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Neurology- Physiology > The Somatosensory System > Flashcards

The Somatosensory System Flashcards

1
Q

What are the two main categories of sensation?

A

Somatic sensation and special sensation

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2
Q

The somatosensory pathways usually consist of how many neurones?

A

Three

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3
Q

With regards to the first order neurone (i.e. the primary sensory afferent), where will the a) receptor and b) soma be found?

A

a) in the periphery e.g. the skin b) more central, though still in the PNS e.g. dorsal root ganglion or cranial ganglia

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4
Q

What is found in the dorsal root ganglion? Where is this found?

A

A cluster of first order neurones (i.e. primary sensory afferents) / in the dorsal root of a spinal nerve, in the intervertebral foraminae

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5
Q

Complete the following sentence: when a sensory receptor is activated, the information is received by ? - this carries information within a ? to the ? where it connects with the ?

A

The first order neurone (primary sensory afferent) / peripheral nerve / CNS / second order neurone

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6
Q

Complete the following sentence: a projection from a second order neurone carries sensory information to the ?, often via a ? in the ? before reaching the ? for processing

A

Brain / 3rd order neurone / thalamus / cortex

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7
Q

Where are the cell bodies of somatosensory neurones located?

A

In clusters outside the vertebral column in the dorsal root ganglia

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8
Q

The afferent projections from first order sensory neurones enter the spinal cord where?

A

At the dorsal horns

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9
Q

What is the terminal of the 1st order sensory neurone?

A

The receptor

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10
Q

Where would the cell body be found of each of the following neurones in a somatosensory pathway coming from the limbs/trunk or posterior head: a) first order? b) second order? c) third order?

A

a) dorsal root ganglion b) dorsal horn of spinal cord c) thalamus

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11
Q

Where would the cell body be found of each of the following neurones in a somatosensory pathway coming from the anterior head: a) first order? b) second order? c) third order?

A

a) cranial ganglia b) brainstem nuclei c) thalamus

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12
Q

What is the sensory unit?

A

The whole first order neurone, including the cell body and the receptor

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13
Q

Sensory units/primary afferent neurones are especially tuned to respond to a specific type of energy which normally excites them. This is known as what?

A

Their modality

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14
Q

What do low threshold units respond to?

A

Low intensity, non-damaging stimuli

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15
Q

What do high threshold units respond to? What type of receptors are these?

A

High, noxious stimuli only / nociceptors

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16
Q

Thermal nociceptors respond to extremes of heat - what would these be?

A

< 10 degrees or > 45 degrees

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17
Q

Sensory receptors can be what three main types?

A

Free nerve endings, encapsulated nerve endings or specialised receptors

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18
Q

Which type of sensory receptor will detect tactile sensation e.g. touch and pressure?

A

Mechanoreceptors

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19
Q

Which type of sensory receptor will detect temperature changes?

A

Thermoreceptors

20
Q

Which type of sensory receptor will detect painful stimuli?

A

Nociceptors

21
Q

Which type of sensory receptor will detect changes in the position and movement of the body?

A

Proprioceptors

22
Q

The area of skin innervates by the left and right dorsal roots of a single spinal segment is termed what?

A

A dermatome

23
Q

What is the only part of the body which is not innervated dermatomally?

A

Anterior face

24
Q

If a single dorsal root is cut, the corresponding dermatome does not lose all sensation. Why is this?

A

There is a degree of overlap with the region of adjacent dorsal roots

25
Q

Axons from 2nd order sensory neurones form what?

A

Sensory ascending tracts

26
Q

What are the two main sensory ascending tracts and where do each of them decussate?

A

DCML - in the medulla / spinothalamic - in the spinal cord

27
Q

Complete the sentence: axons from the ascending spinal cord tracts reach the ? where they communicate with ? which project into the ? where signals give rise to the awareness of the feeling

A

Thalamus / 3rd order neurones / cortex

28
Q

What is stereognosis? Which ascending spinal cord pathway allows this to be possible?

A

The ability to recognise an object by feeling it / DCML

29
Q

Complete the following sentence about trigeminal sensation: impulses originate at the terminals of two trigeminal nerves, each of which has ? divisions. The soma of sensory neurones are located in the ?

A

Three / trigeminal sensory ganglion

30
Q

Central terminals of the trigeminal nerve synapse upon second order neurones where, for general tactile stimuli?

A

The main sensory nucleus

31
Q

Central terminals of the trigeminal nerve synapse upon second order neurones where, for pain and temperature?

A

The spinal nucleus

32
Q

Complete the following sentence about trigeminal sensation: central terminals of the trigeminal nerve synapse upon 2nd order neurones in the respective nucleus. These in turn decussate and project via the ? to the ? nucleus of the ?

A

Trigeminal lemniscus / ventroposteriomedial (VPM) / thalamus

33
Q

Complete the following sentence about trigeminal sensation: 3rd order neurones relay information to the cortex via ?

A

Thalamocortical neurones

34
Q

In general, where are the somatosensory cortices located?

A

In the postcentral gyrus

35
Q

Where is the primary somatosensory cortex located?

A

Immediately posterior to the central sulcus

36
Q

Where is the secondary somatosensory cortex located?

A

Adjacent to the posterior parietal cortex

37
Q

The primary somatosensory cortex is classically described as consisting of what?

A

Brodmann areas

38
Q

The primary somatosensory cortex receives input from where?

A

The ventral posterior nucleus in the thalamus

39
Q

Briefly, describe the order of structures on the somatosensory homunculus from medial to lateral?

A

Genitals, lower limb, trunk, upper limb, face, mouth viscera

40
Q

How many cell layers are there in the somatosensory cortex?

A

6

41
Q

What happens if a finger is lost in an accident or amputated?

A

After months, the area that used to represent that finger will now represent the adjacent fingers

42
Q

What happens if the sensory input from a finger increases?

A

The area of cortex associated to that finger enlarges

43
Q

What is the function of the secondary somatosensory cortex?

A

The integrate sensory information with other cortical areas

44
Q

What is agnosia?

A

You can see a structure but can’t tell what it is

45
Q

What is astereognosia?

A

Can touch an object but can’t tell what it is

46
Q

What is hemispatial neglect syndrome?

A

The patient neglects the contralateral half of their body

Neurology- Physiology (7 decks)

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