the conversion of a specific type of energy (stimulus) into an electrical signal
What is specificity?
a narrow range of stimuli
What is adequate stimulus?
the appropriate stimulus that activates a specific type of receptor at a low energy level
Sensory system is....
sensory receptors + neural pathways + target areas in brain
Define Perception.
internal representation of the outside world
Each sensory system is organized to code 4 basic types of information.
modality
intensity
timing
location
Modality is...
vision, somatic sensation, taste and smell, hearing and balance
what is labeled line code?
excitation of a given sensory neauron gives rise to the same sensation whether natural or direct electrical stimulation
Location?
representation of stimulus location is given by the sneosry receptros which are arranged topographically.
Intensity?
amount of energy is given by the response amplitude of the receptor.
Represented by a change in action potential frequency or an increase in trasmitter release. The size of a receptor potential is related to stimulus intensity. (GRADED)
Timing?
Duration
sensory receptor can respond to the stimulus for the duration of a stimulus, or just at the beginning and end of the stimulus
receptive field?
area within a receptive structure where stimuluation excites cell
a receptor responds only to stimulation w/in its receptive field
Depolarizing receptor potential is the _____ current with _______ ions moving into the cell. It will bring the membrane potential closer to the ____ for AP.
inward. positive. threshold
A _______ receptor potential is the outward current with positive ions moving out of cell. it will move the membrane potential further away from threshold for AP.
hyperpolarizing
What do mechanoreceptors do?
They respond to mechanical deformation of the surrounding tissue and convert mechanical stimulus into electrical energy.
Give 2 examples of mechanoreceptors.
1. stretch - sensitive ion channels: cell membrane open and allow cations into the cell => depolarization
2. hair cells in ear: detect fluid movement and give rise to sensations of hearing and balance.
Which touch receptors in the skin adapt rapidly to a stimulus? Which adapt slowly?
Meissner's and panician corpuscles - rapidly.
Ruffini's endings and Merkel cells - slowly
Chemoreceptors can detect these....
pain, itch, oxygen, carbon dioxide, smell, taste
T or F. Nasal chemoreceptors bind odorant molecules, a second messenger system causes an increase in cAMP leading to a depolarization.
T.
What does thermoreceptors respond to?
respond to hot, warm, cool or cold.
warm and cold receptors fire continuously at 34 degree C.
Photoreceptors _____ in response to light.
hyperpolize.
T or F. vertebrate receptor potential is generated by
a cyclic guanosine 3’-5’ monophosphate (cGMP)-second messenger cascade
T
______ is a sensory receptor that detect signal stimuli that cause tissue damage.
Nociceptors
____ is a prereq for nociception and releases chemicals. chemoreceptors respond indirectly to these chemicals.
Noxious stimuli.
What do mechanical nociceptors do?
Give rise to a sharp pain, stimulated by strong signals. Ex. Pinch, sharp object
1. Thermal nociceptors: activated by heat extremes (less than 5C and more than 45C ) and by strong mechanical stimuli.
2. Polymodal nociceptors: give rise to slow burning sensation of pain respond to mechanical, thermal and chemical stimuli. Small unmyelinated fibers transmit information.
What decide how many receptors are stimulated?
1. size of the stimulus
2. density: # of receptor in the area
3. Spatial discrimination: fingertip vs. forearm
Sensory threshold....
the lowest stimulus strength a subject can detect
in experiments, this is defined as the amplitude detected in 1/2 the trials
Receptors that respond to a wide range of stimulus intensities perform a ______ in converting the initial stimulus energy (S) into a receptor potential (R).
log transformation
R is proportional to log S
Receptors which operate over a narrow range usually respond in a ______ fashion.
linear
a slowly adapting receptor will respond to a prolonged stimulus with a _____________.
with a prolonged depolarization and action potential firing.
____________ adapting receptor will stop firing during a constant stimulus and is only active when stimulus intensity increases or decreases.
rapidly adapting
Pacinian corpuscle is what type of adapting mechanoreceptor?
rapidly adapting
Describe the Pacinian corpuscle.
Several layers of fluid -filled connective tissue lamellae (like an onion) surround the nerve terminal.
How does the Pacinian corpuscle respond to a vibrating stimulus?
The receptor fires at each stimulus cycle.
Where does the AP take the information to?
The brain
Receptor potential is a _____ signal.
Local
The timing of AP will depend on the _____ and ______
threshold and refractor period
what determines the speed at which signals are carried to CNS?
fiber size
Touch, proprioception, nociception, and temperature sense have specialized sensory terminals and project to _______.
Dorsal root ganglion neurons: convey all somatosensory info from the limbs and trunk
________ relays information from the cranial areas.
Trigeminal nerve
Large diameter fibers = have myelinated axons
fast pain carried by group II and III fibers.
Dull pain by _____
C fibers
1st order neuron: receptor to spinal cord
2nd order: spinal cord to brain stem to thalamus
3rd order: thalamus cerebral cortex
4th corder: cebral cortex to....
the specific area...
What is the rule of thumb for conduction velocity?
CV = 6 times diameter
What does rods detect?
Dim light
low acuity
many synapse onto bipolar cell
Where are cones mostly found? What does it detect?
a. concentrated in fovea
b. color vision
only few cones synapse onto bipolar cell
Both types (rods and cones) respond to light with ______ changes in receptor potential.
graded
Describe the 3 regions of the photoreceptor structure.
1. outer segment: has photopigment rhodospin/cone pigment. stacked membranous disks increase surface area to allow concentration of light-absorbing molecules
2. inner segment: contains nucleus and biosynthetic machinery
3. synaptic terminal: makes contact with target cell
Describe the steps in phototransduction.
1)cGMP in photoreceptors gates a cation channel and when open this
channel allows Na+ to flow into the cell. cGMP concentration is high in the
dark, maintains channels in an open state (causes the “dark current”) and cell is relatively
depolarized (RMP -40 mV).
2) Light stimulates cGMP phosphodiesterase and cGMP concentration decreases.
3) As cGMP concentration falls, channels close and the photoreceptor hyperpolarizes.
4) Decreased release of either excitatory or inhibitory NT from synaptic terminals of
photoreceptor leads to either a depolarization or hyperpolarization of bipolar and horizontal cells.
light leads to formation of Metarhodopsin II => activation of transducin (G protein) => activation of phosphodiesterase => decrease in cGMP => cation channels close (sodium influx stops) => photoreceptor hyperpolarizes
What does odorant molecules bind to?
Receptros on cilia (mucus layer)
Describe the cascade after the binding to the receptors.
Receptors are coupled to G proteins, which when bound to oderant activates adenyl cyclase.
Adenyl cyclase does what?
It enhances the conversion of ATP to cAMP leading to activation of a cation channel and sodium influx.
AP created from the olfactory receptor cells travel down axon of olfactory receptor cells towards _____.
The olfactory bulb.
Other signalling pathways may involve these for the olfactory receptor cells.....
the activation of phospholipase PLC and a rise in IP3
What are found in taste buds on the tongue surface?
Taste receptors. THey are constantly being replaced.
Taste receptors respond to what?
Salt, sour, bitter, sweet and umami
How are the ion channels affected by these taste receptors?
