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NHB > Somatosensation > Flashcards

Somatosensation Flashcards

1
Q

What is proprioception and kinesthesis

A

proprioception - the sense of limb
position)

kinesthesis - the sense of limb movement

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2
Q

How many principal mechanoreceptors innervate the glabrous skin of the hand?

What are they?

How do they all respond to mechanical stimulation

A

4

Slow adapting type 1 (SAI)
Rapidly adapting (RAI)
Rapidly adapting Pacinian corpuscles (PC)
Slow adapting type 2 (SAII)

by depolarising

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3
Q

What do slowly adapting type 1 fibres end in

What about type II

A

Merkel cells

Ruffini cells

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4
Q

What is a Pacinian corpuscle composed of

A

concentric layers of cellular membranes alternating with fluid filled spaces

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5
Q

Where are Pacinian corpuscles found?

A

distributed widely, including connective tissue in muscles,

periosteum of bones and mesentery of the abdomem

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6
Q

How are Pacinian corpuscles distributed in the hand

A

finger has 350

800 in the palm

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7
Q

How sensitive are Pacinian corpuscles

A

responding to 10 nm of skin motion at 200 Hz

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8
Q

Describe the receptive field of Pacinian corpuscles

A

central zone of maximal sensitivity surrounded by a large continuous surface on the fingers or palm.

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9
Q

What are Meissner’s corpuscles attached to

A

RAI afferents

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10
Q

What is the receptive field of Meissner’s corpuscles?

A

3-5 mm in diameter and they respond best to low frequency vibration

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11
Q

What is the density of Meissner’s corpuscles

A

150/cm^2

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12
Q

What can Meissner’s corpsucles be compared to in the visual system

A

analogous to the receptors used in scotopic vision—they show enhanced sensitivity and poorer spatial resolution whereas the SAI afferents (Merkel cells) correspond more closely to receptors in photopic conditions with their higher spatial resolution and decreased sensitivi

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13
Q

Broadly, when do rapidly and slowly adapting receptors respond during stimulation

A

rapid- onset of stimulus

slow- tonic response to a steady stimulus

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14
Q

How does a rapidly adapting receptor respond to stimuli

A

phase locking

responds to low frequency sinusoidal mechanical stimuli with a single action potential for each phase of the stimulus

effectively treats each period of the waveform as a new stimulus

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15
Q

True or false

the intensity of the sinusoidal stimulus must be encoded by the firing rate

A

false

encoded by number of sensory fibres active

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16
Q

How is number of rapidly adapting touch fibres active related to vibrations

A

The number of active fibres is linearly related to the amplitude of vibration.

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17
Q

True or false

the Pacinian corpuscle is rapidly adapting

A

true

it is RAII

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18
Q

How can we examine the influence of the lamallae in Pacinian corpuscles adaptation

A

by peeling them away

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19
Q

Describe an experiment assessing the purpose of PC lamallae in adaptation by peeling them away

A

In response to the onset of step pulse the receptor potential usually rises and then decays (adapts) quite rapidly. A similar response is seen to the turning off the stimulus. In contrast, when recorded direct from the nerve ending (i.e. de-sheathed), the receptor potential produced in response to a step pulse was slowly adapting.

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20
Q

What are accessory structures

A

Structural components of sense organs
which may play an important role in protection, conduction,
concentration, analysis, sensitization or inhibition; but they are
not directly involved in the transduction process

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21
Q

Give 4 examples of accessory structures

A

e.g. lamellae of the Pacinian corpuscle,
the intrafusal fibres of the muscle spindle,
eye structures,
basilar membrane.

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22
Q

How can human vibration sensitivity be altered

A

by changing the responsiveness of

RA I and RA II

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23
Q

How does local anesthetic affect detection of vibration if it is applied to superficial layers

A

reduces the effectiveness of the Meissner’s corpuscles as they lie close to the surface

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24
Q

How can you use vibrations to desensitise Pacinian and Meissner’s corpuscles

A

effectiveness of the
Pacinian corpuscle can be reduced by pre-adapting the
receptor to stimulation around 250 Hz.

Meissner’s: preadapting the skin with a low frequency stimulus

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25
Q

What are Merkel cells attached to

A

SAI afferents

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26
Q

Describe the recepetive field of Merkel cells

A

small, highly localised receptive fields

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27
Q

Where do Merkel cells innervate and how do they respond/ what do they respond to

A

innervate the skin
densely

respond to indentation with a linear response to 1500μm.

sensitive to points, edges and curvature and can resolve spatial detail of 0.5 mm.

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28
Q

True or false

Merkel cell spike discharge is largely invariant

A

true

they are very good at discrimination

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29
Q

Describe the dynamic range of Merkel cells

A

usually between 200micrometer indentation to 1500 micrometers

less than 1 order of magnitude (much smaller than visual and auditory systems)

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30
Q

What happens if you knock out Piezo2

A

Merkel cells will not produce an inward current in response to touch

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31
Q

Compare stimuation of Merkel cells in a skin-nerve preparation for wild type and Piezo2 KO mice

A

strong neural response from SA1 fibres in wild-type mice (WT) whereas the response from the same fibres in which Piezo2 had been knocked out failed to demonstrate a sustained response.

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32
Q

Which nerves has Piezo2 been expressed in

A

dorsal root ganglion, Aβ, Aδ and C-fibre low threshold mechanoreceptors

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33
Q

How does the role of SA1 nerve terminals differ from the role of the attached Merkel cells

A

The SA1 nerve terminals are responsible for the rapid and dynamic response to mechanical stimuli while the Merkel cells are responsible for the sustained response.

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34
Q

What are Ruffini thought to play a role in

How is this supported

A

perception of object motion and in providing information about hand shape and finger position.

this role is reflected in Ruffini endings residing deep

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35
Q

What are Ruffini endings attached to

A

SAII afferents

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36
Q

Which afferents are most accurate for reading Braille

Describe an experiment to show this

A

SAI

The Braille patterns were scanned (60 mm/s) repeatedly over the afferent fibres’ receptive fields, which were located on the distal finger pads. The patterns were shifted vertically after each scan. Each black dot represents an action potential
evoked by the Braille pattern. These spatial event plots show that the response of SAI fibres looks rather similar to the original dot pattern.

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37
Q

Is tactile acuity equal across the body

A

no

better in the hands than back for instance

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38
Q

What is the compass test

What are the results

A

to determine the smallest discriminable distance between two points of contact, the so called two-point limen.

In general, the two-point limen improves up to twenty-fold from the shoulder (40mm) to the fingers (2mm).

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39
Q

What is tactile acuity correlated with (2)

A

acuity increases with mobility (less true for lower extremities)

areas of high acuity have small receptive fields

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40
Q

What happens if two points contacting the skin stimulate just one receptive field?

A

we have no information that two points on the skin were stimulated.

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41
Q

Acuity appears to increase with increase in mobility. Areas with high tactile acuity have small receptive fields. What can we therefore predict about RAI and SAI fibres

A

have small receptive fields

and the highest density on the fingertips.

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42
Q

What is our perception of hand held objects determined by

A

the overall pattern of activity

produced by all these receptors.

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43
Q

What was the first evidence that warm and cold should be considered as different modalities

A

maps of warmth and cold spots

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44
Q

How does the number of warmth spots compare to cold spots on a map

A

concentration of cold spots can far exceed that of warmth spots.

can be at least ~30 times as many cold as warmth spots.

Different body areas have different proportions of cold
and warmth spots i.e. the lip has six times as many cold spots as the sole

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45
Q

Does 1 warmth spot equate to 1 warmth receptor?

A

no - then large areas of the body should be insensitive to warmth

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46
Q

What is spatial summation in the somatosensory system

A

more receptors may exist than there are spots and that it usually requires the simultaneous activation of many receptors to elicit the sensation of warmth.

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47
Q

Give 2 things TRPV1 responds to

A

capsaicin, and also to painful increases in temperature above 43°C

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48
Q

Name 2 things TRPM8 responds to

A

menthol and are activated by non-painful decreases in temperature below 28°C

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49
Q

What are warm and cold receptors attached to

A

‘cold’ receptors are connected to A-delta and C-fibres

‘warm’ receptors by a sub-population of C fibre

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50
Q

What happens when a heat stimulus of >45 degrees is applied to a cold spot on the skin

A

paradoxical cold

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51
Q

What is paradoxical cold

What is this an example of

A

high temperature (>45 degrees) is usually perceived as painful when applied to a diffuse area of the skin, however, when applied to a single cold spot it is perceived as cold.

Therefore, activity in the cold fibre is experienced as cold
irrespective of the physical nature of the stimulus

example of labelled line coding

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52
Q

What are the specialised endings to nociceptor axons

A

do not possess any specialised endings and hence referred to as bare or free nerve endings

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53
Q

What does the bare nerve endings of nociceptors provide

A

makes them particularly sensitive to chemicals produced or released at a site of injury.

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54
Q

How is pain often separated

A

into an early (first), sharp pain and a second, dull, burning pain.

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55
Q

How does abolishing A-delta fibres affect pain

What about blocking C fibres

A

removes early (first) sharp pain

abolishes second pain

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56
Q

Are c fibres myelinated

what do they respond to

A

no

polymodal: respond to thermal (< 15°C and >43°C), mechanical (strong not mild) and chemical stimuli (e.g. chilli peppers, acid)

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57
Q

What encodes pleasant touch

A

C fibre tactile afferents (CT)

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58
Q

What do C fibre tactile afferents respond to

A

light touch, low-velocity stroking. Such stimulation is usually regarded as pleasant

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59
Q

What characterises pleasant touch fibres (2)

how was this confirmed

A

a low conduction velocity (~ 1m/s) and are only found in hairy skin.

This was confirmed using the technique of microneurography.

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60
Q

How do the responses of A-delta and CT afferents to a small tap stimulus compare

A

The response of the
myelinated Aβ afferent has a much shorter latency than the
response of the CT afferent

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61
Q

What is the velocity of long latency CT responses

A

conduction velocity of around 1 m/s.

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62
Q

How does stroke velocity correspond with rate of AP firing

A

As stroke velocity increases there is a non-linear relationship with action potential firing

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63
Q

How does pleasantness correspond with stroke velocity

What has this discoveruy led to speculation of

A

non-linear relationship is seen when subjects are asked to rate the pleasantness of
the stimulation as stroke velocity increases

similar to AP firing v stroke velocity

leads to a positive
correlation between CT output with the pleasantness of the stimulation.

CT afferents afferents are more concerned with emotional feeling than touch.

64
Q

What do sensory peripheral nerves tend to consist of

A

bundles of axons grouped by fibre

diameter

65
Q

What are the different types of somatosensory fibres

Give them in size order and state whether they have myeline

A

largest, myelinated:
Aα and Aβ;

intermediate, thinly myelinated group: Aδ.

the smallest, unmyelinated: C fibres.

66
Q

Order the sensory afferent types according to length of delay

A

Aβ

afferents have the shortest delay whereas the unmyelinated Cfibres conduct slowly producing a late peak.

67
Q

Which sensory afferent fibres are affected by anoxia

A

the large Aβ fibres

68
Q

Which sensory fibres are primarily affected by local anaesthetic

A

small ‘C’ and Aδ axons

69
Q

Describe the pain evoked when Aβ afferents are stimulated alone

A

no pain, , even at intensities sufficient to
mimic an intense mechanical stimulus.

Pain is only evoked by stimulation of the Aδ and C fibres

70
Q

Which fibres are required for pain to be felt

A

stimulation of the Aδ and C fibres

71
Q

Give 2 conditions when the myelin sheath of large diameter fibres is broken down

what does this lead to

A

diabetes
MS

slowing of nerve conduction or
failure of impulse transmission.

72
Q

How many spinal nerves

A

31

73
Q

Is the diameter of the spinal cord constant

A

varies considerably at different levels and it has two enlargements, cervical and lumbar

74
Q

Where is the cauda equina

A

lies below approximately L2

75
Q

What is a lumbar puncture and where can it be done

which space

A

below L2

hollow needles can be inserted into the subarachnoid space to remove CSF for diagnostic purposes

76
Q

Which space can you insert anaesthetics into for surgery

A

epidural space

77
Q

Are epidural blocks and lumbar punctures performed in the same meningeal space

A

no

lumbar puncture: subarachnoid space

78
Q

How do dermatomes overlap

A

dermatomal boundaries overlap by mixing fibres from several dorsal roots in the peripheral nerve.

79
Q

Describe a general cross-section of the spinal cord

A

divided into two symmetrical halves by the dorsal median sulcus and the ventral median fissure.

Surrounding the central canal is the
‘H’-shaped grey matter consisting of nerve cell bodies.

Afferent and efferent axons run in the white matter.

80
Q

How is the white and grey matter divided in the spinal cord?

A

The white matter can be divided into three regions, defined relative to the grey matter: dorsal, lateral
and ventral.

The grey matter is divided into functionally distinct laminae (aka Rexed’s laminae).

81
Q

What is the main pathway for proprioception and touch

What kind of fibres convey which information?

A

dorsal column – medial lemniscal
(DC-ML) system

consists of large-diameter myelinated fibres that convey tactile, vibratory and proprioceptive sensations.

82
Q

What happens when tactile fibres enter the spinal cord?

A

primary afferent bifurcates:
A short branch
enters the dorsal horn and a long branch enters the dorsal columns

83
Q

What happens to the axons that form the long branch of the primary tactile afferents

a) below mid thoracic level
b) above mid thorax

A

a) ascend in the fasciculus gracilis and terminate in gracile nucleus.
b) enter the fasciculus cuneatus and terminate in the cuneate nucleus

84
Q

How are the cells in the dorsal column nuclei arranged

What is this arrangement called and is it common?

A

according to their somatic origin with the leg located medially and the arm laterally

somatotopic organisation is preserved at all levels of the pathway

85
Q

What do the axons leaving the dorsal column nuclei do generally?

A

cross the brainstem and then ascend to the thalamus in the medial lemniscus.

86
Q

What is the major nociceptive tract in the spinal cord

what does it comprise

A

spinothalamic tract

axons from neurons in layers I and V-VII of the dorsal horn.

87
Q

What is the spinothalamic tract also called?

Why?

A

anterolateral system

The axons ascend in the contralateral,
anterolateral, white matter

88
Q

Does cutting the spine carefully reduce pain

A

yes
Lesions of the spinothalamic tract (usually achieved surgically by an anterolateral cordotomy) reduce pain sensations from the contralateral side of the body. Unfortunately, pain relief is often only temporary

89
Q

Where does the spinoreticular tract extend from to

A

t projects from laminae VII and VIII and terminates in the reticular formation and thalamus

90
Q

Do axons of the spinoreticular tract cross the midline in the spine?

A

no they travel ipsilaterally

91
Q

Where does the spinomesencephalic tract begin and end

A

projects from laminae I and V, via the anterolateral quadrant of the spinal cord to the mesencephalic reticular formation and the periaqueductal gray

92
Q

What does Brown Sequard syndrome describe

A

consequence of a hemi-section through the spinal column.

affects both the spinothalamic tract and DC-ML on the same side of the cord resulting in a loss of pain and
temperature sensation below and contralateral to the site of the lesion and loss of fine touch and proprioception below and ipsilateral to the site of the lesion

93
Q

What is syringomyelia: cause and symptoms

A

caused by a fluid-filled cavity within the spinal (usually cervical) cord.

cavitation usually disrupts the decussating fibres of the anterolateral system but not the ascending fibres of the DCML system

resulting in the characteristic “cape-like” distribution of loss of pain and temperature sensation in the upper limbs and trunk but preservation of touch and pressure sensation.

94
Q

What is the characteristic symptom of syringomyelia

A

“cape-like” distribution of loss of pain and temperature sensation in the upper limbs and trunk but preservation of touch and pressure sensation.

95
Q

What causes posterior column syndrome

A

tabes dorsalis – tertiary syphillis

96
Q

What is the symptoms of posterior column syndrome

A

a bilateral absence of touch below the level of the lesion. There is also a loss of
proprioceptive feedback below the site of the lesion leading to a characteristic stamping gait.

97
Q

How would sensory modalities be affected by a complete transection of the spinal cord

A

complete transection leads to the impairment of all sensory modalities below the level of the transection

98
Q

what is Tic douloureux?

A

trigeminal neuralgia

a syndrome whereby gentle stroking of the face or mouth provokes a massive stabbing pain.

99
Q

What is Tic douloureux an example of

A

allodynia

100
Q

what are the fibres of the CN V branches

A

ophthalmic and maxilliary branches are purely sensory while the mandibular is a mixed sensory and motor branch

101
Q

Does the somatosensory system have lateral inhibition

A

yes

This allows the amplification of differences in the output of neighbouring neurons and effectively enhances contrast

102
Q

What does stimulation of a single point of skin produce

What happens when stimulating 2 adjacent points

What can we see based on this

A

an excitatory
response surrounded by a small inhibitory response

lateral inhibition suppresses excitation of the neurons between the points thus sharpening the focus or spatial clarity of the two points.

importance of inhibitory interactions in fine tactile discriminations such as reading Braille.

103
Q

Where does the DCML system terminate in the thalamus

A

in a group of cells known as the ventral posterior nucleus

104
Q

Is the thalamus involved in pain?

A

identified the posterior part of the ventral medial nucleus (VMPO) as a specific nucleus for pain and temperature sensation in both monkeys and humans.

105
Q

Can a CNS cell’s receptive field change?

A

yes:

Blocking of normal input to cells in the CNS may be followed by immediate unmasking of previously ineffective inputs

106
Q

Give an example of immediate unmasking of a previously ineffective sensory input to the CNS following blockage of the original input

What is this an example of

A

Initially the cell responded only to pressure on its toes (the no block condition).

When all input to the leg was temporarily removed by cooling of the lumbar spinal cord the cell responded to touch on an area of the flank (during block).

Removal of the cold block returned the receptive field
to the area of the toes

gate control

107
Q

How can gate control be described?

A

whereby the failure of one input unmasks the presence of inputs which are ordinarily suppressed by ‘inhibitory’ mechanisms

108
Q

Where do tactile signals from the thalamus go?

A

to the primary somatosensory cortex (S-I) in the post central gyrus

109
Q

Where is the post central gyrus located

A

immediately posterior to the central sulcus

110
Q

What are particularly pronounced sulci in the brain referred to as

A

fissures

111
Q

Which of Brodman’s areas does S-I occupy

A

areas 3, 1 and 2

112
Q

How is the cortex organised

A

in a series of vertical columns, 300-600 μm wide, spanning all six layers from the cortical surface to the white matter

113
Q

How is stimulus location preserved in the brain

A

r. All neurons within a

column receive input from the same area of skin

114
Q

How do the columns in the cortex preserve touch modality

A

In addition to sharing a common location, all neurons also only respond to a single modality e.g. touch, temperature etc

115
Q

Where do somatosensory afferents from the thalamus terminate

Which layer projects back to the thalamus

A

layer IV

layer VI

116
Q

Where do layers II, III and V in the cortex project to

A

II, III: other cortical regions

V: to subcortical structures

117
Q

What is the homunculus

What does it represent

A

The map of somatosensory inputs to the cortex

does not represent the topography of the skin exactly but rather exaggerates certain body regions. Each part of the body is represented in the brain according to its importance to the organism

118
Q

In humans, where is much of the cortical map of somatosensation (homunculus)

what about in rodents

A

hands and face

whiskers

119
Q

Can you get direction sensitive somatosensory neurons?

A

yes
a neuron in area 2 of S-I could respond strongly eg to movement from the ulnar side of the wrist to the radial fingers

Moving the stimulus in the opposite direction
produced the smallest response

120
Q

How can we explain the direction sensitivity of tactile neurons

A

The spatial arrangement of excitatory and inhibitory inputs

121
Q

How can you predict the responses of S-I neurons to somatosensory stimuli

Is this the same as the responses in S-II

What does this mean

A

by the bottom-up input from the periphery

responses of neurons in
area S-II are influenced by top-down processes such as attention

by decreasing attention on the stimulus, response to the stimulus is decreased

122
Q

Do somatosensory neurons have memory?

A

yes S-II can understand analyse the value of a stimulus - ie uses reward pathway

123
Q

What is passive touch

What is the problem with this

A

the experimenter
presents a stimulus to a static receptive field.

This is a relatively unusual situation

124
Q

What is the difference on the respective fMRIs in an experiment where activity of cortical areas was
examined following passive stroking of the right hand
with a sponge, or active touching of the sponge?

A

In both conditions, areas 3b and 1 were activated in the left hemisphere.

In active touch, however, areas M1 (primary motor cortex) and ACC (anterior cingulate
cortex) were also engaged.

125
Q

How does the ability for neuronal
activity to predict behavioural performance change as we progress along a pathway from primary somatosensory cortex to parietal cortex and finally to the premotor cortex?

A

graded increase

eg . Rapidly adapting neurons in area 3b/1 in the primary somatosensory cortex had a neural detection threshold that matched the perceptual/ behavioural
threshold. While these neurons carry the information necessary to detect a stimulus, they could only predict behavioural performance at chance level

126
Q

Can activity in M1 predict behavioural performance?

Which study is this

A

no

Luo, 2016

127
Q

Are cortical receptive fields fixed

A

no

can be modified by experience or injury

128
Q

How did scientists examine the effect of differential stimulation of restricted skin surfaces of the hand on the representation of these surfaces in 3b?

What was the result?

A

b a monkey was trained to maintain contact with a rotating disc in
order to get a reward.

The cortical hand representation of the same monkey, following 20 weeks of daily training, showed a marked expansion of the representations of the distal aspects of digits 2 and 3.

129
Q

Give evidence that supports the results of the monkey touching a rotating disc experiment

A

In support of this finding, musicians who play stringed instruments have a greater than normal cortical
representation for the highly stimulated fingers on their left hand.

(cortical representation increases with use - plasticity)

130
Q

What is the theory to explain phantom limbs

use an example of a someone with left arm amputation

A

There is a complete
map of the fingers on both the face and upper arm. The hypothesis is that the
sensory input from these areas is now innervating the hand area of the
somatosensory thalamus or cortex.

131
Q

Is reorganisation of the sensory input from amputated regions beneficial

A

can be - without phantom limb it can be impossible to use a prosthetic

but greater the reorganisation the
greater the amount of pain felt!

132
Q

Are phantom sensations unique to the somatosensory system?

A

no

tinnitus is a phantom auditory sensation with many similarities to phantom limbs.

133
Q

How can pain be described

A

an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

134
Q

What does lamina I receive input from in the dorsal horn

lamina V?

A

myelinated Aδ nociceptive fibres and both direct
and indirect input from ‘C’ fibres

input from both large diameter fibres (Aβ) from mechanoreceptors as well as input from other nociceptors. Lamina V neurons
therefore respond to innocuous stimuli at low intensity and noxious stimuli at high intensities and they are known as wide-dynamic range neuron

135
Q

Describe the basis of referred pain

A

Signals from an inflamed visceral organ converge on projection neurons at the dorsal horn of the spinal cord. Sensory input from a distant somatic
structure converges on the same neurones. The CNS
cannot distinguish between superficial and deep pain and
this failure results in the incorrect assignment of pain to the healthy somatic area.

136
Q

What is a well known referred pain

A

from angina pectoris

This is triggered by an inadequate supply of blood to the heart and is experienced as referred pain in the chest and left arm.

137
Q

Which areas of the cerebral cortex respond to pain

A

The main areas are

located in S-I, the anterior cingulate cortex (ACC) and insula

138
Q

What are the ACC and insula and what is their role in pain>

A

The anterior cingulate is part
of the limbic system and is thought to be
responsible for the emotional element of pain

The insular cortex processes information on the internal state of the body and thus contributes to the autonomic component of the overall pain
response.

139
Q

why might you get a cingulotomy

A

to treat psychiatric disease

140
Q

What did the original simplified gate control hypothesis lead to the development of

A

transcutaneous electrical nerve stimulation (TENS)

for pain relief

141
Q

Describe the neuronal circuitry of the gate control system

A

there is are 3 connections to the projection neuron:
Aβ fibers (tactile), inhibitory interneuron, and C fibre (nociceptor)

Both Aβ fibers and C fibres connect to both inhibitory interneuron and projection neuron

Aβ fibers excite both interneuron and projection neuron. C fibre inhibits interneuron and excites projection neuron

C fibres activating therefore activate projection neuron
Aβ fibers firing activates interneuron, decreasing projection neuron firing

142
Q

Where does gate control happen

A

substantia gelitanosa

143
Q

What is the influence of descending systems on gate control

A

diverting attention away from painful stimulus decreases pain felt

The PAG is thought to control
the ‘nociceptive’ gate in the dorsal horn by integrating inputs from the
cortex, thalamus and hypothalamus.

144
Q

What characterises the projection or transmission neurons in gate control

A

a wide dynamic range (WDR), i.e. they can
signal changes in stimulus intensity by increases in spike discharge rate over a wide range of intensities - the intensity theory of pain

(cf. a neuron with a narrow dynamic range can only signal changes in
intensity over a limited range of amplitudes.)

145
Q

What does the specifity theory of pain require

How is this seen in the body

A

neurons that respond selectively to touch (the mechanoreceptors) and other neurons that respond selectively to high amplitude stimuli that produce pain (the nociceptors).

both types of neural response are observed in the spinal cord; nociceptors are prominent in lamina I while WDR
neurons are in lamina V

146
Q

Why is pain so moodulated

A

enables it to be integrated
with many other body systems including skin reflexes, autonomic
regulation, emotion, and attention

147
Q

Where are the descending systems that modulate pain located (3)

A

in the periaqueductal gray (PAG) matter of the mid-brain, the raphe nuclei, and other nuclei of the rostral medulla.

148
Q

How can the PAG be used in surgery

A

Electrical stimulation of the PAG can produce sufficient analgesia to
perform abdominal surgery without the need for anaesthesia. Other,
non-painful, sensations were left intact

149
Q

How is morphine induced analgesia blocked

A

by injection of naloxone (an opiate antagonist) into the PAG.

150
Q

Bilateral transection of the dorsolateral funiculus leads to…

A

Bilateral transection of the dorsolateral funiculus blocks both descending gate control
stimulation- and morphine-induced analgesia.

151
Q

What does placebo analgesia refer to

A

the situation where administration of a substance known to be non-analgesic
produces an analgesic response when the subject is told that it is a pain killer.
NB the placebo effect also works for asthma, cough, diabetes, ulcers, multiple sclerosis and Parkinsonism

152
Q

How can we test the neural mechanisms of pain placebo

Results?

A

capsaicin applied to the distal region of all four limbs and were then asked to report the magnitude of pain felt at each site.

Following subcutaneous injection of capsaicin, specific expectations were
induced by the topical application of a placebo cream and by telling the subjects
that it was a powerful local anaesthetic.

placebo analgesia only occurred in treated part

153
Q

Can you abolish spatially specific placebo effect?

A

abolished with the
intravenous infusion of naloxone (an opioid antagonist) suggesting that it was mediated by one of the endogenous opioid systems

154
Q

Does non-specific release of endogenous opioids

throughout the nervous system underlie placeo?

A

no
rather that attentional
mechanisms, via expectation of analgesia, can be directed to specific parts of the body. It is argued that
spatial specific expectations have their own organization that is maintained at the level of the endogenous
opioid systems

155
Q

It is argued that spatial specific expectations have their own organization that is maintained at the level of the endogenous opioid systems. Give evidence from a rat model to support this

A

a somatotopic organization of the PAG (in rats) has been found such that stimulation of different areas produced analgesia in different cutaneous regions.

NHB (17 decks)

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