p.11
Physiology of Peripheral Nerves
What is the primary function of a nerve?
To carry messages from one part of the body to another.
p.20
Mechanism of Action of Local Anesthetics
What does the specific receptor theory propose about the action of local anesthetics?
Local anesthetics act by binding to specific receptors on the sodium channel.
p.27
Mechanism of Action of Local Anesthetics
What are the two factors involved in the action of a local anesthetic on nerve membranes?
Diffusion of the drug through the nerve sheath and binding at the receptor site in the ion channel.
p.17
Electrophysiology of Nerve Conduction
What is the result of increased sodium ion permeability in the cell membrane?
More sodium ions enter the cell membrane, leading to depolarization.
p.7
Axon Structure and Function
What covers the nerve membrane in some nerves?
An insulating lipid-rich layer of myelin.
p.10
Classification of Nerve Fibers
What are the characteristics of A fibers?
A fibers are the largest nerve fibers, either motor or sensory, myelinated, and have the fastest conduction velocity.
p.18
Electrophysiology of Nerve Conduction
Which channels open to facilitate repolarization?
Voltage-gated potassium channels open to facilitate repolarization.
p.23
Factors Affecting Local Anesthetic Action
What is the relationship between lipid solubility and anesthetic potency?
Increased lipid solubility results in increased anesthetic potency.
p.8
Structure and Function of Neurons
How is the cell membrane described?
As a flexible, nonstretchable structure consisting of two layers of lipid molecules (bilipid layer of phospholipids) and associated proteins, lipids, and carbohydrates.
p.9
Classification of Nerve Fibers
What encloses myelinated nerve fibers?
Spirally wrapped layers of lipoprotein myelin sheaths, which are a specialized form of Schwann cells.
p.6
Types of Neurons: Sensory and Motor
What role does the cell body play in motor neurons?
It is an integral component of the impulse transmission system and provides metabolic support for the cell.
p.10
Classification of Nerve Fibers
What is the function of Alpha (α) fibers?
Alpha (α) fibers are the largest and fastest, responsible for muscle movement and light touch.
p.23
Factors Affecting Local Anesthetic Action
How does a lower pKa affect the onset of local anesthetic action?
A lower pKa results in a more rapid onset of action as more RN molecules are present to diffuse through the nerve sheath, decreasing the onset time.
p.19
Axon Structure and Function
How does impulse propagation occur in nonmyelinated axons?
The impulse moves forward by sequential depolarization of short adjoining membrane segments.
p.7
Axon Structure and Function
What is an axon?
A single nerve fiber that is a long cylinder of neural cytoplasm (axoplasm) encased in a thin sheath called the nerve membrane or axolemma.
p.22
Mechanism of Action of Local Anesthetics
What is the role of the terminal amine in local anesthetics?
It is the hydrophilic (acid) component that binds to the receptor sites on the nerve membrane.
p.5
Types of Neurons: Sensory and Motor
What type of neurons are capable of transmitting the sensation of pain?
Sensory neurons (afferent).
p.18
Electrophysiology of Nerve Conduction
How does repolarization contribute to the action potential cycle?
Repolarization restores the resting membrane potential, allowing the neuron to be ready for the next action potential.
p.10
Classification of Nerve Fibers
What sensations are Delta (δ) fibers responsible for?
Delta (δ) fibers are responsible for pain and temperature.
p.12
Electrophysiology of Nerve Conduction
What is the resting potential of a nerve?
A negative electrical potential of -70 mV.
p.24
Recovery from Local Anesthetic Block
What regions do mantle fibers innervate?
More proximal regions, such as the molar area with an inferior alveolar nerve block.
p.26
Factors Affecting Local Anesthetic Action
Why doesn't local anesthesia work effectively in an infection?
The acidic environment associated with infection causes a lower tissue pH, reducing the amount of free base (RN) available to penetrate the nerve.
p.3
Structure and Function of Neurons
What is the structural unit of the nervous system?
The neuron, or nerve cell.
p.17
Electrophysiology of Nerve Conduction
What occurs when the firing threshold of a nerve segment is reached?
Membrane permeability to sodium increases dramatically, and sodium ions rapidly enter the axoplasm.
p.22
Mechanism of Action of Local Anesthetics
What are the three principal components of local anesthetics?
Aromatic ring, intermediate chain, and terminal amine.
p.22
Mechanism of Action of Local Anesthetics
What does the intermediate chain in local anesthetics determine?
It determines whether the anesthetic is an ester or an amide.
p.21
Mechanism of Action of Local Anesthetics
What is the first step in the proposed mechanism of action of local anesthetics?
Displacement of calcium ions from the sodium channel receptor site.
p.25
Mechanism of Action of Local Anesthetics
What happens to the equilibrium of local anesthetics as hydrogen ion concentration decreases (higher pH)?
The equilibrium shifts toward the free base form (RNH+ < RN + H+).
p.8
Structure and Function of Neurons
What are the main components of the cell membrane?
Two layers of lipid molecules (bilipid layer of phospholipids) and associated proteins, lipids, and carbohydrates.
p.19
Axon Structure and Function
How does impulse propagation occur in myelinated axons?
The impulse leaps forward from node to node.
p.6
Types of Neurons: Sensory and Motor
What is the function of motor (efferent) nerve cells?
They conduct impulses from the CNS toward the periphery.
p.26
Factors Affecting Local Anesthetic Action
How does the acidic environment in an infection affect local anesthesia?
It lowers the tissue pH, reducing the amount of free base (RN) molecules that can penetrate the nerve.
p.10
Classification of Nerve Fibers
What do Gamma (γ) fibers detect?
Gamma (γ) fibers detect touch and pressure.
p.23
Factors Affecting Local Anesthetic Action
How does increased protein binding affect the duration of local anesthetic action?
Increased protein binding allows anesthetic cations (RNH+) to be more firmly attached to proteins at receptor sites, increasing the duration of action.
p.21
Mechanism of Action of Local Anesthetics
What happens when the rate of electrical depolarization is depressed?
There is a failure to achieve the threshold potential level.
p.11
Physiology of Peripheral Nerves
In what form are the messages carried by nerves?
In the form of electrical action potentials called impulses.
p.12
Electrophysiology of Nerve Conduction
What happens during the initial phase of nerve excitation?
There is a slow depolarization where the electrical potential within the nerve becomes slightly less negative.
p.27
Mechanism of Action of Local Anesthetics
What is the second factor involved in the action of a local anesthetic?
Binding at the receptor site in the ion channel.
p.7
Axon Structure and Function
What separates the axoplasm from extracellular fluids?
A continuous nerve membrane.
p.21
Mechanism of Action of Local Anesthetics
What is the result of the local anesthetic molecule binding to the receptor site?
Blockade of the sodium channel.
p.23
Factors Affecting Local Anesthetic Action
What does the pKa measure in the context of local anesthetics?
The pKa measures the affinity of a molecule for hydrogen ions (H+).
p.1
Definition of Local Anaesthesia
What is the definition of local anaesthesia?
Local anaesthesia is the loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or inhibition of the conduction process in peripheral nerves.
p.17
Electrophysiology of Nerve Conduction
What happens to the cell membrane's permeability during the excitation of a nerve segment?
It increases, allowing sodium ions (Na+) to enter the cell.
p.3
Types of Neurons: Sensory and Motor
What are the two basic types of neurons?
Sensory (afferent) and motor (efferent) neurons.
p.12
Electrophysiology of Nerve Conduction
What occurs during the rapid phase of depolarization in nerve conduction?
There is a reversal of the electrical potential across the nerve membrane.
p.7
Axon Structure and Function
What is the axoplasm?
A gelatinous substance within the axon.
p.7
Axon Structure and Function
What is the function of biological membranes in relation to water-soluble molecules?
To block the diffusion of water-soluble molecules and be selectively permeable to certain molecules via specialized pores or channels.
p.25
Mechanism of Action of Local Anesthetics
Which form of local anesthetic binds with the receptor site?
The positively charged cation (RNH+).
p.10
Classification of Nerve Fibers
What are the characteristics and primary function of C fibers?
C fibers are the most numerous and smallest, usually unmyelinated, and primarily responsible for dull, aching pain.
p.23
Factors Affecting Local Anesthetic Action
How does greater vasodilator activity affect anesthetic potency and duration?
Greater vasodilator activity results in increased blood flow to the region, leading to rapid removal of anesthetic molecules from the injection site, thus decreasing anesthetic potency and duration.
p.20
Mechanism of Action of Local Anesthetics
What happens once local anesthetics bind to specific receptors on the sodium channel?
Permeability to sodium ions is decreased or eliminated, and nerve conduction is interrupted.
p.11
Physiology of Peripheral Nerves
What are the types of stimuli that can initiate nerve impulses?
Chemical, thermal, mechanical, or electrical stimuli.
p.12
Electrophysiology of Nerve Conduction
What is the threshold potential or firing threshold in nerve conduction?
It is the critical level reached during the rapid phase of depolarization.
p.22
Mechanism of Action of Local Anesthetics
What is the function of the aromatic ring in local anesthetics?
It is the lipophilic (base) component that determines the anesthetic potency.
p.26
Factors Affecting Local Anesthetic Action
What role does edema and increased inflammation play in the effectiveness of local anesthesia during an infection?
Edema and increased inflammation can further hinder the penetration and effectiveness of local anesthetics.
p.5
Types of Neurons: Sensory and Motor
What are the three major portions of a sensory nerve (afferent)?
The peripheral process (free nerve endings), the axon, and the cell body.
p.5
Types of Neurons: Sensory and Motor
What is the primary function of the cell body in a sensory nerve?
To provide vital metabolic support for the entire neuron.
p.18
Electrophysiology of Nerve Conduction
What ions are primarily involved in repolarization?
Potassium ions (K+) are primarily involved in repolarization as they move out of the neuron.
p.15
Electrophysiology of Nerve Conduction
What happens to the electrical potential inside the nerve cell during repolarization?
It gradually becomes more negative relative to the outside.
p.25
Mechanism of Action of Local Anesthetics
What happens to the equilibrium of local anesthetics in a high concentration of hydrogen ions (low pH)?
The equilibrium shifts to the cation form (RNH+ > RN + H+).
p.21
Mechanism of Action of Local Anesthetics
What is the consequence of failing to achieve the threshold potential level?
Lack of development of propagated action potentials.
p.9
Classification of Nerve Fibers
What are the two types of nerve fibers?
Myelinated nerve fibers and unmyelinated nerve fibers.
p.27
Mechanism of Action of Local Anesthetics
What is the first factor involved in the action of a local anesthetic?
Diffusion of the drug through the nerve sheath.
p.24
Recovery from Local Anesthetic Block
What regions do core bundles innervate?
The more distal points of the nerve, such as the incisors and canines.
p.18
Electrophysiology of Nerve Conduction
What happens to the membrane potential during repolarization?
During repolarization, the membrane potential becomes more negative, returning to its resting state.
p.10
Classification of Nerve Fibers
What is the role of Beta (β) fibers?
Beta (β) fibers are responsible for proprioception (awareness of position/equilibrium).
p.10
Classification of Nerve Fibers
What are the characteristics of B fibers?
B fibers have medium diameters, are lightly myelinated motor fibers.
p.10
Classification of Nerve Fibers
Which types of nerve fibers are found abundantly in the oral cavity?
Both A and C fibers are found abundantly in the oral cavity, with C fibers in greater distribution.
p.3
Structure and Function of Neurons
What is the primary function of a neuron?
To transmit messages between the central nervous system (CNS) and all parts of the body.
p.19
Axon Structure and Function
What is the key difference in depolarization between nonmyelinated and myelinated axons?
In nonmyelinated axons, depolarization is sequential, while in myelinated axons, depolarization is discontinuous.
p.18
Electrophysiology of Nerve Conduction
What is repolarization?
Repolarization is the process by which the membrane potential of a neuron returns to its resting state after depolarization.
p.5
Types of Neurons: Sensory and Motor
Is the cell body of a sensory nerve involved in impulse transmission?
No, it is not involved in impulse transmission.
p.21
Mechanism of Action of Local Anesthetics
What effect does the blockade of the sodium channel have on sodium conductance?
It decreases sodium conductance.
p.6
Axon Structure and Function
What happens to the axon near its termination in motor neurons?
The axon branches, with each branch ending as a bulbous axon terminal (or bouton).
p.21
Mechanism of Action of Local Anesthetics
What happens after calcium ions are displaced from the sodium channel receptor site in the mechanism of local anesthetics?
The local anesthetic molecule binds to the receptor site.
p.21
Mechanism of Action of Local Anesthetics
How does a decrease in sodium conductance affect electrical depolarization?
It depresses the rate of electrical depolarization.
p.23
Factors Affecting Local Anesthetic Action
What effect does increased diffusibility have on the onset of local anesthetic action?
Increased diffusibility results in a decreased time of onset.
