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Physiology 2. Neurophysiology. > Pain. The Somatosensory System. > Flashcards

Pain. The Somatosensory System. Flashcards

1
Q

What is pain?

A

An unpleasant emotional and sensory experience.

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2
Q

Where in the brain is pain processed?

A

In the hypothalamus and the cortex.

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3
Q

What is the purpose of pain?

A

To protect the body by withdrawing from whatever is causing the damage.

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4
Q

What kind of sensory receptors respond to pain?

A

Nociceptors.

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5
Q

What name is given to the transduction of pain through the nervous system?

A

Nociception.

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6
Q

Where must a pain stimulus get to if it is to be felt as pain?

A

The cortex.

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7
Q

Why do nociceptors also communicate with motor neurons?

A

So we can have a fast withdrawal reflex.

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8
Q

Is the brain involved in the withdrawal reflex that is involved in pain?

A

No, it is a local circuit.

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9
Q

What tissues are nociceptors found in?

A

All tissues except the brain.

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10
Q

What kind of receptors are nociceptors?

A

Ligand gated channels and they are basically activated by chemoreceptors.

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11
Q

When are nociceptors activated?

A

When tissue is damaged.

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12
Q

How does tissue damage activate a nociceptor?

A

When cells are damaged the intracellular contents will leak out of the cell.

They then act as the chemicals that initiate pain by binding to their particular ligand gated receptor on the nociceptor.

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13
Q

Why are nociceptors known as polymodal receptors?

A

As they have ligand gated receptors for multiple substances.

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14
Q

Can a nociceptor be activated by multiple chemicals?

A

Yes.

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15
Q

What kind of sense is pain?

A

A chemo-receptive sense.

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16
Q

How are nociceptors activated if we cut ourselves with a knife?

A

Chemicals are released from damaged cells and they bind to their receptors on a nociceptor.

The binding depolarises the nociceptors and an action potential is sent to the brain.

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17
Q

What nerve fibres are involved in the chemoreception of pain?

A

A delta fibres.

These are quite small fibres.

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18
Q

The first pain is transmitted by what kind of fibres?

A

A delta fibres.

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19
Q

What is step 2 of pain transmission?

A

When the body develops a system that maintains a painful sensation.

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20
Q

Why does the body generate 2nd pain?

A

To make the affected area painful so that you do not bash it or bang it again.

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21
Q

When is 2nd pain initiated?

A

When activated nociceptors release substance P and calcitonin gene related peptide (CGRP).

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22
Q

What are the 2 roles of substance P and CGRP in 2nd pain?

A

They cause more pain.

They attract white blood cells to the infected area meaning they initiate inflammation.

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23
Q

Do inflammatory substances contribute towards 2nd pain?

A

Yes.

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24
Q

What kind of nociceptors will be activated by 2nd pain?

A

Ligand gated receptors.

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25
Q

What nerve fibres transmit 2nd pain?

A

C fibres.

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26
Q

What kind of fibres are C fibres?

A

Small unmyelinated fibres that maintain pain for as long as the inflammatory mediators are there.

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27
Q

What happens when prostaglandins bind to the nociceptors that initiate 2nd pain?

A

They cause ion channels to stay open for a longer time.

There will also be increased synthesis of neurotransmitters.

There will be increased recruitment of dormant nociceptors.

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28
Q

What effects does the increased opening time of ion channels have on the cell?

A

It allows more ions to flow in and out of the cell and leads to higher graded potentials.

This results in more action potentials being released from this neuron.

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29
Q

During 2nd pain, what is the idea behind increasing the opening times of the ion channels in nociceptors following the binding of prostaglandins?

A

To make the nociceptors more sensitive so that even a light touch will trigger pain.

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30
Q

What is pain sensitisation?

A

This process by which prostaglandins increase sensitivity during 2nd pain.

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31
Q

What are the 2 categories of pain sensitisation?

A

Hyperalgesia.

Allodynia.

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32
Q

What is hyperalgesia?

A

An exaggerated pain response to a noxious substance.

33
Q

What is allodynia?

A

A pain response to a non-noxious stimulus e.g. a gentle touch.

This is basically a painful response to something that is not normally painful.

34
Q

How long does the enhancement of pain in secondary pain last for?

A

As long as the inflammatory process is active.

35
Q

What is chronic pain?

A

Secondary pain that does not subside.

36
Q

When is a pain stimulus not considered to be pain?

A

If it does not reach the cortex of the brain.

37
Q

What neurons does a pain stimulus use to travel to the brain?

A

1st, 2nd and 3rd order neurons.

38
Q

What fibres will be found in first order neurons that respond to pain?

A

A delta fibres or C fibres depending on whether it is first or second pain.

39
Q

What fibres are responsible for transmitting initial pain?

A

A delta fibres within a plexus nerve.

40
Q

What are the 2 major neurotransmitters in the pain pathway?

A

Glutamate.

Substance P.

41
Q

For pain, what spinal tract will the 2nd order neurons run up?

A

The spinal-thalamic tract within the lateral funniculus.

42
Q

In primates will pain run up the spinal cord ispilaterally or contralaterally?

A

It always cross from one side of the spinal cord to the other and this said to be contralateral.

43
Q

How will the pain stimulus travel up the spinal cord of a gorilla if you hit its right toe?

A

The stimulus will travel up the left side of the spinal cord.

44
Q

In animals that are not primates, will pain run up the spinal cord ispilaterally or contralaterally?

A

Half of the pain stimuli will be contralateral and half will be ipsilateral.

This means half will cross over and half will remain on the same side.

45
Q

Where will 2nd order neurons deliver pain to?

A

The thalamus where the stimulus will synapse over to a 3rd order neuron.

To

46
Q

What are the 3 destinations that 3rd order neurons deliver pain stimuli too?

A

The cortex.

The hypothalamus.

The limbic system.

47
Q

What effects are felt when pain is delivered to the hypothalamus and limbic system?

A

Emotional and physical responses to pain e.g. nausea, anger and increased heart rate.

48
Q

Can pain stimuli activate the limbic system?

A

Yes.

This is why pain is said to be an emotional experience.

49
Q

Pain must be delivered to what part of the brain in order to be felt?

A

The cortex.

50
Q

What nerve fibres are used by pain stimuli to travel to the limbic system?

A

C fibres.

51
Q

Where are the chemoreceptors that initiate the pain response found?

A

Only at the nerve endings of nociceptors.

52
Q

What is neuropathic pain?

A

Pain generated in a nerve or axon at a location away from the chemoreceptors of the nociceptors.

53
Q

What is an example of neuropathic pain?

A

Sciatic pain.

54
Q

What is sciatic pain caused by?

A

Compression of the sciatic nerve in the back, however the pain is felt in the leg.

55
Q

How is neuropathic pain generated?

A

The stimulus is generated high up the neuron.

The pain is felt at the nerve endings as the brain assumes the pain is coming from the nociceptors of that neuron.

56
Q

What is responsible for phantom pain?

A

Nociceptive pain.

57
Q

What is an example of phantom pain?

A

Pain felt in a part of the body that is not longer there.

58
Q

How is phantom pain generated?

A

The neurons can still create action potentials and the brain believes that the pain is coming from below the amputation site.

59
Q

What does the analgesia pathway allow for?

A

The moderation and inhibition of pain.

60
Q

Why is the analgesia pathway said to be life saving?

A

As it means the animal is not distracted by pain and can get out of the bad situation.

61
Q

What is the analgesia pathway also known as?

A

The descending pain pathway.

62
Q

When will the analgesia pathway be activated?

A

When there is extreme pain caused by extreme stimulation.

63
Q

What happens if the analgesia pathway is activated?

A

If the pain transmitted is intense enough then the brain activates a descending pathway that dulls the pain.

64
Q

What spinal cord tract does the analgesia pathway run down?

A

A tract that is in close contact with the ascending pathway.

65
Q

What are the neurotransmitters in the descending pain pathway?

A

Norepinephrine and serotonin.

66
Q

Where does in the spinal cord will stimuli in the descending pain pathway arrive to?

A

At the dorsal grey horn in the part of the spinal cord that is receiving the pain stimulus from the affected area.

67
Q

What happens when the analgesic stimulus arrives at the dorsal grey horn in the descending pain pathway?

A

It releases inhibitory neurotransmitters where the pain is synapsed from a first order neuron to a second order neuron.

68
Q

How does the analgesic pathway stop pain from being transmitted?

A

It prevents synapsis from a 1st order neuron to a 2nd order neuron.

69
Q

What are the 5 inhibitory neurotransmitters that are released by the analgesic pathway?

A

Enkephalins.

Endorphins.

Dynorphins.

GABA.

Glycine.

70
Q

What is released into circulation once the analgesia pathway is activated?

A

Endorphins which lead to good feelings in the body.

71
Q

What is chronic pain?

A

Pain that serves no purpose as the injury has already healed, but the pain is still felt.

72
Q

What is chronic pain characterised by?

A

The hypersensitivity of the pain transmission system (hyperalgesia and allodynia).

73
Q

What are the mechanisms for chronic pain?

A

The same as those for acute pain.

74
Q

What neurotransmitter leads to chronic pain?

A

Glutamate.

75
Q

Where does chronic pain originate from?

A

The nociceptors as it causes them to remain in their remodelled state.

76
Q

What is neuropathic pain?

A

When there are changes in the location where the pain stimulus synapses from 1st to 2nd order neurons or from 2nd to 3rd order neurons.

77
Q

What is neuropathic pain characterised by?

A

The hyper-excitability of neurons in the locations where synapsis takes place.

78
Q

What are the consequences of pain to the animal?

A

Huge stress such as loss of appetite etc.

79
Q

What is the main stress hormone?

A

Cortisol.

Physiology 2. Neurophysiology. (17 decks)

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