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Neurology > Introduction to Sensory Receptors and Sensory Neurones The Somatosensory System > Flashcards

Introduction to Sensory Receptors and Sensory Neurones The Somatosensory System Flashcards

1
Q

What are the sensory modalities?

A
  • Fine discriminatory touch [Light touch, pressure, vibration, flutter and stretch (mechanosensation)]
  • Joint and muscle position sense (proprioception)
  • Temperature (thermosensation)
  • Pain (nociception)
  • Itch (pruriception)
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2
Q

What are the broad categories of sensory modalities?

A
  • Exteroceptive division (cutaenous senses) registers information from the surface of the body by numerous receptor types
  • Proptioceptive division monitors posture and movement (sensors in muscle, tendons and joints)
  • Enteroceptive division reports upon the internal state of the body and is closely related to autonomic function
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3
Q

How is sensory stimulus converted to electrical activity?

A

Stimulus opens cation selective ion channels in peripheral terminal of primary sensory afferent eliciting a depolarising receptor potential

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4
Q

Action potentials ariving at the central terminal cause the graded release of ___________ on to ______ order neurones

A

Action potentials ariving at the central terminal cause the graded release of neurotransmitter on to second order neurones

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5
Q

What is adaptation rate?

A

Does the sensory unit discharge action potentials continuously during the stimulus, or does it respond preferentially to a changing stimulus

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6
Q

What is the sensory unit for touch, pressure, vibration?

A

Skin mechanoreceptors

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7
Q

What is the sensory unit for proprioception?

A

Joint and muscle mechanoreceptors

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8
Q

What is the sensory unit for temperature?

A

Cold and warm thermoceptors

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9
Q

What is the sensory unit for pain?

A

Mechanical, thermal and polymodal nociceptors

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10
Q

What is the sensory unit for itch?

A

Itch receptors

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11
Q

What is the role of low threshold units?

A

To respond to low-intensity (non-damaging) stimuli

  • low threshold mechanoreceptors: mediate fine discriminatory touch
  • low threshold thermoreceptors: mediate cold through to hot
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12
Q

What is the role of high threshold units?

A

Respond to high (noxious, potentially damaging), but not (normally) low, intensity stimuli

  • high threshold mechanoreceptors: respond to high intensity mechanical stimuli
  • thermal nociceptors: respond to extreme degrees of heat (>45 degrees celcius)
  • chemical nociceptors: respond to substances in tissue [e.g. as in inflammmation: prostaglandins, bradykinin, serotonin (5-HT), histamine, K, H and ATP)
  • polymodal nociceptors resopond to at least two of the above
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13
Q

Where are slowly adapting sensory units found?

What information do they provide?

A

Stretch receptors

Information about position, degree of stretch, or force

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14
Q

Where are fast adapting sensory units found?

What information do they convey?

A

Some muscle spindle afferents, hair follicle afferents

Detects changes in stimulus strength (range of movement) number of impulses proportional to rate of change of stimulus.

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15
Q

Where are very fast adapting sensory units found?

What information do they convey?

A

Pacinian corpuscle

Responds to very fast movement, such as rapid vibration

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16
Q

What do Group I, Aα axons conduct? How fast are they and are they myelinated?

A

From proprioceptors of skeletal muscle

80-120ms-1

Thick myelin

17
Q

What do Group II, Ab axons conduct? How fast are they and are they myelinated?

A

Mechanoreceptors of skin

35-75ms-1

Moderately myelinated

18
Q

What do Group III, Aδ axons conduct? How fast are they and are they myelinated?

A

Pain, temperature

5-30ms-1

Thinly myelinated

19
Q

What do Group IV, C axons conduct? How fast are they and are they myelinated?

A

Temperature, pain, itch

0.5-2.0ms-1

Not myelinated

20
Q

The peripheral teminal of cutaenous afferent fibres branch into many fine processes, the tips of these can be;

A

Free nerve endings (partially naked)

Associated with specialised structures

21
Q

Receptive field is inversely related to ________ _______

A

Receptive field is inversely related to innervation density

22
Q

How does sensory acuity correlate to receptive field size?

A

Inverse relationship

23
Q

How is two-point discrimination tested?

A

By applying simultaenously two sharp point stimuli, separated by a variable distance, at different sites on the body surface

24
Q

Regions with the highest discriminative capacity have the _______ receptive fields?

A

Regions with the highest discriminative capacity have the smallest receptive fields?

25
Q

What should two-point discrimination be on the finger tip, palm and forearm?

A

Fingertip - 2mm

Palm- 10mm

Forearm- 40mm

26
Q

What are meissner’s corpuscles?

A

Found in locations where two point discrimination is highest, not present in hairy skin.

27
Q

Where are merkel’s discs found?

A

In the same places as meissner’s corpuscles but also present in hairy skin

28
Q

What are ruffini endings?

A

Responsible for detecting pressure, found in dermis and joint capsules

29
Q

What are pacinian corpuscles?

A

Responsible for detecting pressure, found in dermis and fascia

30
Q

What are the subdivisions of skin low threshold mechanoreceptors?

A

FA1

FA2

SA1

SA2

31
Q

Which physiological sub-class do;

  • merkel cell-neurite complexes
  • meissner corpuscles
  • ruffini endings
  • pacinian corpuscles

belong to?

A

SA1

FA1

SA2

FA2

32
Q

Spinal cord consists of ____ (cell bodies and sensory afferent terminals) and _____ (fibre tracts) matter the relative proportions of which vary along its length

____ matter subdivided into ______ (posterior) and ______ (anterior) horns and ten distinct laminae of Rexed

A

Spinal cord consists of grey (cell bodies and sensory afferent terminals) and white (fibre tracts) matter the relative proportions of which vary along its length

Grey matter subdivided into dorsal (posterior) and ventral (anterior) horns and ten distinct laminae of Rexed

33
Q

Where are nociceptors located in the dorsal horn?

A

Laminae I and II

34
Q

Where are LTMs located in the dorsal horn?

A

Laminae III to VI

35
Q

Where are proprioceptors located in the dorsal horn?

A

Laminae VII to IX

Neurology (41 decks)

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