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NEU 7a: Somatosensory system - chronic pain $10.44   Add to cart

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NEU 7a: Somatosensory system - chronic pain

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Lecture notes from Imperial College London, Medical Biosciences BSc, 2nd year, Neuroscience (NEU) module. The afferent (sensory) and efferent (motor) divisions of the nervous system provide vital information about our outside world and allow us to implement an appropriate behaviour. We will look...

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  • October 5, 2023
  • 9
  • 2022/2023
  • Class notes
  • Laura canevari
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Somatosensory system - Chronic pain
- afferent (sensory) division of the nervous system provides vital info about outside world

What are somatosensory modalities?
- sensory neurons: pseudounipolar (peripheral branch + central branch) + in the dorsal root ganglia




pressure, vibration...
- ≠ types of somatosensory modalities (convey info about the body) travel via ≠ pathways to brain

dorsal column pathway (medial lemniscus system)
=> fine touch, pressure, vibration, proprioception


unconscious tract


spinothalamic pathway (anterolateral system)
=> nociception, temperature

- special senses also have their modalities (vision, hearing...) // visceral sensation via interoceptors

Somatosensory receptors
encapsulated within
Mechanoreceptors (touch, vibration, pressure....) non-neural cells
- nerve endings enclosed within capsules (layers of connective tissue)
- ≠ encapsulated receptors:

Merkel cell Meissner corpuscle Ruffini ending Pacinian corpuscle
⑦@°-

light touch (Braille), fine discriminative continuous pressure deep pressure, i


superficial pressure touch (grip force) touch, stretch vibration, tickling
in epidermis closest to skin elongated capsules deep in dermis

, - mechanoreceptors specialised for proprioception (info on position body): proprioceptors
=> muscle spindles
=> Golgi organs (in tendons)
=> joint receptors


Thermoreceptors (temperature)
- free sensory nerve endings in skin (see previous image)
- specific temperatures activate transient receptor potential (TRP) channels
=> cold-activated: TRPM8, TRPA1 thermal nociceptor & chemoceptor
=> heat-activated: TRPV1, TRPV2, TRPV3, TRPV4
n
noxious heat
=> thermal nociceptors




cold pain innocuous - cool painfully hot (50+)
moderate cold painfully hot (40+)
(menthol) (capsaicin chili)

Nociceptors (nociception)
- free sensory nerve endings in skin, joints & other tissues
- respond to damaging/ potentially damaging (noxious) stimuli
=> thermal (extreme temperature)
=> mechanical (intense pressure)
=> polymodal (thermal, mechanical, chemical: low pH, ATP, immune mediators...)


- specific receptors sensitive to histamine => itch sensation (urge to scratch)

Sensory transduction & stimulus threshold

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