Pain Mechanisms in Physiology
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Questions and Answers

According to the International Association for the Study of Pain (IASP), what is the definition of pain?

  • An unpleasant sensory and emotional experience associated with actual or potential tissue damage (correct)
  • A neural response triggered by physical injury and interpreted by the brain
  • A subjective response to external stimuli causing physical harm
  • A purely sensory experience related to tissue damage

    • Which of the following best describes 'nociception'?

  • The neural response to potentially tissue-damaging stimuli (correct)
  • The body’s reaction to remove the stimulus
  • The conscious perception of pain
  • The emotional response to pain

    • Which of the following is a characteristic of fast pain?

  • Associated with unmyelinated C fibers
  • Felt after 1 second or more and increases slowly
  • Felt within 0.1 second of stimulus and well localized (correct)
  • Poorly localized and long-lasting

    • Which of the following is FALSE regarding slow pain?

    <p>It is also known as acute pain (C)</p> Signup and view all the answers

    What type of nerve fibers are responsible for transmitting fast pain?

    <p>Thin myelinated A delta fibers (C)</p> Signup and view all the answers

    Where are pain receptors NOT typically found?

    <p>Brain tissue and lung parenchyma (D)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of pain?

    <p>Always objective (C)</p> Signup and view all the answers

    Which of the following is a synonym for “pricking pain”?

    <p>Sharp pain (D)</p> Signup and view all the answers

    Which of the following best describes the primary neurotransmitter released by Aδ fibers in the spinal cord for fast pain transmission?

    <p>Glutamate (C)</p> Signup and view all the answers

    Hyperalgesia, an increased sensitivity to pain, occurs due to which of the following?

    <p>Progressively greater excitation of pain fibers as a stimulus continues (C)</p> Signup and view all the answers

    What is the primary pathway for the transmission of fast, acute pain signals?

    <p>Neospinothalamic pathway (B)</p> Signup and view all the answers

    Besides bradykinin, which of these is also a major contributor to pain during tissue ischemia?

    <p>Large accumulation of lactic acid (C)</p> Signup and view all the answers

    Which of the following does not directly stimulate nociceptors, but instead increases their sensitivity?

    <p>Prostaglandins (D)</p> Signup and view all the answers

    The intensity of pain resulting from heat is most closely associated with which factor?

    <p>The rate of tissue damage (C)</p> Signup and view all the answers

    Which of the following describes the non-adapting nature of pain receptors?

    <p>They adapt very little, and sometimes not at all, upon continuous stimulation. (D)</p> Signup and view all the answers

    In the neospinothalamic pathway, where does the second-order neuron decussate to the opposite side of the spinal cord?

    <p>Anterior commissure (B)</p> Signup and view all the answers

    Which type of pain is triggered by mechanical and thermal stimuli?

    <p>Fast pain (D)</p> Signup and view all the answers

    Besides directly stimulating mechanosensitive pain receptors, muscle spasm can also indirectly cause pain through which mechanism?

    <p>Compressing blood vessels, leading to ischemia. (B)</p> Signup and view all the answers

    Which of the following best describes the path of the second-order neuron in the paleospinothalamic pathway?

    <p>It ascends through the lateral spinothalamic tracts. (A)</p> Signup and view all the answers

    What is the neurotransmitter involved in the first synapse of the paleospinothalamic pathway?

    <p>Substance P (A)</p> Signup and view all the answers

    In the context of referred pain, the convergence theory suggests that:

    <p>The number of peripheral pain fibers exceeds the number of lateral spinothalamic tract neurons. (A)</p> Signup and view all the answers

    If a patient reports pain in their left arm and chest, which of the following sources is most likely?

    <p>Cardiac tissue (D)</p> Signup and view all the answers

    Where does the first-order neuron of the paleospinothalamic pathway synapse in the spinal cord?

    <p>Substantia gelatinosa (C)</p> Signup and view all the answers

    Which area receives the majority of pain signals that do not reach the thalamus in the paleospinothalamic pathway?

    <p>Reticular nuclei, tectal area &amp; periaqueductal gray region (B)</p> Signup and view all the answers

    Pain from the diaphragm is commonly referred to which area?

    <p>The shoulder (B)</p> Signup and view all the answers

    Which of these is true about fast pain?

    <p>It can be localized very precisely (C)</p> Signup and view all the answers

    Which of the following is NOT a primary component of the pain suppression system?

    <p>Cerebral cortex (C)</p> Signup and view all the answers

    Which neurotransmitter is responsible for causing both pre- and post-synaptic inhibition of incoming pain fibers?

    <p>Enkephalin (A)</p> Signup and view all the answers

    Endorphins are primarily produced in which locations?

    <p>Hypothalamus and Pituitary (C)</p> Signup and view all the answers

    What is the primary action of exogenous opioid peptides at the presynaptic membrane?

    <p>Inhibit the release of pain neurotransmitters (B)</p> Signup and view all the answers

    How do exogenous opioid peptides cause hyperpolarization of the membrane?

    <p>By opening $K^{+}$ channels (D)</p> Signup and view all the answers

    Which of the following actions is NOT a direct effect of exogenous opioid peptides?

    <p>Stimulating release of substance P (C)</p> Signup and view all the answers

    What is the main principle behind the gate control theory of pain modulation?

    <p>Non-painful input can reduce the perception of painful input (B)</p> Signup and view all the answers

    According to the content, what is the role of Serotonin in the pain modulation pathway?

    <p>It is released from dorsal horn and causes release of enkephalin (D)</p> Signup and view all the answers

    Which nerve carries sensory input from the face and mouth to the brainstem?

    <p>Trigeminal nerve (CN V) (B)</p> Signup and view all the answers

    Where are the first-order neurons of the orthodontic pain pathway located?

    <p>Trigeminal ganglia (B)</p> Signup and view all the answers

    Which area receives the third-order neuron impulses to converge and integrate orthodontic pain?

    <p>Somatosensory cortex (C)</p> Signup and view all the answers

    Which of the following best describes dental pain of pulpal origin?

    <p>Visceral in character, non-localized, and threshold-type (D)</p> Signup and view all the answers

    Which of the following is a characteristic of dental pain of periodontal ligament (PDL) origin?

    <p>Characterized by discomfort during biting and under occlusal pressure (D)</p> Signup and view all the answers

    What type of pain is described as deep somatic and musculoskeletal in nature?

    <p>PDL pain (C)</p> Signup and view all the answers

    What is the primary difference in how somatic inputs enter the spinal cord from the face and oral structures compared to other parts of the body?

    <p>They travel via cranial nerves, specifically the trigeminal nerve. (B)</p> Signup and view all the answers

    What is the location of second-order neurons within the orthodontic pain pathway?

    <p>Trigeminal nucleus caudalis (D)</p> Signup and view all the answers

    According to the gate control theory, what is the role of the substantia gelatinosa (SG) in the dorsal horn?

    <p>It acts as a gate, selectively allowing or blocking the passage of different types of impulses. (C)</p> Signup and view all the answers

    What is the effect of stimulating Aβ neurons on the substantia gelatinosa (SG)?

    <p>It activates the SG, closing the gate to Aδ and C neurons. (A)</p> Signup and view all the answers

    Which nerve fibers, upon stimulation, block the SG and therefore open the gate for pain transmission?

    <p>Aδ and C fibers only (D)</p> Signup and view all the answers

    According to the gate control theory, which of the following is NOT a method of pain relief?

    <p>Applying heat to a painful area. (A)</p> Signup and view all the answers

    Which type of sensory fibers are responsible for sending collaterals to the cells of SG in the dorsal gray horn?

    <p>Touch fibers (Aβ) (B)</p> Signup and view all the answers

    What is the mechanism by which impulses from touch fibers suppress pain sensation in the substantia gelatinosa?

    <p>They inhibit the release of Substance P by pain nerve endings. (C)</p> Signup and view all the answers

    Which of the following best describes phantom pain?

    <p>Pain felt in the absence of any external stimuli. (D)</p> Signup and view all the answers

    How does damage to a peripheral nerve cause neuropathic pain according to the text?

    <p>It leads to continuous pain because of repeated activation due to adrenaline release triggering sympathetic discharge. (D)</p> Signup and view all the answers

    Study Notes

    Pathway Theory and Pain

    • Pathway theory and pain are interconnected
    • Understanding pain involves understanding the pathway it takes through the body
    • Key elements of pain include nociceptors, spinal ganglia, and the lateral spinothalamic tract.

    Pain Perception and Types

    • Nociceptors are pain receptors (receptors)

    • Pain is a protective mechanism

    • Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage

    • Two main types of pain: fast pain and slow pain.

    • Fast pain is sharp and acute, while slow pain is lingering or throbbing.

    • Fast pain is located precisely and felt quickly. Slow pain is poorly localized.

    • Fast pain is elicited by mechanical and thermal stimuli

    • Slow pain results from a combination of mechanical, thermal, and chemical stimuli

    Nerve Fiber Classification

    • Nerve fibers are categorized by size (diameter) and myelination (presence of a fatty sheath).
    • Larger myelinated fibers transmit signals faster than smaller, unmyelinated ones
    • Different nerve fibers carry different types of sensory information

    Pain Receptors and Their Stimulation

    • Pain receptors are free nerve endings
    • They're widespread across the body, except in the brain, and in internal tissues like arteries
    • Stimuli can include mechanical, thermal, or chemical types.
    • Chemicals can include bradykinin, serotonin, K+ ions, histamine, H+, lactic acids, ACH, proteolytic enzymes, leukotrienes, cytokines, and capsaicin
    • Prostaglandins and substance P sensitize nociceptors.

    Pain Receptors and Their Stimulation - Continued

    • Pain receptors adapt to stimuli, becoming less sensitive or more sensitive over time if the stimuli continues
    • Pain resulting from heat above 45 degrees Celsius is closely related to the rate of tissue damage, not the overall amount of damage
    • Intensity of pain corresponds to the rate of tissue damage from varied causes (such as bacterial infection or ischemia).

    Neurotransmitters of Pain

    • Neurotransmitters are chemicals that transmit signals between nerve cells.
    • Neurotransmitters involved in pain include histamine, substance P, ATP, H+, 5-HT, 4-HNE, bradykinin, and prostaglandins.
    • They activate and sensitize nociceptors when they are released
    • These molecules work in a complex system to create pain perception.

    Causes of Pain

    • Tissue damage is a leading cause of pain, and the intensity of the pain often correlates with the extent of tissue damage
    • Tissue ischemia (reduced blood flow) also causes pain, often intense and with the degree of pain increasing in direct correlation to the metabolism rate
    • Muscle spasms can trigger pain both directly, by stimulating mechanosensitive receptors, and indirectly, by compressing blood vessels and increasing ischemia

    Dual Pain Pathways: Neospinothalamic

    • The neospinothalamic pathway is for fast pain transmission.
    • It involves first-order neuron termination in lamina I of the dorsal horn, then excites second order neurons of the neospinothalamic tract.
    • Glutamate is the principle neurotransmitter.
    • The pathway crosses to the opposite side of the spinal cord and ascends through the anterolateral columns,
    • Ultimately leading to the thalamus where the pain is further processed.

    Dual Pain Pathways: Paleospinothalamic

    • The paleospinothalamic pathway is for slow pain transmission.
    • First order neurons, or C fibres, synapse in the substantia gelatinosa, or laminae II and III in the dorsal horn
    • Neurotransmitters are primarily substance P.
    • The impulse decussates and travels through the spinothalamic tracts to eventually reach various locations in the brain.

    Referred Pain

    • Referred pain arises from an internal organ but is perceived in a different body region.
    • It occurs because nerve pathways from the organ and the referred site overlap at the spinal cord level
    • There are many diverse examples of referred pain that can occur.

    Referred Pain - Theories

    • Convergence theory describes overlapping pain pathways at the spinal cord level.
    • Visceral and somatic pain input can thus trigger the perception of pain in the skin.
    • Another perspective is the facilitator theory, which suggests that visceral pain signals can activate somatic pain pathways, potentially causing pain in the skin

    Pain Perception - Aware of Pain

    • Pain perception occurs in multiple locations and stages in the brain.
    • The thalamus is critical for pain perception as it directs the sensory information.
    • The cortex, reticular formation, limbic areas, and the hypothalamus have implications in pain perception. The stimuli are interpreted as pain

    Process of Pain Physiology

    • Transduction turns noxious stimuli into electrical energy
    • Transmission of this electrical energy occurs through peripheral nerve fibers (nociceptors). These receptors then carry the impulse.
    • Perception of pain occurs when this impulse reaches the brain's cortex, triggering a response
    • Modulation occurs as the CNS regulates pain signals through inhibition.

    Pain Modulation/ Pain Modification

    • Pain modulation refers to the variable nature of pain perception.
    • Pain modulation depends on both endogenous and exogenous factors which can modify pain perception or increase/decrease pain thresholds
    • The nervous system plays a crucial role in regulating pain

    Pain Modulation (Pain Suppression)

    • Pain suppression involves the analgesia system which blocks pain signals through different parts of the brain and spinal cord
    • Included in this process are the periaqueductal gray and the periventricular areas, as well as the nuclei of the medulla oblongata
    • Pain signal suppression happens as enkephalin, serotonin, and other substances suppress incoming pain fibers in particular parts of the nervous system

    Opioid Actions

    • Opioids (including endogenous and exogenous types) affect pain perception by various mechanisms
    • They block calcium channels and reduce calcium influx, essentially shutting down pain neurotransmitter release
    • They open potassium channels triggering efflux and hyperpolarization which reduces pain neurotransmitter activity
    • Activation of descending pain pathways and inhibition of GABA pathways are also effects that opioids have

    Pain Modulation (Gate Control Theory)

    • Gate control theory suggests that non-painful stimuli can close the "gates" to pain signals in the spinal cord by activating certain nerve fibers.
    • This modulation of pain signals occurs in the substantia gelatinosa of the spinal cord.
    • Different types of stimuli can stimulate various parts of the nervous system, potentially alleviating pain.

    Varieties of Pain

    • Phantom pain is felt in a missing limb (or other removed body part), with no stimulus to trigger the sensation.
    • Psychogenic pain stems from emotional factors, unlike physical pain.
    • Neuropathic pain originates from damage to the nervous system, as opposed to musculoskeletal harm, with repetitive stimulation as a potential cause

    Pain in Dentistry

    • Dental pain can be categorized into fast (and acute) pain and slow (and more chronic) pain
    • Fast pain is caused by stimuli like temperature changes, drilling, and air; slow pain is associated with inflammation and tissue damage
    • Different types of pain in the mouth have corresponding pathways and stimuli triggers, which differ based on the origin of the pain.

    Dental Pain of Pulpal Origin

    • Pain of pulpal origin is of a visceral type and generally less precisely localized.
    • It does not persist indefinitely, but can become chronic
    • Pain often stems from the pulp tissue of a tooth

    Dental Pain of PDL Origin

    • Pain originating from the periodontal ligament (PDL) is distinct in being more localized and closely linked to musculoskeletal function.
    • It's often triggered by occlusal pressure or biting and felt as soreness or elongation.

    Orofacial Pain Pathway

    • Orofacial pain pathways stem from the trigeminal nerve (CN V), not the spinal nerves.
    • The pathway from the face/oral structures relays signals to the brain.
    • Orofacial pain has a distinct pathway from other types of pain.

    Orthodontic Pain Pathway

    • The pathway for orthodontic pain is similar but begins with trigeminal neurons in the trigeminal ganglia. Nociceptors send signals via the trigeminal nucleus caudalis in the medulla oblongata up to the thalamus and eventually to the cortex, where it is interpreted.

    Dental Pain of Pulpal Origin

    • Visceral in character
    • Low threshold pain type
    • Responds to different stimuli for pain
    • Non-localized pain
    • Often not persistent, can become chronic

    Dental Pain of PDL Origin

    • Deep somatic pain with a musculoskeletal link
    • More localized than pulpal pain
    • Linked to mechanical functions (mastication)
    • PDL receptors are sensitive to precise localization via occlusal pressure.

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    Description

    This quiz explores essential concepts related to the understanding of pain, including definitions, types, and mechanisms involved in pain transmission. It covers topics like nociception, fast and slow pain characteristics, and relevant neurotransmitters. Ideal for students studying pain physiology or related fields.

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