Term
| Describe the structure of nociceptors. |
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Definition
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Term
| What are the 2 main types of nociceptor? |
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Definition
1) Mechanical nociceptors
2) Polymodal nociceptors |
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Term
| How are mechanical nociceptors innervated? |
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Definition
| Thinly myelinated Ad fibres. These produce sharp, highly localised pricking pain. |
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Term
| How are polymodal nociceptors innervated? |
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Definition
| Unmyelinated C fibres. These receptors produce dull, poorly localised burning pain. |
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Term
| Explain how tissue reacts to inform nociceptors of damage. |
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Definition
1) Injury or tissue damage releases bradykinin and prostaglandins both of which activate and sensitise nociceptors
2) Nociceptor activation leads to the release of substance P and other peptides
3) Substance P acts on mast cells in the vicinity of sensory endngs to evoke degranulation and the release of histamine which directly excites nociceptors
4) Substance P also produces dilation of peripheral blood vessels and the resultant oedema causes a further liberation of bradykinin. |
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Term
| Where are the cell bodies of nociceptors? |
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Definition
1) Dorsal root ganglia (pain from body)
2) Trigeminal ganglion (facial pain). |
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Term
| Where do nociceptor afferents terminate? |
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Definition
| Laminae II and V of the spinal cord and the spinal V nucleus. |
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Term
| Describe the ascending pathway for facial pain. |
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Definition
CNV- Spinal V nucleus- Ventral trigeminothalamic tract- VPM nucleus of the thalamus- Primary somatic sensory cortex
-This is a contralateral pathway. |
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Term
| What is the main ascending tract for ascending body pain? |
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Definition
| Spiothalamic. Contralateral. |
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Term
| Describe the endogenous analgesia system. |
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Definition
1) Electrical stimulation in the midbrain periaqueductal grey matter activates the raphespinal tract (5-HT)
2) This tract inhibits pain transmission in the dorsal horn (substantia gelatinosa) of the spinal cord
3) Interneurones containing opioid are involved in the system at each level. |
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Term
| What are the 3 main classes of naturally occuring opioids? |
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Definition
1) Enkephalins
2) Dynorphins
3) Endorphins. |
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Term
| Describe the gate control theory of pain control. |
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Definition
1) Dull pain mediated by C fibres can be suppressed by simultaeneoous stimulation of AB fibres from light touch receptors in skin of the same region
2) This occurs in the dorsal horn and spinal V. |
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Term
| How does referred pain work? |
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Definition
| It arises when skin and visceral nociceptors synapse on common spinothalamic tract organs. |
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Term
| Where does general anaesthesia have it's effect? |
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Definition
| At the reticular formation. |
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