8.3. Physiology of pain sensation. Flashcards
I. Pain
1. What are the pain receptors? Their features?
- Pain receptors are called nociceptors, because they detect ‘’noxious’’ stimuli that may indicate damage taking place (ex: tissue damage).
- All nociceptors are free nerve endings of Aδ- or C-fibers.
I. Pain
2A. What are the 4 types of nociceptors?
- Mechanical nociceptors (Aδ + (C) – fibers)
- Thermal nociceptors (Aδ + (C) – fibers)
- Thermal nociceptors (Aδ + (C) – fibers)
- Silent nociceptors (C-fibers)
I. Pain
2B. What are the features of Mechanical nociceptors?
Mechanical nociceptors (Aδ + (C) – fibers)
- respond to mechanical stimuli, like being hit by a hammer
I. Pain
2C. What are the features of Thermal nociceptors?
Thermal nociceptors (Aδ + (C) – fibers)
- activated by noxious heat (>45 degrees)
- activated by noxious cold (<5-10 degrees)
I. Pain
2D. What are the features of Polymodal nociceptors?
Polymodal receptors (C-fibers)
- respond to many different stimuli (mechanical, thermal, extreme acidity -> tissue damaging)
I. Pain
2E. What are the features of Silent nociceptors (C-fibers)?
- do not respond to mechanical, thermal or extreme acidic conditions, but do mediate
pain sensation
-> if they are sensitized -> sensitization can occur, e.g. in inflammation - if an inflammation occurs, then the silent nociceptors will get activated and mediate
pain sensation - present in skin and viscera (internal organs)
I. Pain
3. What happen if there is itching?
Itching belongs to these groups, but it is different from pain sensation.
- Specific free nerve endings are responsible for mediating itching.
- The nerve endings have histamine receptors - will activate these fibers when histamine is present.
I. Pain
4. What is pain sensation?
Pain sensation is an independent sensory modality, and not an ‘’over-activation’’ of mechanoreceptors.
I. Pain - Propagation of pain sensation in sensory nerves:
5A. What type of nerve fibers responsible for pain sensation in sensory nerves?
Aδ- and C-fibers are responsible for pain sensation
I. Pain - Propagation of pain sensation in sensory nerves
6. Describe Propagation of pain sensation in sensory nerves
- Aδ- and C-fibers are responsible for pain sensation
- Pain is felt in 2 different stages, because it is carried by slow and fast fibers
- First pain:
+) Sharp, well-localized pain sensation
+) Mediated by the faster Aδ-fibers (arrives first to the cortex) - Second pain:
+) Diffuse, dull, aching/burning pain sensation
+) Mediated by the slower C-fibers
I. Pain - Nerve endings – ion channels
7. What types of fibers are heat and pain sensing fibers?
Heat and pain sensing fibers are free nerve endings
I. Pain - Nerve endings – ion channels
8. What makes the free nerve endings specific to a certain sensation?
ion channels
I. Pain - Nerve endings – ion channels
9A. What are the features of Capsaicin (chili) receptor (TRP-V1?
1/ TRP = transient receptor potential, V1 = vanilloid type 1
2/ TRP channels are cation channels -> opened by acidic pH + hot temperatures
I. Pain - Nerve endings – ion channels
10B. Receptor: TRP–V1
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ???
- Heat sensitivity: ≥ 43°C
- Activating agent: Capsaicin
- Sensation: (noxious) Heat sensation
I. Pain - Nerve endings – ion channels
9C. Receptor: TRP–V2
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ???
- Heat sensitivity: ≥ 52°C
- Activating agent: -
- Sensation: (noxious) Heat sensation
I. Pain - Nerve endings – ion channels
9D. Receptor: TRP–V3
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ??
- Heat sensitivity: ≥ 34°C
- Activating agent: Camphor (creams/lotions)
- Sensation: (non-noxious) Warm sensation
I. Pain - Nerve endings – ion channels
9E. Receptor: TRP–V4
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ???
- Heat sensitivity: ≥ 27°C
- Activating agent: -
- Sensation: (non-noxious) Warm sensation
I. Pain - Nerve endings – ion channels
9F. Receptor: TRP–M8
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ???
- Heat sensitivity: ≤ 28°C
- Activating agent: Menthol
- Sensation: Cold sensation (act. of cold sensing fibers)
I. Pain - Nerve endings – ion channels
9G. Receptor: TRP–A1
- Heat sensitivity: ???
- Activating agent: ???
- Sensation: ???
- Heat sensitivity: < 17°C
- Activating agent: Mustard oil
- Sensation: Noxious cold sensation
I. Pain - Nerve endings – ion channels
10. Why do we need presence of these receptors?
The presence of these receptors make the free nerve endings specific for different sensory modalities
I. Pain - Pain sensation
10. Pain sensation
- Formal definition: ‘’unpleasant sensory and emotional experience associated with actual or potential tissue damage’’
-> How can sensory experience be separated?
- The sensory experience can be separated from the emotional experience:
- Sensory experience: pain is a feeling
- Emotional experience: pain is unpleasant
- Pain is also a sensation of tissue damage -> nociception = sensation of noxious
stimuli
I. Pain - Basic terms
11. What are the features of Congenital insensitivity to pain?
- Cannot feel pain or feel less pain than normal due to genetic causes
- Often correlates with shorter life expectancy, due to inability to perceive dangerous
situations -> pain is basically a warning of tissue damage - Example: joint problem -> person will force movement which ↑ the damage
I. Pain - Basic terms
12. What are the features of Acquired pain sensitivity?
- As in the case of syringomyelia, which is the degradation of tissue (white + gray matter) around the central canal of spinal cord
- Causes loss of pain sensation in certain body areas
I. Pain - Basic terms
13. What are the features of Acute, persistent and chronic pain?
- Acute pain: noxious stimulus -> pain sensation
- Persistent and chronic pain: pain is constantly present and patient cannot remove the stimulus or ‘’run away’’ -> suffering (e.g. tumors/cancers: cause tissue damage + strong pain sensation)
I. Pain - Basic terms
14. What are the features of Analgesia?
Reduction/removal of pain.
=> 2 kind of analgesics:
- Minor: for acute pain – interfere with synthesis of prostaglandins
- Major: for chronic pain – morphine and its derivatives
II. Types of pain
1. What are the 3 types of pains?
- Nociceptive pain
- Neuropathic pain
- Central pain
II. Types of pain
2. What is Nociceptive pain?
pain related to tissue damage (noxious stimuli)
II. Types of pain
3A. What is Neuropathic pain?
pain caused by a problem with the free pathway, such as damage to the sensory nerve fibers
II. Types of pain
3B. What are the 2 examples of Neuropathic pain?
- Deafferentation pain: sensory nerve damaged/cut -> degeneration -> pain
- Phantom pain: occurs after surgical removal of extremities -> patient can localize pain in amputated hand/leg
II. Types of pain
4A. What is central pain?
It is the central pathway of the pain sensory mechanism is affected
II. Types of pain
4B. What is an example of central pain?
Thalamic pain syndrome: damages to the thalamus
III. Nociceptive pathways in the dorsal horn of the spinal cord
1. Describe Nociceptive pathways in the dorsal horn of the spinal cord
The central axon of the pseudounipolar neuron and the projection neurons get connected in the dorsal horn of the spinal cord projection will go to the thalamus
- The Aδ-fibers give connections with projection neurons in lamina 1 + 5
- C-fibers go to interneurons and connect with projection neurons in lamina 2
- The Aβ-fibers, which are not nociceptors but mechanoreceptors (=touch), also give collaterals to projection neurons in the dorsal horn
III. Nociceptive pathways in the dorsal horn of the spinal cord
2. What is the role of the Aδ-fibers?
The Aδ-fibers give connections with projection neurons in lamina 1 + 5
III. Nociceptive pathways in the dorsal horn of the spinal cord
3. What is the role of C-fibers?
C-fibers go to interneurons and connect with projection neurons in lamina 2
III. Nociceptive pathways in the dorsal horn of the spinal cord
4. What is the role of Aβ-fibers?
The Aβ-fibers, which are not nociceptors but mechanoreceptors (=touch), also give collaterals to projection neurons in the dorsal horn