Processing of somatosensory input Flashcards

1
Q

The somatosensory system and its modalities?

A

Mediates all sensations that are not visual, auditory, gustatory, olfactory or the vestibular sense of equilibrium; special sensory.

Includes the sensory modalities of:
* Touch, pressure and vibration (mechanosensation)
* Joint and muscle position sense (proprioception)
* Temperature (thermosensation)
* Pain (nociception)
* Itch (pruriception)

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2
Q

The —– of sensory neurons transduce a stimulus (e.g. mechanical) into electrical activity.
Stimulus (e.g. mechanical) opens cation-selective ion channels in nerve terminal to elicit a —– receptor potential.
The receptor potential is —- and proportional to stimulus —–
Local current flow triggers ‘—–’ action potentials at a frequency proportional to the —— of the receptor potential

A

terminals
depolarising
graded
intensity
all or none
amplitude

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3
Q

what are the Sensory receptive/unit properties of primary afferent neurons?

A

Modality
Threshold
Adaptation
Conduction velocity
Site and extent of peripheral termination [receptive field (RF)]

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4
Q

Modality?

A

The principal type of adequate stimulus that causes a signal

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5
Q

Threshold?

A
  • what intensity of the stimulus is required for excitation of the sensory receptor?
    • e.g. low threshold mechanoreceptors mediate fine discriminatory touch, high threshold (HT) (nociceptor) mechanoreceptors respond to high intensity mechanical stimuli; Information from HT units can be perceived as painful, but is subject to modulation.
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6
Q

Adaption?

A
  • Adaption rate - does the sensory unit discharge action potentials continuously during the stimulus, or does it respond preferentially to a changing stimulus?
    • Slowly adapting/tonic response - continuous information to CNS while terminal deformed e.g. stretch receptors
    • Fast adaptic/phasic response - detects changes in stimulus strength, number of impulses proportional to rate of change of stimulus e.g. some muscle spindle afferents
    • Very fast adapting response - responds only to very fast movement such as rapid vibration e.g. Pacinian corpuscle
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7
Q

Conduction velocity?

A
  • how rapidly does the sensory unit conduct action potentials along its axon?
    • Depends on diameter of axon and whether the axon is myelinated
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8
Q

Site and extent of peripheral termination

A

where is the peripheral terminal of the sensory unit located, do its sensory receptors have a small or large anatomical distribution?
- The peripheral termination of cutaneous afferent fibres branch into many fine processes, the tips of which can be free nerve endings or associated with specialised structures
- Receptor field (RF): target territory from which a sensory unit that can be excited
- Sensory acuity correlates inversely with RF size

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9
Q

Two-point discrimination (or spatial acuity)

A
  • Two-point discrimunation is an important measure of somatosensory function
  • Clinically tested by applying simultaneously two sharp point stimuli, separated by a variable distance, at different sites on the body surface
  • Subject reports on whether one point, are two, are sensed and a threshold distance between the two is established
  • Two-point thresholds match the diameter of the corresponding RF, regions with the highest discriminative capacity have the smallest RFs
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10
Q

Cutaneous receptors

A
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11
Q

Cutaneous and subcutaneous receptors, associated nerve fibres and sensory modality

A
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12
Q
A
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