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Neurology > Somatosensation II > Flashcards

Somatosensation II Flashcards

1
Q

What are the 2 major pathways of the somatosensory system?

A

The 2 major pathways are:

  • Dorsal column-medial lemniscal system (DCML)
  • Spinothalamic tract (STT)
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2
Q

What is the role of the DCML?

A

Receives input from large A-β fibres detecting Proprioception, touch,

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3
Q

What is the function of the STT?

A

Receives input from small C and ẟ fibres detecting Pain

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4
Q

How is pain detection mediated?

A

Ascending pathways mediate sensory aspects of pain for body and face

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5
Q

Which thalamic nuclei receive input about pain?

A

2nd order neurons decussate and project to ventral-posterior nuclear complex of thalamus

  • VPL: body
  • VPM: face
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6
Q

What are the 2 aspects of the dual aspect pain model

A
  1. Sensory-discriminative

2. Affective motivational

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7
Q

What is the sensory discriminative part of the dual aspect pain model?

A
  1. Sensory-discriminative
    - Location
    - Intensity
    - Duration
    - Quality
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8
Q

Describe the Affective motivational part of the dual aspect pain model

A
  1. Affective motivational
    - Unpleasantness – the painfulness of pain
    - Effects on arousal, mood (affect), behaviour
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9
Q

Which receptors detect pain?

A

Nociceptors are neurons specialized for detection of painful stimuli

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10
Q

How are nociceptors activated?

A

Nociceptors respond to warmth as skin fibre temperature raises, the rate of firing of action potentials increases up to a certain point

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11
Q

How do the 2 somatosensory pathways respond to pain?

A

A-δ (DCML) and C-fibres (STT) contribute different aspects of pain sensation

A-δ fibres are thinly myelinated and moderately fast conducting ~30mm/s

C fibres are thin and unmyelinated - slow conduction 1mm/s

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12
Q

How does nociceptor transduction vary?

A

Tactile mechanoreceptors have mechanically sensitive ion channels sensitive to stretch - specialised endings in merkel’s depolarise to cause action potential firing

Thermoreceptors have a range of ion channels that act as transducers

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13
Q

What receptor is responsible for dealing with noxious heat stimuli?

A

The TRPV1 receptor is involved in transduction of noxious heat
Originally called vanilloid receptor, present in A-δ and C-fibres

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14
Q

How is the TRPV1 receptor activated?

A

Ion channel permeable to Na+ and K+ opened by heat and acid

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15
Q

Explain why we still feel burning even after the noxious heat stimuli is removed

A

Following the removal of noxious stimulus, an ‘Inflammatory soup’ of cytokines, prostaglandins and small signalling molecules maintains depolarisation and sensitivity of C-fibre terminals after the original stimulus

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16
Q

What role does substance P have in the maintenance of nociceptor activity after injury?

A

Substance P released provides positive feedback to continue release of inflammatory signals

17
Q

What is hyperglasia?

A

hypersensitivity to pain

18
Q

What is allodynia?

A

normally innocuous stimulus elicits pain

19
Q

Outline how the anterolateral system allow us to detect pain signals

A

Dosal horn interneurons located in superficial and deep layers of the dorsal horn

  1. Dorsal horn interneurons receive synaptic input from C-
    and A-δ fibres
  2. Axons cross and ascend in anterolateral white matter
  3. Some are multi-modal (receive convergent nociceptive
    and non-nociceptive inputs)
  4. Some receive convergent input from visceral afferents
20
Q

Give an example of referred pain

A

E.g. angina - pain originates due to tissue damage of myocardium but pain is felt in the neck, back of shoulder and arms

21
Q

Explain why in angina pain is felt in arms and shoulders despite being due to the myocardium

A

Due to visceral afferents from the heart coming into the spinal cord via the sympathetic plexus synapsing onto the dorsal horn interneurons receive inputs from arms, shoulders etc.

The activity from those dorsal horn interneurons perceived from the higher orders as coming from the somatic sensory afferents

22
Q

Explain how referred pain works

A

So when these interneurons are activated from a non-typical way (e.g. convergence) then the pain is perceived as originating from the interneuron somatic sensory afferents

23
Q

Outline the STT pain pathway

A

STT projects through anterolateral white matter columns of the spinal cord to the thalamus.
STT projects to primary somatosensory cortex from S1 via VP nuclei of thalamus (like DCML system)

however, STT and DCML axons do not converge on same thalamic neurons – pathways are parallel

24
Q

What is the role of S1 in the cortical representation of pain

A

S1 is necessary for the localization of pain, but stimulation of S1 gives rise to referred tactile, not painful, sensations
Additional areas are involved in pain sensations

25
Q

What are the 2 cortical systems involved in central pain processing?

A
  • Lateral system

- Medial system

26
Q

Outline the Lateral system

A

Lateral system (do not confuse with anterolateral system)

  • VP nuclei of thalamus, in parallel with DCML system
  • Primary and secondary somatosensory cortex (SI and SII)
  • Sensory-discriminative
  • Project via specific somatosensory thalamic nuclei
27
Q

Describe the medial system

A

Medial system

  • Midline nuclei of thalamus (intralaminar)
  • Anterior cingulate and insular cortex
  • Affective-motivational
  • Project to different cortical areas via (non-specific)
    midline thalamic nuclei
28
Q

What are the endogenous modulators of the descending pain pathway

A 
Analgesic properties of opium known for centuries
Endogenous opioids (enkephalins, endorphins) are the natural ligands for opioid receptors discovered 1970s-80s
29
Q

Why are opioids good pain treatment?

A

Successful at treating pain as neurophysiological response to tissue damage

  • NSAID
  • Opiate drugs
30
Q

What is chronic pain?

A

> 3 months

Alarmingly high prevalence

Neurology (20 decks)

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