1
Q

What are the two major pathways of the somatosensory system?

A

β†’ Dorsal column

β†’ spinothalamic tract

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2
Q

What does the dorsal column receive inputs from?

A

β†’ Large diameter myelinated afferents : tactile

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3
Q

What does the spinothalamic tract receive inputs from?

A

β†’ small diameter
β†’ thinly myelinated
β†’ 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

β†’ You interrupt all the ascending axons on one side

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5
Q

What are the two types of pain?

A

β†’ Sensory discriminative

β†’ Affective motivational

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6
Q

What are nociceptors?

A

β†’ Neurons specialized for the detection of painful stimuli

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7
Q

What are the 3 types of nociceptors?

A

β†’ Mechanical
β†’ Chemosensory
β†’ Thermal

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8
Q

When does temperature become painful?

A

β†’ 45 degrees or higher

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9
Q

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

A

β†’ non nociceptive plateau above a certain range

β†’ 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

β†’ Transduction of noxious heat

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11
Q

What kind of a receptor is TRPV1?

A

β†’ Ion channel that allows both Na+ and Ca2+ to pass

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12
Q

What can activate TRPV1 and why?

A

β†’ Capsaicin

β†’ it is lipid soluble

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13
Q

What does capsaicin binding to TRPV1 cause?

A

β†’ Activation of thermal nociceptor

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14
Q

What is the conduction of the A delta fibres like?

A

β†’ Slowest of the myelinated fibres

β†’ Conduct moderately compared to C fibres

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15
Q

How do C fibres conduct?

A

β†’ Unmyelinated

β†’ Slowly

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16
Q

What pain does the A delta fibre mediate?

A

β†’ Mediates the sharp first pain

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17
Q

What pain does the C fibre mediate?

A

β†’ second dull burning pain

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18
Q

What blocks the smallest fibres?

A

β†’ low dose anaesthetic

19
Q

What blocks larger axons?

A

β†’ Pressure

20
Q

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

A

β†’ Prostaglandins
β†’ Cytokines
β†’ Signaling molecules

21
Q

Why is there inflammation?

A

β†’ Tissue damage

22
Q

What is hyperalgesia?

A

β†’ Increased sensitivity to pain

23
Q

What is allodynia?

A

β†’ Something painless like gentle touch will be painful

24
Q

What do peripheral neurons release?

A

β†’ Substance P which reinforces the release of inflammatory molecules

25
Q

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

A

β†’ Cells are damaged and release PGE
β†’ Sensory nerve fibres send the impulse to the dorsal horn (1ST ORDER NEURONS)
β†’ The 1st order neurons synapse with 2nd order neurons in the dorsal horn
β†’ The 2nd order neuron crosses over contralaterally and enters the spinothalamic tract
β†’ 2nd order neuron continues moving up to the thalamus where it synapses with a 3rd order neuron
β†’ 3rd order neuron sends impulse to somatosensory cortex

26
Q

Where do C fibres terminate?

A

β†’ Exclusively in superficial layers

27
Q

Where do A delta fibres terminate?

A

β†’ in both superficial and deep

28
Q

Why is angina not felt in the heart?

A

β†’ 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

β†’ Parallel

30
Q

What is necessary for the localisation of pain?

A

β†’ primary somatosensory cortex

31
Q

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

A

β†’Diverge at the level of the thalamus

32
Q

Where is the cingulate gyrus?

A

β†’ Just above the corpus callosum

33
Q

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

A

β†’ ventral posterior nucleus of the thalamus

β†’ primary and secondary somatosensory cortex

34
Q

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

A

β†’ Midline nuclei of the thalamus

β†’ Anterior cingulate and insular cortex

35
Q

What type of pain does the lateral system mediate?

A

β†’ Sensory discriminative

36
Q

What type of pain does the medial system mediate?

A

β†’ Affective motivational

37
Q

What are the effects of a lobotomy?

A

β†’ Behaviour is more docile

β†’ loss of sensitivity to pain

38
Q

What procedure is done for intractable pain?

A

β†’ Anterior cingulotomy

39
Q

What are 2 endogenous opioids?

A

β†’ Enkephalins

β†’ Endorphins

40
Q

Describe how the descending pathways modulate pain

A

β†’ 5-HT neurons project to the place where the 1st order neurons synapse with 2nd order neurons
β†’ they release NA and 5-HT which inhibits the release of substance P from the 1st order neuron
β†’ They stimulate interneurons
β†’ Interneurons inhibit the 2nd order neurons and release enkephalins

41
Q

Why does phantom limb pain occur?

A

β†’ The somatosensory part of the cortex that corresponds to the limb is still there

42
Q

What is chronic pain defined as?

A

β†’ >3 months

43
Q

What is neuropathic pain attributable to?

A

β†’ Nerve damage