Chapter 03 - Neuroanatomy & Neurophysiology of Pain Control

Question 1

Name the 4 structural areas of neurons

Answer 1

1. dentritic zone
2. axon
3. cell body
4. terminal arborization

Question 2

What is the composition and function of the neurolemma?

Answer 2

neurolemmas (aka nerve membranes) = bi-layered phospholipid membranes.
The are composed of phospholipids having both lipophilic and hydrophilic ends. The membranes are held together by the attraction of the lipophilic ends at their centers.
Their function is to act as a barrier.

Question 3

Function of Schwann cells

Answer 3

Schwann cells = specialized connective tissue cells
-> produce myelin
-> surround & protect peripheral nerves
-> insulate & protect the nerve membranes from environment
axons & their Schwann cells = “nerve fibers”

Question 4

Nodes of Ranvier: Significance in administration of LA

Answer 4

LA cannot diffuse through myelinated nerves except in areas where they come into direct contact with the membrane at the nodes of Ranvier

Question 5

Define saltatory conduction

Answer 5

Process by which impulses are more rapidly conducted along myelinated nerves

Question 6

Which 2 layers within the fasciculi are the most significant barriers to the diffusion of anesthetic solution?

Answer 6

Perilemma & perineurium (perilemma poses the greatest obsticale to diffusion)

Question 7

Resting potential of axoplasm

Answer 7

approx. -70mV

Question 8

Which ions bind to specific protein receptor sites within the ion channels of the nerve membrane in its resting state?

Answer 8

During resting state, Ca+2 ions bind to specific protein receptor sites in the nerve membrane ion channels, thereby closing or gating the channels

Question 9

What occurs to create a firing threshold and impulse generation?

Answer 9

Nerve is stimulated -> ion channels release the gate keeper Ca+2 ions -> channels become wide enough to allow positively charged, hydrated Na+ ions to begin entering into the more negatively charged axoplasm to reduce potential by ~ 15-20 mV -> more Na+ ions flood into axoplasm -> when threshold potential of -50 to -55 mV is reached an impulse is generated (“Slow Depolarization” until Firing Threshold is reached)

Question 10

Compare the conduction speeds of Aδ and C nerve fibers.

Answer 10

Aδ nerve fibers: more rapid conduction on sharper pain
C nerve fibers: more slowly conduction on duller, aching pain
Dental pulp has both types (more C than A)

Question 11

Define refractory and absolute refractory state

Answer 11

REFRACTORY STATE - inability to re-stimulate a section of membrane after impulse generation and conduction.
RELATIVE REFRACTORY STATE - stimulation may be successful during repolarization when resting state is partially attained, when a larger stimulus is required to fire.
ABSOLUTE REFRACTORY STATE - previously fired membrane section cannot be stimulated no matter how great the stimulus

Question 12

How does repolarization occur?

Answer 12

• During rapid depolarization, axoplasm potential reached +40 mV
• Na+ ion influx is prevented & Na+ ions start returning to extracellular environment via ion channels
• Na+ ion movement out of axoplasm enhanced by Na+-pumps
  = reversal of the ion concentration in the recovery phase is called repolarization

Question 13

How long does the process of DEPOLARIZATION to REPOLARIZATION take

Answer 13

One millisecond

Question 14

Define IMPULSE EXTINCTION related to the use of LA drugs

Answer 14

• Na+ ion influx through nerve membrane is blocked & sodium-dependent depolarization is prevented
• Both, generation & conduction of nerve impulses, are inhibited
• Impulse extinction result in decreased responsiveness to stimuli and failure to transmit an impulse toward the CNS

Question 15

Which structures do CORE and MANTLE BUNDLES innervate?

Answer 15

MANTLE BUNDLES house nerve fibers innervating structures in close proximity
CORE BUNDLES house nerve fibers that innervate distant structures
E.g., IA nerve: Mantle layer fibers –> molars; Core layer fibers –> anterior mandible incl. chin & lips

Question 16

Explain why the CORE BUNDLES innervating ANTERIOR MANDIBLE can be difficult to anesthetize

Answer 16

Because the LA soln. reaches them only after penetrating through mantle layer. That takes longer and dilutes the LA b/c drug molecules bind to receptors in the mantle bundle leaving fewer molecules to bind to receptors in the core fibers.

Question 17

Define local anesthesia

Answer 17

Temporary loss of sensation in a specific, usually small area of the body.
Primary distinction to general anesthesia: Pt remains conscious

Question 18

Explain how LA works

Answer 18

LA drugs all work similarly.
LA molecules have a greater affinity for protein receptor sites within nerve membranes compared to Ca+2 ions, subsequently displacing them.
Different LA drugs have varying affinity for receptor sites => clinically significant differences in drug action

Question 19

Are both SENSORY & MOTOR nerves anesthetized by LA?

Answer 19

Yes, but they typically anesthetize smaller before larger and sensory before motor nerves

Question 20

Although desired effects of LA drugs are local, what other parts of the body are affected by LA drugs?

Answer 20

Systemic absorption exposes other tissues to their potentially toxic actions, incl.: CNS, CVS, and skeletal muscle

Question 21

1: Which of the following statements most accurately describe(s) the major differences between sensory and motor neurons?
1. Sensory neurons are afferent and conduct impulses toward the CNS.
2. Motor neurons are efferent and conduct impulses to effector tissues and organs.
3. Sensory neuronal cell bodies do not participate in impulse conduction and they are located away from the axon.
4. Motor neuronal cell bodies participate in impulse conduction and are located along the length of the neuron at their terminal arborizations.
a. 3 only
b. 1 and 2
c. 1, 3, and 4
d. all of the above

Answer 21

D. all of the above

Question 22

2. Which of the following sequences best describes the events in a successful impulse generation?
   a. Stimulation, slow depolarization, firing threshold, rapid depolarization, recovery
   b. Stimulation, firing threshold, rapid depolarization, slow depolarization, resting state
   c. Resting state, stimulation, slow depolarization, rapid depolarization, firing threshold
   d. Resting state, stimulation, slow depolarization, rapid depolarization, slow depolarization

Answer 22

A - Stimulation slowly depolarizes. In a successful impulse generation, the firing threshold is reached and rapid depolarization occurs followed by recovery to the resting state.

Question 23

3. How are Schwann cells and nodes of Ranvier related?
   a. Schwann cells are nodes of Ranvier.
   b. At the nodes of Ranvier, Schwann cells are on layer thick.
   c. Gaps between Schwann cells are called nodes of Ranvier.
   d. They are not related.

Answer 23

C - Gaps between cells on the nerve membranes are called nodes of Ranvier.

Question 24

4. Which fiber types are responsible for providing sensory information from dental and periodontal tissues?
   a. C and B fibers
   b. B and A delta fibers
   c. Gamma and C fibers
   d. A delta and C fibers.

Answer 24

A-delta and C fibers are responsible for providing sensory information from dental and periodontal tissues.

Question 25

5. Which of the fibers providing sensory info from dental and periodontal tissues are myelinated?
   a. Both A delta and C fibers.
   b. Both B and C fibers
   c. A fibers
   d. None of the above

Answer 25

C - “A delta” fibers are lightly myelinated; “C” fibers are nonmyelinated

Question 26

6. What are the 3 divisions of the dental plexus?
   a. Interdental, interradicular, and periodontal
   b. Inner dental, interradicular, and dental
   c. Interdental, interradicular, and dental
   d. Inner dental, interradicular, and periodontal

Answer 26

C - Interdental, interradicular, and dental

Question 27

Peripheral Nerve Anatomy deep to superficial

Answer 27

• individual nerve fibers separated from each other by ENDONEURIUM (insulates electrical activity of individual nerve fiber)
• bundled by PERINEURIUM into FASCICULI; inner layer of perioneurium is called PERILEMMA
• EPINEURIUM surrounds all fasciculi and their assoc. supporting structures (blood vessels, lymphatics, and perineuria
• epineurium has its own sheath on its superficial circumference that surrounds the entire nerve = EPINEURAL SHEATH