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CNS CLERKSHIP > Sensory receptors and neurones - the Somatosensory system. > Flashcards

Sensory receptors and neurones - the Somatosensory system. Flashcards

1
Q

The somatosensory mediates all sensations other than what?

A

Special senses.

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2
Q

Give an example of a special sense.

A
  • Mechanosensation (fine discriminatory touch e.g. light touch, pressure, vibration, flutter and stretch).
  • Proprioception (joint and muscle position sense).
  • Thermosensation (temp.).
  • Nociception (pain).
  • Pruriception (itch).
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3
Q

What are the three broad categories into which the Somatosensory system can be divided?

A
  • Exteroceptive division.
  • Proprioceptive division.
  • Enteroceptive division.
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4
Q

What is the function of the exteroceptive division of the Somatosensory system?

A

Cutaneous senses - i.e. registering information from body surface by numerous receptors.

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5
Q

What is the function of the proprioceptive division of the Somatosensory system?

A

Monitors posture and movements via sensors in muscles and tendons and joints.

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6
Q

What is the function of the enteroceptive division of the Somatosensory system?

A

Reports on internal body state in close relation to autonomic function.

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7
Q

How are stimuli transduced into electrical activity by sensory neurone terminals?

A

Stimulus opens a cation selective ion channel in the peripheral terminal of a primary sensory afferent to elicit a depolarising receptor potential.

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8
Q

The amplitude of receptor potential is graded and proportional to what?

A

Stimulus intensity.

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9
Q

Action potentials arriving at the central terminal cause graded release of what to where?

A

Neurotransmitter on to second order neurones.

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10
Q

What type of sensory unit would sense a mechanical force acting on the skin?

A

Skin mechanoreceptors

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11
Q

What type of sensory unit would sense a mechanical force acting on joints and muscles?

A

Joint and muscle mechanoreceptors.

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12
Q

What type of sensory unit would sense heat?

A

Cold and warm thermoreceptors.

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13
Q

What type of sensory unit would sense pain?

- e.g. strong mechanical force on skin or viscera, high heat on skin/mucous/membranes/viscera?

A

Mechanical, thermal and polymodal nociceptors.

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14
Q

Threshold is the intensity of a stimulus required to what?

A

Excite a sensory unit.

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15
Q

Low threshold units respond to what?

A

Low intensity stimuli.

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16
Q

Low intensity stimuli tend to be what?

A

Non-damaging/innocuous.

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17
Q

High threshold units respond to what?

A

High intensity stimuli.

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18
Q

High intensity stimuli tend to be what?

A

Noxious, potentially damaging.

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19
Q

Thermal nociceptors respond to what?

A

Extreme degrees of heat (>45oC) or cold (<10-15oC).

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20
Q

Polymocal nociceptors respond to what?

A

At least TWO of the following:

  • High intensity mechanical stimuli.
  • Extreme degrees of heat or cold.
  • Substances in tissue.
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21
Q

What type of nociceptors respond to substances in tissue?

A

Chemical nociceptors.

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22
Q

This feature of sensory units determines whether firing rate is changed in response to stimuli of changing intensity or remains consistent throughout a constant stimulus.

A

Adaptation.

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23
Q

Give an example of a slowly adapting receptor.

A

Stretch receptors.

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24
Q

Give an example of a fast adapting receptor.

A

Some muscle spindle afferents, hair follicle afferents.

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25
Q

Give an example of a very fast adapting receptor.

A

Pascinian corpuscle.

26
Q

Slowly adapting receptors e.g. stretch receptors provide what information?

A

Position, degree of stretch or force.

27
Q

Fast adapting receptors e.g. some muscle spindle afferents, hair follicle afferents detect what?

A

Changes in stimulus strength e.g. rate of movement.

28
Q

Very fast adapting receptors e.g. Pacinian corpuscles respond to what?

A

Only to very fast movement e.g. rapid vibration.

29
Q

What type of response is associated with slowly adapting receptors?

A

Tonic/static response.

30
Q

What type of response is associated with fast adapting receptors?

A

Phasic/dynamic response.

31
Q

What type of response is associated with very fast adapting receptors?

A

Very phasic/dynamic response.

32
Q

Peripheral terminals of cutaneous afferent fibres branch into many fine processes, the tips of which may be what?

A
  • Free nerve endings.

- Associated with specialised structures.

33
Q

Receptive field size is inversely related to what?

A

Innervation density.

34
Q

How does receptive field size correlate with sensory acuity?

A

Sensory acuity correlates inversely with receptive field size.

35
Q

Two-point discrimination is an important measure of what?

A

Somatosensory function.

36
Q

How is two-point discrimination tested?

A

Simultaneously applying two sharp point stimuli separated by a variable distance at different sites on the body surface.

37
Q

Regions with the highest discriminative capacity have what receptive field size?

A

The smallest.

38
Q

What are the sensory receptors of glabrous (hairless) skin?

A
  • Merkel cell-neurite complexes.
  • Meissner corpuscle.
  • Ruffini endings.
  • Pacinian corpuscle.
39
Q

What are Merkel cell-neurite complexes formed of?

A

Expanded nerve terminals closely associated with a merkel cell as a synapse like structure.

40
Q

Where are Merkel cell-neurite complexes located?

A

Basal epithelium (pegs and ridges) of skin with high sensory acuity e.g. fingers.

41
Q

What collectively accounts for the SA1 characteristic of the Merkel cell-neurite complexes?

A

The mechanosensitivity of the merkel cell AND the afferent fibre terminal.

42
Q

What is a Meissner corpuscle formed of?

A

A capsule in which several axons zigzag between modified Schwann cells (teloglia).

43
Q

Where are Meissner corpuscles located?

A

Close to basal epithelium (intermediate ridges) of skin with high sensory acuity.

44
Q

Meissner corpuscles are not found in what type of skin?

A

Hairy skin.

45
Q

Meissner corpuscles are sensitive to what?

A

Stroking, flutter, low frequency vibration.

46
Q

What allows for the detection of textured surfaces?

A
  • Merkel cell neurite complexes.
  • Meissner corpuscles.
    + small RF and high density.
47
Q

Sensory receptors of glabrous skin with a collagenous core in which axons branch.

A

Ruffini endings.

48
Q

Where are Ruffini endings located?

A

In the dermis of both glabrous and hairy skin.

49
Q

Ruffini endings are sensitive to what?

A

Drag i.e. shearing forces.

50
Q

These sensory receptors of glabrous skin are described as having a large onion-like structure.

A

Pacinian corpuscle.

51
Q

Where are Pacinian corpuscles found?

A

Subcutaneously close to the periosteum of bone.

52
Q

Pacinian corpuscles are very sensitive to what?

A

Vibration over a frequency range higher than that of a Meissner corpuscle.

53
Q

Pacinian corpuscles act as what during the manipulation of objects?

A

Event detectors.

54
Q

What do hair units functionally replace?

A

Meissner corpuscles.

55
Q

Hair units are comprised of what?

A

Follicular nerve endings that either:

  • wrap around the follicle.
  • run parallel to the follicle.
56
Q

Follicular nerve endings that wrap around the follicle are known as what?

A

Circumferential fibres.

57
Q

Follicular nerve endings that run parallel to the follicle are known as what?

A

Palisade fibres.

58
Q

Areas of skin innervated by the left and right dorsal roots of a single segment is referred to was what?

A

A dermatome.

59
Q

Shingles is due to what?

A

Dorsal root ganglion infection by Varicella Zoster Virus.

60
Q

Grey matter is divided into ten distinct what?

A

Laminae of Rexed.

CNS CLERKSHIP (43 decks)

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