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
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).
R is proportional to log S
Receptors which operate over a narrow range usually respond in a ______ fashion.
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.
Pacinian corpuscle is what type of adapting mechanoreceptor?
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?
Receptor potential is a _____ signal.
The timing of AP will depend on the _____ and ______
threshold and refractor period
what determines the speed at which signals are carried to CNS?
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.
Large diameter fibers = have myelinated axons
fast pain carried by group II and III fibers.
Dull pain by _____
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?
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.
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?