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ABOP Orofacial Pain study materials
ABOP Orofacial Pain study resources

ABOP Orofacial Pain practice questions

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Question 1Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which cranial nerve provides general sensory innervation to the anterior two-thirds of the tongue?

  1. Facial nerve
  2. Mandibular division of the trigeminal nerve Correct answer.
  3. Hypoglossal nerve
  4. Glossopharyngeal nerve

Explanation

General sensation from the anterior two-thirds of the tongue travels with the lingual branch of the mandibular division of the trigeminal nerve. Taste from the same region is carried by the facial nerve, so sensory modalities must be distinguished.

Question 2Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A patient reports numbness confined to the lower lip and chin on one side after a dental procedure. Which nerve is most likely affected?

  1. Auriculotemporal nerve
  2. Mylohyoid nerve
  3. Long buccal nerve
  4. Inferior alveolar nerve Correct answer.

Explanation

The inferior alveolar nerve supplies the mandibular teeth and continues as the mental nerve, which innervates the lower lip and chin. Numbness in that distribution points to injury along its course.

Question 3Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which nerve carries taste from the posterior third of the tongue?

  1. Facial nerve
  2. Lingual nerve
  3. Vagus nerve
  4. Glossopharyngeal nerve Correct answer.

Explanation

Taste from the posterior third of the tongue is carried by the glossopharyngeal nerve. The facial nerve serves the anterior two-thirds, and the vagus serves the epiglottis region.

Question 4Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which muscle of mastication is primarily responsible for protrusion of the mandible?

  1. Temporalis
  2. Medial pterygoid
  3. Masseter
  4. Lateral pterygoid Correct answer.

Explanation

The lateral pterygoid, particularly its inferior head, protrudes the mandible and assists in opening. The masseter, temporalis, and medial pterygoid primarily elevate the mandible.

Question 5Anatomy, Physiology, and Pathophysiology of the Orofacial Region

The temporomandibular joint is best described by which structural feature?

  1. A hyaline cartilage cap with a single joint cavity
  2. A fibrocartilaginous articular disc dividing a synovial joint into two compartments Correct answer.
  3. A ball-and-socket joint with a continuous capsule
  4. A fibrous symphysis with no synovial lining

Explanation

The temporomandibular joint is a synovial joint in which a fibrocartilaginous disc separates the upper and lower compartments, permitting both rotation and translation. Its articular surfaces are covered by fibrocartilage rather than hyaline cartilage.

Question 6Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which type of nerve fiber is most responsible for transmitting sharp, well-localized pain?

  1. Preganglionic B fibers
  2. C fibers
  3. A-delta fibers Correct answer.
  4. A-beta fibers

Explanation

A-delta fibers are thinly myelinated and conduct quickly, producing sharp first pain. Unmyelinated C fibers conduct slowly and mediate dull, aching second pain.

Question 7Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which salivary gland is the largest and produces the majority of stimulated saliva?

  1. Submandibular gland
  2. Parotid gland Correct answer.
  3. Sublingual gland
  4. Minor palatal glands

Explanation

The parotid is the largest salivary gland and contributes most of the flow during stimulation. At rest, the submandibular gland contributes the largest resting volume.

Question 8Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which structure separates the upper and lower compartments of the temporomandibular joint?

  1. The articular disc Correct answer.
  2. The joint capsule
  3. The sphenomandibular ligament
  4. The stylomandibular ligament

Explanation

The fibrocartilaginous articular disc divides the joint into an upper compartment for translation and a lower compartment for rotation. The ligaments are extracapsular and do not divide the joint space.

Question 9Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A patient describes a dull, aching pain that is difficult to localize and persists after a noxious stimulus. Which fiber type is most associated with this quality?

  1. A-alpha motor fibers
  2. Preganglionic autonomic fibers
  3. C fibers Correct answer.
  4. A-beta fibers

Explanation

Unmyelinated C fibers conduct slowly and produce dull, aching, poorly localized pain that often outlasts the stimulus. This contrasts with the sharp, rapid signal of A-delta fibers.

Question 10Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which mechanism best explains referred pain in the orofacial region?

  1. Convergence of primary afferents onto shared second-order neurons Correct answer.
  2. Loss of myelin along peripheral axons
  3. Retrograde axonal transport of inflammatory mediators
  4. Increased parasympathetic outflow to the gland

Explanation

When multiple primary afferents converge on the same second-order neuron, the brain cannot distinguish the true source, so pain is referred to another region sharing that pathway. This convergence is central to referred orofacial pain patterns.

Question 11Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Central sensitization in the trigeminal system is best characterized by which change?

  1. Selective loss of A-beta fibers
  2. Increased excitability of second-order neurons with expanded receptive fields Correct answer.
  3. Reduced neurotransmitter release from primary afferents
  4. Decreased synaptic efficacy in the trigeminal nucleus

Explanation

Central sensitization involves heightened excitability of second-order neurons, recruitment of previously silent synapses, and enlargement of receptive fields, which can produce hyperalgesia and allodynia. It reflects enhanced, not reduced, synaptic efficacy.

Question 12Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which phenomenon describes pain evoked by a normally non-painful stimulus such as light touch?

  1. Dysesthesia
  2. Hyperalgesia
  3. Allodynia Correct answer.
  4. Paresthesia

Explanation

Allodynia is pain produced by a stimulus that does not normally provoke pain. Hyperalgesia, by contrast, is an exaggerated response to a stimulus that is already painful.

Question 13Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which primary afferent neurotransmitter is most associated with synaptic transmission from nociceptors in the trigeminal nucleus caudalis?

  1. Glutamate Correct answer.
  2. GABA
  3. Acetylcholine
  4. Dopamine

Explanation

Nociceptive primary afferents release glutamate, often with substance P and CGRP, onto second-order neurons in the trigeminal nucleus caudalis. Acetylcholine and dopamine serve other circuits, and GABA is inhibitory.

Question 14Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A patient experiences sharp shooting pain in the distribution of the maxillary division of the trigeminal nerve triggered by touching the cheek. This pattern is most consistent with involvement of which structure?

  1. Greater occipital nerve
  2. Facial nerve motor fibers
  3. Hypoglossal nerve
  4. Trigeminal ganglion with ectopic discharges in the maxillary division Correct answer.

Explanation

Paroxysmal electric-shock pain confined to a trigeminal division with a trigger zone reflects ectopic discharges within that division, classically near the trigeminal ganglion or root. The distribution follows the maxillary division rather than motor or occipital nerves.

Question 15Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which cranial nerve provides motor innervation to the muscles of facial expression?

  1. Trigeminal nerve
  2. Facial nerve Correct answer.
  3. Glossopharyngeal nerve
  4. Accessory nerve

Explanation

The facial nerve supplies the muscles of facial expression through its branches. The trigeminal motor root supplies the muscles of mastication, not the muscles of expression.

Question 16Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which structure is the principal blood supply to the maxillary teeth and the maxillary sinus mucosa?

  1. Lingual artery
  2. Facial artery
  3. Maxillary artery Correct answer.
  4. Superficial temporal artery

Explanation

Branches of the maxillary artery, including the posterior superior alveolar and infraorbital arteries, supply the maxillary teeth and sinus lining. The facial, lingual, and superficial temporal arteries serve other regions.

Question 17Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which receptor type primarily mediates the sensation of jaw position and mandibular movement (proprioception)?

  1. Merkel discs
  2. Ruffini endings in the periodontal ligament
  3. Free nerve endings
  4. Muscle spindles Correct answer.

Explanation

Muscle spindles in the jaw-closing muscles detect changes in muscle length and are the principal proprioceptors for jaw position. Periodontal mechanoreceptors also contribute but are not the primary spindle-based system.

Question 18Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which nucleus is the principal relay for nociceptive input from the orofacial region?

  1. Mesencephalic trigeminal nucleus
  2. Principal sensory trigeminal nucleus
  3. Trigeminal nucleus caudalis Correct answer.
  4. Trigeminal motor nucleus

Explanation

The nucleus caudalis, the most caudal part of the spinal trigeminal nucleus, receives most nociceptive and thermal input from the face and mouth and resembles the dorsal horn. The mesencephalic nucleus handles proprioception, and the principal nucleus handles discriminative touch.

Question 19Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A reduced resting salivary flow with a normal stimulated response most directly suggests dysfunction of which gland?

  1. Parotid gland
  2. Sublingual gland
  3. Von Ebner glands
  4. Submandibular gland Correct answer.

Explanation

The submandibular gland provides most resting salivary flow, so its dysfunction lowers resting output while stimulated flow (largely parotid) may remain normal. Parotid disease would more strongly reduce stimulated flow.

Question 20Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which change in the peripheral terminal of a nociceptor characterizes peripheral sensitization?

  1. Lowered threshold with increased responsiveness to stimuli Correct answer.
  2. Loss of the axon reflex
  3. Reduced expression of sodium channels
  4. Decreased release of inflammatory mediators

Explanation

Inflammatory mediators sensitize peripheral nociceptor terminals, lowering their threshold and increasing responsiveness so that normally innocuous stimuli may provoke pain. This involves enhanced ion channel activity rather than reduced excitability.

Question 21Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which feature distinguishes the blood-brain barrier properties of the trigeminal ganglion from those of the central nervous system?

  1. The trigeminal ganglion contains no neurons
  2. The trigeminal ganglion has no satellite cells
  3. The trigeminal ganglion lacks a complete blood-nerve barrier, permitting exposure to circulating agents Correct answer.
  4. The trigeminal ganglion is entirely myelinated

Explanation

The trigeminal ganglion has a relatively permeable vasculature and incomplete barrier, so circulating substances can influence its neurons and contribute to ectopic excitability. It is a sensory ganglion containing neuronal cell bodies with satellite cells.

Question 22Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which mechanism best accounts for neuropathic pain arising after injury to a peripheral trigeminal branch?

  1. Ectopic impulse generation from injured axons with altered ion channel expression Correct answer.
  2. Reduced central inhibition alone with normal peripheral nerves
  3. Local infection of the nerve sheath
  4. Simple loss of all sensory input from the affected area

Explanation

After nerve injury, axons can develop ectopic pacemaker activity through altered sodium channel distribution, producing spontaneous and evoked pain even without ongoing peripheral stimulation. Central changes may follow, but ectopic axonal activity is a key peripheral driver.

Question 23Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which structure transmits proprioceptive information from the periodontal ligament and jaw muscles to the mesencephalic trigeminal nucleus?

  1. Primary afferent fibers with cell bodies in the mesencephalic nucleus Correct answer.
  2. Preganglionic parasympathetic fibers
  3. Motor fibers of the facial nerve
  4. Postganglionic sympathetic fibers

Explanation

The mesencephalic trigeminal nucleus uniquely contains the cell bodies of primary proprioceptive afferents from the jaw muscles and periodontal ligament. These fibers project centrally to modulate jaw reflexes.

Question 24Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which relationship explains why pain from the lower molars can be perceived in the ear region?

  1. Cross-innervation of the ear by the hypoglossal nerve
  2. Direct anastomosis between the inferior alveolar and facial nerves
  3. Shared central terminations of mandibular and auriculotemporal afferents in the trigeminal nuclear complex Correct answer.
  4. Overlap of the vagus and glossopharyngeal nerves in the tongue

Explanation

Afferents from mandibular structures and from the auriculotemporal distribution converge on shared second-order neurons in the trigeminal nuclear complex, so input from one site can be mislocalized to the other. This is a central convergence mechanism, not a peripheral anastomosis.

Question 25Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which feature of the trigeminal system most contributes to the difficulty of localizing deep orofacial pain?

  1. Complete absence of nociceptive input from deep tissues
  2. Lack of any crossover of trigeminal fibers
  3. Extensive divergence of afferents within the spinal trigeminal nucleus Correct answer.
  4. Absence of descending modulation to the trigeminal system

Explanation

Trigeminal nociceptive afferents diverge widely onto second-order neurons, so deep inputs activate broad populations and are poorly localized. Descending modulation and crossing pathways do exist and can further complicate localization.

Question 26Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which sensory ganglion contains the cell bodies of primary afferent neurons that innervate the mandibular teeth and chin?

  1. Ciliary ganglion
  2. Superior vagal ganglion
  3. Geniculate ganglion
  4. Trigeminal ganglion Correct answer.

Explanation

Primary afferent cell bodies for the three divisions of the trigeminal nerve, including mandibular branches supplying the lower teeth and chin, reside in the trigeminal (semilunar) ganglion. The other listed ganglia belong to different cranial nerves or are parasympathetic relay stations.

Question 27Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Injury to which muscle of mastication would most directly impair elevation of the mandible?

  1. Lateral pterygoid
  2. Medial pterygoid Correct answer.
  3. Posterior belly of the digastric
  4. Platysma

Explanation

The medial pterygoid, together with the masseter and temporalis, is an elevator of the mandible. The lateral pterygoid and suprahyoid muscles act mainly in depression and protrusion.

Question 28Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A patient reports numbness of the lower lip and chin with preserved sensation of the upper lip after a mandibular surgical procedure. Which nerve branch is most likely injured?

  1. Auriculotemporal nerve
  2. Mental nerve Correct answer.
  3. Long buccal nerve
  4. Infraorbital nerve

Explanation

The mental nerve is the terminal branch of the inferior alveolar nerve and supplies sensation to the lower lip and chin skin. Sparing of the upper lip is consistent with an intact maxillary (infraorbital) distribution.

Question 29Anatomy, Physiology, and Pathophysiology of the Orofacial Region

Which feature of the temporomandibular joint disc best explains why it can sustain compressive loads during clenching?

  1. It is highly vascularized throughout
  2. It contains a synovial membrane lining
  3. It is heavily innervated by nociceptors
  4. It is composed of dense fibrocartilage with collagen bundles Correct answer.

Explanation

The articular disc is a dense fibrous connective tissue with fibrocartilaginous characteristics and organized collagen bundles, which resist compression and shear. It is largely avascular and aneural in its central region.

Question 30Anatomy, Physiology, and Pathophysiology of the Orofacial Region

A patient develops burning pain and allodynia over the cheek weeks after a seemingly minor blow to the face. Which pathophysiologic process best accounts for this presentation?

  1. Loss of periodontal mechanoreceptor input to the mesencephalic nucleus
  2. Ectopic firing from demyelinated afferents and central amplification Correct answer.
  3. Increased parasympathetic salivary secretion
  4. Acute mechanical compression of the trigeminal root by a tumor

Explanation

After peripheral nerve trauma, ectopic impulse generation from injured and demyelinated axons combined with central sensitization can produce burning pain and touch-evoked allodynia. This reflects a neuropathic rather than a simple compressive or secretory mechanism.

Question 31Neurobiology of Pain and Pain Mechanisms

Which primary afferent fiber type is most responsible for conveying sharp, well-localized first pain?

  1. A-delta fibers Correct answer.
  2. Preganglionic sympathetic fibers
  3. C fibers
  4. A-beta fibers

Explanation

First pain is fast and sharp because it travels on thinly myelinated A-delta fibers, which conduct rapidly and terminate in superficial laminae. Unmyelinated C fibers conduct slowly and produce dull, delayed second pain.

Question 32Neurobiology of Pain and Pain Mechanisms

Nociceptors are best described as sensory endings that respond to which type of stimulus?

  1. Potentially tissue-damaging or noxious stimuli Correct answer.
  2. Only mechanical pressure
  3. Light touch and vibration
  4. Joint position and muscle length

Explanation

Nociceptors are high-threshold endings that transduce stimuli intense enough to threaten tissue, including thermal, mechanical, and chemical modalities. They are not dedicated to innocuous sensation.

Question 33Neurobiology of Pain and Pain Mechanisms

In the spinal dorsal horn, which neurotransmitter is the principal fast excitatory transmitter released by primary nociceptive afferents?

  1. Acetylcholine
  2. GABA
  3. Glutamate Correct answer.
  4. Glycine

Explanation

Primary afferents, including nociceptors, release glutamate to produce fast excitatory postsynaptic potentials in dorsal horn neurons. Peptides such as substance P modulate transmission but are not the main fast transmitter.

Question 34Neurobiology of Pain and Pain Mechanisms

Which ascending pathway carries nociceptive information from the face to the contralateral thalamus?

  1. Trigeminothalamic tract Correct answer.
  2. Spinocerebellar tract
  3. Dorsal column-medial lemniscus pathway
  4. Spinothalamic tract

Explanation

Facial nociception travels via the trigeminal system; second-order neurons cross the midline and ascend in the trigeminothalamic tract to the thalamus. The spinothalamic tract serves the body, not the face.

Question 35Neurobiology of Pain and Pain Mechanisms

A patient's dull, poorly localized second pain after an injury is best explained by which feature of C fibers?

  1. Absence of central projections
  2. Heavy myelination and large diameter
  3. Low threshold for light touch
  4. Slow conduction velocity and wide receptive fields Correct answer.

Explanation

C fibers are unmyelinated, conduct slowly, and have broad receptive fields, so their input is perceived as delayed and poorly localized. This contrasts with the fast, precise A-delta first pain.

Question 36Neurobiology of Pain and Pain Mechanisms

Which receptor class is a ligand-gated ion channel that is activated by capsaicin and by noxious heat?

  1. NMDA receptor
  2. GABA-A receptor
  3. 5-HT3 receptor
  4. TRPV1 Correct answer.

Explanation

TRPV1 is a transient receptor potential channel expressed on nociceptors that opens in response to capsaicin, protons, and noxious heat. Its activation depolarizes the terminal and generates nociceptive signals.

Question 37Neurobiology of Pain and Pain Mechanisms

Peripheral sensitization of nociceptors after tissue injury is characterized by which change?

  1. Lowered activation threshold and increased spontaneous firing Correct answer.
  2. Reduced membrane excitability
  3. Complete loss of transduction channels
  4. Increased threshold and reduced firing

Explanation

Inflammatory mediators reduce nociceptor thresholds and increase responsiveness, producing spontaneous activity and hypersensitivity. This underlies primary hyperalgesia at the injury site.

Question 38Neurobiology of Pain and Pain Mechanisms

Wind-up of dorsal horn neurons during repeated C-fiber stimulation depends primarily on which mechanism?

  1. Reduced glutamate release
  2. NMDA receptor activation with progressive depolarization Correct answer.
  3. Opioid receptor upregulation
  4. GABA-A receptor blockade

Explanation

Repeated C-fiber input causes cumulative depolarization that relieves the magnesium block of NMDA receptors, producing frequency-dependent amplification of responses. This is wind-up, a form of short-term synaptic plasticity.

Question 39Neurobiology of Pain and Pain Mechanisms

Which phenomenon explains why a patient with myocardial ischemia feels pain in the left arm and jaw?

  1. Phantom pain
  2. Allodynia
  3. Referred pain from viscerosomatic convergence Correct answer.
  4. Hyperalgesia

Explanation

Visceral and somatic afferents converge on the same second-order neurons, so visceral nociceptive input is misattributed to the somatic territory. This convergence produces referred pain.

Question 40Neurobiology of Pain and Pain Mechanisms

Descending modulation of nociception from the periaqueductal gray is mediated in part by which mechanism?

  1. Increased sympathetic outflow to the skin
  2. Release of enkephalins onto dorsal horn neurons Correct answer.
  3. Direct activation of primary afferents
  4. Blockade of serotonin receptors in the thalamus

Explanation

Periaqueductal gray output engages the rostral ventromedial medulla, and descending pathways release endogenous opioids and serotonin that inhibit dorsal horn nociceptive neurons. This produces descending analgesia.

Question 41Neurobiology of Pain and Pain Mechanisms

According to the gate control theory, which input most effectively closes the gate for nociceptive transmission in the dorsal horn?

  1. Sympathetic efferent firing
  2. Silent nociceptor activation
  3. Large-diameter A-beta afferent activity Correct answer.
  4. Small-diameter C-fiber activity

Explanation

Gate control theory holds that large-diameter mechanoreceptive input activates inhibitory interneurons that suppress nociceptive transmission. This explains why rubbing a painful area can reduce pain.

Question 42Neurobiology of Pain and Pain Mechanisms

Which brain region is most consistently activated during the affective-emotional dimension of pain?

  1. Cerebellum
  2. Primary somatosensory cortex
  3. Anterior cingulate cortex Correct answer.
  4. Lateral geniculate nucleus

Explanation

The anterior cingulate cortex contributes to the unpleasantness and emotional salience of pain, while primary somatosensory cortex encodes location and intensity. This dissociation is supported by imaging and lesion studies.

Question 43Neurobiology of Pain and Pain Mechanisms

Allodynia is best defined as which of the following?

  1. Spontaneous pain without any stimulus
  2. An exaggerated response to a noxious stimulus
  3. Loss of pain sensation in a dermatome
  4. Pain evoked by a normally non-noxious stimulus Correct answer.

Explanation

Allodynia is pain produced by a stimulus that normally does not provoke pain, such as light touch. It differs from hyperalgesia, which is an increased response to a noxious stimulus.

Question 44Neurobiology of Pain and Pain Mechanisms

A patient reports burning pain in the tongue after a minor dental procedure, with pain triggered by light touch of the mucosa. Which mechanism best explains the touch-evoked pain?

  1. Muscle spindle hypersensitivity
  2. Peripheral nerve regeneration with ectopic firing only
  3. Central sensitization with A-beta input activating nociceptive circuits Correct answer.
  4. Reduced descending inhibition alone

Explanation

After nerve injury, central sensitization can allow low-threshold A-beta input to access nociceptive pathways, producing touch-evoked pain. This reflects altered central processing rather than simple ectopic firing.

Question 45Neurobiology of Pain and Pain Mechanisms

Which structure is the principal relay for nociceptive input from the orofacial region before it reaches the thalamus?

  1. Geniculate ganglion
  2. Spinal trigeminal nucleus Correct answer.
  3. Trigeminal ganglion
  4. Nodose ganglion

Explanation

Primary trigeminal afferents synapse in the spinal trigeminal nucleus, particularly its caudal part, which relays nociceptive and thermal information. Second-order neurons then cross and ascend to the thalamus.

Question 46Neurobiology of Pain and Pain Mechanisms

Which of the following best describes the role of substance P in nociceptive transmission?

  1. It is a myelin protein in A-delta fibers
  2. It is a peptide that modulates synaptic transmission and contributes to neurogenic inflammation Correct answer.
  3. It is an inhibitory transmitter that closes the dorsal horn gate
  4. It is an enzyme that degrades glutamate

Explanation

Substance P is released from nociceptive afferent terminals and enhances transmission while promoting plasma extravasation and mast cell activation. This contributes to neurogenic inflammation and sensitization.

Question 47Neurobiology of Pain and Pain Mechanisms

Neuropathic pain is distinguished from nociceptive pain primarily by which feature?

  1. It is always proportional to the extent of tissue injury
  2. It results from a lesion or disease of the somatosensory nervous system Correct answer.
  3. It arises from direct activation of intact nociceptors by tissue damage
  4. It resolves with removal of the noxious stimulus

Explanation

Neuropathic pain is defined by a lesion or disease affecting the somatosensory system, producing pain without ongoing tissue damage. Nociceptive pain, by contrast, is driven by activation of intact nociceptors.

Question 48Neurobiology of Pain and Pain Mechanisms

Which change in ion channel expression is commonly associated with hyperexcitability of injured sensory neurons?

  1. Increased chloride conductance
  2. Upregulation of sodium channels such as Nav1.7 and Nav1.8 Correct answer.
  3. Loss of potassium channel function exclusively
  4. Downregulation of all sodium channels

Explanation

Nerve injury alters sodium channel expression, often increasing Nav1.7 and Nav1.8 density at ectopic sites, which lowers firing threshold. This contributes to spontaneous and ectopic discharges.

Question 49Neurobiology of Pain and Pain Mechanisms

Which of the following is an example of a silent nociceptor becoming active after inflammation?

  1. A parasympathetic efferent to the salivary gland
  2. A mechanoreceptor responding to light brushing
  3. A high-threshold afferent that gains responsiveness after sensitization Correct answer.
  4. A proprioceptor signaling joint position

Explanation

Silent nociceptors are normally unresponsive to moderate stimuli but become responsive after inflammatory sensitization. Their recruitment increases nociceptive input and contributes to hyperalgesia.

Question 50Neurobiology of Pain and Pain Mechanisms

Which statement best describes the relationship between stimulus intensity and nociceptor firing?

  1. Firing rate is independent of stimulus intensity
  2. Firing rate decreases as intensity increases
  3. Firing rate increases with stimulus intensity up to a plateau Correct answer.
  4. Firing occurs only at a single fixed intensity

Explanation

Nociceptors encode intensity through graded increases in firing rate, which then plateaus at high intensities. This rate coding underlies the perceived intensity of pain.