Introduction to Sensory Physiology and Perception Flashcards
what do receptors do?
detect the stimulus
types of receptors
photoreceptors, chemoreceptors, thermoreceptors, mechanoreceptors
examples of mechanoreceptors
pressure on skin, pressure in musculoskeletal system (proprioception), head movement (equilibirum), sound
samtosenroy system
inflammatory chemicals, temperature, pressure on skin, pressure in musculoskeletal system
what is the main somatosensory pathway?
primary afferent -> medulla –> thalamus –> cortex
what are somatosensory receptors also known as?
primary afferents
what are all-in-one receptors resilient to?
injury
whats different about other systems compared to somatosensory/olfactory?
receptors are separate cells. e.g. visual system, auditory and vestibular systems.
what is special about separate receptors?
they are delicate and irreplaceable e.g. photoreceptors
what are photoreceptors susceptible to?
light damage, genetic mutations, metabolic diseases, malnourishment
what are auditory hair cells susceptible to?
noise trauma, genetic mutations, ototoxicity, (chemotherapy agents, amino-glycoside antibiotics)
how can sensation be resorted?
if afferent survives, electronic system can stimulate sensation back. any acitivity in afferents will be interpreted as sensation so if rest of system is intact, function is restored
what is cochlear implant?
25 electrodes in ear that can stimulate afferents
how can gene therapy be used for photoreceptor restoration?
produce retinal cells to be photosensitive
what does transduction do?
produce electronic potentials
what does pressing on sensitive endings do?
produces receptor potentials that may give rise to action potentials
action potential threshold
Membrane potential at which action potentials are triggered.
This is a function of the vgNa+ channel and can be treated as a constant
‘activation’ threshold
Minimum stimulus strength that will depolarise a receptor enough to generate action potentials.
Sensory systems use receptors with a range of
different activation thresholds.
“Perceptual” threshold
Minimum stimulus strength that will generate enough action potentials to be detected.
Perceptual threshold is the bit we can most easily test in a
clinical environment.
is afferent signal a faithful copy of stimulus?
NO
spatial resolution is limited
due to receptive field
why cant you read braille with skin of arm?
receptive field sizes vary across the body
why can you read braille with skin of fingertips?
1mm receptive fields. smaller receptive fields means higher innervation density
spatial resolution is variable
the higher the innervation density, the more cortex needed to deal with the input
characteristic of temporal resolution
it is limited and varies with receptor type
what happens if you press down on skin with finger?
rigorous action potentials, but then the sensory systems will adapt to constant stimuli and go back to original state
what is the implication of adapting to unchanging stimuli?
- By damping down responses to unchanging stimuli, adaptation highlights moments when stimulus strength changes
- and allows vigorous responses to small changes
without saturation - Different receptors types adapt at different rates
why does sensory system adapt?
So that it can respond to changes in the stimulus pressure, instead of action potentials getting worse. It means it can notice the change better
what is lateral inhibition?
same as adaptation but in spatial rather than temporal. highlights locations where stimulus strength changes. Increases spatial resolution
what are inhibitory interneurones?
causes secondary afferents to dampen down responses to homogeneous stimuli. increase spatial resolution
What are the dynamic ranges?
Adaptation and lateral inhibition damp down responses to homogeneous temporal and spatial stimulation
what do afferents do?
encode changes/differences rather than absolute levels so that they can therefore respond strongly to small changes over large stimulus range
what does increasing dynamic range mean?
reduces issue of saturation
perceptual threshold
what youre measuring if you do clinical sensory testing
receptive fields
determine the dimensions of test stimuli
adaptation
determines the temporal characteristics of test stimuli
lateral inhibition
feature of sensory processing
Implication of Damage and Disease
Can differentially affect different types of receptor (you need to choose the right test)
Can increase perceptual threshold where receptors are lost (look for loss of sensation)
BUT neural damage can disrupt inhibitory systems and lead to hypersensitivity
why are there different receptors in the skin?
they each detect different qualities of touch
how are quaities represented in primary cortical areas?
by columns
what do you actual experience?
a reconstruction based on the pattern of AP firing in the cerebral cortex
examples of the brain/somatosensory system getting the reconstruction wrong?
- epileptic activity e.g. somatosensory system, can generate phantom sensations running across the body surface.
- phantom limbs
- synaesthsia e.g. auditory input activates visual colour processing area, so a person “sees” sounds as coloured.
- pain
what is synaesthesia?
auditory input activates visual colour processing area, so a person “sees” sounds as coloured.
