Sensory systems (physiology of pain) Flashcards
List some of the different receptor types
nociceptor, mechanoreceptor, chemoreceptor, thermoreceptor, proprioceptor
Pacinian and Meissners corpuscles
pacinnian - deep pressure
meissners - light touch
What is the receptive field?
area in which the receptor responds to the stimulus
What is the adequate stimulus transduced into?
generator potential
What does the size of receptor potential tell us?
intensity of stimulus
Does amplitude or frequency of AP tell us about intensity of stimulus?
frequency
What does the receptive field tell us about the stimulus?
location
What 2 things is acuity dependent on?
density of innervation and size of receptive field
A beta fibres
large, myelinated - touch, pressure, vibration
A delta fibres
small, myelinated, cold fast pain, pressure
C fibres
unmyelinated - warmth and slow pain
What primary afferent fibres mediate proprioception?
A alpha and A beta
Termination of sensory information?
somatosensory cortex of post central gyrus
What may convergence underlie?
referred pain
2 types of adaption
fast and slow adapting
1 positive and 1 negative of convergence
saves on neurons
reduces acuity - increase receptive field size
Lateral inhibition positives
gives better definition of boundaries and cleans up sensory information
What is perception?
state of mind
Explain the gate control theory
mechanoreceptors activate inhibitory interneurons
release endorphins to inhibit transmitter release from nociceptive fibres to close the gate
descending pathways from PAG and NRM
NSAIDS - how do they work?
inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
work well with pain associated with inflammation
What do prostaglandins sensitise nociceptors to?
bradykinin
Local anaesthetics - how do they work?
block sodium action potential and hence axonal transmission
opiates - how do they work?
reduce nociceptor sensitivity and activate descending pathways to block NT release in dorsal horn
