L22 Sensory Systems Flashcards
describe the common plan of sensory systems
- designed to detect a physical stimulus (light, sounds etc.)
- stimulus is translated/signal transducted into cell activities into sensory receptor cells/neurons/transducers
- sensory receptor cells pass the signal onto second order neurons
- passes through thalamus (relay station)
- info reaches cerebral cortex - (sensory = parietal, occipital, temporal, insular)
what are the components of the common plan of sensory systems?
stimulus – receptor – pathway – perception/behavior
in what part of the brain does sensory info reach consciousness?
cerebral cortex - trigger behavior
define perception
the process of interpretation of sensory input
what are the 6 sensory systems?
- somatosensory
- visual
- vestibular
- auditory
- olfactory
- gustatory
*olfactory and gustatory are closely related = chemical senses
what are the 4 basic sensory receptor classes?
mechanoreceptors - pressure on skin
thermoreceptors - sense temp changes
chemoreceptors - sense chemical changes
photoreceptors - sense light
what sensory receptor classes does the somatosensory system need
- mechanoreceptors
- thermoreceptors
- chemoreceptors
what sensory receptor classes does the visual system need
photoreceptors
what sensory receptor classes does the vestibular system need
mechanoreceptors
what sensory receptor classes does the auditory system need
mechanoreceptors
what sensory receptor classes does the olfactory system need
chemoreceptors
what sensory receptor classes does the gustatory system need
chemoreceptors
what are the components of a sensory receptor
cell body - soma, perikaryon
t
ransduction site - stimulus is converted to nerve signal
axon
synaptic terminal
what morphology (type) of neurons are somatosensory receptors?
pseudo-unipolar neurons
what is a receptor potential
“graded potentials” = do not follow “all or none rule”
- variable durations and intensities
- variability lies in the number of AP per unit time
where do receptor potentials take place
transduction site
what is an action potential
stimulus conducted from distal to proximal axon to synaptic terminal
*note - in sensory receptor neuron, AP are NOT generated in axon hillock like seen in multipolar motor neurons
where do action potentials take place
trigger zone
what are transmitter release
transmitter is released into cleft and binds to receptors within the postsyn membrane of the postsym cells = second order neuron of the sensory pathway
where does transmitter release take place
synaptic terminals of sensory receptor
what are the morphological characteristics of sensory receptor cells?
- example - hair cell
- specialized epithelial cells (not neuronal origin)
- apical pole is transduction site
- lack an axon
- do NOT produce AP
- have graded potential that directly induces the release of signaling substances at the base of these cells
- form a synapse onto an afferent (sensory) fiber of the first neuron in the sensory pathway => neuron produces AP carried along its afferent fibers!
what are the 4 attributes of stimulus
modality
intensity
duration
location
define modality
the physical type (quality) of stimulus energy - may be light (visual system), sound (auditory system), touch (somatosensory system) etc.
Define intensity
the amplitude (or quantity) of a stimulus
define duration
the time between the start and the end of a stimulus
define location
the place where the stimulus is located or originated - maybe some place in our 3D environment around us (light or sound) or a place on the surface of our body (touch)
how is modality encoded?
labeled line code - pathways carrying sensory information centrally are therefore also specific, forming a “labelled line” regarding a particular stimulus
how is intensity encoded?
- subthreshold stimuli may elicit a small receptor potential but may not induce an AP
- frequency code
- population code
what is frequency code in wrt intensity encoding
assuming receptor potentials are above threshold, the higher the stimulus intensity is the more AP will be generated per unit time
applies to individual neurons and their axons
what is population code wrt intensity encoding
- high intensity stimuli can activate more individual axons than a low intensity stimulus
- example -press harder and harder on your hand = stimulates a larger area thus more axon stimulation
how is duration encoded?
-receptor adaptation - the disappearance of a sensation induced by a stimulus when the duration is too long
example => disappearing feeling of wearing clothes all day even though you felt them when you put them on
-slow adapting receptors
-rapid adapting receptors
what are slow adapting receptors wrt duration encoding
- used for constant monitoring
- important for regulatory function of tight physiologic windows
- they remain depolarized for the duration of the stimulus and maintain a constant output of APs
what are rapid adapting receptors wrt duration encoding
- only signal at the onset of stimulus where the receptor potential quickly returns to baseline
- no further APs are generated despite the persistence of the stimulus
- much better equipped for sensitivity to changes and not constant stimulation
what receptors are better in constantly monitoring levels of stimulation wrt duration
slowly adapting receptors
what receptors are most sensitive to changes, not to constant stimulation?
rapidly adapting receptors
define receptive field wrt location
the area monitored by a single neuron = the area where a stimulus would induce a response
what happens if a stimulus is placed within the receptive field?
AP!
what happens if a stimulus is placed outside of the receptive field
never be an AP on that neuron
what are the 3 basic wiring mechanisms
- convergence
- divergence
- lateral inhibition
what is convergence?
- when a second order neurons gets input from more than 1 first order receptor neuron
- the inputs will summate and give a larger summation than the parts alone
what is divergence
the signal from 1 first order neuron stimulates multiple second order neurons
what is lateral inhibition
a situation where a first order neuron stimulates an interneuron which will relay that stimulus to an adjacent second order neuron only it is inhibiting that adjacent neuron
