Sensory Systems Flashcards
How do sensory receptors generate a receptor potential?
They transduce their adequate stimulus into a depolarisation a.k.a the receptor potential
What does the size of receptor potential encode for?
The intensity of stimulus
What allows for long distance transmission?
Receptor potentials evoking AP firing
What does frequency of AP encode for?
The intensity of stimulus
What determines acuity?
Density of innervations and size of receptive fields
What are features of AB afferent fibres?
Large, myelinated, respond to touch, pressure and vibration
What are features of AS fibres?
Small, myelinated, respond to cold, fast pain and pressure
What are features of C fibres?
Unmyelinated fibres, respond to warmth, slow pain
What is proprioception mediated by?
Aa and AB fibres
Where do primary afferent fibres enter the CNS?
The spinal cord via the DRG
How are mechanoreceptive signals transmitted ?
Via Aa and Ab fibres —> project straight up through ipsilateral dorsal columns –> synapse in cuneate and gracile nuclei.
2nd order fibres decussate in brain stem and project to reticular formation, thalamus and cortex
How are thermoreceptive and nociceptive signals transmitted?
Via AS and C fibres which synapse in the dorsal horn. 2nd Order fibres cross over the midline in the spinal cord which project up the spinothalamic tract to reticular formation, thalamus and cortex
What occurs when the dorsal column is damaged?
Loss of touch, vibration, proprioception below lesion on ipsilateral side
What happens when the anterolateral quadrant is damaged?
Loss of nociceptive and temperature sensation below lesion on contralateral side
What do NSAID’s do?
they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins.
They sensitise nociceptors to bradykinin
