Receptor Physiology and the Somatosensory System Flashcards
Define receptor.
Transducers that can convert various forms of energy to an action potential.
How do we classify sensory receptors?
Adequate stimulus
Location
Duration of adaptations
Describe how free/specialized nerve endings work.
Stimulus applied on afferent
opens Na+ channels
local current flow depolarized and adjacent regions.
Opens voltage-gated Na+ channels
Reaches graded potential threshold
initiates an AP in afferent nerve self propagates to CNS
Describe how a separate receptor cell works.
Stimulus on cell
influx of Na+
local depolarizing
Opens Voltage-gated Ca2+ channels
influx of Ca2+
causes exocytosis of neurotransmitters.
binds to the afferent end on chemically gated receptors
permitting influx of Na+
Depolarizes adjacent region
voltage-gated Na channels open
self propagates AP
List the different tactile receptors and their functions.
Hair receptor- hair movement, gentle touch
Merkel- light sustained touch
Pacinian corpuscle- vibrations and deep pressure
Ruffini endings- deep pressure
Meissner’s corpuscle, light fluttering touch
Describe the modality.
an adequate stimulus is a partial form of energy to which a receptor is most sensitive.
receptors respond to other forms of energy or stimuli, but the thresholds for these are higher
Define the sensory unit and how it relates to the receptive field.
it refers to a single sensory axon and all its peripheral branches. it determines the spatial distribution in which a stimulus can produce a response.
Explain the lateral inhibition phenomenon.
info from neurons whose receptors are at the peripheral edge of the stimulus is inhibited, compared to information from the sensory neurons at the center of a stimulus
Describe the doctrine of specific energies.
When the nerve pathways from a particular sense organ are stimulated, the sensation evoked is that for which the receptor is specialized no matter how or where along the pathway the activity is initiated.
Describe the law of projection
If we stimulate a sensory pathway along its course to the sensory cortex, the conscious sensation produced is perceived to be from the location of receptors
Describe Weber-Frechner Law.
The amount of change needed for sensory detection to occur increases with the initial intensity of the stimulus, and is proportional to it.
Describe rapidly adapting receptors.
When RARs are stimulated, they quickly respond with a burst of electrical activity, but then rapidly decrease their firing rate, even if the stimulus remains constant.
This rapid adaptation allows RARs to be particularly sensitive to changes in stimuli, such as a sudden change in pressure, but less sensitive to constant pressure or vibration.
M and P Corpuscles
Describe Slow adapting receptors.
When SARs are stimulated, they respond with a sustained burst of electrical activity that persists as long as the stimulus is present. This slow adaptation allows SARs to be particularly sensitive to the magnitude and duration of a stimulus.
Merkels disk and ruffini endnig
Compare axon firing in large vs small receptive field size.
small- faster
What is sensory coding?
conversion of a receptor stimulus to a recognizable sensation
