Pain Sensitivity and Its Mechanisms

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Questions and Answers

What is characterized by non-painful stimuli causing pain in sunburnt areas?

Allodynia (correct)

Hyperalgesia

Primary hyperalgesia

Secondary hyperalgesia

Which of the following substances is NOT typically associated with peripheral sensitization?

Insulin (correct)

Bradykinin

Serotonin

Histamine

What initiates the series of reactions in the inflammatory area during primary hyperalgesia?

Axon reflex (correct)

Mast cell degranulation

Histamine release

Endothelial cell activation

What term describes increased pain sensitivity in undamaged tissues surrounding a painful area?

Secondary hyperalgesia Signup and view all the answers

Which process promotes the activation of immune system cells and causes vasodilation in inflamed areas?

Histamine release Signup and view all the answers

What causes a higher impulse frequency to be sent to the brain when a painful stimulus is applied?

Increased sensitivity of pain nerve endings Signup and view all the answers

Which cell type is primarily responsible for the release of inflammatory substances in peripheral tissues?

Immune system cells Signup and view all the answers

Which neurotransmitter is released from pain nerve endings during primary hyperalgesia?

Substance P Signup and view all the answers

What is the primary function of the antinociceptive system?

To inhibit pain signal transmission. Signup and view all the answers

Which fibers are primarily responsible for transmitting pain signals through the peripheral antinociceptive system?

C fibers Signup and view all the answers

What role do large diameter myelinated non-pain fibers play in the peripheral antinociceptive system?

They inhibit impulse transmission from pain fibers. Signup and view all the answers

What occurs when pain receptors are stimulated?

Pain signals are transmitted to the brain. Signup and view all the answers

What happens when touch-pressure conducting Aß fibers are activated in the same region as pain endings?

They activate touch-pressure nerve endings and suppress pain sensation. Signup and view all the answers

What is the role of descending nerve fibers from the brain in the central antinociceptive system?

To inhibit pain impulse transmission from the spinal cord. Signup and view all the answers

Which of the following describes secondary pain sensation?

Dull and less intense. Signup and view all the answers

What do the C fibers do in the pain pathway?

Transmit impulses from the free nerve endings. Signup and view all the answers

What is the primary way through which acupuncture and massage alleviate pain?

By stimulating inhibitory neurons in the dorsal horn Signup and view all the answers

How does the central antinociceptive system function in response to pain signals?

It suppresses pain signal transmission to brain centers. Signup and view all the answers

What role do the limbic system structures play in pain perception?

They enable cognitive and emotional responses to pain. Signup and view all the answers

Which neurotransmitter is released by the raphe nuclei in response to pain signals?

Serotonin Signup and view all the answers

What happens when touch and pressure nerve endings are stimulated?

They inhibit pain impulse transmission to the CNS. Signup and view all the answers

What is the effect of dopamine and opioid peptide secreting neurons in the periaqueductal grey matter?

They facilitate the activation of pain suppressing regions. Signup and view all the answers

Which structure is NOT a part of the brainstem that activates in response to pain signals?

Amygdaloid nucleus Signup and view all the answers

What type of synaptic activity occurs between the touch pathway and the pain pathway?

Excitatory and low activity Signup and view all the answers

What condition is characterized by the absence of the sense of smell due to damage to receptors, pathways, or centers?

Anosmia Signup and view all the answers

Which of the following is the most common cause of decreased smell sensation?

Blockage of the nasal cavity Signup and view all the answers

In which age group does the number of smell receptors begin to progressively decrease?

After 60 years Signup and view all the answers

Which statement is true regarding the decreased sense of smell in neurodegenerative diseases?

It occurs before cognitive changes. Signup and view all the answers

What is a common cause of hyposmia during the common cold?

Inflammatory reactions Signup and view all the answers

Which component is NOT affected by the SARS-CoV-2 virus in relation to smell?

Olfactory epithelium receptor cells Signup and view all the answers

What can cause total nasal cavity obstruction leading to smell loss?

Chronic sinusitis Signup and view all the answers

What is commonly associated with a decreased sense of smell in both males and females as they age?

Progressive decrease in receptor numbers Signup and view all the answers

Which of the following factors can stimulate the olfactory epithelium even in the absence of external odor substances?

Bacteria-related products Signup and view all the answers

What term describes a partial loss of smell, often noted in patients with some damage to olfactory structures?

Hyposmia Signup and view all the answers

What happens after the influx of Ca2+ in the synapse?

It stimulates the release of neurotransmitters. Signup and view all the answers

How is the bitter taste signal transduced to initiate neurotransmitter release?

Phospholipase C is activated by G protein stimulation. Signup and view all the answers

Which of the following substances is primarily associated with the umami taste?

L-glutamate Signup and view all the answers

Which statement is true regarding taste receptor cells?

There are around 30 different genes for bitter taste receptors. Signup and view all the answers

Which statement correctly describes the role of phosphatidylinositol bisphosphate (PIP2) in taste transduction?

PIP2 is converted into DAG and IP3. Signup and view all the answers

Which of the following ions are known to influence taste perception?

K+ and Mg2+ Signup and view all the answers

What is the role of IP3 and DAG in the taste transduction process?

They lead to the opening of Ca2+ channels. Signup and view all the answers

What is characteristic of individuals with genetic defects related to bitter taste receptors?

They completely lack bitter taste perception. Signup and view all the answers

What structure is responsible for the conscious feeling of pain localization?

Postcentral gyrus Signup and view all the answers

Which pathway primarily transmits pain and temperature sensations?

Lateral spinothalamic tract Signup and view all the answers

Where do the first-order neurons of the lateral spinothalamic tract synapse?

Dorsal horn of the spinal cord Signup and view all the answers

What is the second step in the lateral spinothalamic tract pathway?

First-order neuron crosses to the opposite side Signup and view all the answers

How does the primary sensory pathway for touch and proprioception begin?

With free nerve endings in the periphery Signup and view all the answers

What happens after the second-order neuron in the lateral spinothalamic tract crosses to the opposite side of the spinal cord?

It ascends to the thalamus Signup and view all the answers

What is the primary function of free nerve endings in the nociceptive sensory system?

To transmit pain signals Signup and view all the answers

Which of the following best describes the pathway taken by pain impulses from the periphery to the brain?

Lateral spinothalamic tract to thalamus, then to postcentral gyrus Signup and view all the answers

What is the primary function of the sensory component in pain perception?

To allow conscious awareness of pain localization Signup and view all the answers

What physiological changes cause hyperalgesia?

Increased impulse frequency and synapse reorganization Signup and view all the answers

Which statement accurately describes the affective component of pain?

It is linked to the emotional and behavioral regulation of pain. Signup and view all the answers

How does the autonomic component affect an individual experiencing pain?

It increases heart rate and elevates blood pressure in response to pain. Signup and view all the answers

Which of the following accurately describes allodynia?

Touch pathways sensitize pain pathways leading to pain from non-painful stimuli. Signup and view all the answers

What distinguishes chronic pain from acute pain?

Chronic pain persists for longer than 3 months. Signup and view all the answers

What mechanism is activated in response to nociceptive input in an extremity?

The crossed extensor reflex to maintain postural stability. Signup and view all the answers

Which of the following pathways is NOT involved in transmitting pain impulses to conscious centers?

Dorsal column-medial lemniscal pathway Signup and view all the answers

What mechanism underlies the reorganization of synapses in hyperalgesia?

Increased amount of neurotransmitters and receptors due to high impulse frequency Signup and view all the answers

Which of the following describes a key effect of central sensitization?

Enhanced pain sensitivity in surrounding tissues Signup and view all the answers

What role do the limbic structures play in pain experiences?

They regulate emotional responses related to pain. Signup and view all the answers

In the context of pain pathways, what happens to inhibitory neurons during central sensitization?

They undergo loss and dysfunction, diminishing their protective effects. Signup and view all the answers

Which statement about the motor component in pain response is correct?

It primarily activates flexor muscles to prevent movement. Signup and view all the answers

What results from the stimulation of pain receptors in the body?

Initiation of various reflex actions and sensory responses. Signup and view all the answers

What is the primary consequence of the reorganization of synapses between touch and pain neurons in allodynia?

Touch pathways start transmitting additional signals to pain pathways. Signup and view all the answers

What is a characteristic feature of acute pain?

It results from sudden damage to previously intact tissues. Signup and view all the answers

Which inflammatory substance is primarily responsible for causing pain receptor sensitization during secondary hyperalgesia?

Histamine Signup and view all the answers

What mechanism is responsible for the increase in impulse frequency when a painful stimulus is applied?

Enhanced peripheral sensitization Signup and view all the answers

What is the primary role of calcitonin gene related peptide (CGRP) released from pain nerve endings?

Stimulation of neighboring cells Signup and view all the answers

What does primary hyperalgesia primarily involve?

Local inflammation and pain in damaged tissues Signup and view all the answers

Which process is NOT directly involved in the development of primary hyperalgesia?

Calcitonin release Signup and view all the answers

Which of the following best describes the difference between primary and secondary hyperalgesia?

Primary occurs directly in damaged tissues, secondary in surrounding undamaged tissues. Signup and view all the answers

What type of cells release inflammatory substances that contribute to peripheral sensitization?

Immune system cells and damaged tissues Signup and view all the answers

Which of the following best describes the role of ATP in the context of peripheral sensitization?

It increases sensitivity of pain nerve endings. Signup and view all the answers

What is the first step in the signaling pathway for bitter, sweet, or umami tastes?

Substance binding to the receptor on the taste receptor cell Signup and view all the answers

Which of the following accurately describes the role of diacylglycerol (DAG) in taste transduction?

DAG is converted from phosphatidylinositol bisphosphate (PIP2) Signup and view all the answers

How many different genes encode bitter taste receptors in taste receptor cells?

About 30 different genes Signup and view all the answers

What initiates neurotransmitter release in synapses with afferent nerve fibers upon taste transduction?

Ca2+ influx due to opened voltage-gated Ca2+ channels Signup and view all the answers

Which of the following substances is linked primarily to the perception of sweet taste?

Sorbitol Signup and view all the answers

What is the biological significance of distinct taste qualities being activated by different receptors?

Promotes refined detection of nutritional information Signup and view all the answers

Which sequence correctly depicts the process of taste transduction for bitter taste?

Substance binding → Activation of phospholipase C → Production of IP3 and DAG Signup and view all the answers

What is a characteristic feature of bitter taste receptors among the different taste receptor types?

Bitter taste receptors are superior in number on receptor cells Signup and view all the answers

Study Notes

Pain sensitivity

Pain sensitivity increases after damage to tissues.
Pain can be caused by previously non-painful stimuli.
Hyperalgesia: Increased pain sensitivity to painful stimuli.
Allodynia: Pain caused by non-painful stimuli.
Peripheral and central sensitization contribute to the development of both hyperalgesia and allodynia.

Peripheral Sensitization

Occurs when inflammatory substances are released in peripheral tissues.
These substances are primarily released from immune system cells, endothelial cells, damaged tissues, and platelets.
Inflammatory substances, such as histamine, bradykinin, interleukins, ATP, adenosine, serotonin, endothelin, and growth factors, increase the sensitivity of pain nerve endings.

Primary Hyperalgesia

Refers to pain sensitivity in damaged tissues.
Pain nerve endings release calcitonin gene-related peptide (CGRP), substance P, and neurokinins through the axon reflex.
These neurotransmitters stimulate neighboring cells and trigger a series of reactions, including:
- Proliferation of keratinocytes.
- Activation of immune system cells.
- Vasodilation in the skin, leading to edema formation and redness.
- Smooth muscle contraction in the irritated region.

Secondary Hyperalgesia

Refers to pain sensitivity in undamaged tissues surrounding the injured area.
Mast cell degranulation releases histamine.
Histamine causes pain receptor sensitization and inflammatory reactions.

Antinociceptive System

This system works to suppress the transmission of pain signals.
Its purpose is to decrease pain sensation after the nociceptive system has sent its warning signal.
It enables us to move away from a painful area, preventing further damage.
It consists of two parts:
- Peripheral antinociceptive system: Large diameter myelinated non-pain fibers inhibit impulse transmission from pain fibers to the central nervous system.
- Central antinociceptive system: Descending nerve fibers from the brain decrease pain impulse transmission from the spinal cord to higher centers of the nociceptive system.

Peripheral Antinociceptive System

Pain signals are transmitted through unmyelinated C nerve fibers.
These fibers start at free nerve endings and carry impulses to the posterior horn of the spinal cord.
C fibers activate second-order neurons, which send impulses through the lateral spinothalamic tract.
They also inhibit the inhibitory neuron that normally suppresses pain transmission.

Touch & Pressure Pathway

Myelinated Aß fibers carry impulses about touch and pressure.
When activated, Aß fibers stimulate an inhibitory neuron in the dorsal horn of the spinal cord.
The inhibitory neuron suppresses the transmission of pain impulses.
This is why rubbing or applying pressure to a painful area often reduces pain.

Central Antinociceptive System

Enables the brain to suppress pain signal transmission.
Pain signals are sent to the brain stem structures:
- Limbic system (limbic cortex, amygdaloid nucleus, hypothalamus).
- Periaqueductal grey matter.
- Raphe nuclei and locus coeruleus.
The limbic system, responsible for emotional and cognitive responses, sends impulses to the periaqueductal grey matter in the midbrain.
The periaqueductal grey matter stimulates the raphe nuclei and locus coeruleus, which release serotonin and norepinephrine, respectively.

Taste Qualities & Receptors

Different taste qualities rely on different receptors, but the general mechanism is the same.
Taste receptors are located on taste receptor cells and activate different second messenger pathways.
These pathways ultimately lead to the release of neurotransmitters from the taste receptor cells.
Bitter Taste:
- Stimulated by ions (K+ and Mg2+) and organic substances like long-chain nitrogen-containing substances and alkaloids.
Sweet Taste:
- Stimulated by sugars, alcohols like sorbitol, aldehydes, ketones, amino acids, and proteins.
Umami Taste:
- Stimulated by L-glutamate.

Smell Disturbances

Anosmia: Complete loss of smell.
Hyposmia: Decreased sense of smell.
Common causes include:
- Nasal cavity blockage (running nose).
- Physical damage to the olfactory epithelium, nerve, or brain pathways.
Smell disturbances are also associated with:
- Aging (decreased number of smell receptors).
- Neurodegenerative diseases like Parkinson's and Alzheimer's.
- COVID-19.

Smell Disturbances and COVID-19

COVID-19 infection can cause hyposmia due to inflammation in the nasal, paranasal, and oral cavities.
The SARS-CoV-2 virus does not directly affect smell receptors.
The virus targets sustentacular cells and respiratory cells, triggering inflammation and inhibiting impulse transmission from olfactory cells to the central nervous system.

Nociceptive Sensory System

The nociceptive sensory system is responsible for detecting and transmitting pain signals.
Receptors: Free nerve endings located in the skin, subcutaneous tissues, and internal organs are sensitive to pain signals.
Pathway: Impulses are primarily conducted through the lateral spinothalamic tract, with impulses from the head transmitted through the trigeminal pathway.
Center: The postcentral gyrus of the cerebral cortex is where the conscious feeling of pain is produced.
Pain and temperature are transmitted via the lateral spinothalamic tract pathway.
Touch and proprioception are transmitted via the dorsal column medial lemniscus system/pathway.

Hyperalgesia & Allodynia

Hyperalgesia is an increased sensitivity to pain, where previously non-painful stimuli now cause pain.
Allodynia is pain caused by a stimulus that does not normally cause pain.
Both hyperalgesia and allodynia are caused by peripheral and central sensitization.

Peripheral Sensitization

Peripheral sensitization occurs when inflammatory substances are released in peripheral tissues.
Key inflammatory substances include histamine, bradykinin, interleukins, ATP, adenosine, serotonin, endothelin, and different growth factors.
These substances are released by immune system cells, endothelial cells, damaged tissues, and platelets.
Inflammatory substances increase the sensitivity of pain nerve endings, leading to a higher frequency of impulses sent to the brain.
Primary hyperalgesia refers to pain sensitivity directly in the damaged tissues.
Secondary hyperalgesia refers to pain sensitivity that occurs in surrounding undamaged tissues.

Central Sensitization

Central sensitization involves the reorganization of impulse transmission in the central nervous system.
Normal Sensation: Stimulation of pain nerve endings transmits impulses through pain pathways, causing pain sensation while stimulation of touch nerve endings transmits impulses through touch pathways, causing touch sensation.
Hyperalgesia: High impulse frequency is transmitted through pain pathways, leading to:
- Increased neurotransmitter release.
- Increased receptor number on postsynaptic membranes.
- Loss and dysfunction of inhibitory neurons.
Allodynia: Reorganization of pain synapses affects the touch pathway, causing:
- Increased neurotransmitter amount.
- Increased receptor number in touch pathway synapses.
- Loss and dysfunction of inhibitory neurons, leading to decreased inhibition of the pain pathway.
- Touch pathway starts sending more impulses to the pain pathway.

Pain Types

Acute pain is physiological pain in previously intact tissues, caused by sudden tissue damage.
Chronic pain persists for longer than 3 months.

Pain Components

Sensory: The subjective feeling of pain, produced by impulse transmission to the cortical centers.
Cognitive: Pain impulses are transmitted to the limbic cortex, allowing for classification and evaluation of pain compared to previous experiences.
Affective: Pain impulses are transmitted to the limbic system structures, causing negative emotions.
Autonomic: Pain signals are transmitted from the spinal cord to the hypothalamus, stimulating sympathetic reactions.
Motor: Pain signals are transmitted to the somatic nervous system innervating skeletal muscles, causing tension in flexor muscles.

Nociceptive Reflex & Crossed Extensor Reflex

Nociceptive reflex: Pain receptors send impulses to the spinal cord, activating motor neurons that innervate flexor muscles, leading to muscle contraction.
Crossed extensor reflex: A reflex that occurs in the opposite limb from the one that received painful input.

Taste Qualities

Bitter: Bitter taste receptors are superior in number on taste receptor cells.
Sweet, Umami: The general mechanism for sweet, umami, and bitter taste involves G protein activation, Phospholipase C conversion of PIP2 into IP3 and DAG, Ca2+ channel opening, and neurotransmitter release.
Bitter taste receptors are encoded by approximately 30 different genes.
Taste thresholds refer to the minimum concentration of a substance needed to elicit a taste perception.
Biological role of taste: Taste is essential for selecting appropriate food, detecting toxic substances, and contributing to overall food enjoyment.

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Description

Explore the concepts of pain sensitivity, hyperalgesia, and allodynia in this quiz. Understand how tissue damage and inflammatory substances influence pain perception. Test your knowledge on peripheral sensitization and neurotransmitter roles in pain signaling.