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SO-Nervous System > Somatosensory System > Flashcards

Somatosensory System Flashcards

1
Q

What is the somatosensory system concerned with?

A

Conscious sensation

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2
Q

What sensory modalities are carried by the somatosensory system?

A
  • Temperature
  • Pain
  • Vibration
  • Pressure
  • Stretch
  • 2 point discrimination
  • Proprioception
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3
Q

What do the different sensory modalities carried in the somatosensory system require?

A

Different types of receptor

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4
Q

What is the clinical relevance of the different sensory modalities in the somatosensory system travelling through different CNS pathways?

A

Clinically assessing functions can help localise damage

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5
Q

What is the quality of a sensation determined by?

A
  • The way a receptor is activated
  • The receptor subtype
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6
Q

How is the quality of sensation determined by receptor subtypes?

A

Different proteins fire at different rates of stimulation

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7
Q

How does sensory information in the somatosensory system begin?

A

With detection of a stimuli at its receptor

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8
Q

What happens once a stimuli has been detected in the somatosensory sysetm?

A

The information passes down the first order neurone, to the spinal cord

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9
Q

Where is the cell body of the first order neurone found?

A

Always in the dorsal root ganglia, or the trigeminal ganglia if it supplies the head and neck

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10
Q

What does the first order neurone synapse with?

A

The second order neurone

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11
Q

Where does the second order neurone pass?

A

Up the spinal cord to the thalamus

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12
Q

What does the second order neurone always do?

A

Cross the midline

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13
Q

What is the thalamus considered to be in the somatosensory system?

A

The sensory relay station

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14
Q

What happens to the second order neurone in the thalamus?

A

It synapses with the third order neurone

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15
Q

Where does the third order neurone go from the thalamus?

A

It projects from the thalamus to the primary sensory cortex in the post-central gyrus

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16
Q

How is sensory information encoded?

A

The amount of stimulation is proportional to the frequency of action potentials propagated- higher stimulation results in more APs

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17
Q

What does the way that the frequency of the APs change with levels of stimulation depend on?

A

The receptor types

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18
Q

What are the two broad classes of receptor types?

A
  • Phasic receptors
  • Tonic receptors
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19
Q

Give an example of a sensation picked up by phasic receptors

A

Pressure

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20
Q

What happens with phasic receptors?

A

The initial stimulatus is rapid firing, but the rate of firing then decreases as receptors adapt. The frequency gets so low that you become unaware of the stimulus

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21
Q

Give an example of a sensation picked up by tonic receptors

A

Pain

22
Q

What happens with tonic receptors?

A

Frequency of APs doesn’t change with prolonged stimulation

23
Q

What is sensory acuity proportional to?

A

1/The size of the receptive field

24
Q

What is meant by the receptive field?

A

The area of skin provided by 1 primary afferent

25
Q

What does a large RF mean for sensory resolution?

A

Poor sensory resolution

26
Q

Can receptive fields overlap?

A

Yes

27
Q

What is the importance of the potential for sensory fields to overlap?

A

it can be clinically important when assessing dermatomes - if one neurone has been damaged, you would still get reduced sensation provided by the other

28
Q

In what parts of the sensory system does lateral inhibition occur?

A

All parts of the sensory system

29
Q

When happens when the skin is depressed, e.g. by a sharp object?

A

More than one sensory neurone is stimulated, however the receptor closest to the depression is stimulated the most

30
Q

What is the purpose of lateral inhibition when considering skin depression by a sharp object?

A

It is a mechanism to localise the depression

31
Q

How does lateral inhibition occur?

A

The first order neurone synapse with inhibitory interneurones, which synapse with the second order neurones of adjacent neurones, inhibiting them, and therefore maximising contrast

32
Q

What is a tract?

A

A white matter connective between 2 areas of grey matter

33
Q

What does the dorsal column medial lemniscus pathway detect?

A
  • Light touch
  • Joint position sense
  • Vibration
  • Two point discrimination
34
Q

What are the names of the dorsal columns?

A
  • Fasciculus gracilis
  • Fasciculus cuneatus
35
Q

What does the fasciculus gracilis supply?

A

The lower half of the body

36
Q

What does the fasciculus cuneatus supply?

A

The upper 1/2 of the body

37
Q

Where does the first order neurone enter the dorsal column pathway?

A

In the spinal cord

38
Q

What happens to the first order neurone once it has entered the dorsal column pathway in the spinal cord?

A

It enters the white matter of the dorsal column, and ascends up the cord

39
Q

Does the first order neurone in the dorsal column cross the midline?

A

No, it travels close to it, but does not cross it

40
Q

Where does the first order neurone synapse with the second order neurone in the dorsal column medial lemiscus pathway?

A

In the medulla

41
Q

Where does the second order neurone synapse with the third order neurone in the dorsal column medial lemiscus pathway?

A

In the thalamus

42
Q

Which fibres travel closest to the midline in the dorsal column medial lemiscus pathway?

A

Those from the lower half of the body

43
Q

Why are fibres from higher levels added to the outside in the dorsal column medial lemiscus pathway?

A

It economises myelin and axon

44
Q

What does the spinothalamic pathway detect?

A
  • Pain
  • Temperature
  • Crude touch
45
Q

Where does the first order neurone synapse with the second order neurone in the spinothalamic pathway?

A

In the spinal cord

46
Q

Where does the second order neurone synapse with the third order neurone in the spinothalamic pathway?

A

In the thalamus

47
Q

Which neurones run on the outside in the spinothalamic pathway?

A

Those entering lower

48
Q

Which fibres carry pain?

A

C fibres

49
Q

What fibres carry impulses from the mechanoreceptors in the skin?

A

A-fibres

50
Q

What effect does activation of mechanoreceptors have on pain?

A

It alleviates pain

51
Q

How does activation of mechanoreceptors alleviate pain?

A

It excites inhibitory enkephalinergic interneurones in the cord

SO-Nervous System (18 decks)

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