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Somatosensation Flashcards

1
Q

What kind of stimuli can somatosensation neurons detect?

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 three locations can somatosensation receptors be found?

A
  • Exteroceptive division (cutaneous senses) surface of the body
  • Proprioceptive 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 many neurons are located in the somatosensory pathway?

A

3- 1 peripheral and 2 central

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4
Q

Describe the somatosensory pathway

A 
1st order (Sensory receptors, PNA, soma in DRG, synapse in dorsal column)
2nd order (projection, CNS, soma in dorsal horn, synapse in thalamus)
2nd order (projection, CNA, soma in thalamus, synapse in somatosensory cortex)
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5
Q

What does grading of potential mean?

A

Greater stimulation leads to firing of more AP which can add up/surmise- increase firing = increase AP release
AP frequency proportional to stimuli intensity

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6
Q

What is the modality of a neuron?

A

What kind of stimuli it transmits

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7
Q

When are neurons most sensitive?

A

At lower stimuli strength

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8
Q

What is the adaptation rate?

A

If receptor continues firing with stimuli or needs change

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9
Q

What do skin mechanoreceptors sense?

A

Touch, vibration, pressure

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10
Q

What do joint and muscle mechanoreceptors sense?

A

Propioception

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11
Q

What receptors sense pain?

A

Mechanical, thermal and polymodal nociceptors

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12
Q

What kind of receptors are low threshold?

A

Low threshold mechanoreceptors (LTMs): mediate fine discriminatory touch
Low threshold thermoreceptors: mediate cold through to hot

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13
Q

What kind of receptors are high threshold?

A
  • High threshold mechanoreceptors (HTMs) (mechanical nociceptors) respond to high intensity mechanical stimuli
  • Thermal nociceptors respond to extreme degrees of heat (>45°C), or cold < 10-15°C)
  • Chemical nociceptors respond to substances in tissue [e.g. as in inflammation: prostaglandins, bradykinin, serotonin (5-HT), histamine, K+, H+ and ATP and many others]
  • Polymodal nociceptors respond to at least two of the above
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14
Q

What kind of adaptations are there?

A

Slow adapting/tonic/satic
Fast adapting/phasic/dynamic
Very fast adapting

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15
Q

What kind of pattern does a slow adapting neuron give?

A

Fires regularly with continued stimuli and proportional to the stimuli.
Position and stretch etc

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16
Q

What kind of pattern does a fast adapting neuron give?

A

Fires when stimuli first applied but soon tails off.

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17
Q

What kind of pattern does a very fast adapting neuron give?

A

Changing stimuli- tends to just fire once when stimuli first applied.

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18
Q

What 4 axon types are there?

A

Aa/group 1
Ab/group 2
Ad/group 3
C

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19
Q

How do the axon types change

A

Aa -> C: Diameter decrease (20microm, 1.5microm), Myelination decrease (Thick, none), conduction velocity decrease (100m/s, 2m/s)

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20
Q

What stimuli do Aa axons conduct?

A

Proprioception

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21
Q

What stimuli do Ab axons conduct?

A

Mechano from skin

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22
Q

What stimuli do Ad axons conduct?

A

Pain and temp

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23
Q

What stimuli do C axons conduct?

A

Temp, pain and itch

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24
Q

How does two point discrimination work?

A

Apply 2 pointed stimuli separated by variable distance to part of body.
Patient says if can detect 1 or 2 points.

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25
Q

What 7 kinds of cutaneous nerve endings are there?

A 
Free Nerve Endings
Meissner’s corpuscles (encapsulated) 
Merkel’s discs 
Hair-end organs
Krause end bulbs 
Ruffini endings (encapsulated) 
Pacinian corpuscles (encapsulated)
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26
Q

Describe free nerve endings

A

Everywhere

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27
Q

Describe Meissner’s corpuscles

A

Skin where 2 point discrimination needed.
Not in hairy skin.
Stroking, flutter, low frequency vibration (approx. 10 – 100 Hz)

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28
Q

Describe Merkel’s discs

A

Skin where 2 point discrimination needed.
Small number in hairy skin.
Very sensitive to touch (surface/texture/edges) and sustained pressure

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29
Q

Describe Krause end bulbs

A

Border of dry skin and mucous membranes.

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30
Q

Describe Ruffini endings

A

Dermis and joint capsules.

Strong mechanical pressure and drag/shearing force.

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31
Q

Describe Pacinian corpuscles

A

Dermis and fascia- close to bone.
Vibration (200-300Hz). Event detector…
Big in size and onion shaped.

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32
Q

What two types of LT MechanoR are there?

A 
Fast adapting (FA)
Slow adapting (SA)
33
Q

Describe the RF of the FA and SA LTM

A

FA- Small

SA- Large

34
Q

What receptors do FA1 LTM have?

A

Meissner’s corpuscles- V small RF

35
Q

What receptors do FA2 LTM have?

A

Pacinian corpuscles- Small RF

36
Q

What receptors do SA1 LTM have?

A

Merkel’s discs

37
Q

What receptors do SA2 LTM have?

A

Ruffini endings

38
Q

What is the grey matter of the spinal cord divided into?

A

Dorsal and ventral horns

Laminae of Rexed

39
Q

What lamina of Rexed do Ad and C fibres (nociception) go to?

40
Q

What lamina of Rexed do Ab fibres (LTM) go to?

41
Q

What manina of Rexed do Aa fibres (proprioception) go to?

42
Q

What are the two somatosensory pathways?

A

Dorsal column medial leminscal (DCML) pathway

Spinothalamic tract

43
Q

What sensations does the DCML transfer?

A

Discriminatory touch, pressure, vibration, conscious proprioception- Aa and Ab

44
Q

What sensations does the STT transfer?

A

Pain, thermosensation, crude touch, itch, tickle- Ad and C

45
Q

Where are the primary neuron soma found in the DCML and where do they synapse?

A

DRG and synapse in brain stem (and SC for reflexes)

46
Q

Where are the primary neuron soma found in the STT and where do they synapse?

A

DRG and synapse in the spinal cord

47
Q

Where do the secondary neurons of the DCML decussate and where do they synapse?

A

Decussate in brain stem and synapse in thalamus.

48
Q

Where do the secondary neurons of the STT decussate and where do they synapse?

A

Decussate in spinal cord and synapse in thalamus.

49
Q

Where do the third order neurons in both DCML and STT arise and synapse?

A

Thalamus to primary somatosensory cortex

50
Q

What are the two parts of the DCML?

A

Fasciculus gracilis

Fasciculus cuneatus

51
Q

What spinal level distinguished whether somatosensation is part of the fasciculus gracilis or fasciculus cuneatus?

A

T6- Below FG and above FC

52
Q

What nucli do the FG and FC synapse in?

A

Dorsal column gracile nucleus (GN) or cuneate nucleus (CN)

53
Q

Where can the DCGN and DCCN be found?

54
Q

How do you test stereognosis?

A

Ask them to ID a familiar object by touch alone

55
Q

How do you test vibration detection?

A

128Hz tuning fork on bone and feel for buzz

56
Q

How do you test conscious proprioception?

A

Patient closes eyes and clinician moves limb them ID where it is/up or down.

57
Q

What is lateral inhibition?

A

When one neuron is active, it inhibits the activity of its neighbours via inhibitory interneurons.

58
Q

Why do we have lateral inhibition?

A

To improve discrimination

59
Q

Which order neurons activate inhibitory neurons in lateral inhibition?

60
Q

Which order neurons do inhibitory neurons inhibit in lateral inhibition?

61
Q

Which nerves supply somatic sensory info from the face?

A

Trigeminal

62
Q

What tract does somatosensation from trigeminal nerves travel through?

A

Trigeminothalamic tract

63
Q

Where are somas of the trigeminothalamic tract located?

A

Trigeminal sensory ganglion (found in dura mater near petrous part of temporal bone).

64
Q

Where do trigeminal neurons synapse to second order neurons?

A 
Chief sensory nucleus (general tactile stimuli)
Spinal nucleus (pain, temperature information)
65
Q

What do second order neurons of the trigeminothalamic tract do and where do they synapse?

A

Decussate and synapse in ventroposteriomedial (VPM) nucleus of the thalamus.

66
Q

Where is the primary somatosensory cortex found?

A

Postcentral gyrus

67
Q

What areas can the primary somatosensory cortex be broken down to?

A

Bodmann’s areas

68
Q

Which Bodmann’s areas are found in the primary somatosensory cortex?

A

1, 2, 3a, 3b

69
Q

Where does the primary somatosensory cortex receive input from?

70
Q

Name the Bodmann’s areas from anterior to posterior

A

3a, 3b, 1, 2

71
Q

What input does Bodmann’s area 3a receive?

A

Proprioception (body position)

72
Q

What input does Bodmann’s area 3b receive?

A

SA1 and FA1 (Touch)

73
Q

What input does Bodmann’s area 1 receive?

A

FA mechanoreceptors (texture discrimination)

74
Q

What input does Bodmann’s area 2 receive?

A

Pressure and joint position: object perception (size, shape of object – stereognosis)

75
Q

How many layers make up the somatosensory cortex?

76
Q

Which layer of the somatosensory cortex receives input from the thalamus?

77
Q

What happens to the somatosensory cortex area for a body part that is lost?

A

It is co opted by neighbouring areas (ie. lose middle finger then ring and index take over)

78
Q

What major area can the somatosensory cortex project to?

A

Posterior Parietal Cortex (SII)

79
Q

WHat does the Posterior Parietal Cortex (SII) do?

A

Receives and integrates information from SI and other cortical areas (visual, auditory) to interpret them.

Neurology (30 decks)

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