Definitions and Types of Pain

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which type of sensation is primarily associated with the dorsal column tract?

Pain

Fine touch (correct)

Temperature

Crude touch

What type of pain is associated with the neospinothalamic pathway?

Slow pain

Chronic pain

Visceral pain

Fast pain (correct)

Which sensation is NOT a function of the lateral spinothalamic tract?

Temperature

Fine touch (correct)

Tickling

Pain

What type of sensation can be classified as visceral pain?

Deep pain Signup and view all the answers

Which type of pain is characterized as slow and aching?

Visceral pain Signup and view all the answers

Which sensation is a feature of mechanoreceptive sensation?

Pressure Signup and view all the answers

In which portion of the pain pathway does the second order neuron reside for the paleospinothalamic pathway?

Lamina II, III Signup and view all the answers

Which of the following sensations is NOT included in mechanoreceptive sensations?

Cutaneous pain Signup and view all the answers

What is the primary purpose of pain as a sensation?

To protect the body by prompting a reaction to avoid further injury Signup and view all the answers

Which type of pain receptor is stimulated by extreme temperatures?

Thermal pain receptors Signup and view all the answers

How do pain responses differ between acute and saver pain?

Acute pain shows sympathetic stimulation, saver pain shows parasympathetic effects Signup and view all the answers

What characterizes hyperalgesia as a response to pain?

Increased pain sensation from previously non-painful stimuli Signup and view all the answers

Which part of the nervous system is primarily involved in autonomic reactions to pain?

Hypothalamus Signup and view all the answers

What is considered the 'inflammatory soup' released during tissue damage?

Chemical mediators like histamine and bradykinins released from dying cells Signup and view all the answers

Which statement about pain receptors is true?

Polymodal receptors can respond to various types of stimuli Signup and view all the answers

What role does Substance P play in the process of pain sensation?

It increases capillary permeability and contributes to inflammation Signup and view all the answers

Which channel is directly activated by nociceptive stimuli such as heat?

TRPV1 Signup and view all the answers

What type of cells release mediators during tissue injury and inflammation?

Non-neuronal and neuronal cells Signup and view all the answers

Which substance is NOT considered a mediator released during tissue injury?

Dopamine Signup and view all the answers

Peptidergic neurons contain which of the following peptides?

Substance P Signup and view all the answers

What information is conveyed by the anterolateral system?

Pain and temperature Signup and view all the answers

Which cell body location is associated with nociceptive afferents?

Dorsal root ganglia (DRGs) Signup and view all the answers

Which structure is specifically responsible for processing fine touch and proprioception?

Nucleus gracilis Signup and view all the answers

What role does the TRPV3 channel play in nociceptive signaling?

Mediates pain from keratinocytes Signup and view all the answers

Which type of pain is characterized by being felt within 0.1 sec after a stimulus and localized well?

Fast Pain Signup and view all the answers

What type of pain is primarily induced by ischemia resulting from decreased blood supply to muscles?

Deep Pain Signup and view all the answers

Which statement best describes visceral pain?

It is often associated with symptoms like hypotension and bradycardia. Signup and view all the answers

Which pain type is typically described as diffuse and poorly localized?

Visceral Pain Signup and view all the answers

In which scenario is referred pain likely to be experienced?

Gall bladder pain felt in the right shoulder blade area. Signup and view all the answers

Which fiber type primarily transmits slow pain signals?

C fibers Signup and view all the answers

Which character does NOT describe visceral pain?

Localized sharp sensations Signup and view all the answers

What describes the pain experienced during intermittent claudication?

Ischemic pain resulting from muscle oxygen deprivation Signup and view all the answers

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

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
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

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.
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

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.
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.
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.
Causes:
- Ischemic pain: Caused by reduced blood supply to muscles due to vessel wall narrowing, compression, or intravascular thrombosis.
  - Examples:
    - Cardiac muscle ischemia: Anginal pain.
    - Skeletal muscle ischemia: Intermittent claudication (pain in the legs during exercise).

3- Visceral Pain

Visceral pain originates from internal organs located in the abdomen and pelvis.
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.
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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

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.