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Year 2 Collin > Neuro 7 - Sensory pathways > Flashcards

Neuro 7 - Sensory pathways Flashcards

1
Q

What are sensory modalities?

A

Types of stimulus

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2
Q

Mechanoreceptors of skin are which sensory fibre?

A

A-beta (v fast)

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3
Q

Pain / temperature fibres are which sensory fibre

A

A-delta (fast-ish)

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4
Q

Slow pain/temperature/itch fibres are which sensory fibre?

A

C fibres

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5
Q

How are axons adapted to sensing different stimuli?

A

They have different modified nerve endings/terminals

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6
Q

What is the absolute threshold?

A

Stimulus strength which produces a positive response 50% of the time (i.e. is detected 50% of the time)

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7
Q

Increasing stimulus strength and duration does what?

A

Increases neurotransmitter release causing greater intensity

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8
Q

Describe TRP channels

A

They are free nerve endings with high thermal sensitivity - temperature changes activates TRP channels

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9
Q

How many heat activated TRP channels are there?

A

4

TRPV1-4

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10
Q

How many cold activated TRP channels are there?

A

2

TRPM8
TRPA1

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11
Q

Name the 4 mechanoreceptors

A
  1. Meissners corpuscle
  2. Merkel cells
  3. Pacinian corpuscle
  4. Ruffini endings
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12
Q

What type of touch are Meissners corpuscles for?

A

Fine discriminative touch

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13
Q

What type of touch are Merkel cells used for?

A

Light touch and superficial pressure

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14
Q

What type of touch are Pacinian corpuscles used for?

A

Detecting deep pressure, vibration and tickling

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15
Q

What type of touch are Ruffini endings for?

A

Continuous pressure / touch and stretch

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16
Q

Describe tonic receptors

A

Detect continuous stimulus strength - transmits impulses for stimulus duration

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17
Q

Give an example of a tonic receptor

A

Merkel cells

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18
Q

Do tonic receptors adapt?

A

No, or they adapt very slowly.

Keeps brain constantly informed of body status

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19
Q

Describe phasic receptors

A

These detect changes in stimulus strength - fire impulses at start and end of stimulus (i.e. when a change is taking place)

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20
Q

Give an example of a phasic receptor?

A

Pacinian corpuscle

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21
Q

What is a receptive field?

A

Region on the skin which activates one single sensory neurone when stimulated

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22
Q

If you want fine detail, how big should the receptive field be?

A

Small

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23
Q

Describe two point discrimination

A

Minimum distance at which 2 points are perceieved as separate - related to size of receptive field

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24
Q

What type of sensory fibres are nociceptors?

A

A-delta fibres

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25
A-delta fibres are myelinated. There are 2 types - describe
Type 1: A-delta mechanoheat receptors (noxious mechanical/thermal stimuli) Type 2: A-delta mechanoreceptors (noxious mechanical stimuli)
26
Which type of sensory fibre is unmyelinated?
C fibres
27
What modalities do C fibres respond to?
Thermal, mechanical and chemical stimuli They are polymodal
28
In the sensory pathway, where are cell bodies present?
DRG and Trigeminal ganglia (face)
29
How many rexed laminae are there?
7
30
Where do mechanical stimuli terminate (A-beta and A-alpha) in the dorsal horn?
3-6 rexed laminae Deep
31
Where do pain and temperature (A-delta and C fibres) stimuli terminate in the dorsal horn?
Rexed laminae 1-2 Superficial
32
What is the main excitatory neurotransmitter of the dorsal horn?
Glutamate
33
How can overlapping receptive fields be overcome?
Via lateral inhibition - facilitates pinpoint accuracy in localising stimulus. Thus facilitates enhanced sensory perception
34
What mediates lateral inhibition?
Interneurons in the dorsal horn of SC
35
S1 = Primary somatosensory cortex. Where is it located?
Postcentral gyrus
36
S2 = Secondary somatosensory cortex. Where is it located?
Parietal operculum
37
What is the posterior parietal cortex needed for?
Spacial awareness of body
38
When innocuous mechanical stimuli enter the ascending dorsal column pathway (via A-beta) , what are the differences between lower limbs and upper limbs? (AP1)
Below T6 = lower limb = travels ipsilaterally along gracile tract Above T6 = lower limb = travels ipsilaterally along cuneate tract
39
Where do first order neurone terminate? | AP1
In the medulla
40
Within the medulla, gracile tract fibres have their first synapse where? (AP1)
In the gracile nucleus
41
Within the medulla, cuneate tract fibres have their first synapse where? (AP1)
In the cuneate nucleus
42
What do the second order neurons do? | AP1
They decussate in the caudal medulla, forming the contralateral medial lemniscus tract
43
Where do second order neurons terminate? | AP1
In the Ventral Posterior Lateral Nucleus (VPL) of the nucleus
44
Where does sensory information from lower limbs terminate in relation to the vPL (AP1)
More laterally
45
What do 3rd order neurons do? | AP1
3rd order neurons convey information from VPL to Somatosensory cortex
46
What is meant by somatosensory humunculus | AP1
Area whereby size of somatotopic areas is proportional to density of sensory receptors in that body region
47
What is AP1?
Ascending pathway 1 - innocuous mechanical stimuli
48
AP2 =?
Ascending pathway 2 - pain/temperature/crude touch
49
The spinathalamic pathway involves 2 aspects which are?
AKA anterolateral pathway "Lateral" aspect of spinothalamic tract is where pain/temperature sensations ascend "Anterior" aspect of spinothalamic tract is where crude touch sensations ascend
50
In AP2, where do the primary afferent axons terminate? What happens next?
Primary afferent axons (first order) terminate upon entering SC (in the dorsal horn) Second order neurons decussate immediately and form spinothalamic tract
51
Where do second order neurons terminate? AP2
Ventral posterior lateral nucleus (VPL) Lower extremities more lateral
52
What are key differences between dorsal column and spinothalamic tracts?
Dorsal column = decussates in medulla ST tract = decussates in SC Dorsal column = light touch, vibration, 2 point discrimination ST = Pain, temperature, coarse touch
53
There is an emotional component to pain, where does the signal from the SC go to?
The parabrachial area
54
How can we test the integrity of the ascending sensory pathways?
Quantitative sensory testing (QST)
55
If someone gets an anterior SC lesion, they cannot feel pain and temperature below the level of the lesion. What can they feel?
Light touch and vibration below the level of the lesion
56
What are the 6 different types of pain?
1. Nociceptive (usually acute) 2. Muscle 3. Somatic 4. Visceral 5. Referred 6. Neuropathic
57
What is neuropathic pain?
Pain caused by a lesion/disease of the somatosensory nervous system
58
Do analgesic drugs (e.g. opiates) have a good relieving effect for neuropathic pain?
No, poor response to analgesics
59
What is the most common form of neuropathic pain?
Radicular low back pain (sciatica)
60
What is allodynia?
Pain caused by a stimulus that usually does not cause pain
61
What is hyperalgesia?
Increased pain from a stimulus that normally provokes pain
62
What is paraesthesia?
Abnormal sensation (whether spontaneous or evoked)
63
How can synaptic plasticity cause chronic pain? | or central sensitisation
NMDA receptor activation causes Ca2+ mediated synaptic plasticity meaning increased synaptic strength which reduces inhibitory influences on dorsal horn neurons Constant NMDA activation therefore causes chronic pain development
64
Name some neuropathic phenotypes
``` Heat hyperalgesia Cold hyperalgesia Mechanical hyperalgesia Mechanical allodynia Loss of sensation ```
65
What are the 2 inhibitory pathways for descending control of nociception?
1. PAG-RVM axis (brainstem) which uses 5-HT (aka serotonin) as its inhibitory monoamine 2. Locus cereleus (pons), inhibitory via noradrenaline
66
How do endogenous opioids increase descending inhibition?
1. PAG-RVM contains lots of miu-opioid receptors 2. Endogenous opioids inhibit glutamate release (less spinothalamic neurones activated) Opioids part of endogenous analgesic system
67
Aside from opioids, what other class of drugs may have some efficacy in neuropathic pain?
Anti-depressants
68
Why may SNRIs (class of antidepressants) enhance descending NA inhibition?
Stimulate NA and inhibitory influences within the synapse
69
What is conditioned pain modulation used for?
To measure the level of descending control in patients

Year 2 Collin (114 decks)

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