Physiology of Pain Flashcards
(92 cards)
1
Q
What is pain?
A
Unwanted sensation that belongs to the class of sensory information that moves from the periphery to the CNS.
2
Q
What is pain due to?
A
Several forms of stimuli which can be chemical, mechanical, electrical, or photogenic and are usually of a high intensity.
3
Q
What is unique about pain in veterinary medicine?
A
Cannot be described by the subject, so we must rely on behavioral signs.
4
Q
Why is pain often ignored or dismissed?
A
Because of its beneficial effect as pain is adaptive for survival.
5
Q
Why is reduced activity often seen with acute pain?
A
To hasten tissue and recovery.
6
Q
Pain may induce an _______ response.
A
Immobilization.
7
Q
What kinds of activity and vigilance might be seen with pain?
A
- Hypoactivity or hyperactivity
- hypovigilance or hypervigilance
8
Q
What autonomic signs may be caused by pain?
A
- Muscle twitching
- salivation
- pupillary response
- sweating
- excitation
- urination
- etc.
9
Q
In most cases, animals will show some kind of _______ sign to indicate that they feel pain.
A
Motor sign, such as aggression, withdrawal, etc.
10
Q
What is actual/ sustained pain?
A
An event that directly causes the feeling of pain
11
Q
What is potential pain?
A
Some condition that might cause pain, but might be tolerable
12
Q
What is nociception?
A
All of the events that lead up to pain
follows a given pathway. Activity by a noxious stimulus
13
Q
What does the process of nociception require?
A
appropriate stimulus acting on nociceptors.
14
Q
What are nociceptors?
A
Receptors for pain that, when stimulated appropriately, stimulate pain sensation.
15
Q
What are the two fibers that carry pain sensation from the nociceptors?
A
- A-delta: fast, myelinated
- C fibers: slow, unmyelinated
16
Q
Where do pain fibers enter the spinal cord?
A
Through the dorsal horn of the gray matter.
17
Q
What 2 neurotransmitters do pain fibers release?
A
- Glutamate: from A-delta fibers, excitatory pain NT
- Substance P: from C-fibers, excitatory pain NT.
18
Q
Excitatory pain neurotransmitters act on what receptors?
A
N-methyl-D-aspartate (NMDA) receptors.
19
Q
Where do interneurons in the dorsal column of the spinal cord carry the pain signal?
where in the brain
A
To the thalamus and then the cerebral cortex.
20
Q
What is the nature of the descending pathway for pain?
A
Analgesic.
21
Q
What is the name of the descending pain pathway?
A
Endogenous analgesic system.
22
Q
How is the descending pain pathway analgesic in nature?
A
It controls further entry of impulses either before or at the dorsal horn either by presynaptic inhibition or postsynaptic inhibition.
23
Q
What is presynaptic inhibition?
A
Inhibition of further transmission of pain fibers by the descending pain pathway via action directly on the sensory fibers coming into the dorsal horn.
24
Q
What is postsynaptic inhibition?
A
Inhibition of further transmission of pain fibers by the descending pain pathway via action on the ascending fiber as it leaves the dorsal horn.
25
What are the 4 levels of nociception?
- Transduction
- Transmission
- Modulation
- Perception
26
What is transduction?
the signal that activates afferent nerve fibers (to the brain)
| the initiation of action potential
27
What is transmission?
the movement of action potential from periphery to the dorsal horn of spinal cord
28
What is modulation?
processing that controls whether or not pain impulses continue to enter or are modulated
29
What is perception?
When the signal makes it to the brain and the animal is now aware of it.
30
What are the two main ways pain can be modulated?
- Descending pathway
- Drugs
31
What are the 4 causes of pain?
- Tissue/nerve damage
- Inflammatory processes
- Viral/bacterial infections
- Demyelination.
32
In what 3 ways can pain be classified by?
- Site
- Origin
- Duration.
33
What are the 3 catagories of pain according to site?
- Somatic: muscles
- Visceral: viscera
- Neuropathic: nervous system.
34
What are the 3 classifications of pain in relation to origin?
- Superficial: skin
- Deep: body cavities
- Visceral: internal organs.
35
How is pain classified according to duration?
- Acute
- Chronic
36
Describe acute pain:
- sharp pain
- short duration
- easily identified causes
- often localized in a small area before spreading
- treated by medications
37
Describe chronic pain:
- intermittent or constant with different intensities
- lasts for longer periods
- usually difficult to treat
38
What must be realized about various organs and tissues in relation to pain?
They can have varying responses to acute and chronic pain.
39
What are the 3 characteristics of visceral pain?
- Pain of the abdominal or thoracic organs
- Poorly localized (difficult to pinpoint)
- Referred (can be felt anywhere in the body)
40
What is referred pain?
Pain occurring in the internal portion of the body that can be expressed on the surface of the skin.
41
Referred pain is the basis for what form of treatment?
Acupuncture.
42
How does acupuncture treat pain?
It targets neural connections between internal organs and particular surfaces of the body so that pressure in those areas send impulses to said organ.
43
What are the 2 types of somatic pain?
- Superficial: skin
- Deep: tendons, joints, muscles, periosteum (easily localized)
44
What type of pain is easily localized?
Somatic pain
45
Visceral pain is usually described as more ______ and ________ than somatic pain.
Diffuse (can extends from one system to another) and unpleasant.
46
What does it mean when pain is described as diffuse?
It tends to spread to more than just the organ of origin; seen with diverse neural connections.
47
What causes the diffuse nature of true visceral pain?
The low density of visceral sensory innervation and extensive divergence of the visceral input within the CNS.
48
What is neuropathic pain?
- damage to the peripheral nerves or the spinal cord
- often difficult to treat appropriately
49
How does neuropathic pain arise?
As a disorder of processing of nociceptive activity or as a result of abnormal activity in nociceptive pathways.
50
In what 3 ways does neuropathic pain typically manifest?
- **Hyperalgesia**: disproportionate hypersensitivity to stimuli
- **Hyperpathia**: abnormal pins and needles sensations
- **Allodynia**: nociceptive responses to harmless stimuli.
## Footnote
sudden cahnges in genetic makeup of the nn. for no reason, they express receptors that are super sensititve.
51
What are 4 causes of visceral pain?
- Ischemia (low blood supply- bradykinin and proteolytic enzymes)
- Chemical stimuli
- Spasm of hollow organs (excessive contraction of smooth mm.)
- Over-distension of hollow organs.
52
What can be used to assist in the diagnosis of pain if behavior is not enough?
Cortisol levels in blood as an antigen
53
What is central sensitization or wind-up pain?
When pain sensation becomes exaggerated and the animal becomes hypersensitive to pain.
54
What are the 4 reasons that central sensitization might happen?
- Synaptic potentiation: receptor numbers suddenly increase
- Natural breaks or pain inhibitors become inhibited themselves
- Mg inhibition
- Simultaneous release of glutamate and substance P in large amounts where substance P begins to act on neurokinin 1 receptors.
55
How does Mg inhibition cause central sensitization?
Mg naturally blocks pain and when it is inhibited Ca is allowed to enter freely, increasing receptors sensitivity to pain; becomes blocked when glutamate is released progressively and in a prolonged manner.
56
What is the gate control theory?
A theory that states that rubbing the site of injury reduces pain by activating pain and touch fibers simultaneously, thus ensuring competition between the fibers.
The signal from the touch fibers reaches the spinal cord faster, thus inhibiting the signal that reaches the brain.
57
How does gate control theory work?
- When the site of pain is rubbed, it excites A-beta fibers (touch fibers), which are faster than both of the pain fibers (A-delta & C-fibers).
- A-beta reaches the spinothalamic tract before either of the pain fibers do and elicits inhibitory signals.
- A-beta essentially closes the gate and inhibits C and A-delta fibers from transmitting their pain signals to the brain.
58
What is transcutaneous electrical nerve stimulation (TENS)?
Use of the gate control theory with TENS units (heating pad), vibration, licking, rubbing, etc.
59
What are 4 causes of acute pain?
* Injury
* surgery
* inflammation
* infection
60
Chronic pain is usually related to what?
Age related disorders
61
What 2 parameters must be assessed to evaluate pain in animals?
Physiological and behavioral parameters.
62
What are 6 different ways to assess pain in animals?
- Clinical responses measuring the activity of the SNS
- Measurement of plasma cortisol levels by radioimmunoassay (RIA)
- Changes in plasma immunoreactive beta-endorphin by means of RIA
- Body weight, quality and quantity of feces
- EEG (Electroencephalogram): will see a different pattern than normal
- Sweating to the point of dehydration in horses.
63
What are 7 common behavioral responses to pain in dogs?
* Changes in posture
* anxious glance
* tail between legs
* distinctive bark
* aggression or extreme submissiveness
* penile protrusion
* frequent urination and defecation.
64
What are 3 common behavioral responses to pain in lambs?
* Abnormal lying (ventral with one partially extended leg
* abnormal standing
* other behaviors referred to as SPB (specific pain behavior).
65
What are 5 common behavioral responses to pain in horses?
* Changes in facial expressions
* groaning, rolling
* kicking at abdomen
* stretching
* limb guarding
* etc.
66
How does cortisol indicate pain?
- Pain causes stress which activates the hypothalamic-pituitary adrenal axis (HPA system).
- HPA induces hypothalamic release of ACTH releasing factor which causes increased release of ACTH by the anterior pituitary.
- ACTH causes increased activity of the adrenal cortex (zona fasciculata).
- Adrenal cortex releases cortisol which results in increased glycogenolysis and gluconeogenesis (from non-CHO sources).
67
How does stress and anxiety affect pain?
They exacerbate it
68
How do anxiolytics work?
Inhibits recognition of pain in the cerebral cortex; too much sedation can mask signs of pain and be inhumane.
69
How does pain result in wind-up?
After a progressive increase in the magnitude of C-fiber activity on the dorsal horn, especially following repetitive activation of the C-fibers.
70
What is the difference between unimodal and polymodal transduction?
- Unimodal: sensitive to only one stimuli
- Polymodal: sensitive to more than one stimulus.
71
Which pain fiber is responsible for transmitting acute pain?
A-delta fibers.
72
Which pain fiber is responsible for transmitting chronic pain?
C fibers.
73
What are the 3 orders of pain fibers?
- 1st: from periphery to lamina 1, 2, and 5 of dorsal horn
- 2nd: from dorsal horn up the spinothalamic tract through the medulla to the thalamus
- 3rd: relays the signal from the thalamus through the midbrain and to the somatosensory cortex and prefrontal cortex of the cerebrum.
74
Where in the thalamus does the second order pain neuron synapse?
With the ventral posterior thalamic nuclei.
75
What does upward modulation of pain mean?
Pain has been facilitated.
76
What does downward modulation of pain mean?
Pain has been killed; analgesia.
77
Inhibition of pain usually takes place where?
Dorsal horn of the spinal cord.
78
What does perception deal with?
Awareness of pain; all about memory of what type of pain it is, the intensity of the pain, the reason for the pain, has this kind of pain happened before, etc.
79
What aspect of pain does the somatosensory cortex of the cerebrum deal with?
Localization and characterization of intensity of pain.
80
What aspect of pain does the limbic system deal with?
Exhibits emotional response to pain and assigns emotion and memory.
81
Affected attributes from pain sensation include:
- Feelings of arousal
- Aversiveness
- Motivation
- Learned detection
- Avoidance.
82
What are 3 common reactions to pain seen in animals?
- Vocalization
- Withdrawal of affected limb
- Separation of stimulus from affected nociceptors.
83
What is nociceptor or pain threshold?
The minimum amount of stimulation that reliably elicits a pain response.
84
How is pain threshold measured/ identified?
Experimentally by simple spinal reflexes such as paw licking, lifting of leg, etc.
85
Describe the hot plate experiment.
- Rats are placed on a hot plate which gradually warms the skin.
- The rats are timed for the occurrence of paw licking or hind foot lifting reflexes.
- Generally occurs within 5 seconds signaling the pain threshold.
- When a strong analgesic such as morphine is given to the rats, the reaction time is usually prolonged indicating the morphine has elevated the pain threshold.
86
What is used during surgery to assess the onset of anesthetic effect in animals?
Skin or toe pinch response.
87
What does the hot plate test check?
Whether or not a painkiller drug is effective.
88
What are the 6 structures involved in the ascending pathway?
- Nociceptors
- Neurons
- Marginal nucleus and substantia gelatinosa of the spinal cord
- Reticular formation of medulla and midbrain
- Thalamus
- Sensory cortex.
89
What are the two parts of the brain that makeup the endogenous analgesic system?
Periaqueductal gray matter of midbrain and raphe magnus of the medulla.
90
Segmental pain modulation is the basis for what?
The gate control theory: competition between A-beta fibers and C fibers/A-delta fibers whereby A-beta wins the race.
91
True or false: Different locations within the pain pathway respond to analgesics the same way.
False: they respond differently.
92
What is the positive purpose of inflammation?
Aimed at dealing with a foreign body; it is protective.
