Anatomy and Physiology of Pain Flashcards
What is pain? What type of information is it usually associated with?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage. A cerebral construct - a perception usually associated with tissue-damaging stimuli.
Nociceptive information
What are the physiological mechanisms of pain?
Transduction
Transmission
Perception
Modulation
What is transduction?
Noxious stimuli translated into electrical activity at sensory nerve endings.
What is transmission?
Propagation of impulses along pain pathways
What is perception?
Discrimination/affect
What is modulation?
Positive and negative modulation occurs. Transduction, transmission and perception are modified.
What is another name for acute pain?
Normal or nociceptive
What is a nociceptor?
A sensory neuron transducing potentially harmful stimuli. Normal pain results from activity of these.
What are the two main nociceptors involved?
C fibres
A delta fibres
What do the membranes of nociceptors contain that allow response to noxious stimuli?
Receptor proteins
What are the following receptor proteins for?
TRPV1
TRPM8
ASIC
Hot stimuli
Acid
Cold stimuli
Diabetes causes peripheral neuropathy. What does this result in the lack of?
Pain fibres
What are the A delta fibres for?
Sharp pricking fast pain (thermal and mechanical)
Precise localisation of stimulus
Reflex withdrawal
What are the two broad classes of C fibres?
Peptidergic
Peptide-poor
What are C fibres for in general?
Slow burning pain
What do peptidergic C fibres release peripherally? What does this promote?
Peptides e.g. substance P and CGRP
Inflammatory responses and healing
What is special about peptide-poor C fibres?
They have distinct receptors and projections e.g. P2X3 ATP receptors
What type of nociception for peptidergic fibres? What type for peptide-poor fibres?
Thermal
Mechanical
What are the main two lamina that A delta and C nociceptors connect to?
Which horn is this?
I and II
Dorsal horn
What is NaV1.7?
What does loss of it cause?
A sodium channel sub-unit
Congenital indifference to pain
What does loss of mutation of NGF receptor trkA cause?
Congenital insensitivity to pain with anhydrosis (CIPA) due to loss of C fibres.
Where does the lateral spinothalamic tract end? (3) What for? Where does it not end?
Limbic system - subjective sensations of pain and pleasure
Reticular formation - pain-induced arousal and descending control of nociceptor input
Intralaminar (reticular) nuclei of thalamus - alerting cerebral cortex and focus of attention on pain
NOT the VPL (ventral posterolateral nucleus of the thalamus)
The unpleasant character of pain is mediated via projections to what system?
Limbic
What lamina do C fibres innervate? (3)
I and inter-neurons in lamina II (they also innervate lamina V through these inter-neurons)
What lamina do A delta fibres innervate?
Lamina I and V projection neurons
From where do projection neurons in lamina V receive input?
A beta fibres (touch) - direct input
C fibres - indirect input via inter-neurons
A delta fibres
Where do axons of projection neurons decussate close to? Where do the axons travel after decussating?
Where the nociceptors enter the spinal cord
In the anterior spinothalamic tract (lamina V) and lateral spinothalamic tract (lamina I)
What do projection neurons carry and to where?
Pain message onward from the primary afferent