Pathophysiology of pain and nociceptor classification Flashcards
What is the physiological definition of pain?
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage
Why type of damage does pain resemble or is associated with?
Actual/potential tissue damage
What does the fact that pain is an unpleasant and emotional experience suggest about brain regions involved?
Indicates that pain is a conscious experience coming from integrated activity in multiple sensory and emotional centres in brain
Is pain felt when unconscious?
No
Why does the fact that pain is not felt when unconscious make it difficult to understand the physiology of pain mechanisms?
This means that pain isn’t a sensation and is multidimensional and there is lack of physiology of consciousness
What are the 2 functions of pain as a protective mechanism?
Warns about ongoing damage
Promotes recovery
When does perception occur relative to the stimulus?
Perception happens after reflex withdrawal from stimulus
Define noxious stimulus?
Stimulus that is actually/potentially damaging to tissue and liable to cause pain, but doesn’t always cause pain in a situation
Define nociception?
Neural process (brain function) of encoding noxious stimuli (eg. tissue injury)
What are the 3 physiological processed that make up nociception when signals travel from periphery to CNS, and does nociception need consciousness?
Involves transduction, transmission, modulation of neural signals from periphery to CNS, and doesn’t need consciousness
What 2 types of directional neuroanatomical pathways are involved in nociceptive transmission, and what is the resulting experience?
Ascending (afferent) and descending (efferent) neuroanatomical pathways
result in subjective experience of pain
Define nociceptor?
Neuron that responds specifically to noxious stimuli
What are the 4 types of noxious stimuli?
Mechanical (sharp)
Thermal (damaging heat or cold)
Chemical
Polymodal (combination of mechanical, thermal, chemical)
What is the morphology/structure of a nociceptor?
Primary afferent pseudounipolar neuron
What is meant by a nociceptor being primary?
It is a neuron that receives sensory input
What is meant by a nociceptor being afferent?
It transduces info received in PNS and transmits it to CNS
What is meant by a nociceptor being pseudounipolar?
Gives impression that it has more than one extension from the cell body, but actually only has one extension from the cell body
What is the difference in length between proximal and distal axons of a nociceptor, and where does each axon project to?
Smaller proximal/central axon projects to spinal cord
long distal/peripheral axon that can terminate in fat or tissue that senses noxious injury except in brain eg. skin, muscle, tendon
Where in the nociceptor structure are nociceptive stimuli transduced into electrical signals?
Free nerve endings: Dendrites that aren’t encapsulated by connective tissue
Explain what is meant by a nociceptor being a functional unit of a glio-neural end organ?
End organ: specialised structure at end of peripheral nerve that acts as a receptor for a specific sensation
Glio-neural refers to interaction between neurons and glial cells, which provide support and protection of neurons and produce myelin
What is the function of glial cells?
To provide support and protection of neurons and produce myelin
What 2 structures is a nociceptor a part of?
Nociceptors form part of each spinal nerve and dorsal root ganglion (cluster of cells found in PNS) adjacent to spinal cord at each segment
How do sensory neurons travel from the dorsal root ganglion to within the spinal cord?
Dorsal root ganglion found just outside dorsal root, where it allows the sensory neurons in the ganglion to enter the spinal cord via the dorsal root
What 2 classes of neuron are nociceptors, and what kind of pain does each class transmit signals for?
Aδ nociceptors signal for fast nociception
C fibre nociceptors signal for slow nociception
