LECTURE 5

exterior sensory

receptor potential : change in MP due to receipt of signal from _________ (tough info, light info) cue

receptor potential

_________ : change in MP due to receipt of signal from exterior sensory (tough info, light info) cue

depolarization, energy, hyperpolarize

Receptor Potential

• The energy from the environment will react with membrane proteins and in general this will cause __________

• Depolarization of sensory receptors upon receipt of specific ________ (ex . pressure)

• exception : photoreceptors ______

sensory cell membrane

Receptor Potential

Similar to PSP, the receptor proteins are embedded in _________

change shape

Receptor Potential

• The receptor proteins of the sensory cells will __________ when specific energy (ex. touch) is received

  • & generally depolarize membrane

opens , amplifying

Receptor Potential

• When the receptor protein changes shape, it can either

  • directly ______ ion channels (ex. cation channels → leads to depolarization of the membrane) (like ionotropic)

  • enzyme is activated via g protein coupling → leading to production of 2nd messenger (cAMP, cGMP, InP3)→ lots of 2nd messenger → _________ the signal (like metabotropic pathway)

G-protein coupled, ion channels

Receptor Potential

• Chemical stimulus binds to specific metabotropic receptor (___________) → activation of G protein → activates adjacent enzyme (adenyl cyclase)→ produces 2nd messengers (cAMP) → cAMP activates kinases → directly interact with ______ or phosphorylate other

2

Stages of Amplification

• There are __ stages of amplification

activate, enzyme

Stages of Amplification

1. G protein can ________ a number of different _____ molecules

2nd messenger , lots

Stages of Amplification

2. each of these enzyme molecules will produce lots of ________(cAMP)

thus one stimulus molecule can produce ____ of 2nd messenger (cAMP)

amplifcation

added advantage of metabotropic effect : enzyme activation leads to process of _______

classic metabotropic receptor : sensory proteins are embedded in the membrane in the sensory terminal

• olfactory receptors line the mucus layer (so they are embedded in mucus)

olfactory

this is where the chemical stimuli/odorant dissolved in the mucus layer binds to specific receptors in _________ cell membrane

odorant

Olfactory Receptor

the specific receptor proteins bind specific ________

G protein, production , ion channels, cations

• specific receptor proteins bind specific odorant (ex. roses) → activates ______ → activates adenylyl cyclase → _______ of cAMP → cAMP directly binds _______ → allows ______ (Na+ and Ca++) to go thru → depolarization of the membrane

  • this may lead to firing of AP that goes to ur brain “hmm I smell roses”

trigger , passively , strong

The depolarizing current has to travel down the membrane and down to ______ zone of the axon (_______)

• receptor potential is not AP → graded potential

• if the depolarizing current is _____ enough and brings trigger one to threshold , u fire AP

amplification

bc we are generating current indirectly thru metabotropic mechanism → result = _______ of signal

this is why olfactory cells are v sensitive, to even just 1 or 2 molecules in the air

• compare with ionotropic pathway : just 1 or 2 channels open , this means you’ll never be able to detect that odorant

AP, spike generating zone , vesicles

Sensory Cell Transmission

• categories of sensory cell transmission:

• 1. sensory cell generates an ______ at a ______________

• 2. sensory cell releases _____ when depolarized; impulses generated in post - synaptic neuron

branch point, summation

Transmission of Signal (AP)

• located at the axon terminal (eg. in the sensory axon innervating the skin)

• first patch of excitable membrane will generally be at the _______, thus the receptor potential will have to travel and generate ________ at a branch point to reach threshold to get an AP

ion channels , summation

depolarizing current → reach trigger zone & bring to threshold to fire AP

• mechanoreceptors found in skin that respond to pressure

• pinch yourself & the pressure will open some ________ in membrane & generate the depolarizing current (RP)

• the RP (which is a graded potential) travels and generates ______ at branchpoints to reach threshold and fire AP

volt-gated sodium

branch point = where we have ________ channels (lots)

• AP can be generated here

release

2nd category of sensory cell transmission

• sensory cell releases vesicles when depolarized, impulses generated in post synaptic neuron

idea is that sensory cell does NOT have to generate its own AP as long as it can _______ neurotransmitters

exocytosis, vesicles

Transmission of Signal (Vesicles)

• The depolarizing current don’t produce any AP → travel throughout the membrane and at the other end → they depolarize the membrane sufficiently →influx of Ca++ ions and trigger _______ vesicles -→ sensory cell is releasing ______ and not producing an AP

next

Transmission of Signal (Vesicles)

• if sensory cell release transmitters: ____ cell picks this up & acts a post synaptic neuron & fires AP

• depolarization in 1st order neuron (sensory cell that does not generate AP) → release neurotransmitter by opening calcium channels

Taste Receptor

• RP travel throughout the membrane and at the other end → influx of Ca++ ions → vesicles released vesicles (not producing an AP)

Taste Receptor

depolarizing current (generated due to chemical stimulus binding) passively travels thru the membrane & reaches other end of cell

• opens volt-gated calcium channels → triggers calcium influx

• calcium triggers exocytosis of vesicles

• neighbouring, produce

Taste Receptor

• releasing to ________ neuron and job of 2nd order neuron to _______ AP

decay , sustained, constant

Adaptation

The MP can _____ over time leading to adaptation

• the original voltage is not __________ and it’s dropped over time, even though the stimulus may be _______

ex. hot bath (v hot at beginning, doesn’t feel as hot after tho)

slowly, rapidly

Types of adaptation

• ______ adapting

• ________ adapting

duration, magnitude

Adaptation (Slow)

• slowly adapting : receptor potential sustained for _______ of stimulus

• interested in overall ______ of stimulus

• always some RP that is sustained as long as you maintain stimulus

• decay is slow

zero, constant ,quickly

Adaptation (Rapid )

• Rapidly adapting : RP elicited by change in stimulus energy, decays to _____ when stimulus is _______

• interested in how ______ the stimulus is being delivered, the velocity of stimulus being delivered

hyperpolarization

removing stimulus : response in opposite direction = _______

successive, repeated, weaker

Habituation

• is the response to _______ stimuli in time

• Habituation : ________ stimuli (identical) in succession elicit progressively _______ responses

large

Habituation response depends on the cell, some will show _____ degree and some won’t

successive

adaptation = not subject to conscious control

• sensory cells will do this on their own

• is us becoming accustomed to _____ stimuli that we pay less and less attention

if you wait an hour or longer tho before the next identical stimuli , you won’t get habituation

intensity

Coding of Stimulus Intensity

• The RP will vary directly in proportion with the ______ of the stimulus

depolarization , released , frequency

Coding of Stimulus Intensity

• Greater the stimulus intensity→ the greater the receptor _____ (graded potential) → more transmitter _______ OR higher AP ________

receptor potential

Coding of Stimulus Intensity

huge stimulus vs little stimulus

• big pinch = greater change in _______

• more AP being fired in given time (frequency coding) or more transmitters being released (taste cells)

depolarization, hyperpolarization , spike

Coding of Stimulus Intensity

The greater the ________ → the faster the membrane will be brought up from ________ to generate a new _______

great stimulus → great receptor depolarization → membrane reach threshold faster to generate new AP , spike

spike train

Coding of Stimulus Intensity

great long lasting stimulus → generation of _______

refractory

Coding of Stimulus Intensity

• The impulse frequency will always be limited by _______ period

there is a limit to how many AP in one second and the limit is bound by existence of refractory period

• need some time to restore volt-gated sodium channels, can only fire 1000 AP in one second

ceiling, refractory

Coding of Stimulus Intensity

• After a while, you will reach a _____ due to ________ period

recruit , neurons, threshold

Coding of Stimulus Intensity

to code above the ceiling, the strategy is to _____ additional _____

as stimulus intensity increases (beyond limit of AP frequency = 1000 AP/second), we recruit higher __________ sensory neurons (require greater stimulus before tehy generated RP)

receptor B

Post Synaptic Receptors

Strategies to code for the strength of stimulus

• Increase frequency of AP at excitable membrane ( incr in intensity of stimulus → incr in frequency of AP [receptor A])

• With increasing stimulus strength, we recruit an additional ________, which has a higher threshold

reach maximal discharge rate (1000 AP) , can’t fire AP’s faster

labeled line

Coding for Modality

• how to code for diff types of stimulus?

• we use ________ strategy

nothing

Coding for Modality

labelled lined strategy means that activity in one pathway means a particular stimulus quality and _____ else

sub modalities

Coding for Modality

• within a modality, we could have a variety of stimulus qualities (diff colours)

• all sensations have ______ that you could distinguish (ex. touch : smooth, rough, oily, etc)

• not enough space for a diff receptor for all these qualities + not efficient

ratio

Population Code

• is coding using the ____ of activity from a restricted number of different receptor types

• specific stimulus is coded by ratio of activity across population of receptors and not by seeing the specific effect on one receptor type

peak, strongly

Population Code

• a given receptor (ex. A), type will respond to wide range, but it has a ____ which is different from others

• thus, any given stimulus (dotted line) will activate one receptor (C) very ______ but others (A,B) more weakly

spatial

Receptive Field

• Each sensory neuron is going to respond to a particular ______ area (e.g. skin, it’s the territory on the skin) → Receptive Field

what territory does each neuron cover

activate, sensory, different

Receptive Field

• of a given sensory neuron is the territory in which you could _____ that neuron

• Receptive Field is always defined in relation to a given _______ neuron, each sensory neuron will have a _______ Receptive Field

skin, smaller

Receptive Field in cutaneous sensory neuron is the ____ territory in which adequate stimulation elicits a response and is generally about 10-20 mm across (in the fingertips, it can be as little as 1 mm across)

• finger tips = ______ receptive fields than back

• can squeeze more sensory neurons → make denser → greater sensitivity