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Neurology > Pain 1 Peripheral Mechanisms and Central Pathways > Flashcards

Pain 1 Peripheral Mechanisms and Central Pathways Flashcards

1
Q

Describe the process by which stimuli activate and travel through the brian?

A

1) stimuli activate receptor (temperature, pain, touch or pressure)
2) AP is elicited in nerve (Dorsal route ganglion nerve)
3) AP enters spinal cord and synapses on ascending nerve in dorsal route horn
4) nerves travel across the spinal cord and ascends to brain
5) signal travels to sensory cortex where processed and acted upon

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2
Q

What are somatic senses?

A

not dependant on a specialised organ e.g. thermoception, magnetoception (direction), nociception

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3
Q

Define pain?

A

unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

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4
Q

What are the pain receptors called and where are they located?

A

Nociceptors - across body but very few in brain

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5
Q

What are the three types of pain stimuli?

A
  • Chemical e.g. change in PH causes pain
  • Mechanical e.g. trauma
  • Thermal e.g. pain due to cold or hot temperatures
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6
Q

Describe what happens on cellular levels to activate nociceptors?

A
  • chemical mediators activate nociceptors

-

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7
Q

Give examples of what can activate nociceptors

A
  • hydrogen ions
  • stretch
  • extreme temperatures
  • strong pressures (mechanical stimuli)
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8
Q

What is the difference between unmyelinated and myelinated neurones?

A

myelinated

  • faster conduction velocity (fast pain)
  • sharp pain (unmyelinated = dull)
  • almost immediate (delay in unmyelinated)
  • Localised
  • only in superficial tissue (unmyelinated also in deep)
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9
Q

What autonomic responses to pain are there?

A 
Sympathetic 
- Fear 
- Pupillary dilation 
- Pallor
- Sweating 
Parasympathetic 
- Bradycardia 
- Syncope
- Hypotension
- Urination
- Nausea
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10
Q

What is referred pain?

A

Pain is perceived as coming from a different region to its origin e.g. visceral organ pain felt in superficial area of body

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11
Q

where is the sensory cortex located?

A

outer area of the cerebrum close to motor cortex

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12
Q

What is the sensory homunculus?

A

distorted representation of the brain showing which areas of the body have greatest sensory capacity and so brain mass devoted to them

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13
Q

How is the sensory cortex arranged?

A

different regions for different areas of the body, each nerve coming from the body part goes to the region of that body part

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14
Q

What are the two components of pain?

A
  • unconscious detection of harmful stimuli using sensory receptors (nociception)
  • strong emotional and subjective response to it
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15
Q

What are the alternate names for myelinated and unmyelinated nerves?

A 
myelinated = A(delta sign)
unmyelinated = C fibres
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16
Q

What are the proprioception senses?

A
  • nociception (pain)
  • equilibrioception (balance)
  • proprioception (sense of position adn movement of parts of ones body)
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17
Q

What are interceptive senses?

A

senses that perceive sensations in internal organs

18
Q

What the chemical mediators of pain?

A

potassium
histamine
bradykinin

19
Q

What immune cells release histamine and bradykinin?

A

mast cells and basophils which are triggered by attaching of IgE coated antigens

20
Q

How does tissue damage further stimulate pain?

A

tissue damage means production of prostaglandins which make nociceptors more sensitive

21
Q

What is allodynia?

A

When a pain response is triggered by a stimuli which wouldn’t ordinarily cause pain

22
Q

How can high intensity exercise cause pain response?

A

working muscle relies on anaerobic metabolism so produce excess of H+

23
Q

When else will anaerobic metabolism increase?

A

tissue distension as tissue becomes ischaemic

24
Q

What hormone, released by activated platelets, is a nociceptor activator?

A

serotonin

25
Q

What is a polymodal nociceptor?

A

pain receptor which responds to more than one kind of stimuli

26
Q

What are the different TRP channels?

A 
TRPV1 = capsaicin receptor (sensitive to temp, H+ and mechanical) 
TRPM8 = methanol and cold 
TRPA1 = irritant and cold receptor
27
Q

Give examples of different routes pain fibres take from body to the brain?

A

gracile fasciculus - carries A(delta) fibres up spinal cord > gracile nucleus (in medulla oblongata) > thalamus and cortex
Trigeminal nerve - pathway of facial pain signal, C-fibres travel through pons > medulla > thalamus and cortex

28
Q

How is a nerve signal carried from limb to the brain?

A

Nociceptor in limb activated

  • pain fibres (either A or C) carry signal to dorsal horn spinal cord
  • synapse onto 2nd order neurone
  • 2nd order neurones ascend from dorsal horn via spinoreticular or spinothalamic tracts
  • arrive at somatosensory cortex on opposite side of the brain (to where original activation was)
29
Q

Through what tracts can the 2nd order neurone ascend to the brain and where will the neurones synapse?

A

spinoreticular (synapse in reticular formation of brainstem) or spinothalamic (synapse in thalamus)

30
Q

Where do the 3rd order neurones of the spinoreticular tract innervate?

A

Hypothalamus and limbic system and somatosensory cortex

31
Q

What transmitters are released by A(d) and C fibres?

A 
A(d) = glutamate 
C = Glutamate and substance P
32
Q

Why do you get referred pain?

A

visceral pain fibres (from organs) synapse with the spinal cord at the same point where pain fibres from skin synapse
as there are far more pain fibres in the skin it is assumed they come from their

33
Q

What are the two types of pain?

A

Chronic/pathological (usually nerve injury) and acute/physiological (nociceptive or inflammatory pain which has sudden onset and goes away after healing, usually caused by bone fracture or skin trauma)

34
Q

Give examples of pathologies causing neuropathic pain?

A

Diabetic neuropathy, multiple sclerosis, fibromyalgia and spinal cord injury

35
Q

What variations of neuropathic pain are there?

A

can feel:

  • Normal pain felt on skin
  • burning or tingling
  • allodynia
  • Hyperalgesia
36
Q

What causes neuropathic pain?

A
  • sensitisation of the peripheral and central neurones involved in nociception
  • peripheral C and A fibres start becoming stimulated spontaneously or after weaker stimuli
  • increased expression of voltage dependant Na+ channels in peripheral nerves
37
Q

What is central sensitization?

A

increase in nociceptive signal C and A fibres results in secondary changes at the spinal cord

  • increased glutamate release overwhelms the dorsal horn neurones and increases expression of the NMDA (glutamate receptor)
  • this means the threshold potential of the dorsal horn neurone is more likely to be reached even with weak stimuli (hyperalgesia)
38
Q

How does the NMDA receptor fucntion?

A

Ionotropic and permeable to Na+ and Ca2+

39
Q

What is the pathophysiology behind allodynia?

A

A(beta) mechanoreceptor fibres can begin to sprout when the fibres are damaged allowing them to make connections to 2nd order pain fibres meaning stimuli normally perceived as mechanical activity is perceived as pain

40
Q

What causes phantom limb pain?

A
  • Normal inputs to the cortex are disrupted causing remaining adjacent cortical circuits to be rearranged so neurones from remaining limbs now terminate in part of cortex where nerves from amputate limb used to go
  • This results in touch of one limb being felt in amputated limb
  • damage to nerves can also cause central sensitisation so other stimuli (mechanical or temperature) can be perceived as pain
41
Q

How can chronic pain be treated?

A

Talk therapy
Stress reduction skills
Opioids
Peer support

Neurology (53 decks)

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