Pain. The Somatosensory System.

Question 1

What is pain?

Answer 1

An unpleasant emotional and sensory experience.

Question 2

Where in the brain is pain processed?

Answer 2

In the hypothalamus and the cortex.

Question 3

What is the purpose of pain?

Answer 3

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

Question 4

What kind of sensory receptors respond to pain?

Answer 4

Nociceptors.

Question 5

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

Answer 5

Nociception.

Question 6

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

Answer 6

The cortex.

Question 7

Why do nociceptors also communicate with motor neurons?

Answer 7

So we can have a fast withdrawal reflex.

Question 8

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

Answer 8

No, it is a local circuit.

Question 9

What tissues are nociceptors found in?

Answer 9

All tissues except the brain.

Question 10

What kind of receptors are nociceptors?

Answer 10

Ligand gated channels and they are basically activated by chemoreceptors.

Question 11

When are nociceptors activated?

Answer 11

When tissue is damaged.

Question 12

How does tissue damage activate a nociceptor?

Answer 12

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.

Question 13

Why are nociceptors known as polymodal receptors?

Answer 13

As they have ligand gated receptors for multiple substances.

Question 14

Can a nociceptor be activated by multiple chemicals?

Answer 14

Yes.

Question 15

What kind of sense is pain?

Answer 15

A chemo-receptive sense.

Question 16

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

Answer 16

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.

Question 17

What nerve fibres are involved in the chemoreception of pain?

Answer 17

A delta fibres.

These are quite small fibres.

Question 18

The first pain is transmitted by what kind of fibres?

Answer 18

A delta fibres.

Question 19

What is step 2 of pain transmission?

Answer 19

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

Question 20

Why does the body generate 2nd pain?

Answer 20

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

Question 21

When is 2nd pain initiated?

Answer 21

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

Question 22

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

Answer 22

They cause more pain.

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

Question 23

Do inflammatory substances contribute towards 2nd pain?

Answer 23

Yes.

Question 24

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

Answer 24

Ligand gated receptors.

Question 25

What nerve fibres transmit 2nd pain?

Answer 25

C fibres.

Question 26

What kind of fibres are C fibres?

Answer 26

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

Question 27

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

Answer 27

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.

Question 28

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

Answer 28

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.

Question 29

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

Answer 29

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

Question 30

What is pain sensitisation?

Answer 30

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

Question 31

What are the 2 categories of pain sensitisation?

Answer 31

Hyperalgesia. Allodynia.

Question 32

What is hyperalgesia?

Answer 32

An exaggerated pain response to a noxious substance.

Question 33

What is allodynia?

Answer 33

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.

Question 34

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

Answer 34

As long as the inflammatory process is active.

Question 35

What is chronic pain?

Answer 35

Secondary pain that does not subside.

Question 36

When is a pain stimulus not considered to be pain?

Answer 36

If it does not reach the cortex of the brain.

Question 37

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

Answer 37

1st, 2nd and 3rd order neurons.

Question 38

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

Answer 38

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

Question 39

What fibres are responsible for transmitting initial pain?

Answer 39

A delta fibres within a plexus nerve.

Question 40

What are the 2 major neurotransmitters in the pain pathway?

Answer 40

Glutamate. Substance P.

Question 41

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

Answer 41

The spinal-thalamic tract within the lateral funniculus.

Question 42

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

Answer 42

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

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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.

Question 45

Where will 2nd order neurons deliver pain to?

Answer 45

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

Question 46

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

Answer 46

The cortex. The hypothalamus. The limbic system.

Question 47

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

Answer 47

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

Question 48

Can pain stimuli activate the limbic system?

Answer 48

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

Question 49

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

Answer 49

The cortex.

Question 50

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

Answer 50

C fibres.

Question 51

Where are the chemoreceptors that initiate the pain response found?

Answer 51

Only at the nerve endings of nociceptors.

Question 52

What is neuropathic pain?

Answer 52

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

Question 53

What is an example of neuropathic pain?

Answer 53

Sciatic pain.

Question 54

What is sciatic pain caused by?

Answer 54

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

Question 55

How is neuropathic pain generated?

Answer 55

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.

Question 56

What is responsible for phantom pain?

Answer 56

Nociceptive pain.

Question 57

What is an example of phantom pain?

Answer 57

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

Question 58

How is phantom pain generated?

Answer 58

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

Question 59

What does the analgesia pathway allow for?

Answer 59

The moderation and inhibition of pain.

Question 60

Why is the analgesia pathway said to be life saving?

Answer 60

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

Question 61

What is the analgesia pathway also known as?

Answer 61

The descending pain pathway.

Question 62

When will the analgesia pathway be activated?

Answer 62

When there is extreme pain caused by extreme stimulation.

Question 63

What happens if the analgesia pathway is activated?

Answer 63

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

Question 64

What spinal cord tract does the analgesia pathway run down?

Answer 64

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

Question 65

What are the neurotransmitters in the descending pain pathway?

Answer 65

Norepinephrine and serotonin.

Question 66

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

Answer 66

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

Question 67

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

Answer 67

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

Question 68

How does the analgesic pathway stop pain from being transmitted?

Answer 68

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

Question 69

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

Answer 69

Enkephalins. Endorphins. Dynorphins. GABA. Glycine.

Question 70

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

Answer 70

Endorphins which lead to good feelings in the body.

Question 71

What is chronic pain?

Answer 71

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

Question 72

What is chronic pain characterised by?

Answer 72

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

Question 73

What are the mechanisms for chronic pain?

Answer 73

The same as those for acute pain.

Question 74

What neurotransmitter leads to chronic pain?

Answer 74

Glutamate.

Question 75

Where does chronic pain originate from?

Answer 75

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

Question 76

What is neuropathic pain?

Answer 76

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.

Question 77

What is neuropathic pain characterised by?

Answer 77

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

Question 78

What are the consequences of pain to the animal?

Answer 78

Huge stress such as loss of appetite etc.

Question 79

What is the main stress hormone?

Answer 79

Cortisol.