Physiology of pain Flashcards
What are the different receptor types associated with the senses?
Mechanoreceptors Chemoreceptors Thermoreceptors Nocireceptors Proprioceptors
What is the area called which receptors cover in their function?
Receptive field
What determines the magnitude of response from a sensory stimuli?
The amplitude of depolarisation triggered
Which factors determine the acuity of a sense over any given area?
Density of innervation
Size of receptive field
Cutaneous sensation is transmitted through which 3 fibre types?
Aß
Aδ
C
Describe Aß fibres.
Large
Myelinated
Responsible for, touch, vibration and pressure
Describe Aδ fibres.
Small
Myelinated
Responsible for cold, “fast” pain and pressure
Describe C fibres.
Unmyelinated
Responsible for warmth and “slow” pain
Which receptor types mediate proprioception?
Aα
Aß
(In muscle spindle and GTO)
Which receptor types mediate mechanoception?
Aα
Aß
Which fibre types mediate nociception and thermoception?
Aδ
C
Where is the ultimate termination of sensory information?
Somatosensory cortex (S1)
What does constant stimulus do?
Decrease in sensitivity over time
Describe lateral inhibition.
Activation of one sensory input causes synaptic inhibition of its neighbours
This cleans up sensory info
What is convergence?
Saves on neurons
Reduces sensitivity
What are some factors which may activate nocireceptor signal transduction?
Low pH
Heat
Local chemical mediators (histamine, prostaglandins)
What is the mechanism of action of NSAIDs?
They inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
What is the mechanism of action of local anaesthetics?
Blocks Na+ action potentials and as a result, blocks all axonal transmission to the area
What is transcutaneous nerve stimulation?
An electric current is produced by a device to stimulate the nerves for pain relief
What is the mechanism of action of opiates?
Reduces sensitivity of nocireceptors
Blocks transmitter release at dorsal horn
What is Gate Control Theory?
Non-painful sensations can override and reduce painful sensation when its input closes the nerve gates to painful input
What is the function of the thalamus in pain sensation?
It is a secondary relay point
Receives input from the ascending pathway of the spinothalamic tract
Relays this info to the cingulate cortex and somatosensory cortex as well as the limbic system
What is hyperalgesia?
Increased perception of pain
May even perceive non-noxious stimuli as noxious
What is allodynia?
Decreased threshold for response
What is neuropathic pain?
Pain which is caused by a primary lesion or dysfunction in the somatosensory nervous system
