Molecular Basis of Excitation

Question 1

Typical values of resting membrane potential are ___ for nerve cells and ___ for muscle cells

Answer 1

-70 mV; -90 mV

Question 2

Normally the charge separation occurs in a region less than __ um wide on either side of the membrane

Answer 2

1

note: bulk of cytoplasm and ECF is electrically neutral

Question 3

In this type of conduction, localized depolarization that spreads to neighboring membrane regions, but neighboring regions do not depolarize quite as much as the site of the NT deposition

Answer 3

decremental conduction

Question 4

True or false? Hyper polarization is conducted decremental across dendrites and cell body

Answer 4

true

Question 5

In this type of conduction, the membrane in one part of the cell reaches threshold, and the action potential is passed on to all parts of the cell. The magnitude of the AP is the same everywhere as it spreads down the nerve

Answer 5

non-decremental conduction

Question 6

Chemical concentration differences across a membrane result in diffusive ___ energy driving forces

Answer 6

potential

Question 7

Free energy is released by ions flowing down their concentration gradient. True or false?

Answer 7

true

note: free energy = RT ln [K+]out/[K+]in

Question 8

Free energy is released when cations move toward the ___ side of a membrane or anions move toward the ___ side of the membrane

hint: electrical forces at play (think attraction)

Answer 8

negative; positive

Question 9

The ___ force acting on a charged molecule is the sum of the electrical and diffusive forces

Answer 9

electrochemical

Question 10

In regards to membrane selectivity, when a membrane is selectively permeable to ionic species of one charge, an ___ potential develops across that membrane. As this permeable cation moves down its concentration gradient, anions are left behind, resulting in charge ____.

Answer 10

electrical; separation

note: the gradually increasing charge separation limits makes it harder and harder for additional cations to leave

Question 11

Net movement of ions ceases when the electrical and chemical forces are ___ in magnitude but ___ in direction

Answer 11

equal; opposite

Question 12

The Nernst potential (Eion) measures what?

Answer 12

the membrane potential a given ion reaches electrochemical equilibrium (stops moving)

Question 13

By convention, ionic current is ___ when a cation moves toward the negative side of membrane

Answer 13

positive

Question 14

The electrical characteristic that makes ion movement difficult is called _____.

Answer 14

resistance

note: cell membranes have resistance in that they restrict the free flow of the ions from one side of the cell to the other

Question 15

The driving force for ion movement across a membrane is what?

Answer 15

the difference between the existing membrane potential and the Nernst potential for the ion under consideration

Question 16

What is the reciprocal of resistance?

Answer 16

conductance

Question 17

A membrane with a high conductance for a given ion lets the ion move ___ for any given difference between membrane potential and the ion’s Nernst potential.

Answer 17

easily

note: high conductance means free ion movement through core of a protein channel

Question 18

Based on Ohm’s Law, the ionic flux can be expressed as what?

Answer 18

I = g (Vm - Eion) = (Vm - Eion) / Rion

I = outward potassium current
R = membrane potassium resistance
g = membrane potassium conductance
Vm-Eion = driving force, difference in membrane and potassium equilibrium (Nernst) potentials

Question 19

Unique membrane conductance, gion, which is controlled by “____” that selectively let that type of ion across the membrane

Answer 19

channels

Question 20

True or false? the relative permeability (conductance) of the various ion channels in a cell membrane determine the membrane potential.

Answer 20

true

note: the ion with the greatest conductance pulls the membrane potential to a value near its Nernst potential

Question 21

Membranes are more permeable to ___ than to other ions.

Answer 21

potassium

Question 22

Cells are slightly permeable to ___ so Vm is not quite as negative as it would be otherwise

Answer 22

Na+

Question 23

Vm is generally closer to____ than ___ because cells are much more permeable to K+ than Na+

Answer 23

Ek; Ena

Question 24

Give the Goldman-Hodgkin-Katz Equation which describes the relative permeability to Na+, K+, and Cl- and determine Vm

Answer 24

Vm = 61 log Pk [K]out + Pna [Na]out + Pcl [Cl]in
————————————————-
Pk [K]in + Pna [Na]in + Pcl [Cl]out

Question 25

A decrease in the Pna/Pk ratio An increase in [K+]in - [K+]out When does this occur? What is the clinical correlation?

Answer 25

depolarizaiton; clinical correlation: hyperkalemia

Question 26

The Na+/K+ pump, pumps __ Na+ out for every ___ K+ pumped in

Answer 26

3; 2 note: pump is electronegative

Question 27

Ligand operated channels tend to be smaller and more ion specific than voltage-gated channels. True or false?

Answer 27

false; larger, less ion-specific

Question 28

____-gated channels are responsible for the sequential movement of ions across the membrane during the generation of APs

Answer 28

voltage

Question 29

Voltage-gated channels open in an "all or none" fashion. True or false?

Answer 29

true

Question 30

Ion selectivity is based on what three things?

Answer 30

size, charge, energy of hydration

Question 31

Voltage-gated Na+ channels have a ___ activation gate (m-gate) and a ___ inactivation gate (h-gate)

Answer 31

fast; slow

Question 32

The Na+ fast activation gate opens rapidly in response to ___ and closes rapidly upon ____

Answer 32

depolarization; repolarization

Question 33

The Na+ slow inactivation gate closes slowly upon ____ and opens slowly upon ____. It is open in the ___ state but closed in the ___ state.

Answer 33

depolarization; repolarization; resting; inactive

Question 34

For the following phases of the sodium channel cycle, tell if fast gate and slow gate is open or closed: resting state

Answer 34

fast gate: closed slow gate: open note: Pna or gna is low

Question 35

For the following phases of the sodium channel cycle, tell if fast gate and slow gate is open or closed: rising phase

Answer 35

fast gate: open slow gate: open note: Pna or gna is high

Question 36

For the following phases of the sodium channel cycle, tell if fast gate and slow gate is open or closed: falling phase

Answer 36

fast gate: open slow gate: closed note: Pna or gna is low

Question 37

What is the rate limiting step in return to the resting conformation?

Answer 37

the rate at which the h gates open (recover from inactivation) - refractory period

Question 38

This is the time when all h gates are closed. The cell in not excitable by any stimulus

Answer 38

absolute refractory period

Question 39

This is the time when some but not all h gates have reopened. The cell is excitable with a supranormal stimulus

Answer 39

relative refractory period

Question 40

Voltage-gated K+ channels open slowly in response to membrane ____

Answer 40

depolarization (Pk or gk increases)

Question 41

Voltage-gated K+ channels close slowly in response to membrane ____

Answer 41

repolarization (Pk or gk decreases)

Question 42

Voltage-gated K+ channels may remain open for a short time after completion of action potential, accounting for the after-_____ that is sometimes seen

Answer 42

hyperpolarization

Question 43

The falling phase of the AP is due to what?

Answer 43

delayed inactivation of Na+ channels and the depolarization-induced delayed rise in K+ conductance

Question 44

Does the amplitude of the AP change as it traverses the length of the axon

Answer 44

no

Question 45

A faster neuron would have a ___ diameter and have ___ fibers

Answer 45

large; myelinated

Question 46

In regards to motor neurons, these are large, myelinated fibers that innervate extrafusal skeletal muscle

Answer 46

Type A-alpha

Question 47

In regards to motorn neurons, these are smaller, myelinated fibers that innervate intrafusal muscle. These have slower conduction velocities and are involved in reflex tone adjustments

Answer 47

Type A-gamma

Question 48

These fibers are small and unmyelinated. Usually refer to sensory afferent fibers

Answer 48

Type C

Question 49

In regards to somatosensory neurons, Type ___ afferents are large myelinated nerves carrying information like tactile sensation to the brain

Answer 49

I

Question 50

In regards to somatosensory neurons, Types ___ and ___ sensory afferents are unmyelinated and cary information about sensations like proprioception, pain, and temperature

Answer 50

III; IV