What makes photoreceptors unique?

Only have membrane potential changes

decrease NT release when excited

Active PDE results DIRECTLY in conversion of:

Rho -->ospin + all trans retinal

Light Transduction + Receptive Field

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| By Tseemore

Tseemore

Community Contributor

Quizzes Created: 24 | Total Attempts: 12,964

Questions: 12 | Attempts: 97 | Updated: Mar 21, 2023

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1.

What makes photoreceptors unique?
- A.
  
  Only have membrane potential changes
- B.
  
  Hyperpolarize when excited
- C.
  
  Decrease NT release when excited
- D.
  
  2 of the above
- E.
  
  All of the above
Correct Answer
E. All of the above

Explanation
Photoreceptors are unique because they exhibit all of the mentioned characteristics. They only have membrane potential changes, meaning that their response to light stimuli is solely based on changes in their membrane potential. Additionally, they hyperpolarize when excited, which means that their membrane potential becomes more negative. Lastly, they decrease neurotransmitter (NT) release when excited, indicating that their response to light leads to a reduction in the release of neurotransmitters. Therefore, all of the above statements accurately describe the unique features of photoreceptors.

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2.

Rods follow the stimulus change closely, whereas cones have a latency in their response.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
Latency of response for rods is longer- rise time and fall time are longer- and then membrane changes slower in rods whereas cone response follows the stimulus change more closely

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3.

In the dark, Na channels are closed, preventing Na to enter the OS.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
In the dark, Na channels are open and Na flows into the OS. Light results in a closure of the Na channels so that Na doesn't flow back into the OS.

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4.

In the dark, photoreceptors release NTs continuously
- A.
  
  True
- B.
  
  False
Correct Answer
A. True

Explanation
In the dark, photoreceptors release neurotransmitters continuously. This is because in the absence of light, the photoreceptors are constantly depolarized, causing them to release neurotransmitters. This continuous release of neurotransmitters helps to maintain a baseline level of activity in the visual system, allowing for the detection of even very low levels of light.

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5.

As part of the dark current, Na is continuously pumped out of the OS and follows it's concentration gradient and enters the photoreceptor in the IS
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
Opposite is true. Na pumped out of IS and then follows gradient to flow back into the PR through the OS.

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6.

What is the voltage potential inside a photoreceptor in the dark? What is it in presence of light?
- A.
  
  -60mV; -20mV
- B.
  
  -20mV; -50mV
- C.
  
  -20mV; -60mV
- D.
  
  -50mV; -20mV
Correct Answer
C. -20mV; -60mV

Explanation
In the light, the Na channels in the OS are closed and therefore the Na that's being pumped out of the IS cannot get back into the PR. Since Na is + charged, there will be a decrease in the membrane potential (more negative) when light is present vs in the dark.

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7.

When a photon of light strikes Rhodopsin, phosphodiesterase (PDE) becomes:
- A.
  
  Active
- B.
  
  Inactive
Correct Answer
A. Active

Explanation
When a photon of light strikes Rhodopsin, it causes a conformational change in the molecule. This conformational change activates phosphodiesterase (PDE). Therefore, the correct answer is "active".

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8.

Active PDE results DIRECTLY in conversion of:
- A.
  
  GMP --> cGMP
- B.
  
  Rho -->ospin + all trans retinal
- C.
  
  CGMP --> GMP
- D.
  
  Rho --> active Rho
Correct Answer
C. CGMP --> GMP

Explanation
This results in a decrease in the cGMP concentration in the cytosol of the PR because it has been converted into GMP

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9.

What is the purpose of cGMP in photorecptors?
- A.
  
  Closes Na channels
- B.
  
  Keeps Na channels open
- C.
  
  Inhibits PDE
- D.
  
  Regenerates Rho
Correct Answer
B. Keeps Na channels open

Explanation
Decreasing the cGMP in the cytosol results in the CLOSURE of the Na channels when light is around

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10.

Light needs to be present during the entire time that Rho is being transformed into opsin and all-trans retinal
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
(I'm not sure that I've articulated this question very well...but check out pg. 161 picture for more clarification)

The only thing that the absorption of light does to Rho is convert it to Beta-Rho. All other changes occur at normal body temperature.

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11.

What is Hartline's definition of a receptive field?
12.

The definition of a receptive field is only applied to ganglion cells.
- A.
  
  True
- B.
  
  False
Correct Answer
B. False

Explanation
can be applied to any visual neuron: PR, BP, GC, H, A

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Light Transduction + Receptive Field

What makes photoreceptors unique?

Rods follow the stimulus change closely, whereas cones have a latency in their response.

In the dark, Na channels are closed, preventing Na to enter the OS.

In the dark, photoreceptors release NTs continuously

As part of the dark current, Na is continuously pumped out of the OS and follows it's concentration gradient and enters the photoreceptor in the IS

What is the voltage potential inside a photoreceptor in the dark? What is it in presence of light?

When a photon of light strikes Rhodopsin, phosphodiesterase (PDE) becomes:

Active PDE results DIRECTLY in conversion of:

What is the purpose of cGMP in photorecptors?

Light needs to be present during the entire time that Rho is being transformed into opsin and all-trans retinal

What is Hartline's definition of a receptive field?

The definition of a receptive field is only applied to ganglion cells.