LO4 Sensory receptors

Question 1

Receptor (generator) potential

Answer 1

The change in membrane potential (either depolarization or hyperpolarization) that is elicited with a stimulus.

-opening or closing of transduction channel underlies the receptor potential

Question 2

How does the receptor potential spread in Short receptor cells?

Answer 2

It spreads to the synaptic end of the cell by passive electrotonic transmission

• very effective at altering rate of NT release
• no regeneration of AP necessary

(ie: photoreceptors and auditory hair cells)

Question 3

How does the receptor potential spread in Long receptor cells?

Answer 3

The receptor potential itself only affects a limited portion of the cells near the receptive ending.
- needs regenerative AP to carry info from receptive ending (skin/muscle) to the synaptic release site (SC/BS)

(ie: somatosensory receptor cell, skin mechanoreceptors)

Question 4

The NT for most sensory receptor cells is ____

Answer 4

Glutamate

can interact with GPCR to directly alter postsyn cell’s membrane pot

Question 5

What underlies the receptor potential?

Answer 5

Opening or closing of transduction channels

just like changing membrane potential, receptor potential is no different

Question 6

Muscle mechanoreceptors generate which type of receptor potentials?

Answer 6

Depolarizing receptor potentials

• the receptive area of these sensory endings have mechanosensitive cation channels that open in response to STRETCH –> depolarizes sensory endings

Question 7

Rod photoreceptors generate which type of receptor potentials?

Answer 7

Hyperpolarizing receptor potentials

• Receptors have a substantial amt of resting cation conductance open in receptive area (resting membrane potential less neg than nI)
• Adequate stimulus –> causes some cation channels to close –> hyperpolarization.

(note that rod photoreceptors are short receptor cells with resting memb pot of -40mV due to opening of cGMP gated cation channels under resting conditions)

Question 8

Explain how light can cause hyperpolarization and what that means for NTs.

Answer 8

1. Light hits photoreceptor, rhodopsin
2. 1-cis-retinal which is bound to rhodopsin is converted to 1-trans-retinal
3. causes rhodopsin to convert to metarhodopsin
4. Stimul. G-protein, transducin
5. activates cGMP phosphodiesterase
6. breaks down cGMP to guanosine
7. Decreased levels of cGMP causes CLOSURE of cGMP gated cation channels
8. hyperpolarizes photoreceptor cells
9. Causes decrease in NT release

THE HIGHER ORDER NEURONS KNOW THAT THIS IS A RESPONSE TO LIGHT

Question 9

Do photoreceptor cells fire action potential?

Answer 9

No, they are short receptor cells

The hyperpolarization is transmitted to the synaptic end by electrotonic transmission

Question 10

Labeled lines

Answer 10

Conscious appreciation of sensory modality is determined by SPECIFIC neuronal cnxns from sensory organs through thalamus to cerebral cortex.

(There is a separate chain of neurons - labeled line - for each sensory system)

physical E sensed by sensory receptor cell –> converted to membrane pot –> transmit info (about the change in memb pot) to second order nerve cells –> info then transmitted to CNS + processed into 3 main fxns

Question 11

Sensory info drives the response before we can perceive it. In general, info that becomes conscious is relayed through what?

Answer 11

Through the thalamus to cerebral cortex.

Question 12

Transduction channel

Answer 12

opens in an all or none fashion

• How long the channel stays open is the reason the receptor potential changes as a function of stimulus intensity
• it will open for a short time with weak touch
• will open most of the time with strong touch
• Not voltage dependent

Question 13

Are transduction channels voltage dependent?

Answer 13

No, they are sensitive ONLY to adequate stimulus and do not open in response to cell depolarization (like VSSC)

-if it were, then the voltage dependence would compromise the encoding of stimulus intensity (as a graded increase of the magnitude of the receptor potential)

Question 14

The magnitude of the _________ potential reflects the intensity of the stimulus

Answer 14

generator potential

• thanks to transduction channels that only respond to stimulus and open/close which determines the generator potential

Question 15

A fibers vs C fibers

1. Which one is unmyelinated?
2. Which one is larger?
3. which one is faster?

Answer 15

1. C fibers
2. A fibers (α largest)
3. A fibers (α fastest)

Question 16

Aα fibers

Answer 16

Ia: muscle spindle afferents (stretch)

Ib: Tendon organ afferent

Question 17

Aβ fibers

Answer 17

II
Mechanoreceptors of skin,

secondary muscle spindle afferents
- (primary are Ia)

Question 18

Aδ fibers

Answer 18

III
Sharp pain,
Cold temp

(icy Dagger)

Question 19

C

Answer 19

IV
Warm temp
Burning (dull) pain
itch
Crude touch

(Cunt)