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Questions and Answers
Which type of sensation is primarily associated with the dorsal column tract?
What type of pain is associated with the neospinothalamic pathway?
Which sensation is NOT a function of the lateral spinothalamic tract?
What type of sensation can be classified as visceral pain?
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Which type of pain is characterized as slow and aching?
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Which sensation is a feature of mechanoreceptive sensation?
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In which portion of the pain pathway does the second order neuron reside for the paleospinothalamic pathway?
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Which of the following sensations is NOT included in mechanoreceptive sensations?
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What is the primary purpose of pain as a sensation?
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Which type of pain receptor is stimulated by extreme temperatures?
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How do pain responses differ between acute and saver pain?
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What characterizes hyperalgesia as a response to pain?
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Which part of the nervous system is primarily involved in autonomic reactions to pain?
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What is considered the 'inflammatory soup' released during tissue damage?
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Which statement about pain receptors is true?
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What role does Substance P play in the process of pain sensation?
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Which channel is directly activated by nociceptive stimuli such as heat?
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What type of cells release mediators during tissue injury and inflammation?
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Which substance is NOT considered a mediator released during tissue injury?
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Peptidergic neurons contain which of the following peptides?
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What information is conveyed by the anterolateral system?
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Which cell body location is associated with nociceptive afferents?
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Which structure is specifically responsible for processing fine touch and proprioception?
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What role does the TRPV3 channel play in nociceptive signaling?
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Which type of pain is characterized by being felt within 0.1 sec after a stimulus and localized well?
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What type of pain is primarily induced by ischemia resulting from decreased blood supply to muscles?
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Which statement best describes visceral pain?
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Which pain type is typically described as diffuse and poorly localized?
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In which scenario is referred pain likely to be experienced?
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Which fiber type primarily transmits slow pain signals?
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Which character does NOT describe visceral pain?
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What describes the pain experienced during intermittent claudication?
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Study Notes
Definitions of Pain
- Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
- The International Association for the Study of Pain (IASP) definition (2020) encompasses individuals who are unable to articulate pain verbally.
Pain Receptors
- Pain receptors are free nerve endings that are slowly adapting.
Types of Pain Receptors
- Mechanical pain receptors: triggered by mechanical injuries.
- Thermal pain receptors: activated by extreme temperatures.
- Chemical pain receptors: stimulated by harmful chemicals.
- Polymodal: respond to all types of stimulation.
Pain Threshold & Response
- The pain threshold is similar across individuals, while the reaction to pain varies.
- Pain fibers project to various areas:
- Reticular formation: responsible for cortical arousal reactions..
- Limbic system: governs emotional reactions, anxiety, and restlessness.
- Anterior horn cells of the spinal cord: mediate motor responses, such as the flexion withdrawal reflex.
- Hypothalamus: governs autonomic reactions.
Pain Responses
- Acute pain: characterized by sympathetic stimulation resulting in increased heart rate, respiratory rate, and blood pressure, along with profuse sweating.
- Saver pain: characterized by parasympathetic activation, leading to hypotension, bradycardia, and gastrointestinal disturbances.
- Hyperalgesia: an exaggerated pain sensation from the skin, where non-painful stimuli become painful in the healthy skin surrounding the injured area.
Hyperalgesia vs. Sensitization
- Hyperalgesia: a subjective heightened pain response.
- Sensitization: an enhanced responsiveness of nerve fibers to stimuli.
Mechanism of Pain Stimulation
- Damaged tissues release chemical mediators, including histamine, bradykinin, potassium ions, and prostaglandins.
Tissue Damage
- Tissue damage creates an "inflammatory soup" involving the release of various substances, including:
- Substance P: increases capillary permeability and contributes to inflammation.
- Histamine: activates nociceptor endings.
Receptors on Nociceptive Terminals
- Direct activation: Nociceptive stimuli, such as heat, can directly activate receptors through transduction of the stimulus energy, like with the transient receptor potential (TRP) channel TRPV1.
- Indirect activation: Activation can occur indirectly through TRP channels on keratinocytes, such as TRPV3.
- Intermediate molecule activation: Nociceptors, like mechanoreceptors, can be activated by the release of molecules like ATP, ASIC (acid-sensitive ion channel), P2X (ionotropic purinoceptor), and P2Y (G-protein-coupled purinergic receptor).
Chemical Mediators in Tissue Injury and Inflammation
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Tissue injury and inflammation lead to the release of chemical mediators from various cells, including:
- Mast cells
- Macrophages
- Platelets
- Immune cells
- Endothelial cells
- Schwann cells
- Keratinocytes
- Fibroblasts
- Peripheral nociceptor terminals
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These mediators include:
- Protons (H+)
- Purines (adenosine, adenosine triphosphate)
- Nerve growth factor (NGF)
- Cytokines, such as tumor necrosis factor (TNF-α) and interleukins (IL-1β, IL-6)
- Leukemia inhibitory factor (LIF)
- Prostaglandin E2 (PGE2)
- Bradykinin
- Histamine
- Serotonin (5-HT)
- Platelet activating factor (PAF)
- Endothelin
Peptidergic Neurons
- Peptidergic neurons contain peptides like substance P (SP), calcitonin gene-related peptide (CGRP), and somatostatin (SST).
- Sensory neurons with cell bodies in the dorsal root ganglia (DRGs) are responsible for transmitting somatic and visceral pain signals.
- Slowly conducting Ad and C fibers, including nociceptors, have small cell bodies.
Somatosensory Pathways
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Dorsal Column System (A): relays fine touch, pressure, and proprioception information.
- Receptor: Sensory receptors located in skin, muscles, and joints.
- First-order neuron: neuron with cell body in dorsal root ganglion, sending axons to the spinal cord.
- Second-order neuron: neuron located in brainstem (nucleus gracilis for lower body, nucleus cuneatus for upper body), sending axons to the thalamus.
- Third-order neuron: neuron in thalamus sending axons to somatosensory cortex.
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Anterolateral System (B): transmits pain, temperature, and light touch information.
- Receptor: Sensory receptors located in skin, muscles, and joints
- First-order neuron: neuron with cell body in dorsal root ganglion, sending axons to the spinal cord.
- Second-order neuron: neuron located in spinal cord, sending axons to thalamus, which relays to the somatosensory cortex.
Ascending Sensory Tracts
- Ventral Spinothalamic Tract: carries information related to crude touch, crude pressure, and tickling/itching sensation.
- Lateral Spinothalamic Tract: transmits pain and temperature sensations.
- Dorsal Column: relays information about fine touch, tactile localization, tactile discrimination, stereognosis, texture, fine pressure, vibration sense, and proprioception.
Physiological Classification of Somatic Sensation
- Mechanoreceptive Sensation: includes tactile sensations (crude touch, tickling/itching, fine touch, pressure, vibration) and position senses (static, kinetic).
- Thermal Sensation: includes sensations of warm and cold.
- Pain Sensation: includes cutaneous (skin), deep (muscles, tendons, joints, ligaments), visceral (internal organs), and neuropathic pain.
Neospinothalamic vs Paleospinothalamic Pathways
| Neospinothalamic | Paleospinothalamic |
|---|---|
| Pathway for fast pain (conducted by Aδ fibers) | Pathway for slow pain (conducted by C fibers) |
| First Order Neuron: Located in dorsal root ganglia (DRG), axons enter the spinal cord via posterior root and terminate on posterior horn cells. | First Order Neuron: Located in dorsal root ganglia (DRG), axons enter the spinal cord via posterior root and terminate on posterior horn cells. |
| Second Order Neuron: Located in lamina marginals (I) of the dorsal horn. | Second Order Neuron: Located in substantia gelatinosa (SGR) lamina II, III. |
| Third Order Neuron: Axons cross to the opposite side of the spinal cord and ascend in the lateral spinothalamic tract to the brainstem, then project to the ventrobasal thalamic nuclei and finally reach the somatosensory cortex. | Third Order Neuron: *90% of fibers project to the reticular formation of the brainstem, activating the cortex to a lesser degree. 10% project to the ventrobasal thalamic nuclei and then to the somatosensory cortex. |
Types of Pain Sensation
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According to site of pain sensation:
- Cutaneous: Pain originating from the skin.
- Deep: Pain arising from muscles, tendons, joints, and ligaments.
- Visceral: Pain coming from internal organs.
- Neuropathic: Pain caused by damage to nerves.
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According to quality of pain sensation:
- Fast (sharp pain, pricking pain, acute pain, electric pain): A rapid and well-defined pain sensation.
- Slow (slow burning pain, aching pain, throbbing pain, nauseous pain, chronic pain): A prolonged, dull, and often diffuse pain sensation.
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According to type of pain sensation:
- Somatic pain (musculoskeletal): Originating from the skin, muscles, and soft tissues.
- Visceral: Originating from internal organs.
1- Fast and Slow Cutaneous Pain
| Fast Pain | Slow Pain |
|---|---|
| Felt within 0.1 seconds after pain stimulus | Felt after 1 second |
| Receptor: Mechanical and thermal | All types of pain receptors |
| Afferent: Aδ fibers (transmitting glutamate) | C fibers (transmitting substance P) |
| Short duration | Prolonged & increases with time |
| Pathway: Neospinothalamic tract | Paleospinothalamic tract |
| Well localized | Poorly localized |
| Occurs in skin, may occur in pleura, peritoneum & pericardium | Occurs in skin, deep tissues, and viscera |
2- Deep Pain
- Deep pain originates from injuries to muscles, tendons, joints, ligaments, and bones, transmitted via C fibers.
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Causes:
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Ischemic pain: Caused by reduced blood supply to muscles due to vessel wall narrowing, compression, or intravascular thrombosis.
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Examples:
- Cardiac muscle ischemia: Anginal pain.
- Skeletal muscle ischemia: Intermittent claudication (pain in the legs during exercise).
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Examples:
-
Ischemic pain: Caused by reduced blood supply to muscles due to vessel wall narrowing, compression, or intravascular thrombosis.
3- Visceral Pain
- Visceral pain originates from internal organs located in the abdomen and pelvis.
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Causes:
- Overdistention of a hollow viscus: Stretching or expansion of a hollow organ.
- Spasm of a hollow viscus: Contractions or spasms of a hollow organ, leading to pain due to blood vessel blockage or mechanical stimulation of pain receptors.
- Chemical irritation: Caused by substances like hydrochloric acid (HCl) in a peptic ulcer.
- Ischemia: Reduced blood flow to an organ, leading to accumulation of pain-inducing metabolites.
- Inflammation: Inflammation of visceral tissues, such as appendicitis.
Characters of Visceral Pain
- Diffuse and poorly localized: Due to limited cortical representation and low nerve density in visceral organs.
- Rhythmic cramps (colic): Occur because of rhythmic smooth muscle contractions. Each peristaltic wave triggers a cramp.
- Referred to surface structures: Pain may be felt in areas of the body that correlate with the affected organ.
- Associated with autonomic changes: Hypotension, bradycardia, nausea, vomiting, sweating.
- Guarding phenomenon: Involuntary muscle spasms to protect the affected area.
4- Referred Pain
- Definition: Pain perceived in a surface area that shares the same dermatome as the diseased internal organ.
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Examples:
- Cardiac pain: Felt retrosternally, in the epigastrium, root of the neck, and inner part of the left arm.
- Appendicitis pain: Felt around the umbilicus.
- Gallbladder pain: Felt in the epigastrium and at the tip of the right scapula.
- Renal pain: Felt in the back, inguinal region, and testicles.
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Description
This quiz explores the definitions of pain and the various types of pain receptors. It includes information on pain thresholds, individual pain responses, and the neurological pathways involved in pain perception. Test your understanding of these crucial concepts related to pain and its impact on the body.
