Somatosensory system

12 important questions on Somatosensory system

What are somatotropic maps?

The representation of the body in separated regions. The man that is formed from this map is called homunculus.

The somatosensory cortex receives input from two type fiber (dorsal root afferents), which two fibers?

  • Touch and pressure: mechanosensory fiber
  • Nocireceptive afferent: pain & temperature

How does the mechanosensory fiber worK?

Touch is a change in pressure on the skin. This causes the ion channels to open and ions can move in to generate an action potential.
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What are the mechanoreceptors in the skin? What are the differences?

  • Merkel cell: small receptive field, high precision
  • Meissner corpuscle: more sensitive but less precise
  • Ruffini corpuscle: detects stretching of the skin and motion/vibration
  • Pacinian corpuscle: detects general pressure (skin stretch)

What is the difference between slowly adapting fibers and rapid adapting fibers?

Slowly adapting fibers detect persistent stimulation, rapid adapting fibers detect change.

What is the difference between touch and proprioception?

Touch is about external stimuli. Proprioception is sensory information about the body itself.

What are the receptors for proprioception?

  • Muscle spindles: changes in muscle length
  • Golgi tendon: changes in muscle tension

Pain perception is mediated by slow fibers. Which fibers? What is the difference?

Aδ and C fibers
Aδ is lightly myelinated and mediates the fast pain/first pain. C fibers are not myelinated and very thin, these mediate the slow pain/second pain.

How is pain & heat transported?

Transient receptor potentials (TRP) are opened in reaction to heat, chemical irritants and substances secreted by damaged tissue.

Why do you feel pain when you eat hot peppers?

Capsaicin activates the 'heat receptor' TRPV1 on C-fibers (slow pain).

Why do you feel pain on your chest or arm when you have pain in your heart of oesophagus?

Visceral pain neurons also project onto dorsal horn neurons that convey cutaneous pain.

How is pain modulated?

  • Descending tracks from e.g. Raphe (serotonin) or locus coeruleus (NA) suppress pain
  • Local mechanosensory input suppresses pain
  • Endocannabinoids & endorphins suppress pain tracks in the spinal cord

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