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PHSL231 > 13: Somatic Sensation > Flashcards

13: Somatic Sensation Flashcards

1
Q

What are the 4 sensory receptors of skin?

A
  • Temperature (thermoreceptors)
  • Position of limbs (proprioceptors)
  • Touch receptors (mechanoreceptors)
  • Pain (nociceptors)
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2
Q

Describe thermoreceptors

A
  • Different types more active at warm or cold temperature ranges, especially responsive to changing temperature
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3
Q

Describe proprioceptors

A
  • (Muscle spindles, golgi tendon organs, joint capsule) skin mechanoreceptors
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4
Q

Decribe touch/mechanoreceptors

A
  • Sensitive to mechanical deformation (mechanoreceptors)

- Various types

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5
Q

Describe nocicepters (pain)

A
  • Respond to extreme mechanical, temperature, and/or chemical stimuli
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6
Q

What are four types of skin touch receptors?

A
  • Meissner’s corpuscles
  • Pacinian corpuscles
  • Merkel cell endings
  • Ruffini’s corpuscles
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7
Q

Draw out/decribe a pacinian corpuscle

A

slides

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8
Q

What are four types of sensory coding?

A
  • Modality
  • Intensity
  • Location
  • Duration
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9
Q

What is modality?

A

(eg; touch vs temperatre)

-Specificity of receptors. ‘labelled line’. (slides)

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10
Q

What is intensity?

A

-Frequency of action potentials in each axon, number of axons activated

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11
Q

What is location?

A

Mapping of receptive fields of individual primary afferents to specific cortical locations (somatotopic representation)

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12
Q

Describe duration

A
  • ‘rapidly adapting’ receptors respond briefly, even if stimulus is sustained. Detect movement, changing pressure.
  • ‘slowly adapting’ receptors signal true duration of stimulus
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13
Q

Where does the anterolateral/ventral pathway cross over, and what is it used for

A
  • Crosses over low in the spinal cord

- For general or broad sensations pain, temperature

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14
Q

Where does dorsal column pathways cross over, an what is it for?

A
  • Crosses over high in the spinal cord, in medulla

- For fine, detailed pathways

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15
Q

What is lateral inhibition?

A

A fundamental mechanism to increase accuracy of sensory information

Slides

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16
Q

What is lateral inhibition mediated by?

A

Inhibitory interneurons

17
Q

When is lateral inhibition used

A
  • In somatic sensation, lateral inhibition localises sensation to a restricted area of skin
  • Lateral inhibition is used wherever accurate location of a stimulus is required -or where a pattern of input needs to be discriminated (eg; vision, smell..)

Lateral inhibition results in centre-surround inhibition

18
Q

Locate the somatosensory cortex

A

slides

19
Q

Describe the somatotopic map

A

-

20
Q

Describe pain (noiception) and its use

A

slides

21
Q

What are the two types of nerve fibres that carries pain/noiciception?

A
  • “C”-fibres

- “Aδ” -fibres

22
Q

Describe C fibres

A
  • Smallest diameter, unmyelinated axons
  • Slow conduction velocity
  • Signal ongoing damage (or potential damage)
  • Polymodal
23
Q

Describe “Aδ” -fibres

A
  • Small diamter myelinated axons
  • Faster conduction velocity
  • Signal acute onset of painful stimulus
  • Primary mechanoreceptors
24
Q

Describe sensitation in pain pathways

A

slides

25
Q

Describe the gate control model for pain

A

slides

26
Q

What are two chemical methods of inhibiting pain

A
  • Endogenous opiates

- Endocannabinoids

27
Q

Describe endogenous opiates

A
  • Released at synapses on pain-pathway neurons
  • “natural analgesia” system, acute response to pain, stress
  • Site of action of ‘centrally acting’ painkillers (morphine, codeine)
28
Q

Describe endocannabinoids

A
  • Synthesised and released by neurons (but not stored in vesicles), pain receptors, as well as centrally
  • Apparently mediate some presumed effects of endogenous opiates
29
Q

Describe referred pain

A

-Occurs when pain is poorly localised

  • Feelings from viscera (gut) is referred to the body surface
  • eg; heart pain to neck and arm
  • activated by stretch, ischemia -except in brain

-Also, nerve compression can cause pain to be felt in region of nerve termination (slipped disc)

30
Q

What is a phatom limb

A

Sensation “felt” in region that no longer exists

31
Q

What are two causes of a phantom limb

A
  1. Ongoing activity in nerves that used to come from that part
    1. Invasion of cortical representation for that part by intact body regions
      - Eg; cortex representation of amputated hand may become activated by inputs from face
      Fibres from the face then occupy the ‘territory’ of the hand -allowing it to become its own sensory input.

PHSL231 (25 decks)

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