Week4 - E - Pharmacology - Pain Mechanisms

Question 1

Pain is not registered as pain until registered in the brain What are the three different forms of pain?

Answer 1

Nociceptive pain Inflammatory pain Pathological pain

Question 2

What are examples of nocieptive, inflammatory and pathological pain?

Answer 2

Nociceptive pain tends to be acute - eg is usually a sharp type pain - eg pin prick, visceral distension Inflammatory pain - tends to be more prolonged eg sunburn, inflamed wound Pathological pain - more neurgenic associated eg fibromyalgia, IBS , cancer, AIDS

Question 3

What are the primary sensory afferent neurones for nociceptive pain?

Answer 3

These are the nociceptors Nociceptors are the nerves which sense and respond to parts of the body which suffer from damage.

Question 4

Where are the cell bodies for nociceptors located?

Answer 4

They are located in the dorsal root gagnlia (and the trigeminal ganglia for the face)

Question 5

What order neurones are nociceptors? Which sensory pathway is for pain? What other sensory modalities is this for?

Answer 5

Nociceptors are 1st order neurones The sensory tract is the spinothalamic tract - crude touch, pressure (anterior spinothalamic), pain and temperature (lateral spinothalamic)

Question 6

What are the nerve fibre types that are for pain?

Answer 6

Adelta and C fibres Adelta fibres are the fast fibres for sharp immediate pain Cfibres are the slow fibres for the burning/throbbing pain

Question 7

Are Cfibres or Adelta fibres myelinated?

Answer 7

Aδ-fibres are mechanical/thermal nociceptors that are thinly myelinated (conduction velocity of 6 – 30 ms-1 ) - respond to noxious mechanical and thermal stimuli. Mediate ‘first’, or fast, pain C-fibres are nociceptors that are unmyelinated (conduction velocity of 0.5 – 2.0 ms-1) – collectively they respond to all noxious stimuli (i.e. they are polymodal). Mediate ‘second’, or slow, pain

Question 8

It is a noxious stimulus that causes a response for nociceptive pain, what is a noxious stimulus?

Answer 8

A noxious stimulus is an actually or potentially tissue damaging event - it is a prerequisite for noiciception which is itself a prerequesite to nociceptive pain

Question 9

What is allodynia?

Answer 9

Allodynia is the sensation of pain from a stimulus that does not usually provoke pain

Question 10

If a patient experiences allodynia, what kind of pain is it thought to be? (ie nociceptive (acute), inflammatory (chronic) or pathological (neurogenic))

Answer 10

Patients experiencing allodynia are thought to have a nerve related problem and therefore pathological (neurogenic) pain is believed to be the cause

Question 11

General somatic information from the anterior head (including: the oral and nasal cavities, paranasal air sinuses, teeth, intracranial dura and cerebral arteries) is mediated by two trigeminothalamic* pathways Where are the soma of the sensory neurones for the trigeminothalamic pathway located?

Answer 11

They are located in the trigeminal ganglion - this is where all three trigeminal nerves meet

Question 12

What are the trigeminal nuclei? What function do they have?

Answer 12

Pontine (primary) nucleus - fine touch and vibration of face Spinal nucleus - pain and temperature Mesencephalic nucleus - proprioception of the face Trigeminal motor nucleus - muscles of mastication

Question 13

In the trigeminothalamic pathway for sensation of the face, where is the first synapse? Which trigeminal nerve carries out a motor function?

Answer 13

The first synapse occurs in the spinal (pain and temperature) or pontine nucleus (vibration and fine touch) Mandibular divsision of the trigeminal nerve is the motor division (also carries sensory axons)

Question 14

After first order neurons synapse in the spinal or pontine nucleus, how does the rest of the trigeminothalamic pathway progress?

Answer 14

2nd order axons travel via trigeminal lemniscus to synapse in the ventroposteromedial nucleus of the thalamus (VPM nucleus) before synapsing and travelling in the thalamocortical tract to the postcentral gyrus where the primary somaotsensory area is located

Question 15

Where can reffered pain from the liver present? Where can referred pain from the stomach and pacreas present?

Answer 15

Referred liver pain - right hand side of neck Referred pain from stomach and pancreas - epigastric/base of chest

Question 16

Second order neurones ascend the spinal cord in the anterolateral system comprising mainly The spinothalamic tract (STT) The spinoreticular tract (SRT) Which spinothalamic tract carries pain? What are the pain fibres again?

Answer 16

Lateral spinothalamic tract carries pain (fast pain) Pain fibres are Aδ and Cfibres (slow pain)

Question 17

What does the spinoreticular tract travel between again?

Answer 17

Spinal cord Reticular formation (in brain stem) Thalamus Primary somatosensory area (postcentral gyrus)

Question 18

Is the spinothalamic tract or the spinoreticular tract the carrier of the fast pain?

Answer 18

Spinothalamic tract is the fast pain pathway - Adelta fibres Spinoreticular tract is the slow pain pathway - Cfibres

Question 19

Pain and nociception are not identical Pain is awareness of suffering: nociception may occur in the absence of pain and vice versa – this is essential to understand Thermoreceptors are neurones that are specialised to respond to small changes in temperature (we can perceive differences as small as 0.01C) What tract carries temperature sensation? - describe this tract in full?

Answer 19

Spinothalamic tract First order neurones carry information to the spinal cord - enter the dorsal column and travel across Lissaeurs tract (fascicularis) to the dorsal horn where they synapse in the substantia gelatinosa - Second order neurones then decussate at the level of entry (or 2vertebral levels above) to travel to the anterolateral column and go to synapse in the ventroposterolateral nucleus in the thalamus before 3rd order neurones reach the potcentral gyrus