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Neuroanatomy & -physiology > 01 Pain Processing > Flashcards

01 Pain Processing Flashcards

1
Q

What are the 4 types of mechanoreceptors and how are they distributed in the skin?

A
  • Merkel cells (25%, epidermis, especially rich in finger tips)
  • Meissner corpuscles (40%, dermis)
  • Ruffini corpuscles (20%, dermis)
  • Pacinian corpuscles (10-15%, dermis/subcutaneous layer)
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2
Q

What is the afferent axon type of all mechanoreceptors?

A

Abeta

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3
Q

What are mechanoreceptors sensitive to?

A
  • sensitive to deformation by vibration at different frequencies
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4
Q

What are the receptors for proprioception and what are their afferent axon types?

A
  • muscle spindles
  • afferent axon type: Ia, II
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5
Q

Order the sensory functions proprioception, touch, pain, temperature and itch according to their axons’s conduction velocity! What is the reason for these differences?

A
  • proprioception > touch > pain, temperature > pain, temperature, itch
  • better myelination leads to higher conduction velocity
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6
Q

How do the different mechanoreceptors react to stimulation?

A
  • Merkel & Ruffini: slowly adapting, constant stimulus elicits constant response
  • Meissner & Pacinian: rapidly adpating, stimulus change elicits response
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7
Q

What is the pathway for proprioceptive and tactile information?

A
  • first-order neurons ascend ipsilaterally through dorsal root ganglia
  • second-order neurons are situated in the brainstem
  • relay in thalamus to primary somatosensory cortex (S1), S2 and parietal association cortex
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8
Q

Which areas belong to S1?

A
  • Broadmann areas 1, 2, 3a and 3b
  • 3b receives bulk / majority of input
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9
Q

What happens in S2 and parietal association cortex?

A
  • integration of tactile object features for recognition by touch (stereognosis)
  • binding of tactile with other features (vision, sound)
  • higher-order interpretations
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10
Q

What is stereognosis?

A

ability to perceive and recognize form of an object by using only tactile information

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11
Q

How are body parts mapped onto S1 and S2?

A

in S1:
- medial: legs, feet, genitalia, trunk neck, head, shoulders
- lateral: face, hands

in S2:
- throat, tongue, teeth, jaw, gums

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12
Q

What body parts are most/least sensible to touch? (receptor density)

A

mean two-point discrimination threshold
- lowest in hands (2mm) and face (lower part)
- highest in shoulders and calves (45mm)

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13
Q

What is nociception?

A

perception of potentially harmful stimuli

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14
Q

How is pain encoded? What are pain receptors?

A

pain not coded in excessive action of somatosensory receptors, but in distinct perception and signaling pathway
- receptors: no specialized corpuscles, but free nerve endings

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15
Q

What are the 2 phases of pain and why do they exist?

A
  • first pain: sharp and clearly localized
  • second pain: dull and diffuse
  • 2 different fiber types: poorly-myelinated (Adelta) and unmyelinated (C)
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16
Q

What are the 3 stages of pain processing?

A
  • transduction: conversion of nociceptive stimuli into electrial or chemical (neuronal) signal (peripheral nervous system)
  • transmission: forwarding of peripheral input through various notes of nociceptive pathway (sensory and postsynaptic neurons) towards the brain
  • modulation: remodeling (down-/upregulation) of nociceptive information at all relay points, translation into framework including specific context and memories
17
Q

Where can pain modulation occur?

A

at all relay points: sensory neuron, dorsal horn, higher-order brain regions

18
Q

Where does pain occur?

A
  • pain perception occurs in the brain
  • “nociception and pain can each happen without the presence of the other”
19
Q

Which role does the transient receptor potential (TRP) family play in pain? How do they work?

A
  • large group of pain receptors
  • mostly highly-selective Ca2+ channels, either open or closed
  • opening (Ca2+ influx) favors nociceptive signal generation (action pot.)
  • evidence for variation in width of opening
  • some TRP may react to temperature-dependent deformation or binding of chemical agents (such as capsaicin)
  • mutations of TRP proteins can lead to complete pain insensitivity or gain of function with chronic pain syndromes
  • genetic variants of TRP types associated with migraine
20
Q

What is the pathway for pain information?

A
  • neural cell bodies of free nerve endings reside in paravertebral ganglia
  • second-order neuron are situated in the spinal chord at the level of entry
  • second-order axon crosses midline and ascends contralaterally to thalamus
21
Q

What might unilateral damage to the spinal chord produce?

A

Brown-Séquard syndrome
- ipsilateral deficits in touch and proprioception (plus ipsilateral paresis)
- contralateral deficits in nociception and thermoception

22
Q

How can referred pain be explained?

A
  • some second order nociceptive neurons receive pain information from both a dermal segment and an inner organ
  • pain arising from the inner organ cannot be distinguished from pain arising from the skin and is perceived as coming from the surface
  • typical example: pain perceived in left arm as symptom of cardiac ischemia
23
Q

How is pain sensitization increased?

A
  • tissue damage
  • local cells (derived from blood or resident tissue) release “inflammatory soup” of mediators (e.g. histamine, prostaglandins) causing swelling, increased blood flow and lowered pain threshold
  • some TRP channel proteins become unlocked at temperatures > 50°C by permanent conformation changes and will then signal temperatures > 30°C
  • effect: protection of area and promotion of healing
24
Q

What are hyperalgesia and allodynia?

A
  • hyperalgesia: abnormally increased sensitivity to pain
  • allodynia: pain caused by stimulus that does not normally elicit pain
25
Q

How can pain be modulated?

A
  • placebo administration can relieve pain, but effect can be blocked by naloxone (opioid antagonist)
  • pain modulating fibers arise predominantly from periaqueductal gray of midbrain and regulate activity of the synapse between first- and second-order neuron
  • local collaterals from somatosensory fibers within the spinal chord can modulate pain (e.g., rubbing the site of injury)
  • pain relief is mainly promoted by endogenous opioids (endorphins, dynorphins, enkephalins) and endocannabinoids (act on TRP)
  • testosteron has pain dampening effect
26
Q

What does the homunculus show?

A

receptor density

Neuroanatomy & -physiology (14 decks)

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