux

Question 9

The system is in ______ ______ when the net flux is 0.

Answer 9

diffusion equilibrium

Question 10

What are the two forms of mediated transport?

Answer 10

1. Facilitated diffusion (no energy)

2. Active transport (requires energy)

Question 11

What is an example of facilitated diffusion?

Answer 11

Glucose transporters

Question 12

T/F: Active transport can move molecules UP a concentration gradient.

Answer 12

TRUE

Question 13

What are two examples of active transport?

Answer 13

1. Na+ out of cells

2. K+ into cells

Question 14

What is secondary active transport?

Answer 14

Energy from ion gradient is used to transport something else in the same direction.

Question 15

What three factors determine flux of transport?

Answer 15

1. Number of transporters in membrane
2. Transporter saturation
3. Rate of transporter conformational change

Question 16

What are three types of channels?

Answer 16

1. Ligand-sensitive
2. Voltage-sensitive
3. Mechanosensitive

Question 17

T/F: If you place a cell in a hypotonic solution the cell will shrink.

Answer 17

FALSE

Swell

Question 18

Which type of endocytosis is performed by all cells?

Answer 18

Pinocytosis

Question 19

T/F: Cl- ions are much more abundant outside of the cell.

Answer 19

TRUE

Question 20

The difference in electrical charge between the inside and outside of a cell is _____.

Answer 20

Voltage

Question 21

Ion movement creates a ______.

Answer 21

current

Question 22

What is Ohm’s law?

Answer 22

V=IR

V = voltage
I = current
R = resistance

Question 23

T/F: Conductance = current.

Answer 23

FALSE

Question 24

T/F: Conductance is the reciprocal of resistance.

Answer 24

TRUE

Question 25

What is the purpose of the Nernst equation?

Answer 25

Balance a concentration gradient with a voltage gradient

Question 26

T/F: Diffusion potentials can be transient (disappear over time).

Answer 26

True

Question 27

T/F: A diffusion potential can be maintained at a steady level over time.

Answer 27

True

Question 28

__+ ions diffuse much more readily than __+ ions.

Answer 28

K; Na

Question 29

Explain the resting membrane potential.

Answer 29

K+ ions move out of cell until electrical gradient balances concentration gradient (Na+ ions also move into the cell at a lower rate than K+ moving out)

Question 30

T/F: The resting membrane potential is a transient potential.

Answer 30

FALSE It is a steady potential

Question 31

What is the function of the Na+/K+-ATPase pump?

Answer 31

Move K+ ions back into the cell and Na+ ions out of the cell

Question 32

An _____ _____ is a large transient change in membrane potential.

Answer 32

Action potential

Question 33

How does an action potential begin?

Answer 33

Stimulus depolarizes dendrites -> depolarize cell body -> AP develops and moves along axon

Question 34

What are the steps involved in an action potential up to the rising phase?

Answer 34

1. Increase in Na+ permeability 2. Na+ enters through voltage-regulated Na channels 3. Membrane potential moves to 0 mV 4. More channels continue to open as charge goes up (rising phase)

Question 35

What are the steps of an action potential after the rising phase?

Answer 35

1. Membrane potential approaches and overshoots 0mV (+40mV) 2. K+ channels open and ions leave the cell 3. Potential goes back down and Na channels close (falling phase) 4. Afterpolarization

Question 36

A _______ stimulus will not push the membrane to a threshold.

Answer 36

Subthreshold

Question 37

What is a graded potential?

Answer 37

A local response to a subthreshold stimulus

Question 38

What types of stimuli result in action potentials?

Answer 38

Threshold or suprathreshold

Question 39

T/F: During the absolute refractory period, a suprathreshold stimulus can cause a second action potential.

Answer 39

FALSE

Question 40

T/F: During the relative refractory period a suprathreshold stimulus can elicit a second action potential.

Answer 40

TRUE

Question 41

T/F: A weaker stimulus needs to be applied for a longer duration to cause an AP?

Answer 41

TRUE

Question 42

The weakest stimulus that can elicit a response is the ______ and it must be given for a duration referred to as the _____ ____.

Answer 42

Rheobase; utilization time

Question 43

The ______ is the duration a stimulus with twice the strength of the rheobase must be given.

Answer 43

chronaxie

Question 44

What charge of ions will move toward the cathode?

Answer 44

Positive charges

Question 45

T/F: The current of positive charges moves from the anode to the cathode.

Answer 45

TRUE

Question 46

Axons with ________ diameters have higher velocities of conduction.

Answer 46

larger

Question 47

T/F: A(alpha) neurons are the largest and C sympathetic neurons are the smallest.

Answer 47

True