Somatosensory System II: Pain and Temperature

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Questions and Answers

Which of the following sensations is primarily transmitted via the lateral aspect of the anterolateral system (ALS)?

  • Vibration
  • Non-discriminative touch
  • Crude touch
  • Thermal sensation (correct)

What type of nerve endings are responsible for detecting pain?

  • Free nerve endings (correct)
  • Ruffini endings
  • Pacinian corpuscles
  • Merkel discs

Which of the following describes the primary function of Aδ and C fibers??

  • Proprioception and fine touch
  • Primary pain and temperature sensation (correct)
  • Vibration sense
  • Motor control

What is the projection target in the thalamus for the anterolateral system (ALS) that carries sensory information from the upper and lower extremities?

<p>Ventral posterolateral nucleus (VPL) (B)</p> Signup and view all the answers

Which of the following best describes the function of nociceptors?

<p>Detection of painful stimuli (B)</p> Signup and view all the answers

What is the definition of hyperalgesia?

<p>Increased response to a painful stimulus (D)</p> Signup and view all the answers

Which of the following terms describes an altered sensation that is distinctly unpleasant?

<p>Dysesthesia (C)</p> Signup and view all the answers

What is the term for pain arising from a non-nociceptive source, often involving nerve pain, such as trigeminal neuralgia?

<p>Neuralgia (D)</p> Signup and view all the answers

Which of the following neurotransmitters or peptides is involved in suppressing pain transmission within the spinal cord?

<p>Enkephalin (A)</p> Signup and view all the answers

Which fibers are activated to relieve pain when using transcutaneous electrical nerve stimulation (TENS)?

<p>Aβ fibers (C)</p> Signup and view all the answers

According to the gate control theory of pain, what is the role of Aβ mechanoreceptors in modulating pain perception?

<p>They activate inhibitory interneurons, reducing pain signals to the brain. (D)</p> Signup and view all the answers

What is the primary function of the anterior white commissure in the context of pain pathways?

<p>Decussation of anterolateral system fibers (C)</p> Signup and view all the answers

What is the definition of allodynia?

<p>Painful response to a normally innocuous stimulus (A)</p> Signup and view all the answers

Which of the following best describes the somatotopic organization of the anterolateral system (ALS)?

<p>Sacral segments are most medial, cervical segments most lateral (B)</p> Signup and view all the answers

After synapsing in the dorsal horn, the second-order neurons of the anterolateral system (ALS) decussate (cross over) and then ascend to which brain structure?

<p>Thalamus (C)</p> Signup and view all the answers

What is the likely effect of a lesion in the spinal cord that selectively damages the anterior white commissure?

<p>Loss of pain and temperature sensation contralaterally (A)</p> Signup and view all the answers

Which of the following describes referred pain?

<p>Pain that is felt in a location different from the site of tissue damage. (C)</p> Signup and view all the answers

What is the primary role of the reticular formation in the context of pain pathways?

<p>Modulation of the emotional and arousal aspects of pain (D)</p> Signup and view all the answers

Which of the following is a characteristic of pain and temperature receptors?

<p>Distinct thresholds and activation of thermo-nociceptors at extreme temperatures (B)</p> Signup and view all the answers

What is the significance of dermatomes in the context of somatosensory function?

<p>They define regions of skin innervated by specific spinal nerves. (B)</p> Signup and view all the answers

What is a myelotomy and what condition is it typically used to treat?

<p>A surgical procedure to cut nerve fibers in the spinal cord, used to treat intractable pain. (D)</p> Signup and view all the answers

Which vascular structure, when occluded, typically results in Lateral Medullary (Wallenberg) Syndrome?

<p>Posterior inferior cerebellar artery (PICA) (B)</p> Signup and view all the answers

In a patient with Brown-Sequard syndrome resulting from spinal cord hemisection, which sensory loss would be expected contralaterally below the level of the lesion?

<p>Loss of pain and temperature sensation (A)</p> Signup and view all the answers

A patient reports loss of pain and temperature sensation on the left side of the body, along with ipsilateral loss of fine touch and proprioception on the right side. Where is the most likely location of the lesion?

<p>Right side of the spinal cord (C)</p> Signup and view all the answers

What sensory deficits are characteristically seen with damage to the Dorsal Columns?

<p>Loss of fine touch and proprioception (B)</p> Signup and view all the answers

What type of stimuli cause the largest response in thermoreceptors?

<p>Changes in temperature (C)</p> Signup and view all the answers

What is the primary target in the thalamus for the Anterior Trigemino-Thalamic System (ATT)?

<p>Ventral posteromedial nucleus (VPM) (D)</p> Signup and view all the answers

In the context of anterolateral system (ALS) pathways, what is the role of the intralaminar nuclei of the thalamus?

<p>Modulating arousal and attention in response to pain (A)</p> Signup and view all the answers

Which of the following would be most effective in providing analgesia that acts at the level of the spinal cord?

<p>A drug that blocks substance P release. (C)</p> Signup and view all the answers

What is a key difference in sensory deficits between a spinal cord lesion and a cortical lesion affecting the anterolateral system (ALS) and dorsal column medial lemniscus (DCML) pathways?

<p>In spinal cord lesions, ALS deficits are post-decussation, while in cortical lesions, both ALS and DCML deficits are post-decussation. (C)</p> Signup and view all the answers

Which of the following is a common feature of both visceral and cutaneous nociceptors that contributes to referred pain?

<p>Convergence on the same dorsal horn neurons (C)</p> Signup and view all the answers

Following static compression of a peripheral nerve, a patient reports altered sensations such as tingling and numbness along the nerve's dermatome. What is the most likely cause of these symptoms?

<p>Peripheral nerve damage (B)</p> Signup and view all the answers

What is the role of lamina I in the spinal cord?

<p>Receiving nociceptive and thermoceptive information (C)</p> Signup and view all the answers

In a patient with a tumor compressing the spinal cord from the lateral aspect, which of the following deficits would be expected?

<p>Ipsilateral loss of motor function as well as pain and temperature sensation (C)</p> Signup and view all the answers

What is the primary role of the periaqueductal gray (PAG) in the context of pain modulation?

<p>Activating descending pathways that inhibit pain transmission (A)</p> Signup and view all the answers

What is the primary mechanism by which nonsteroidal anti-inflammatory drugs (NSAIDs) reduce pain?

<p>Inhibiting the production of prostaglandins. (D)</p> Signup and view all the answers

A patient being treated for cancer experiences severe pain due to intestinal distension. Which type of pain fibers are primarily responsible?

<p>C fibers (A)</p> Signup and view all the answers

Following a stroke affecting the right somatosensory cortex, a patient reports an inability to recognize objects by touch with their left hand, despite intact motor function, what is this condition called?

<p>Astereognosis (C)</p> Signup and view all the answers

Flashcards

Analgesia

Relief of pain

Hyperalgesia

Increased response to painful stimuli

Hyperesthesia

Increased sensitivity to stimuli

Anesthesia

Loss of pain sensation

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Hypesthesia

Reduced pain sensation

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Paresthesia

Altered sensation; numbness, prickling, or tingling

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Dysesthesia

Altered sensation (paresthesia) distinctly unpleasant

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Neuralgia

Non-nociceptive, nerve pain

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Rapid III (Ad) fibers

Ascending information through DRG/ALS; sharp pain

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Slow IV (C) fibers

Ascending information through DRG/ALS; dull pain

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Area of skin innervated by a single spinal nerve

Dermatome

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Referred pain

Phenomenon where pain from a visceral organ is perceived as originating from a specific cutaneous region

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Brown-Sequard Syndrome

Spinal cord hemisection leading to ipsilateral motor control and touch/proprioception loss

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Anterolateral System (ALS)

Pain, temperature, and crude touch pathway to the brain

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Wallenberg syndrome

Lateral medullary syndrome (PICA)

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Hemi-analgesia

Loss of pain sensation

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Hemi-thermoanesthesia

Loss of temperature sensation

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Crude touch

Discriminatory touch, pain and temperature

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Nociceptors and Thermoreceptors

Detects pain and temperature

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Extreme Temps

Activated by intense stimuli, activating thermo-nociceptors

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Allodynia

Sensitization increases

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Myelotomy

Used to treat intractable pain during cancer

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Anterior ALS

Non discriminative touch

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Lateral ALS

Thermal sensation

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Pain

Nociception (pain)

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Nocicereceptors

Free ending nerve cells

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Study Notes

Somatosensory System II: Overview

  • Focuses on pain, temperature, analgesia, referred pain, the anterolateral system (ALS), the anterior trigemino-thalamic system, cord and CNS syndromes, and case studies

Pain, Temperature, and Analgesia

  • Non-discriminative touch is carried by the anterior ALS
  • Thermal sensation and nociception (pain) are carried by the lateral ALS
  • Mechanoreceptors and free nerve endings are involved in these sensations
  • Ad and C fibers are primary pain and temperature neurons
  • Crude touch, pain, and temperature discrimination involves the ALS
  • ALS handles information from upper and lower extremities, projecting to the VPL then somatosensory cortex
  • ATT handles information from the face and head, projecting to the VPM then somatosensory cortex
  • Negative perception/response to crude touch, pain, and temperature involves: reticular nuclei, peri-aqueductal gray, intralaminar nuclei of thalamus, insular and cingulate cortices

Mechanoreceptors and Nociceptors

  • Mechanoreceptors for crude touch are high-threshold and have large receptive fields, responding to rough stimuli with or without tissue damage
  • Mechano-nociceptors respond to pinch, puncture, and tissue damage
  • Nociceptors for pain are "free" nerve endings
  • Nociceptive mediators include H+, K+ ions, venoms, serotonin, histamine, bradykinin, prostaglandins, substance P, and CGRP peptides

Thermoreceptors and Ion Channels

  • Thermoreceptors respond to cool, cold, warm, and hot temperatures
  • Changes elicit the largest response
  • Pain and temperature receptors are distinct, with different thresholds
  • Extreme temperatures activate thermo-nociceptors
  • Nociceptive and thermosensitive ion channels include TRP and ASIC channels

"Painful" Terms

  • Allodynia: increased sensitization, painful response to innocuous stimuli in receptive field past the damaged area
  • Hyperalgesia: increased response to painful stimuli
  • Hyperesthesia: increased sensitivity overall
  • Anesthesia: loss of pain sensation
  • Hypesthesia: reduced pain sensation
  • Paresthesia: positive, altered sensation (numbness, prickling, tingling)
  • Dysesthesia: altered sensation (paresthesia) that is distinctly unpleasant
  • Neuralgia: non-nociceptive, nerve pain (trigeminal neuralgia)
  • Analgesia: relief of pain, achieved through epidural analgesia (opioids, local anesthetics), stimulation, or transcutaneous electrical nerve stimulation (TENS)
  • Shingles (herpes zoster virus) can cause hyperesthesia and post-herpetic neuralgia, with paresthesia in V1/V2 divisions

Central Control of Pain

  • Ascending information travels via DRG/ALS, with rapid III (Ad) fibers for sharp pain and slow IV (C) fibers for dull pain
  • Descending information is modulated via peri-aqueductal gray and raphe nuclei
  • Amines (serotonin, norepinephrine) and endogenous opiate peptides (enkephalin) suppress pain transmission mediated by nociceptive DRG neurons (substance P, glutamate) at the spinal cord level

Gate Theory of Central Pain

  • C fibers inhibit inhibitory INTN and excite ALS INTN
  • Aβ mechanoreceptors excite inhibitory INTN
  • Descending inputs excite inhibitory INTN
  • Strong pain is carried only by C fibers
  • Weak pain is weak with mechanoreceptors
  • Weak pain is also present with descending inputs
  • Trans-cutaneous electrical neural stimulation activates Aβ to relieve pain
  • Shaking a limb has a similar effect
  • Myelotomy is used to treat intractable intestinal pain in cancer patients by cutting the anterior white commissure (AWC)

Dermatomes and Referred Pain

  • Central overlap occurs in dermatome skin regions
  • Dermatomes represent skin areas centrally, organized by trigeminal divisions (V1, V2, V3) and spinal roots
  • Shingles is caused by reactivation of varicella-zoster virus, affecting dermatomes
  • Fingertip and trigeminal regions exhibit less dermatomal overlap, indicating narrower receptive fields
  • 'Visceral' nociceptors and skin nociceptors share common dorsal horn target interneurons
  • Activation of visceral nociceptors is localized as dermal pain (e.g., angina pectoris)

Anterolateral System (ALS)

  • DRG fibers enter the 'posterolateral fasciculus' and Lissauer's tract over several spinal segments
  • Synapse in the dorsal horn with decussation at the anterior white commissure (AWC)
  • somatotropic organization in ALS - VPL, somatosensory cortex
  • Targets for negative perception and response include reticular formation, intralaminar nuclei, tectum, peri-aqueductal gray matter, and cingulate cortices
  • ALS deals with touch, thermal sense and pain

Anterolateral System Pathways

  • Spinothalamic pathway is responsible for localization and perception
  • Spinoreticular pathway mediates arousal
  • Spinomesencephalic pathway mediates response to pain

Vascular Syndromes

  • Damage to anterior spinal artery will affect both corticospinal tracts and the anterolateral system
  • Damage to the posterior spinal arteries will affect dorsal column medial lemniscus

Vascular Supply

  • Spinal cord supplied by anterior spinal artery, posterior spinal arteries
  • Medulla supplied by anterior spinal artery and posterior inferior cerebellar artery (PICA)
  • Thalamus supplied by thalamogeniculate artery, a branch of the posterior cerebral artery
  • Cortex supplied by middle cerebral artery (MCA) and anterior cerebral artery (ACA)

Wallenberg Syndrome

  • Also known as lateral medullary syndrome
  • Typically the result of occlusion of PICA
  • Leads to Hemi-analgesia (loss of pain sensation) and Hemi-thermoanesthesia (loss of temperature sensation)
  • Results in contralateral loss of pain in the body and ipsilateral loss of pain in the face and head

Spinal Cord Hemisection

  • Known as Brown-Sequard Syndrome
  • Results in;
    • Ipsilateral loss of motor control (post-decussation, descending)
    • Ipsilateral loss of touch / proprioception (pre-decussation, ascending)
    • Contralateral loss of pain / temperature (post-decussation, ascending)

Case Studies: Spinal Cord Lesions

  • Spinal meningioma T9, left side, causes:
    • Ipsilateral deficits in lower motor neurons, DCML, and
    • Contralateral ALS deficits
  • Sudden onset numbness in right face/arm/leg due to lacunar infarct in thalamus, affecting VPL (DCML) and VPM (trigeminal)
  • Decreased sensation in right body arm and face, right arm numbness, aphasia and blurred vision, caused by a broad infarct covering somatosensory cortex, parieto-occipital region and Wernicke's area

Lateral Pontine or Medulla Lesions

  • Lateral Pontine or Medulla: contralateral loss of pain and temperature sensation in the body (ALS) and ipsilateral loss of pain and temperature sensation in the face (ATT)

Medial Medulla Lesions

  • Contralateral loss of touch and proprioception in the body (DCML)

Other Cord Sydromes

  • Central cord syndrome: weakness and loss of somatosensory function below the lesion
  • Anterior cord syndrome: weakness and loss of pain and temperature sensation below the lesion
  • Posterior cord syndrome: loss of touch and proprioception below the lesion

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