Local anesthetics

Question 1

The axons of peripheral nerves differ in their

Answer 1

size, structure, speed of conduction, myelination, and sensitivity to the local anesthetic blockade

Question 2

Conduction velocity is increased by

Answer 2

myelination and a wider axonal diameter

Question 3

What are the three major classes of peripheral nerves?

Answer 3

A, B & C

Question 4

In the clinical setting, local anesthetics inhibit peripheral nerves in the following order:

Answer 4

B fibers
C fibers
Small diameter A fibers (delta, gamma)
Large diameter A fibers (alpha, beta)

Question 5

Regression of blockade occurs in the

Answer 5

opposite order of block onset

Question 6

What is saltatory conduction?

Answer 6

when myelin insulates the axon and allows the electrical signal to skip along only the uninsulated regions

Question 7

Conduction velocity is a measure of

Answer 7

how fast an axon transmits the axon potential

Question 8

What is the function of B fibers?

Answer 8

preganglionic ANS fibers

Question 9

What is the function of C fibers with a sympathetic subtype?

Answer 9

postganglionic ANS fibers

Question 10

What is the function of C fibers with a dorsal root subtype?

Answer 10

slow pain
temperature
touch

Question 11

What is the function of A alpha fibers?

Answer 11

skeletal muscle- motor proprioception

Question 12

What is the function of A beta fibers?

Answer 12

touch
pressure

Question 13

What is the function of A gamma fibers

Answer 13

skeletal muscle-tone

Question 14

What is the function of A delta fibers?

Answer 14

fast pain
temperature
touch

Question 15

What is Cm?

Answer 15

a unit of measure that quantifies the concentration of local anesthetic that is required to block conduction
minimum effective concentration

Question 16

Fibers that are more easily blocked have a _________ Cm.

Answer 16

lower

Question 17

Cm is typically _____________ in nerves with a wider diameter

Answer 17

higher

Question 18

Cm is reduced by

Answer 18

higher tissue pH or a high frequency of nerve stimulation

Question 19

Which peripheral nerve fiber type is not myelinated?

Answer 19

C fibers

Question 20

Local anesthetics can bind to the voltage-gated sodium channel when it is in the:
a. resting and active states
b. resting and inactive states
c. active and inactive states
d. active state only

Answer 20

c. active and inactive state

Question 21

What are the three possible states that the sodium channel can exist in?

Answer 21

1. resting (nonconducting)
2. active (conduction)
3. inactive (nonconducting)

Question 22

Local anesthetics reversibly bind to

Answer 22

the alpha subunit of the voltage-gated sodium channel

Question 23

Through their binding of the voltage-gated sodium channel, local anesthetics

Answer 23

reduce sodium conductance and block nerve conduction

Question 24

______________ says that local anesthetics can only bind to sodium channels in their active (open) and inactive (closed refractory) states.

Answer 24

The guarded receptor hypothesis

Question 25

What determines that state of the sodium channel?

Answer 25

voltage

Question 26

What is resting state voltage?

Answer 26

-70 mV

Question 27

At resting membrane potential, the channel is

Answer 27

closed

Question 28

What is the active state voltage?

Answer 28

-70 mV to +35 mV

Question 29

What happens to the Na channel in the active state?

Answer 29

when threshold potential is reached, the channel opens allows Na+ to follow its concentration gradient (outside to inside)

Question 30

What is the voltage in the inactive state?

Answer 30

+35 to -70 mV

Question 31

What happens in the inactive stage?

Answer 31

the channel is closed the inactivation gate plugs the channel until the resting membrane is re-established restoration of the resting membrane potential converts the channel from the inactive state to the resting state

Question 32

Can the channel be opened in the inactive state?

Answer 32

no

Question 33

Can the channel be opened in the resting state?

Answer 33

it's closed but able to be opened

Question 34

What is a use-dependent or phasic blockade?

Answer 34

the more frequently the nerve is depolarized and voltage-gated sodium channels open, the more time available for binding ad the faster the nerve will be blocked

Question 35

Local anesthetics: (select 2) a. increase threshold potential b. decrease resting membrane potential c. have no effect on threshold potential d. have no effect on resting membrane potential

Answer 35

c. have no effect on threshold potential d. have no effect on resting membrane potential

Question 36

In the peripheral nerve the resting membrane potential is

Answer 36

-70 mV

Question 37

In the peripheral nerve, the threshold potential is

Answer 37

-55 mV

Question 38

Describe depolariziation.

Answer 38

An AP is created when an electrical stimulus opens voltage-gated sodium channels sodium enters the cell Once the threshold potential is achieved, the cell depolarizes and propagates an action potential Wave of depolarization travels downstream (since upstream portion is in its refractory phase)

Question 39

Describe repolarization

Answer 39

The voltage gated Na channels inactivate after a set time increased potassium conductance restores transmembrane potential to RMP the Na/K-ATPase maintains RMP until the nerve is depolarized again

Question 40

When a critical number of sodium channels are blocked by local anesthetic,

Answer 40

the cell can't depolarize and the action potential can't be propagated

Question 41

What three things influence resting membrane potential?

Answer 41

1. chemical force (concentration gradient) 2. electrostatic counterforce 3. Na+/K+ ATPase (3 for 2 in)

Question 42

What is the primary determinant of resting membrane potential?

Answer 42

serum K+

Question 43

Decreased serum K+ causes the RMP to

Answer 43

become more negative

Question 44

Increased serum K+ causes the RMP to

Answer 44

become more positive

Question 45

What is the primary determinant of threshold potential?

Answer 45

serum Ca2+

Question 46

Decreased serum Ca2+ causes the threshold potential to

Answer 46

become more negative

Question 47

Increased serum Ca2+ causes the threshold potential to

Answer 47

become more positive

Question 48

Depolarization is __________ phenomenon

Answer 48

all or none- once it begins it cannot be stopped

Question 49

When RMP is closer to TP, the cell is

Answer 49

easier to depolarize

Question 50

When RMP is further from TP, the cell is

Answer 50

harder to depolarize

Question 51

A cell depolarizes when

Answer 51

Na+ or Ca+ enters a cell

Question 52

A cell repolarizes when

Answer 52

K+ leaves or Cl- enters the cell