Nociception: L16-L17

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Questions and Answers

What is the primary function of first order sensory neurons located in the dorsal root ganglia?

Processing visual information

Integrating sensory information from the vestibular system

Conducting pain and temperature signals to the spinal cord (correct)

Transmitting motor signals to muscles

What is the first step in the sensory transduction cascade?

Generator potential

Strong stimulus

Spike potential

Weak stimulus (correct)

Which of the following receptor types is associated with proprioception?

Muscle spindle (correct)

Pacinian corpuscles

Merkel cells

Free nerve endings

Which tract is responsible for pain and temperature sensation from the body?

Spinothalamic tract Signup and view all the answers

Which of the following accurately describes the difference between tonic and phasic receptors?

Tonic receptors respond to static stimuli; phasic receptors respond to dynamic stimuli. Signup and view all the answers

What is the conduction velocity of pain and temperature fibers classified as free nerve endings?

5-30 m/s Signup and view all the answers

Which pathway is involved in the integration of painful stimuli?

Ascending pathways from free nerve endings Signup and view all the answers

Which part of the body is served by the trigeminothalamic tract for pain and temperature sensation?

The face and anterior portion of the head Signup and view all the answers

What physical characteristic determines the speed of action potential propagation in sensory fibers?

Fibre diameter and myelination Signup and view all the answers

What type of signaling does the cortex send to limbic structures such as the amygdala?

Descending signaling Signup and view all the answers

What is the complete representation of the somatic sensory periphery located within the thalamus?

Sensory map Signup and view all the answers

Which sensory function utilizes Meissner and Ruffini cells as receptors?

Fine touch and pressure Signup and view all the answers

What stimulates the generation of action potentials in the sensory transduction cascade?

Generator potential Signup and view all the answers

What characteristic does the conduction velocity of nerve fibers smaller than 1.5 micrometers primarily indicate?

Slow transmission related to pain, temperature, and itch Signup and view all the answers

What type of neuron has its cell body located in the trigeminal ganglion, specifically for facial sensations?

First order sensory neurons Signup and view all the answers

How is pain defined according to the International Association for the Study of Pain?

An unpleasant sensory and emotional experience related to potential tissue damage. Signup and view all the answers

What is required for the generation of action potentials in nerve fibers?

Sufficient depolarization Signup and view all the answers

Which type of nociceptor is associated with sharp and well localised pain?

Aδ fibers Signup and view all the answers

Which component is responsible for rapid/saltatory conduction in myelinated fibers?

Myelin sheath Signup and view all the answers

What is the conduction speed of Aδ fibers?

5-40 m/s Signup and view all the answers

Which neurotransmitter is involved in communication within the dorsal horn of the spinal cord?

Glutamate Signup and view all the answers

What characterizes C fibers among the neuronal fibers?

They are small diameter and slowly conducting. Signup and view all the answers

During mechanotransduction, which process occurs in nociceptors?

Transduction of mechanical energy into electrical signals Signup and view all the answers

What type of pain is typically associated with non-myelinated fibers?

Dull/aching pain Signup and view all the answers

What is the primary function of nociceptors?

To encode noxious stimuli Signup and view all the answers

In which bodily tissues are nociceptors NOT found?

Brain Signup and view all the answers

At what temperature do TRPV1 channels begin to open?

43°C Signup and view all the answers

What initiates the process of depolarization in nociceptive cells?

Ions flowing through channels Signup and view all the answers

What type of stimuli do nociceptive afferents respond to?

Noxious mechanical, thermal, and chemical stimuli Signup and view all the answers

What happens to nociceptor properties during pathological conditions?

They can change and become more sensitive Signup and view all the answers

Which channel is involved in the mechanotransduction process in nociceptive neurons?

Stretch-sensitive cation channel Signup and view all the answers

Which of the following statements about nociceptive pathways is accurate?

Nociceptive signals travel through the spinal cord before reaching the brain Signup and view all the answers

What is the primary action of non-steroidal anti-inflammatory drugs (NSAIDs) regarding pain modulation?

Inhibit the enzyme COX to reduce prostaglandin production Signup and view all the answers

Which inflammatory mediator is NOT listed as increasing neuronal excitability?

Histamine Signup and view all the answers

What is the first level of modulation in the processing of nociceptive signals?

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

What role do C fibers primarily serve in pain signaling?

Directing signal to the reticular formation and limbic areas Signup and view all the answers

How does the gate control theory explain pain modulation?

The spinal cord can modulate incoming signals before they reach the brain. Signup and view all the answers

Which of the following statements best describes the function of prostaglandins in pain pathways?

They are vasodilators and increase neuronal excitability. Signup and view all the answers

Tissue damage leads to pain by increasing the sensitivity of which type of receptors?

Nociceptors Signup and view all the answers

What is a primary effect of the inflammatory mediators on nociceptors in the context of tissue damage?

Decrease their activation threshold Signup and view all the answers

What is the role of enkephalin in pain modulation?

It acts pre-synaptically to limit neurotransmitter release. Signup and view all the answers

Which type of pain is described as pain resulting from a stimulus that does not typically cause pain?

Allodynia Signup and view all the answers

Which statement best describes how pain can be referred?

Myocardial pain may be perceived in the left arm or shoulder. Signup and view all the answers

What is the mechanism by which descending pathways modulate nociceptive signals?

They inhibit transmission of pain signals. Signup and view all the answers

What is a characteristic of opioid analgesics?

They can be endogenous or exogenous. Signup and view all the answers

Which brain region is associated with the production of endogenous opioids that modulate pain?

Periaqueductal gray Signup and view all the answers

Which feature is NOT a part of the gate control theory of pain modulation?

Enhanced perception of visceral pain Signup and view all the answers

What describes neuropathic pain?

Pain that is caused by a lesion or disease of the somatosensory nervous system. Signup and view all the answers

Study Notes

Nociception Overview

Nociception is the neural process of encoding noxious stimuli.
Covers the general overview of sensory systems, focusing specifically on nociception.
Four key learning objectives are outlined for the lectures; defining pain and related terms, describing the afferent pathways for pain and temperature, explaining the physiological mechanisms behind painful stimulus integration, and articulating descending modulation of these pathways.

Learning Objectives

Define pain and terms associated with nociception.
Describe afferent pathways that mediate pain and temperature.
Detail the physiological mechanisms for integrating painful stimuli.
Explain descending modulation of nociceptive pathways.
References are from the Neuroscience textbook by Purves.

Sensory Systems

Sensory systems involve external environment, processing, and behavioral response.
Peripheral sensory input (PNS) travels to the central nervous system (CNS) for integration, culminating in motor output.
Sensory components (sensory ganglia and nerves, sensory receptors) and motor components (visceral motor, somatic motor systems) work together, influencing effectors like smooth muscles, cardiac muscles, and glands, as well as skeletal muscles.

Sensory Pathways

First-order sensory neurons are pseudounipolar, featuring two axon branches. One branch targets the periphery (PNS), the other the spinal cord (CNS).
Somatosensory cell bodies are located in dorsal root ganglia (DRG).
Face's somatosensory cell bodies reside in the trigeminal ganglion.
First-order neurons enter the dorsal root and either connect to the dorsal column or pain and temperature pathways upon entering.

Sensory Receptors

Different receptor types exist with unique characteristics—free nerve endings, Meissner's corpuscles, Pacinian corpuscles, Merkel disks, Ruffini's corpuscles, muscle spindles, Golgi tendon organs, and joint receptors
Nociceptors are present throughout the body, near blood vessels and in between epithelial layers, in the cornea, muscle joints, and viscera, and in connective tissues.
Nociceptors are stimulated by noxious mechanical, thermal, or chemical stimuli, and their characteristics can change with inflammation, damage, and pathology.
They innervate all tissues except the brain.

Sensory Transduction

The process of converting stimulus energy into an electrical signal involves signal transduction, current generation, generator potential formation, and ultimately, action potential firing.
Stimuli, ranging from weak to strong, cause different levels of receptor potential.
If the stimulus reaches a threshold, it generates action potentials.

Sensory Receptors: Types

Different receptor types respond to various stimuli, including touch ("fine touch" mechanosensitive, pressure, low-frequency vibration and proprioception), thermal stimuli, chemical stimulants.

Sensory Receptive Fields

Receptive fields vary depending on receptor type. Some receptors have large receptive fields, others have small receptive fields (e.g., those associated with fine touch).

Sensory Nerve Fibres

A variety of nerve fibres exist, characterized by their myelination type and diameter.
These characteristics affect conduction velocity which is integral in determining the type and duration of the perceived pain.

First-Order Neurons

First-order neurons transmit impulses from the periphery to the spinal cord and synapse with second-order neurons.
Different first-order neurons carry particular types of sensory information.

Nociceptive Ascending Pathways

Nociceptive information follows a specific pathway to the thalamus.
The spinothalamic tract carries temperature and pain information from the body and face, while the trigeminothalamic tract focuses on facial information.
Both ultimately project their signals to the thalamus.

Cortical Integration and Signaling

Thalamic input predominantly reaches layer IV of the cortex.
The cortex projects signals to limbic structures such as the amygdala and hippocampus. The cortex also projects signals to other cortical areas, the subcortical areas, brainstem, and spinal cord.

Measuring Physiological Variables (e.g., blood pressure, sugar levels, cardiac function).

Methods for assessing physiological variables like blood pressure, blood sugar, and cardiac function are relevant to the study.

Pain Scales

Numerical pain rating scales and Wong-Baker FACES pain rating scales aid in quantitatively assessing pain severity.

Definition of Pain

Pain is characterized as an unpleasant sensory and emotional experience.
Different aspects of pain exist including sensory, affective, and autonomic components.

Nociceptive Afferents

Nociceptors are located in many areas of the body.
Nociceptors detect noxious stimuli, such as pressure, heat, cold, chemical signals, and damaging factors.

Ion Channels in Nociception

Specialized TRP ion channels respond to various stimuli, like heat, cold, or chemical signals.
Na+ and Ca2+ ions flow through these channels, leading to action potential generation in pain fibres.

Pain Pathways in the Brain

Descending pain pathways originate in the brain and project to the spinal cord.
These pathways can influence the experience of pain.

Modulation of Pain Signals

The spinal cord serves as a crucial site for pain modulation, where signals can be modified before reaching higher brain centers.
Inhibitory pathways and diffuse inhibitory mechanisms in the brainstem play a role in pain modulation.
Factors like stress, psychological conditions, and endogenous opioids influence pain perception (descending pathways).

Types of Pain

Different types of pain, like sharp/fast and dull/slow pain, are associated with specific fibre types (Aδ and C fibres), influencing their transmission rate and the perceived pain quality.

Referred Pain

Pain can be perceived at a site different from the nociceptor location.
This is known as referred pain and occurs when multiple afferents converge on the same neurons that signal pain from a different region.

Further Definitions

Allodynia: pain from a normally non-painful stimulus.
Neuropathic pain: pain due to damage or disease of the nervous system.

Physiological Variables: Pain Measurement

Various methods exist to measure physiological variables associated with pain, including blood pressure, glucose levels, and cardiac function.

Painkillers: Understanding Pain Modulation

Different mechanisms address pain, including:
- Local anesthetics (nerve block)
- Non-steroidal anti-inflammatory drugs (target prostaglandin production)
- Opioid analgesics (e.g., morphine)
Each of these groups has specific mechanisms of action which target different sites in the pain pathway.

Peripheral Nerve Structure

Peripheral nerves are comprised of nerve fibres, myelinated and unmyelinated. Schwann cells form the myelinated and unmyelinated nerves sheath.

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Description

Test your knowledge on the sensory transduction cascade, the roles of sensory neurons, and the various receptor types involved in proprioception and pain sensation. This quiz covers key concepts related to sensory pathways and their functions within the nervous system.