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Neuroscience > Somatosensation II > Flashcards

Somatosensation II Flashcards

1
Q

What are the two major pathways of the somatosensory system?

A

→ Dorsal column

→ spinothalamic tract

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2
Q

What does the dorsal column receive inputs from?

A

→ Large diameter myelinated afferents : tactile

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3
Q

What does the spinothalamic tract receive inputs from?

A

→ small diameter
→ thinly myelinated

→ coarse touch, nociception and temperature sensitivity

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4
Q

What happens if there is a cut on one half of the spinal cord?

A

→ You interrupt all the ascending axons on one side

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5
Q

What are the two aspects of pain?

A

→ Sensory discriminative

→ Affective motivational

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6
Q

What are nociceptors?

A

→ Neurons specialized for the detection of painful stimuli

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7
Q

What are the 3 types of nociceptors?

A

→ Mechanical
→ Chemosensory

→ Thermal

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8
Q

When does temperature become painful?

A

→ 45 degrees or higher

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9
Q

What is the difference between non nociceptive and nociceptive thermal receptors?

A

→ non nociceptive plateau above a certain range

→ nociceptors don’t response until the temperature approaches the range that is deemed painful

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10
Q

What is the TRPV1 receptor involved in?

A

→ Transduction of noxious heat

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11
Q

What kind of a receptor is TRPV1?

A

→ Ion channel that allows both Na+ and Ca2+ to pass

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12
Q

What can activate TRPV1 and why?

A

→ Capsaicin

→ it is lipid soluble

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13
Q

What does capsaicin binding to TRPV1 cause?

A

→ Activation of thermal nociceptor

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14
Q

What is the conduction of the A delta fibres like?

A

→ Slowest of the myelinated fibres

→ Conduct moderately compared to C fibres

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15
Q

How do C fibres conduct?

A

→ Unmyelinated

→ Slowly

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16
Q

What pain does the A delta fibre mediate?

A

→ Mediates the sharp first pain

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17
Q

What pain does the C fibre mediate?

A

→ second dull burning pain

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18
Q

What blocks the smallest fibres?

A

→ low dose anaesthetic

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19
Q

What blocks larger axons?

A

→ Pressure

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20
Q

What maintains the sensitivity of the C fibres after the original stimulus?

A

→ Prostaglandins
→ Cytokines

→ Signaling molecules

21
Q

Why is there inflammation?

A

→ Tissue damage

22
Q

What is hyperalgesia?

A

→ Increased sensitivity to pain

23
Q

What is allodynia?

A

→ Something painless like gentle touch will be painful

24
Q

What do peripheral neurons release?

A

→ Substance P which reinforces the release of inflammatory molecules

25
Q

Describe the pathway from an injured right hand to the somatosensory cortex

A

→ Cells are damaged and release PGE
→ Sensory nerve fibres send the impulse to the dorsal horn (1ST ORDER NEURONS)

→ The 1st order neurons synapse with 2nd order neurons in the dorsal horn
→ The 2nd order neuron crosses over contralaterally and enters the spinothalamic tract
→ they eventually come to lie alongside the medial lemniscus
→ 2nd order neuron continues moving up to the thalamus where it synapses with a 3rd order neuron
→ 3rd order neuron sends impulse to somatosensory cortex

26
Q

Where do C fibres terminate?

A

→ Exclusively in superficial layers

27
Q

Where do A delta fibres terminate?

A

→ in both superficial and deep

28
Q

Why is angina not felt in the heart?

A

→ Afferents from cardiac muscle are converging on dorsal horn interneurons on the cervical segments

29
Q

What are the pathways of the spinothalamic and the dorsal column like in relation to each other?

A

→ Parallel

30
Q

What is necessary for the localisation of pain?

A

→ primary somatosensory cortex

31
Q

Where do the lateral and the medial systems of the anterolateral system diverge?

A

→Diverge at the level of the thalamus

32
Q

Where is the cingulate gyrus?

A

→ Just above the corpus callosum

33
Q

Where do the lateral system 2nd order neurons project to?

A

→ ventral posterior nucleus of the thalamus

→ primary and secondary somatosensory cortex

34
Q

Where do the medial system 2nd order neurons project to?

A

→ Midline nuclei of the thalamus

→ Anterior cingulate and insular cortex

35
Q

What type of pain does the lateral system mediate?

A

→ Sensory discriminative

36
Q

What type of pain does the medial system mediate?

A

→ Affective motivational

37
Q

What are the effects of a lobotomy?

A

→ Behaviour is more docile

→ loss of sensitivity to pain

38
Q

What procedure is done for intractable pain?

A

→ Anterior cingulotomy

→Unpleasantness/motivational can be dissociated

39
Q

What are 2 endogenous opioids?

A

→ Enkephalins

→ Endorphins

40
Q

Describe how the descending pathways modulate pain

A

→ 5-HT neurons project to the place where the 1st order neurons synapse with 2nd order neurons
→ they release NA and 5-HT which inhibits the release of substance P from the 1st order neuron

→ They stimulate interneurons
→ Interneurons inhibit the 2nd order neurons and release enkephalins

41
Q

Why does phantom limb pain occur?

A

→ The somatosensory part of the cortex that corresponds to the limb is still there

42
Q

What is chronic pain defined as?

A

→ >3 months

43
Q

What is neuropathic pain attributable to?

A

→ Nerve damage

44
Q

Compare the lateral and medial pain systems of the anterior lateral system

A

→ Lateral: Sensory-discriminative
Project via specific somatosensory thalamic nuclei
→medial: Affective-motivational
Project to different cortical areas via (non-specific) midline thalamic nuclei

45
Q

How is the periaqueductal grey involved in descending pain modulation?

A

→Enkephalins are found in midbrain, in the periaqueductal.

→Sends descending projections to structures associated with neuromodulator cells like noradrenaline and serotonin.

→Theses projects to dorsal horn of the spinal cord where A-beta, delta and C fibres
→Stimulation of the midbrain periaqueductal grey induce profound analgesia.
→Activates Raphe neurones which are serotoninergic.
→They project down to spinal cord and activate local spinal cord interneuron(opioid). →They pre-synaptically inhibit incoming C-fibres by binding to opioid receptors on the C-fibre.

46
Q

How does the STT and DCML run?

A

→in parallel

47
Q

What is S1 necessary for?

A

localization of pain, but stimulation of S1 gives rise to referred tactile, not painful, sensations

48
Q

Describe the dorsal horn interneurons

A

→Located in superficial and deep layers of dorsal horn
→Synaptic input from C- and A-δ fibres
→Axons cross and ascend in anterolateral white matter

49
Q

What happens when a person first touches a really hot radiator.

A

→ sharp increase in A-delta fibre action potentials
→increase in C-fibre firing
→ upon continuous exposure, A-delta doesn’t fire but c-fibre fires.
→then A-delta fires but C-fibre stops firing

Neuroscience (21 decks)

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