Pain Classification and Mechanisms

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Questions and Answers

What is referred pain?

Pain felt at the site of injury

Pain that is well localized and sharp

Pain originating from deep tissues but felt in another location (correct)

Pain associated with external injuries only

Which spinal segments are associated with pain from angina?

T1 to T3

S1 to S3

L1 to L3

T1 to T5 (correct)

What are dermatomes?

Areas of skin innervated by a specific nerve root (correct)

Tissues that respond to electrical stimulation

Areas of muscle with no nerve supply

Bone areas that sense pain

Which condition might cause referred pain in the left upper extremity during a heart attack?

Pain radiating from T1 to T2 dermatomes Signup and view all the answers

What characterizes neuropathic pain?

Poorly localized pain described as burning or tingling Signup and view all the answers

What characterizes Aδ fibers?

They are myelinated with fast conduction velocities. Signup and view all the answers

What is allodynia?

Pain resulting from mild stimuli that normally do not provoke pain Signup and view all the answers

How do C fibers primarily transmit pain sensations?

By signaling chronic pain that is aching and poorly localized. Signup and view all the answers

Which of the following can cause nerve damage leading to neuropathic pain?

Certain chemotherapy drugs Signup and view all the answers

Which of the following distinguishes myotomes from dermatomes?

Myotomes are areas of muscle innervated by a nerve root Signup and view all the answers

What is the primary role of the dorsal root ganglion?

To house the cell bodies of sensory neurons. Signup and view all the answers

What type of stimuli activates C-fibers?

Thermal, mechanical, and chemical stimuli. Signup and view all the answers

Which of the following statements about Aδ fibers is correct?

They are involved in sharp, localized pain responses. Signup and view all the answers

Which neurotransmitter is released by primary afferent nociceptors?

Substance P. Signup and view all the answers

What is a primary characteristic of the pain transmitted by C fibers?

It has a slow onset and can last longer. Signup and view all the answers

Where do primary afferent nociceptors primarily synapse in the spinal cord?

In the substantia gelatinosa of the dorsal horn. Signup and view all the answers

What is the primary biological purpose of acute pain?

To serve as a warning against potential harm Signup and view all the answers

Which of the following describes chronic pain?

It persists beyond the normal healing time Signup and view all the answers

What role do nociceptive-specific neurons play in the dorsal horn of the spinal cord?

They assist in the discrimination of pain types. Signup and view all the answers

What is muscle guarding primarily intended to do?

Immobilize the injured area Signup and view all the answers

What type of pain results from stimulation of nociceptors in superficial tissues?

Somatic pain Signup and view all the answers

Which type of cells in the dorsal horn is primarily responsible for localizing burning or pricking pain?

Wide-dynamic-range neurons Signup and view all the answers

What is referred pain thought to arise from in the dorsal horn of the spinal cord?

The convergence of visceral and cutaneous noxious stimuli. Signup and view all the answers

What initiates a new source of pain in a person experiencing trauma?

Inadequate metabolic support due to ischemia Signup and view all the answers

Episodic or recurrent pain is characterized by what feature?

Intermittent occurrences with pain-free periods Signup and view all the answers

Which pain pathway primarily transmits signals to the thalamus?

Neospinothalamic pain pathway Signup and view all the answers

Which of the following is NOT a characteristic of nociceptive pain?

It is primarily psychological in origin Signup and view all the answers

What aspect of sensory information does the thalamus primarily act as?

A general relay station for sensory information. Signup and view all the answers

What often results from compromised circulation following an injury?

Failure to remove metabolic wastes Signup and view all the answers

What are wide-dynamic-range cells also known as?

T (transmission) cells Signup and view all the answers

Which area of the brain receives precise projections from the thalamus related to pain sensation?

Somatosensory cortex Signup and view all the answers

Where do some axons of second-order pain transmission cells cross over in the spinal cord?

Opposite side of the spinal cord Signup and view all the answers

What type of pain does the spinoreticulothalamic pathway primarily convey?

Diffuse poorly localized somatic and visceral pain Signup and view all the answers

Which structures does the spinoreticulothalamic pathway connect to in addition to the thalamus?

Limbic system and periaqueductal gray area Signup and view all the answers

What role does the reticular formation play in the brain?

Regulates arousal and attention Signup and view all the answers

According to the 'gate control' theory of pain, which type of fibers tends to allow transmission cells to fire more readily?

Thin fibers (pain) Signup and view all the answers

What effect does increased activity of large diameter fibers have on pain perception?

It decreases pain perception Signup and view all the answers

Which of the following best describes the limbic system's function?

Involved in motivation, emotion, learning, and memory Signup and view all the answers

What did Melzack and Wall propose in their 'gate control' theory of pain?

Large fibers can inhibit the pain signals from thin fibers Signup and view all the answers

What is the primary function of the periaqueductal gray area in the context of pain?

Propagation and modulation of pain and sympathetic responses Signup and view all the answers

What role does the inhibitory interneuron play in pain perception?

It decreases the chances that the transmission neuron will fire. Signup and view all the answers

How does the firing of C fibers affect the inhibitory interneuron?

C fibers inhibit the inhibitory interneuron indirectly. Signup and view all the answers

What is the role of the periaqueductal grey (PAG) in pain modulation?

It stimulates the raphe nucleus to reduce pain perception. Signup and view all the answers

What neurotransmitter is suppressed by the activation of enkephalin interneurons?

Substance P Signup and view all the answers

What triggers the release of enkephalin in the pain modulation pathway?

Serotonin from serotonergic pathways. Signup and view all the answers

Which pathway is associated with descending pain control?

Dorsal lateral projection from PAG to the raphe nucleus in the medulla. Signup and view all the answers

Which of the following factors does NOT affect pain perception?

Genetic predisposition to pain thresholds. Signup and view all the answers

What do C fibers primarily communicate regarding pain?

They contribute to the perception of chronic and intense pain. Signup and view all the answers

Study Notes

Pain

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
Initially, when experiencing pain from trauma, the person tries to withdraw from the stimulus, and the body guards the injured area to prevent further damage.
Muscle guarding requires high metabolic activity which compresses blood vessels.
Compromised circulation might be insufficient to supply metabolic needs, leading to ischemia (local anemia due to blood supply obstruction).
Ischemia creates a new source of pain.
Compromised circulation hinders the removal of metabolic wastes, which sensitize nociceptors, further intensifying pain.

Classification of Pain (According to Duration)

Acute pain: Short-term pain that resolves within 3 months. It's a body's response to injury or trauma and serves a biological purpose, usually self-limiting.
Chronic pain: Persists longer than 3 months, extending beyond the normal healing time, and leads to long-term loss of function.

Classification of Pain (According to Mechanism)

Nociceptive pain: Pain arising from injured or damaged body tissues stimulating nociceptors (pain receptors).
- Somatic pain: Resulting from stimulation of nociceptors in superficial tissues (e.g., skin). It is typically well-localized, sharp, or burning. Deep tissues (e.g., bone, joints) lead to a localized, dull, or aching sensation that can be referred to the skin.
- Visceral pain: Generated by stimulation of nociceptors in internal organs (e.g., abdominal organs). It is usually poorly localized, diffuse and described as dull, aching, or cramping, and may be referred to other areas of the body.
Referred pain: Pain originating from deep body structures but felt in a different, distant area. This is caused by the convergence of visceral and cutaneous (skin) nerve fibers in the spinal cord.

Neuropathic Pain

Caused by damage or injury to nerve cells in the peripheral or central nervous system.
Often characterized by unusual sensations including allodynia (pain from non-noxious stimuli), hyperalgesia (increased sensitivity to painful stimuli), hypoalgesia (decreased sensitivity to painful stimuli), and dysesthesia (unusual sensations like tingling or burning).
Pain is often poorly localized and described as burning, sharp, tingling or shooting in nature.

Pain Perception

Three types of stimuli activate pain receptors in tissues: mechanical (pressure), heat, and chemical.
Pain is initiated when injury occurs, releasing chemicals like substance P, prostaglandins, and leukotrienes, which lowers the depolarization threshold of nociceptors, making them more sensitive.
Following initial response, a subsequent period of hyperalgesia develops, as chemicals spread throughout the surrounding tissues, increasing the size of the painful area.

Pain Receptors (Nociceptors)

Specialized receptors in peripheral tissues that detect potential tissue damage.
Nociceptors are distinct types of free nerve endings.
Nociceptors respond to various types of stimuli like heat, pressure, and chemicals but normally are not triggered by non-damaging stimuli.

Neural Transmission of Pain

Afferent fibers transmit pain signals from receptors in peripheral tissues towards the brain.
Efferent fibers carry signals from the brain to the periphery.
Nociceptors are stimulated, creating an electrochemical signal that travels along different fibers (Aδ and C fibres) to the spinal cord.
The transmission of pain messages from peripheral tissues to the brain utilizes a series of neurons (first, second, and third-order neurons).

Pain Pathways

The nociceptive message travels to the central nervous system via the primary afferent nociceptors (Aδ and C fibers)
Pain signals are relayed to the brain via two main pathways, the neospinothalamic pathway (for fast, sharp pain) and the paleospinothalamic pathway (for slow, dull pain sensations).
Pain information is ultimately processed in the brain, leading to the perception of pain.

Gate-control Theory

Proposed that pain signals are modulated by a gate mechanism in the spinal cord.
Activating large-diameter fibres (through touch or pressure) stimulates inhibitory interneurons leading to the suppression of pain transmission.

Descending Pain Control

The brain, via the periaqueductal gray (PAG), can modulate pain by releasing endogenous opiates (endorphins).
These opiates can inhibit pain transmission at different levels in the nervous system.

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Description

Explore the concept of pain, including its definition and physiological mechanisms. This quiz also covers the classification of pain based on duration, contrasting acute and chronic pain. Enhance your understanding of how pain impacts the body and the healing process.