sensory physiology

Question 1

initial interaction of stimulus (sensory) with receptor is…

Answer 1

TRANSDUCTION…which is the transformation of physical energy (outside stimulus) into a neuronal signal

Question 2

the type of energy (stimulus) that a given receptor type is most sensitive to is called…

Answer 2

adequate stimulus

Question 3

the sensory specificity of a receptor is due to

Answer 3

the limited sensitivity range of the receptor (can’t respond to many different types of stimuli)

Question 4

what is the “law of specific nerve energies”

Answer 4

central connections (what system in the brain that the nerve is connected with) determine the modality (what you feel/see/etc)

Question 5

what is a physical/direct interaction

Answer 5

stimulus interacts with membrane proteins which directly opens ion channels to trigger the signal

Question 6

what sensory systems use physical/direct interaction

Answer 6

somatosensory, vestibular, auditory and taste

Question 7

what is molecular interaction

Answer 7

stimulus interacts with a membrane protein (like g-protein) to trigger the signal

Question 8

what sensory systems use molecular interaction

Answer 8

vision, taste, and olfaction

Question 9

DIRECT transduction mechanism in the TASTE system for SALTY stimuli

Answer 9

1. Na (salt) enters the cell through ENaCs (epithelial Na channels) which causes depolarization
2. depolarization leads to an a.p which allows Ca2+ to enter (voltage gated channels) the taste receptor cell
3. Ca2+ entry causes the release of ATP as an n.t
4. ATP acts on the afferent nerve for a synapse–>salty sensation (gross)

Question 10

MOLECULAR (g-protein coupled) TRANSDUCTION for SWEET stimuli

Answer 10

1. sugars bind to a g-protein coupled receptor (on taste receptor cell)
2. g-protein cascade leads to Ca release
3. Ca acts as a second messenger to “gate” the TRPm5 channel
4. now Na is allowed to enter the taste receptor cell
5. Na entry leads to depolarization of the cell and then an a.p
6. eventually this leads to ATP (the n.t) being released (to act on the afferent nerve and stimulate a “sweet sensation”)

Question 11

what is a TRP channel

Answer 11

transient receptor potential receptor

• they are a family of ion channels
• composed of 6 transmembrane domains (channel is b/w 5th and 6th domains)
• it is a CATION channel that can pass Ca2+
• variety of mechanisms can cause these TRP channels to open (depending on the type of TRP…ex. TRPm5 opens via Ca)

Question 12

how do neurons sense intensity

Answer 12

increase the intensity of the stimulus–> increase the receptor potential–> increases the # of a.ps

Question 13

threshold is a function of the stimulus (eventually reach it as you increase the stimulus intensity). what else affects when you reach threshold

Answer 13

threshold can be affected by psychological, neurological, or pharmacological factors!

Question 14

sensory afferent neurons with a smaller receptive field have ____ discrimination to location of stimulus than neurons with larger receptive fields

Answer 14

sensory afferent neurons with a smaller receptive field have GREATER DISCRIMINATION TO LOCATION OF STIMULUS than neurons with larger receptive fields

Question 15

do you have “across neuron coding” for the olfactory sensation

Answer 15

no. individual smell/olfaction broadly tuned to SINGLE odors

Question 16

what is lateral inhibition

Answer 16

in neurons with overlapping receptive fields, the afferent neuron that is closest to the stimulation can suppress the activity of the other afferent neurons that aren’t as close via a COLLATERAL inhibitory branch

Question 17

what is the benefit of lateral inhibition

Answer 17

better localization of signal/simuli location (gets rid of “noise”)

Question 18

how does a sensory neuron code for duration of a stimulus

Answer 18

can be either rapidly adapting or slowly adapting. when a neuron receives a stimulus it starts to fire a.ps at an elevated frequency. the neuron will eventually “get used to” a constant stimulus and the a.ps will stop. a rapidly adapting receptor will return back to a “baseline level” of a.ps faster than a slowly adapting receptor (aka duration of stimulus lasts longer with a slowly adapting receptors)

Question 19

how does the CNS modulate/regulate peripheral input

Answer 19

presynaptic inhibition and postsynaptic inhibition

Question 20

what is presynaptic inhibition

Answer 20

CNS inhibitory neuron synapses on the peripheral afferent neuron (before it has synapsed to send info to the CNS) to hyperpolarize the axon terminal and therefore inhibit the incoming stimulus. hyperpolarization leads to less Ca entry and less n.t release by the afferent neuron.

Question 21

what is postsynaptic inhibition

Answer 21

inhibitory CNS neurons interact/synapse after the peripheral synapse on the CNS afferent neuron to modulate the signal to the CNS. Therefore there is interaction b/w the EPSPs (from the PNS) and the IPSPs (from the CNS) to modulate the signal coming in. This includes temporal and spatial summation.