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Neurology > Somatosensory System > Flashcards

Somatosensory System Flashcards

1
Q

What sensory modalities are included in the somatosensory system?

A

Mechanosensation, proprioception, thermosensation, nociception, pruriception

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2
Q

How can somatic sensation be classed?

A

Exteroceptive
Proprioceptive
Visceral
Deep

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3
Q

How do primary sensory afferent fibres confer modality?

A

By their site of termination in the CNS (labelled line principle)

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4
Q

What effect do stimuli (mechanical etc) have on ion channels?

A

Opens them in nerve terminal to elicit a depolarising receptor (or generator) potential

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5
Q

What is the amplitude of a generator potential?

A

Graded and proportional to stimulus intensity

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6
Q

What do low threshold units respond to?

A

Low intensity (non damaging and non-painful) stimuli

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7
Q

What do high threshold units respond to?

A

High intensity (noxious, potentially damaging) stimilu, but are subject to both spinal segmental and supraspinal influences that gate input to second order neurons

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8
Q

What is adaptation?

A

A feature of primary sensory neurones that determines whether they change their firing rate only in response to a stimulus of changing intensity, or fire continuously throughout a constant stimulus

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9
Q

How are primary afferents classified?

A

Aα/I
Aβ/II
Aδ/III
C/IV

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10
Q

What is the receptive field (RF) of an afferent neurone?

A

The region that when stimulated with an adequate stimulus causes a response in that neurone

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11
Q

Where are Meissner’s corpuscles usually found?

A

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

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12
Q

What are Merkel’s discs often grouped in?

A

Iggo domes

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13
Q

Where are Krause end bulbs found?

A

At the border of dry skin and mucous membranes

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14
Q

Where are Ruffini endings (pressure) found?

A

Within dermis and joint capsules

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15
Q

Where are Pacinian corpuscles found?

A

Within dermis and fascia

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16
Q

In the Iggo done what are multiple Merkel cells innervated by?

A

A single myelinated fibre

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17
Q

What receptor type is in the Aβ fibre group?

A 
Meissner's
Merkel
Pacinian
Ruffini
Hair-guard (long)
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18
Q

What receptor type is in the Aδ fibre group?

A

Hair- down (short)

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19
Q

What receptor type is in the C fibre group?

A

C mechanoreceptor

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20
Q

What is contained within grey matter?

A

Cell bodies and sensory afferent terminals

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21
Q

What is contained within white matter?

A

Fibre tracts

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22
Q

What is the grey matter divided into?

A

Dorsal and ventral horns and ten distinct laminae of Rexed

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23
Q

Where do nociceptor afferents terminate?

A

Laminae I and II

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24
Q

Where do LTM afferents terminate?

A

Laminae III to VI

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25
Q

Where do proprioceptor afferents terminate?

A

Laminae VII to IX

26
Q

How many primary afferent fibres cross the brainstem and decussate together in the DCML pathway?

A

All of them at the same point

27
Q

How many sensory fibres in the spinothalamic tract cross over at the spinal cord?

A

All of them along the entire length of the spinal cord

28
Q

Where do first order neurones in DCML pathway synapse?

A

Brainstem

29
Q

Where do second order neurones synapse in the DCML pathway?

A

Thalamus

30
Q

Where do first order neurones synapse in the STT?

A

All levels of the spinal cord

31
Q

Where do second order neurones synapse in the STT?

A

Thalamus

32
Q

What is the DCML pathway?

A

Dorsal column medial leminscal pathway

33
Q

What is the STT?

A

Spinothalamic tract

34
Q

What makes up the dorsal columns?

A

Medial fasciculus gracilis (gracile tract) and the lateral fasciculus cuneatus (cuneate tract)

35
Q

Where does sensory input to T6 and below (including legs and lower trunk) travel in?

A

Gracile tract

36
Q

Where does sensory input above T6 (including arms and upper trunk) travel in?

A

Cuneate tract

37
Q

What is the major route by which touch and proprioceptive information ascends to the cerebral cortex?

A

DCML pathway

38
Q

When primary afferent first order neurones enter the dorsal horn what do they form?

A

Synapses deep in the horn upon second order neurones

An ascending component via gracile/cuneate tract that synapses in the dorsal column gracile and cuneate nucleus

39
Q

What path do axons from second order neurones of the dorsal column nuclei take?

A

Cross collectively in great sensory decussation and ascend in medial lemniscus to ventral posteriolateral (VPL)nucleus of the thalamus

40
Q

Via what do third order neurones project to the primary somatosensory cortex(S1)?

A

The posterior internal capsule

41
Q

What are some capabilities of the dorsal pathway?

A 
Stereognosis-ability to recognise an object by feeling it
Vibration detection
Fine touch
Conscious proprioception
Weight discrimination
42
Q

What is general somatic information from the anterior head mediated by?

A

Two trigeminothalamic pathways

43
Q

What is included in the anterior head mediated by the trigeminal system?

A 
Oral and nasal cavities
Paranasal air sinuses
Teeth
Intracranial dura
Cerebral arteries
44
Q

Where do central terminals of the trigeminal nerve synapse upon second order neurones?

A 
Chief sensory nucleus (general tactile stimuli)
Spinal nucleus (pain, temperature information)
45
Q

Where do second order neurones decussate and project via the trigeminal lemniscus to?

A

The ventroposteriomedial (VPM) nucleus of the thalamus

46
Q

What do third order neurones relay information to the cortex via in the trigeminal system?

A

Thalamocortical neurones

47
Q

Where is the somatosensory cortex located?

A

The post central gyrus of the parietal cortext immediately posterior to the central sulcus and adjacent to the posterior parietal cortex

48
Q

What does the somatosensory cortex consist of?

A

Brodmann areas 1,2,3a,3b

49
Q

What does the somatosensory cortex receive input from?

A

VP thalamus

50
Q

What is the input and modality sensitivity for BA 3a?

A

Proprioceptors (muscle spindles)- body position

51
Q

What is the input, modality sensitivity and lesion effect for BA 3b?

A

Cutaneous- SA (Merkel cells) and RA (Meissner’s) receptors, BA 3a.
Touch
Deficits in texture, shape, discrimination

52
Q

What is the input, modality sensitivity and lesion effect for BA 1?

A

Cutaneous- RA mechanoceptors, BA 3b
Texture discrimination
Loss of texture discrimination

53
Q

What is the input, modality sensitivity and lesion effect for BA 2?

A 
Joint afferents, Golgi tendon organs, deep tissues, BA 3a,3b
Object perception (size, shape, stereognosis)
Impaired grasping and size and shape discrimination (astereognosis)
54
Q

What are the 6 layers of the somatosensory cortex?

A 
Molecular (Lamina I)
External granular (II)
External pyramidal (III)
Internal granular (IV)
Internal pyramidal (V)
Multiform (VI)
55
Q

What extends across the 6 layers of the somatosensory cortex?

A

Columns

56
Q

What do adjacent strips of cortex map?

A

The same body parts in parallel to each other- not identical but mirror images

57
Q

What happens if a body part is lost in an accident or amputated to the area of SI that represents it?

A

It is used by other sensory inputs

58
Q

What happens if sensory input from a finger increases?

A

The cortical representation of that digit, over months, increases relative that of inputs generating less activity

59
Q

What does the posterior parietal cortex do (SII)?

A

Receives and integrates information from SI and other cortical areas (visual, auditory) and sub-cortical areas (thalamus). Important for deeper meaning of SI information

60
Q

What temperatures do thermal nociceptors respond to?

A

> 45°C or

Neurology (27 decks)

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