Pain, nociception and analgesia Flashcards
What is the definition of pain?
The subjective conscious appreciation of a stimulus that is causing, or threatening to cause, tissue damage. Pain exists in your cerebral cortex.
What is nociception?
The physical process of detection and transmission of damaging or potentially damaging stimuli.
What are nociceptors?
Structures that detect noxious stimuli - peripheral tissues?
What is algesia?
The induction of a condition leading to nociception and pain.
What is analgesia?
The reduction or prevention of either nociception or pain without loss of consciousness.
What is the function of pain?
It is a body protection mechanism - prevents harm to the body.
What are mechanosensory receptors involved in?
Motion detection, grip control, form and texture perception, shape, motion detection, stretch, deep pressure and vibration.
What kind of corpuscles are close to the skin surface?
Meissner.
What type of corpuscles are lower down the skin surface?
Pacinian.
How is information sent to the spinal cord from receptors?
Primary afferent neurons such as the mechanosensory afferent fibre or pain and temperature afferent fibre.
What are the two types of nociceptor?
The polymodal nociceptor and mechanical nociceptors.
What do polymodal nociceptors respond to?
They respond to high intensity mechanical pressure, thermal temperatures above 45 degrees or below 10 degrees.
What do mechanical nociceptors respond to?
High intensity mechanical pressure and strong thermal temperatures above 60 degrees.
What are some somatosensory afferent fibres?
Proprioception, touch, pain/temperature, pain/temperature and itch.
What is the sensory function of muscle spindle?
Proprioception.
What is the sensory function of merkel, meissner, pacinian and ruffini cells?
Touch.
What is the sensory function of free nerve endings?
Pain and temperature.
What is the sensory function of unmyelinated free nerve endings?
Pain, temperature and itch.
How does the axon diameter of afferent fibres vary between receptors?
Muscle>merkel/meissner etc>free nerve ending>unmylineated free nerve endings
Are proprioceptors or temperature receptors faster?
Proprioreceptors.
What are the two types of pain?
Fast pain and slow pain.
What are the differences between the two types of pain?
Fast pain is sharp/pricking and usually well tolerated whereas slow pain is usually burning, aching, throbbing and is poorly tolerated.
What is the differences in fibres between fast and slow pain?
Fast - A delta fibre, slow - C_fibre.
How do local anaesthetics work on slow and fast pain?
Different anaesthetics affect fast and slow pain.
What local anaesthetic can stop fast pain?
Procaine.
What local anaesthetic can stop slow pain?
AL-381.
What is the difference between thermoreceptors and thermal nociceptors?
Thermoreceptors tell you when things are hot, but nociceptors tell you when things are dangerously hot.
How does receptivity of thermoreceptors and thermal nociceptors differ?
Nociceptors - signal increased with temperature, thermoreceptors same above certain threshold.
What happens when there is a stimulus that is potentially harmful?
Primary transduction - channels open.
What happens when there is primary transduction of nociceptors?
Secondary transduction - change in membrane voltage.
What happens after secondary transduction in the pathway?
Depolarisation and action potential generation.
What happens after depolarisation in the pathway?
Transmitter release and second order ascending neurone response.
What does it mean that there are graded potentials in nociceptors?
Action potentials vary in size depending on the size of the stimulus.
Why else is nociception not just exaggerated somatosensory transmission?
Nociceptors project to different spinal sites.
What is the main ascending pain pathway?
Spinothalamic-anterolateral system.
What is the pain pathway involving the face?
Trigemino-thalamic pathway.
What pain pathway runs dorsally?
The viscero-thalamic pathway.
What is another reason why somatosensory transmission and nociception is different?
They have different ascending pathways.
What is hyperalgesia?
Increased response to a noxious stimulus.
What is allodynia?
painful responses to a non-noxious stimulus.
What causes sensitisation of nociceptors?
H+, ATP,K+ released from damaged cells sensitise the nociceptors along with 5HT, histamine, bradykinin and prostaglandins released from mast cells and macrophages.
What happens after nociceptors are sensitised?
SP and CGRP cause increased blood flow and there is increased access of inflammatory cells.
What is SP and CGRP?
Substance P and Calcitonin gene-related peptide.
What does SP trigger?
Histamine release.
What is neuropathic pain?
Pain unrelated to peripheral nociception - it serves no purpose.
What are some causes of neuropathic pain?
Thalamic stroke, peripheral nerve damage, spinal damage and peripheral nerve terminal damage/infection.
