Chapter 03 - Neuroanatomy & Neurophysiology of Pain Control Flashcards
Name the 4 structural areas of neurons
- dentritic zone
- axon
- cell body
- terminal arborization
What is the composition and function of the neurolemma?
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.
Function of Schwann cells
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”
Nodes of Ranvier: Significance in administration of LA
LA cannot diffuse through myelinated nerves except in areas where they come into direct contact with the membrane at the nodes of Ranvier
Define saltatory conduction
Process by which impulses are more rapidly conducted along myelinated nerves
Which 2 layers within the fasciculi are the most significant barriers to the diffusion of anesthetic solution?
Perilemma & perineurium (perilemma poses the greatest obsticale to diffusion)
Resting potential of axoplasm
approx. -70mV
Which ions bind to specific protein receptor sites within the ion channels of the nerve membrane in its resting state?
During resting state, Ca+2 ions bind to specific protein receptor sites in the nerve membrane ion channels, thereby closing or gating the channels
What occurs to create a firing threshold and impulse generation?
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)
Compare the conduction speeds of Aδ and C nerve fibers.
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)
Define refractory and absolute refractory state
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
How does repolarization occur?
- 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
How long does the process of DEPOLARIZATION to REPOLARIZATION take
One millisecond
Define IMPULSE EXTINCTION related to the use of LA drugs
- 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
Which structures do CORE and MANTLE BUNDLES innervate?
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
Explain why the CORE BUNDLES innervating ANTERIOR MANDIBLE can be difficult to anesthetize
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.
Define local anesthesia
Temporary loss of sensation in a specific, usually small area of the body.
Primary distinction to general anesthesia: Pt remains conscious
Explain how LA works
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
Are both SENSORY & MOTOR nerves anesthetized by LA?
Yes, but they typically anesthetize smaller before larger and sensory before motor nerves
Although desired effects of LA drugs are local, what other parts of the body are affected by LA drugs?
Systemic absorption exposes other tissues to their potentially toxic actions, incl.: CNS, CVS, and skeletal muscle
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
D. all of the above
- 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
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.
- 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.
C - Gaps between cells on the nerve membranes are called nodes of Ranvier.
- 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.
A-delta and C fibers are responsible for providing sensory information from dental and periodontal tissues.
- 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
C - “A delta” fibers are lightly myelinated; “C” fibers are nonmyelinated
- 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
C - Interdental, interradicular, and dental
Peripheral Nerve Anatomy deep to superficial
- 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
