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Pain Control > L2- Neurophysiology > Flashcards

L2- Neurophysiology Flashcards

1
Q

Local Anesthesia Definition

A

loss of sensation in a circumscribed area of the body caused by a depression of excitation or conduction process in peripheral nerves

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2
Q

Six methods of inducing local anesthesia

A
  1. mechanical trauma
  2. low temperature
  3. anoxia
  4. chemical irritants
  5. neurolytic agents such as alcohol and phenol
  6. chemical agents such as local anesthetics
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3
Q

Desirable properties of LA in terms of effectiveness?

A

Effective regarldess of whether it is injected into the tissue or is applied locally to mucouos membranes

time of onset should be as short as possible

duration should be long enough to complete the procedure

non irritant

no permanent alteration of nerve structure

low systemic toxicity

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4
Q

Bennett’s other desirable properties of an ideal LA

A
  1. should have a potency sufficient to give complete anesthesia without the use of harmful concentrated solutions
  2. relatively free of allergic reactions
  3. it should be stable in solution and should readily undergo bio-transformation in the body
  4. should be sterile or capable of being sterile
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5
Q

Two types of basic neurons and parts

A
  1. sensory (affaretn)
  2. motor (efferent)

Parts

  1. dendritic zone
  2. axon
  3. cell body
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6
Q

cell body in a sensory neuron

A

located at a distance FROM the axon

it is NOT involved in the process of impulse transmission

its primary function is provide vital metabolic support for the entire neuron

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7
Q

motor neurons - basic

A

nerve cells that conduct impulses from the CNS to the periphery

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8
Q

cell body location of motor neuron

A

interposed between the axon and dendrites

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9
Q

difference in cell body of motor vs sensory neuron

A

MOTOR - cell body IS MAJOR COMPONENT OF THE IMPULSE TRANSMISSION SYSTEM and also provides metabolic support for the cell - located between the axon and dendrites

Sensory - location is at distance from the axon and it IS NOT INVOLVED IN TRANSMISSION OF IMPULSE and its major role is for metabolic process

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10
Q

resting state of neuron

A

slightly permeable to sodium ions (Na+)

freely permeable to potassium ions (K+)

freely permeable to chloride ions (Cl-)

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11
Q

why does K+ stay within the membrane at rest?

A

due to the negative charge of the nerve membrane

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12
Q

why does Cl- remain outside at rest?

A

due to the negative charge of membrane

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13
Q

at what point is the primary effect of LA on the nerve and how does it work / primary action

A

the effect occurs during the DEPOLARIZATION PHASE
- decreasing the rate of depolarization *

producing CONDUCTION BLOCKS - to decrease the permeability of the ion channels to sodium ions
*nondepolarizing nerve block

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14
Q

two main theories that are recognized on how local anesthetics works

A

membrane expansion and specific receptor

specific receptor theory is more widely held

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15
Q

membrane expansion theory

A

the LA molecules diffuse to hydrophobic regions of excitable membranes, producing a disturbance of the membrane structre, and thus preventing an increase in permeaility to sodium ions
- changes the membrane, and so sodium cannot go through

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16
Q

specific receptor theory - describe it and what happens to permeability

A

LA act by binding to specific receptors on the sodium channel
action is direct
either on the external or internal axoplasmic surface of the sodium channels

*once the LA gains access to the receptors, the permeability to sodium ions is decreased or eliminated, and nerve conduction is interrupted

most common/ accepted mechanism

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17
Q

where are the tertiary amine LA working?

A

within sodium channel

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18
Q

biotoxins work where?

A

at the outer surface of the sodium channel

- tetrodotoxin, saxitoxin

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19
Q

what works at the activation or inactivation gate?

A

scorpion venom

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20
Q

Class A

Definition and chemical substance

A

agents acting at receptor site on EXTERNAL surface of nerve membrane
Biotoxins - tetrodotoxins, saxitoxin

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21
Q

Class B

Definition and chemical substance

A

Agents acting at receptor site on INTERNAL surface of nerve membrane - closer to the cytoplasm

structure : quarternary ammonium analogs of lidocaine
scorpion venom

22
Q

Class C

Definition and chemical substance

A

Agents acting by a receptor - independent physio-chemical mechanism

Benzocaine (may be one of the membrane receptor theory?)

23
Q

Class D

Definition and chemical substance

A

ONES WE FOCUS ON MOST

Agents acting by combination of receptor and receptor independent mechanisms

Chemical substance - articaine, lidocaine, mepivacaine, prilocaine)

most clinically useful anesthetic agents

24
Q

local anesthetics are classified as? where are each metabolized?

A

Amides = in the liver

Esters = in the blood - more likely to cause allergic reaction and not used as much clinically

25
Q

dissociation of local anesthetics

and available as what?

A

available as SALTS - which allow them to be dissolved in sterile water for clinical use

in this solution it exists as one uncharged base RN and 2 positive charge molecules RNH+ called the cation

1 BASE - RN
2 CATION - RNH+

so RNH + goes to RN and H+

26
Q

dissociation Constant pKA

A

pKa is a measure of a molecules affanity for hydrogen ions

when the pH of a solution has the same pKa as the local anesthetic, exactly half of the drug will exist in teh RNH+ and exactly half in the RN form

27
Q

human physiologic pKA

A
  1. 4

- so if LA has pKa of 7.4 half will exist as base and half will exist as cation

28
Q

mechanism of base and cation in the LA

A

Base- diffuse into the channel / nerve sheath and the cation will BIND AT RECEPTOR SITE will block it - so no depolarization

29
Q

rate of onset of LA related to?

A

the pKa of the LA

  • the pka determines the rate of onset
  • closer the pka is to the ph the quicker the onset
  • an LA with a lower pKa has a greater number of lipophilic FREE BASE MOLECULES to diffuse through the nerves sheath, but intracellular
30
Q

if have decreased tissue pH

A

may not have adequate anesthetic in area

31
Q

what determines the ease with which LA moves from site of administration in the axoplasm of the nerve cell?

A

pH of the extracellular fluid

*note the intracellular pH remains stable and independent of extracellular pH

32
Q

adequate blockade of the nerve in inflammed or infected tissue?

A

harder to achieve because of the smaller number of molecules to be able to cross the nerve sheath

33
Q

mantle bundles

A

these are located near the surface of the nerve, exposed to the highest concentrations

tend to innervate more proximal regions

MOLARS in an IANB - think closer to the nerve in proximal / distal

molars are first to get anesthetized and last to wear off

34
Q

Core bundles

A

closer to the CENTER of the nerve

LONGER to onset, and lower concentration of LA

Tend to innervate more DISTAL points of nerve innervations - incisors, canines with an IANB
- takes longer to anesthetize but will wear off sooner than molars

35
Q

quicker onset?

A

when the pka and ph are more similar

36
Q

Factor - pKA
Action effected?
Description

A

Action Affected – onset

Description : Lower pKA more rapid onset of action - more RN molecules present to diffuse through nerve sheath; thus onset time is decreased

37
Q

Factor - Lipid Solubility
Action effected?
Description

A

Related to the intrinsic potency
Action Affected: anesthetic potency * increased lipid solubility = increased potency

Description: with more lipid solubility - the drug is more potent

38
Q

Factor - protein binding
Action effected?
Description

A

Action Affected: Duration

Description: Increased protein binding allows the anesthetic CATION (RNH+) to be more firmly attached to proteins located at receptor sites; thus the duration of action is increased

39
Q

Factor - Nonnervous tissue diffusibility
Action effected?
Description

A

Action Affected: ONSET - if increased diffusibility there is a LOWER time of onset - able to diffuse into the tissue more

Description:

40
Q

Factor - Vasodilator Activity
Action effected?
Description

A

Action Affected: Anesthetic potency and duration

Description: the greater the vasodialtor activity –> the increased blood flow to a region and this leads to more rapid REMOVAL of anesthetic molecules from the injection site –> thus the anesthetic potency and duration are decreased

41
Q

recovery from LA Block

A

The first to come out of anesthesia are those in the center (core fibers/bundles) - incisors and canines will come out first

the mantle - molars will stay anesthetized longer

42
Q

recurrence of immediate profound anesthesia

A

combination of residual local anesthetic in the nerve fiber and the newly deposited supply

43
Q

difficulty re-achieving profound anesthesia

A

if readministration of anesthesia does not produce the effect this may be due to tachyphylaxis

44
Q

Tachyphylaxis

A

‘an increased tolerance to a drug that is administered repeatedly’
this could be due to edema, localized hemorrhage, clot formation, transduation, hypernatremia, and decreased pH of the tissues

45
Q

duration of the anesthesia - general factors effecting

A

Longer acting - more firmly bound in the nerve membrane (due to increased protein binding)
vascularity of the injection site

presence or absence of vaso-active substance

46
Q

if recovery is slow?

A

LA is bound to the nerve membrane

47
Q

perineurium

A

the SHEATH of connective tissue surrounding a fascile or bundle of nerve fibers within a nerve
* this is the main barrier to diffusion of local anesthetics into a nerve

48
Q

Potassium, sodium, and chloride intracellular, extracellular concentrations

A

Potassium – K+ is higher inside (b/c membrane is negative so stays in)

Sodium - higher concentration on the outside

chloride - higher concentration on the outside

  • most freely permeable to potassium and chloride
  • but doesnt just go in and out because the charge is negative on the inside so keeping the chloride out and the potassium in at rest
49
Q

what happens when the transmembrane potential decreases by 15 mV from resting potential?

A

RAPID depolarization occurs

50
Q

how much nerve needs to be covered by anesthetic solution to ensure a thorough blockade?

A

at least a minimum of 8-10 mm of nerve

Pain Control (12 decks)

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