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Year 1 > Pain transmission > Flashcards

Pain transmission Flashcards

1
Q

Type C fibres

A

Unmyelinated Post ganglionic neuron pseudounipolar with soma in dorsal root ganglion

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2
Q

What are the first order neurons of the spinothalamic tract?

A

A-delta fibres and C fibres

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3
Q

What are nocioceptors?

A

Unspecialised nerve endings in the skin and tissues which respond to noxious stimuli. They are characterised by their axons and their receptor channels.

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4
Q

What are the nociceptive fibres?

A

C-fibres and A-delta fibres which are high threshold for activation. A-delta fibres have a lower threshold than C-fibres and cause first pain.

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5
Q

What are the types of nociceptors?

A

Mechanical, chemical, thermal, polymodal and silent nocioceptors

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6
Q

What is the mechanical nociceptor?

A

Responds to painful mechanical pressure on via the a-delta fibres and c-fibres

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7
Q

What is the thermal nociceptor?

A

Transmits information about painful extreme temperature to the brain via the a-delta or c-fibres

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8
Q

What are the chemical nociceptors?

A

Transmits information about chemicals like irritants and food to the brain via the c fibres

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9
Q

What are polymodal nociceptors?

A

Detect thermal, mechanical and chemical noxious stimuli to the brain and have only c-fibres

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10
Q

What are sleeping/silent nociceptors?

A

Respond to inflammation following injury via c-fibres

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11
Q

How are nocicpetors characterised?

A

Based on their axon properties and receptor channels

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12
Q

What are the primary afferent fibres?

A

Axons/unspecialised nerve endings which respond to stimuli and classified by their diameter; a-alpha, a-beta, a-delta and c fibres

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13
Q

What are the A-alpha fibres?

A

Myelinated with has the largest diameter and highest conductivity and velocity and responds to propioception of skeletal muscle.

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14
Q

What are the A-beta fibres?

A

A-beta fibres have a large diameter with a fast conductivity to respond to non-painful mechanoreceptors in the skin for touch. This is implicated in allodynia.

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15
Q

How are a-beta fibres involved in pain?

A

A-beta fibres respond to normal, innocus touch. In allodynia, a-beta fibres for touch transmit pain.

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16
Q

What is the gate control theory?

A

Activation of A-alpha or a-beta fibres results in the suppression of A-delta and C fibres.

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17
Q

What are the A-delta fibres?

A

Myelinated fibre which responds to mechanical and thermal pain only. Small diameter and lower conductivity.

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18
Q

What is the neurotransmitter for a-delta fibres in the dorsal horn?

A

Glutamate

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19
Q

What kind of pain do a-delta fibres transmit?

A

First pain which is easily localised due to lower threshold.

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20
Q

What kind of pain do c fibres transmit?

A

Second pain which is poorly localised due to high threshold.

21
Q

Which neurotransmitters do c-fibres use in the dorsal horn?

A

Neuropeptide Substance P and glutamate to activate second order neurons in the substantia gelatinosa.

22
Q

What are the C fibres?

A

Polymodal unmyelinated fibres which respond to mechanical, thermal and chemical pain. It has the smallest diameter and lowest conductivity.

23
Q

What is 1st pain?

A

Sharp localised pain in the skin with a fast onset and short duration driven by the a-delta fibres. Responsible for acute pain.

24
Q

What is 2nd pain?

A

Dull/vague poorly localised pain with a slow onset and long duration driven by the c-fibres. Responsible for chronic pain.

25
Q

What are first order somatosensory neurons?

A

Transduce information about the internal/external environment of the body to the spinal cord.

26
Q

What is congenital analgesia?

A

Inability to detect noxious stimuli due to mutations in Na+ channels of nociceptors

27
Q

What is the role of the amygdala in nociception

A

Centre of the limbic system of the brain for behavioural response, stimulated by nociception for emotional response to pain

28
Q

What is the role of the thalamus in nociception?

A

Perception of pain

29
Q

What is the role of the somatosensory cortex in pain?

A

Localisation of pain

30
Q

Where do pain and temperature sensation enter the CNS in the spinal trigeminal tract?

A

Via cranial nerves 5, 6, 7, 8 in the pons

31
Q

What is the pars caudalis?

A

Site of synapse between first oder and second order neurons of the spinal trigeminal tract located in the medulla. It is continuous with the dorsal horn of the spinal cord and extends to the lower medulla. It is a component of the spinal trigeminal nucleus.

32
Q

What is the function of the pars caudalis?

A

Transmits nociception from the face and head in the spinal trigeminal tract. It porjects to the cortex via the ventral posteriomedial nucleus of the thalamus.

33
Q

What is referred pain?

A

Visceral and subcutaneous nociceptors enter the spinal cord at the same route and target the same spinal neurons thtat causes organ pain to be experienced on the skin

34
Q

What is hyperalgesia?

A

Nocioception caused by tissue damage or disease.

35
Q

What is primary hyperalgesia?

A

Primary hyperalgesia is at the site of tissue damage transmitted by A-delta fibres with Increased response to heat and mechanical nociception.

36
Q

What is Secondary hyperalgesia?

A

Around the site of tissue damage. This is driven by C-fibres in response to inflammatory mediators and mechanical nocicpetion.

37
Q

What is allodynia?

A

Nocioception caused by light touch which is non painful from A-beta afferent.

38
Q

What is fibromyalgia?

A

Widespread pain with allodynia present greatly in women, with widespread ymtpoms such as irritable bowel syndrome. Treated with analgesics and antidepressants.

39
Q

What are fast acting nociceptive neurotransmitters released from first order neurons?

A

Glutamate primary from A-delta fibres and lesser extent C-fibres which binds to post synaptic second order neurons in the substantia gelatinosa for activation.

40
Q

What are slow acting neurotransmitters released from first oder neurons?

A

Substance P from C-fibres only which binds to post synaptic second order neurons in the substantia gelatinosa for activation

41
Q

Periaqueductal grey matter-

A

Midbrain region surrounding the cerebral aqueduct. Receives signals from the central nucleus of the amygdala to increase avoidance behaviour in stress and pain.

42
Q

Periaqueductal grey matter- descending pain pathways

A

Projects to the ventromedial medulla which contains serotenergic raphe nuclei to inhibit the release of neurotransmitters of first order neurons in the dorsal horn of the spinal cord of the spinothalamic pathway. This pathway is modulated by serotonin and noradrenaline

43
Q

What neurotransmitters are involved in pain?

A

Glutamate from A-delta fibres. It acts on ionotropic AMPA, NMDA or kainate recepotrs on second order neurons. Substance P is released by C fibres and and acts on neurokinin receptors on second order neurons. It is inhibited by the periaqueductal grey matter descending pain pathway via serotonin.

44
Q

Where do third order neurons terminate of the spinothalamic pathway?

A

From the thalamus to the somatosensory cortex and periaqueductal grey matter

45
Q

What inhibits the periaqueductal descending pain pathways?

A

Mu opioid receptors, GABA

46
Q

Endogenous opioid receptors

A

G protein coupled receptors which arise from terminals of the amygdala and hypothalamus. They regulate neurotransmission of pain by causing hyperpolarisaiton of cells in the dorsal horn. It reduces the release of susbtance P from first order neurons and causes hyperpolarisation of second order neuorns which reduces action potentials

47
Q

How do endogenous opioid receptors act on the periaqueductal grey matter?

A

Enhance descending inhibiton of the pain pathway where it is found in the periaqueductal grey matter and raphe nucleus of the ventromedial medulla

48
Q

Function of periaqueductal grey matter in pain transmission

A

Responsible for descending modulation of pain perception via both inhibition of pain perception (thalamus) and facillitation of pain perception

Year 1 (191 decks)

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