Sensory Systems Flashcards
What is the common purpose of sensory systems?
Provide information about external or internal environment, for generation of adaptive behavior
What is transduction?
Convert physical signal (energy) into neural signal
What is encoding?
Represent qualitative and quantitatie aspects of stimulus
What is perception?
Conscious awareness of stimulation
Doesn’t have to happen, e.g. blood pressure
What is the modality of a stimulus?
Quality or type of energy which is transduced
What are the five basic modalities of sensation?
Somatosensation
Vision
Audition
Olfaction
Gustation
What is an adequate stimulus?
Type of energy that activates a specific receptor at lowest energy level
What is intensity?
The strength of a stimulus
What is sensory threshold?
The lowest intensity which can be detected reliably (50% of the time)
What is the relationship between threshold and sensitivity?
Threshold is inversely related to sensitivity
Threshold is not fixed
Which direction does a decrease in sensitivity shift an intensity-response curve? Increase?
Decrease - shifts curve to the right (raises threshold)
Increase - shifts curve to the left (lowers threshold)
What is duration?
Length of stimulation
What is characteristic of slowly adapting receptors?
Will continue to fire as long as stimulus is present at fixed level
Provides information about stimulus duration
What is characteristic of rapidly adapting receptors?
Will fire in response to a change in stimulus intensity
Provides information about the dynamic aspects of a stimulus
What is a receptive field?
Specific spatial location where stimulus energy is effective in stimulating a receptor
What is the mechanism of a mechanoreceptor?
Tranduces physical energy (membrane deformation) into neural activity
Linked to membrane or cytoskeleton in some way
Cation channel permeable to Na and K that depolarizes the receptor cell
What are thermal receptors?
Transient Receptor Potential (TRP channels) channels that are thermally stimulated (can be stimulated by other means)
Cation channels that vary in ion permeability depending on channel type
What is the difference between cold and warm receptors?
Cold: TRP channels that are activated at low temps (12-35)
Warm: TRP channels activated by high temperatures
What is another type of stimulus for thermally activated TRP channels?
Chemical
Cold: menthol (mint)
Warm: capsaicin
What are thermal nociceptors?
Pain receptors that are activated by extremes of heat or cold (<12C or >47C)
What is receptor potential?
Sensory transduction causes channel opening and creates a graded potential
Fewer channels open: small receptor potential
More channels open: bigger receptor potential
What must happen to trigger an action potential?
The capacitive current created by the receptor potential must depolarize the initial segment of the axon to threshold
How is the intensity of a stimulus coded?
Frequency coding
Low intensity causes low fire rate
High intensity causes high firing rate
How is the duration of a stimulation coded?
Encoded by the length of an action potential train (duration of transmitter release onto the second order neuron)
What is adaptation?
Reduced output despite sustained stimulation
Caused by altered sensory transduction or change in membrane ion conductance
What are two ion conductance adaptation mechanisms?
Inactivation of inward currents (Na or Ca channels)
Activation of outward currents (Ca activated K channel)
What is a calcium-activated potassium channel?
Needed for slow adaptation
Increase in cytoplasmic Ca (due to HVA Ca channels) causes the channel to open
Additional K conductance causes the membrane potential to “sag” back towards resting level, reduced rate of action potential firing
What are the functional zones of sensory receptors?
Transduction - sensory channels
Integration (trigger) - cation channels, Ca-activated K channels
Conduction - axon
Transmission - axon terminal
