Chapter 3

Question 1

Resting membrane potential

Answer 1

the potential energy residing in a non-conducting membrane

• Typical value for excitable cells= -75 to -85 mV
• Inside of the cell is negative with respect to the outside

Question 2

voltage

Answer 2

a measure of the quantity of charges in a given location referenced to another location

Question 3

current

Answer 3

When two areas of different charge density are connected by a conductor, current will flow from high charge density to low charge density.
**Unit=ampere (Amp)
**I=E/R
I=current
E=voltage
R=Resistance

Question 4

resistance

Answer 4

property of a conductor due to which it opposes the flow of current through it; hindrance to charge flow.
**Unit=ohm

Question 5

diffusion potential

Answer 5

develops as a result of the unequal diffusion of ions in opposite directions

Question 6

electrogenic pump

Answer 6

a membrane pump that moves unequal quantities of like charges in opposite directions across the membrane; participates in the membrane potential

Question 7

electroneutral pump

Answer 7

moves equal quantities of like charges in opposite directions across a membrane

Question 8

electrochemical equilibrium

Answer 8

if the work required to move an ion against a chemical gradient is equal and opposite to the work required to move the ion against an electrical gradient, then that ion is said to be in electrochemical equilibrium.

Question 9

Nernst Equation

Answer 9

used to calculate hypothetical transmembrane voltages or potentials that would have to exist to offset the tendency for any given ion to move due to a concentration gradient.

Question 10

work

Answer 10

a force does work and results in movement

Question 11

potential

Answer 11

difference in charge density between two locations

-unit of measure for potential=volt; potential difference that causes one coulomb to do one joule of work.

Question 12

Excitable membranes

Answer 12

specialized for transmitting “electrical messages” from one part of a cell to another.

• *Nerve cells
• *Muscle cells

Question 13

Action potential

Answer 13

changes in transmembrane potential that occur sequentially along the surface of an excitable cell.

• most action potentials in neurons originate in the cell body and move in one direction through the remainder of the cell.
• Action potentials in skeletal muscle cells originate at the neuromuscular junction and move away from it in all directions.

Question 14

propagation

Answer 14

the “movement” of an electrical impulse during action potential.

Question 15

Synapse

Answer 15

a structure that allows neurons to communicate with other neurons.
-electrochemical alterations at this site insures that an electrical change in one cell is properly communicated to the next cell.

Question 16

The main reason that neuronal “messages” leave the central nervous system is to evoke activity in…..?

Answer 16

Effectors, i.e., smooth muscle, cardiac muscle, glands, or skeletal muscle.

Question 17

Neuromuscular Junction

Answer 17

Translates activity of neuron into physical work

Question 18

Common features of neuromuscular junction

Answer 18

1. release of chemical transmitter presynaptically
2. diffusion of transmitter across synapse
3. attachment of transmitter to receptor on postsynaptic membrane
4. creation of new potential in postsynaptic membrane

Question 19

Receptors

Answer 19

specialized cells that are capable of tranducing chemical, mechanical, thermal, electromagnetic, or electrical energy to the language of the nervous system (current flow and AP)

Question 20

Reflexive response

Answer 20

reception of environmental perturbations gives rise to stereotyyped motor response

Question 21

Work

Answer 21

W=FX
F= force (electromotive force or voltage); measure of the quantity of charges in a given location referenced to another location
X=distance
Unit of force= volt (mV)

Question 22

Conductor

Answer 22

• resistance to current flow is low

* Extracellular & Intracellular fluids

Question 23

Insulator

Answer 23

• Resistance to current flow is high

* Lipid molecules

Question 24

Conductance

Answer 24

Movement of ions through membranes

• Reciprocal of resistance
• Unit= mho (opposite of resistance, ohm)

Question 25

Measurement of transmembrane potentials

Answer 25

1. heated glass pipets filled with good conductor (KCl)
2. Electrode passed through cell membrane and connected to volmeter
3. Interior of cell is then referenced to exterior

Question 26

Diffusion potential

Answer 26

develops as a result of unequal diffusion of ions in different directions across a membrane

Question 27

Diffusion potential results from

Answer 27

1. Sodium/ Potassium concentrations
   - K higher con. inside, Na higher con. outside
   - K will efflux, Na influx
2. Membrane Permeability
   - 50-70 x more permeable to K than to Na; more K ions efflux than Na ions influx
3. Non-diffusible anions
   - Large proteins that can’t diffuse out of the cell are negatively charged

Question 28

Since the inside of the membrane is negatively charged, what must be done to pump Cl- into the cell & K+ and Na+ out of the cell

Answer 28

Work must be done to move against an electrical gradient.
-We=ZiFEm
  Zi= valence and charge of ion
  F= Faraday's constant
  Em= transmembrane potential

Question 29

Formula for work that must be done to move against a concentration (chemical) gradient

Answer 29

Wc= RT (logc [ion]i - logc [ion]o
R=gas constant
T=absolute temperature
**since Na is more concentrated outside the cell, work must be done for it to efflux

Question 30

Electrochemical equilibrium

Answer 30

Happens when work required to move an ion against a chemical gradient is equal and opposite to work required to move it against an electrical gradient.

• *We + Wc=0
• this indicates that there is no net force acting on that ion and if the membrane were to become more permeable to that ion, the net flux would be zero

Question 31

The Nernst Equation

Answer 31

Can use this equation to calculate hypothetical transmembrane potentials that would have to exist to offset the tendency for any given ion to move due to a concentration gradient.

• this is done by setting the sum of We + Wc to zero and solving for the theoretical transmembrane potential, Em.
• Substitute in this equation the actual measured concentrations for a given ion.

Question 32

Nernst Equation valuees for K+, Na+, Cl-

Answer 32

1. K+= -97 mV
   * there is a net force operating on K+ and if the permeability of the membrane were to increase to K+ alone it would efflux
2. Na+= +65 mV
   * Indicated a strong tendency for sodium to influx (both chemical and electrical gradients)
3. Cl-= -90 mV
   * close to normal Em
   * indicated that chloride is passively distributed in resting cell
   * Sudden increase in permeability would not result in much Cl- movement