Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
            ween adjacent nodes of 
Ranvier increases with greater axonal 
diameter.  
What if the conduction of an impulse is 
blocked at one node?  
● The local current skips over that node 
enough to raise the membrane potential 
at the next node to its firing potential 
producing depolarization. 
● A minimum of perhaps 8 to 10 mm of 
nerve must be covered by anesthetic 
solution to ensure thorough blockade. 
 
                                
 
 
Mode and Site of Action of Local Anesthetics 
 
● Local anesthetics interfere with the excitation of a nerve in one or more of the following 
ways: 
1. Altering the basic resting potential of the nerve membrane. 
2. Altering the threshold potential (firing level). 
3. Decreasing the rate of depolarization. 
4. Prolonging the rate of repolarization. 
 
● The primary effects of local anesthetics occur during the depolarization phase of the action 
potential, which include a decrease in the rate of depolarization, particularly in the phase 
of slow depolarization.  
Because of this:  
● Cellular depolarization is not sufficient to reduce the membrane potential of a nerve fiber 
to its firing level, so a propagated action potential does not develop. 
● There is no accompanying change in the rate of repolarization.  
1. Where does LA work?? 
 
● We have 5 theories, 3 of which are not supported nowadays and 2 of which are given 
credence today:  
 
states that  
why   
Membrane 
expansion theory  
1. LA molecules diffuse 
to 
hydrophobic 
regions of excitable 
membranes 
2. producing a general 
disturbance of the bulk 
membrane structure 
3. expanding 
some 
critical region(s) in the 
membrane 
4. preventing an increase 
in 
permeability 
to 
sodium ions. 
  
 
● The membrane expansion theory 
serves as a possible explanation 
for the local anesthetic activity of 
a drug such as benzocaine —> 
which does not exist in cationic 
form yet still exhibits potent 
topical anesthetic activity 
● The nerve membranes expand and 
become more fluid when exposed 
to local anesthetics. 
● However, nerve conduction is not 
entirely blocked by membrane 
expansion.   
Specific 
receptor 
theory (the most 
favored today)  
● Local anesthetics act 
by binding to specific 
receptors 
on 
the 
sodium channel (Fig. 
1.14) 
 
● action of the drug is 
direct, not mediated 
by some change in the 
general properties of 
the cell membrane. 
● Once 
the 
local 
anesthetic has gained 
access 
to 
the 
receptors:  
1. permeability 
to 
sodium 
ions 
is 
decreased 
or 
eliminated. 
2. nerve conduction is 
interrupted. 
  (than the membrane expansion 
theory)  
 
Both biochemical and electrophysiologic 
studies have indicated that a specific 
receptor site for local anesthetics exists in 
the sodium channel either on its external 
surface or on the internal axoplasmic 
surface 
 
 
 
According to the specific receptors theory:  
Local anesthetics can alter nerve conduction in at least four sites within the sodium channel 
(see Fig. 1.14): 
1. Withi

            Quiz: