Pathway 13-6-1 The Trigeminal System - Innervation
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Questions and Answers

Which CLASSIC neurotransmitter is primarily found in sympathetic neuron terminals within the tooth pulp? 當然也有 其他的 pro-inflammatory neuropeptide. CGRP 等等。

  • Serotonin
  • Dopamine
  • Acetylcholine
  • Norepinephrine and peptide Y (NPY) (correct)

    • Where does the sympathetic innervation of teeth primarily originate?

  • Superior cervical ganglion (correct)
  • Parasympathetic nuclei
  • Brainstem
  • Cervical spinal nerves

    • ⭐️What effect does stimulation of sympathetic fibers in the tooth pulp have on arterioles?

  • Dilation of arterioles and increased blood flow
  • No effect on arterioles
  • Inflammation of surrounding tissues
  • Constriction of arterioles and decreased blood flow (correct)

    • Which division of the trigeminal nerve supplies the teeth?

    <p>Both maxillary and mandibular divisions</p> Signup and view all the answers

    What is the primary function of NEUROGENIC MODULATION provided by efferent neurons?

    <p>Regulate inflammatory reactions</p> Signup and view all the answers

    What is the effect of noxious stimuli on intradental nerves?

    <p>They initiate a cascade of pain signals.</p> Signup and view all the answers

    ⭐️Which neuropeptide is mentioned as being present in sympathetic neuron terminals in the tooth?

    <p>Neuropeptide Y</p> Signup and view all the answers

    What is the approximate number of unmyelinated （Cfiber） axons found in the early developing tooth?

    <p>1800</p> Signup and view all the answers

    How far can some intratubular fibers penetrate into dentinal tubules?

    <p>As far as 100 mm</p> Signup and view all the answers

    What is the primary function of the subodontoblastic nerve plexus?

    <p>To assist in the sensation of dentin</p> Signup and view all the answers

    What is the significance of the late appearance of A fibers in the pulp?

    <p>It indicates that A fibers may complicate the reliability of the electric pulp test.</p> Signup and view all the answers

    What was the mean number of myelinated axons found in FULLY DEVELOPED canine and incisor teeth?

    <p>360 （400）</p> Signup and view all the answers

    ⭐️What percentage of the axons were found to be unmyelinated in the study of coronal axons?

    <p>80%</p> Signup and view all the answers

    How do the nerve bundles behave as they ascend through the radicular pulp?

    <p>They branch out and form a plexus in the coronal pulp.</p> Signup and view all the answers

    What was the reported number of unmyelinated axons in canines and incisors?

    <p>1600 to 2200</p> Signup and view all the answers

    What role do Schwann cells play in the context of the axons within the apical pulp?

    <p>They enclose the axons singly and in groups.</p> Signup and view all the answers

    Why might multiple branching of axons not reflect the true number of neurons supporting a single tooth?

    <p>Multiple axons can originate from a single neuron.</p> Signup and view all the answers

    In studying the structure of the apical pulp of a canine tooth, what was observed regarding myelinated and unmyelinated axons?

    <p>There were both myelinated and unmyelinated axons present.</p> Signup and view all the answers

    What structures form a dense network beneath the odontoblasts in the coronal pulp?

    <p>Plexus of Raschkow</p> Signup and view all the answers

    How does the nerve branching in the radicular pulp compare to that in the coronal pulp?

    <p>It is sparse in comparison.</p> Signup and view all the answers

    What is the primary characteristic of unmyelinated nerve fibers in the context provided?

    <p>They exhibit slow propagation of action potentials.</p> Signup and view all the answers

    What type of denticles are observed near the dentin in the apical area?

    <p>Free denticles</p> Signup and view all the answers

    In the histological context, what do microvesicles and mitochondria inside the nerve indicate?

    <p>High nerve activity and energy requirement</p> Signup and view all the answers

    Which of the following statements about nerve fibers in the pulp is most accurate?

    <p>Nerve fibers can be both unmyelinated and myelinated.</p> Signup and view all the answers

    ⭐️Which statement correctly describes the relationship between odontoblasts and nerve fibers?

    <p>Nerve fibers twist around odontoblast processes but are not synaptically linked.</p> Signup and view all the answers

    What has been found regarding the membrane potential of odontoblasts?

    <p>It is extremely low, demonstrating poor response to stimuli.</p> Signup and view all the answers

    Which statement is true regarding the anatomical connection between odontoblasts and nerve fibers?

    <p>Classic anatomical structures indicating functional coupling are absent.</p> Signup and view all the answers

    What is known about the response of odontoblasts to electrical stimulation?

    <p>They do not respond to electrical stimulation.</p> Signup and view all the answers

    What is an anatomical feature of nerve fibers near odontoblasts?

    <p>They lie in a groove along the odontoblast process surface.</p> Signup and view all the answers

    What characteristic of odontoblasts is crucial to understanding their function in dentin sensitivity?

    <p>Their low membrane potential and lack of excitability.</p> Signup and view all the answers

    ⭐️What percentage of the A fibers in dental pulp are A-delta fibers?

    <p>90%</p> Signup and view all the answers

    Which types of fibers can act as nociceptors within the pulp?

    <p>Both A and C fibers</p> Signup and view all the answers

    Which of the following statements regarding sensory nerve fibers in the pulp is accurate?

    <p>A fibers include A-b and A-d fiber types</p> Signup and view all the answers

    What is the primary feature distinguishing myelinated A fibers from unmyelinated C fibers?

    <p>A fibers have a higher conduction velocity</p> Signup and view all the answers

    ⭐️What proportion of the A sensory nerve fibers in dental pulp are A-Beta?

    <p>Approximately 10%</p> Signup and view all the answers

    Where are intratubular nerve endings most numerous in dentin?

    <p>At the pulp horns</p> Signup and view all the answers

    What is the percentage of dentinal tubules in root dentin that contain intratubular fibers?

    <p>1%</p> Signup and view all the answers

    How does the number of intratubular fibers change in other parts of dentin compared to the pulp horns?

    <p>They decrease</p> Signup and view all the answers

    What is the significance of the density of intratubular nerve endings at the pulp horns?

    <p>They are primarily responsible for pain perception</p> Signup and view all the answers

    What percentage of tubules may contain intratubular fibers at the pulp horns?

    <p>40%</p> Signup and view all the answers

    Study Notes

    Trigeminal System

    • The trigeminal system is a complex network of nerves responsible for sensation in the face, including teeth.
    • The system includes afferent neurons which transmit sensory impulses, and efferent neurons which modulate the microcirculation, inflammation, and dentinogenesis.
    • The sympathetic innervation of teeth originates in the superior cervical ganglion (SCG).
    • Sympathetic nerve fibers travel alongside the internal carotid nerve, join the trigeminal nerve, and supply teeth and surrounding structures via the maxillary and mandibular divisions of the trigeminal nerve.
    • Sympathetic fibers develop along with blood vessels in the dental papilla and form plexuses around pulpal arterioles in adult teeth.
    • Stimulation of sympathetic fibers constricts arterioles, leading to reduced blood flow.

    Nerve Fibers and their Distribution

    • The majority of nerve fibers in teeth are unmyelinated (C fibers)
    • Unmyelinated fibers compose approximately 80% of the axons innervating teeth.
    • The relatively late appearance of A fibers in pulp may explain the inconsistency of the electric pulp test in young teeth, as A fibers are easily stimulated electrically.
    • Nerve bundles travel upwards through the radicular pulp alongside blood vessels.
    • In the coronal pulp, the nerve bundles branch into networks beneath the cell-rich zone.
    • In the dentin-pulp border zone, nerve fibers branch into different types of nerve endings.
    • Some fibers extend from the subodontoblastic plexus towards the odontoblast layer, but do not reach the predentin.
    • Other fibers extend into the predentin and travel within dentinal tubules, closely associated with odontoblast processes.
    • Intratubular fibers often penetrate only a few micrometers into the dentinal tubules, but some can reach up to 100μm.

    Odontoblasts and Dentin Sensitivity

    • The odontoblast may not be a classic receptor cell and does not demonstrate typical communication with adjacent nerve fibers.
    • No synaptic junctions have been identified between odontoblasts and nerve fibers.
    • Odontoblasts have low membrane potential and do not respond to electrical stimulation, suggesting they lack the properties of excitable cells.
    • The relationship between odontoblasts and nerve fibers in dentin sensitivity requires further research.

    Pulp Nerve Fibers

    • Pulp contains two types of sensory nerve fibers: myelinated (A fibers) and unmyelinated (C fibers)
    • A fibers include both A-b and A-d fibers
    • A-d fibers are the most common type of A fiber, representing about 90% of all A fibers in the pulp
    • Both A and C fibers can be nociceptors (pain receptors)

    Intratubular Nerve Endings

    • Intratubular nerve endings are most common in the pulp horns, where they can be found in up to 40% of dentinal tubules
    • The number of intratubular fibers decreases in other areas of the dentin
    • Root dentin contains only about 1% of dentinal tubules with fibers

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