Vision pt.1

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Questions and Answers

What is the primary function of the retinal molecule in photoreceptor cells?

To directly transmit visual signals to the brain.

To synthesize ATP from light energy.

To regulate the production of different opsins.

To absorb electromagnetic energy of visible light. (correct)

Which type of photoreceptor cell is most sensitive to light?

Blue cone cells

Green cone cells

Rod cells (correct)

Red cone cells

How many types of photoreceptor cells are involved in human vision?

Four types (correct)

Five types

Three types

Two types

What type of opsin do red cone cells express?

Red cone opsin Signup and view all the answers

What is the wavelength range of visible light detected by human eyes?

380 to 760 nm Signup and view all the answers

Which photoreceptor cell type is most sensitive to short wavelengths of light?

Blue cone cells Signup and view all the answers

What occurs when retinal absorbs a wavelength of visible light?

It activates the opsin protein in photoreceptor cells. Signup and view all the answers

What distinguishes the various opsin proteins expressed in photoreceptor cells?

Their sensitivity to different light wavelengths Signup and view all the answers

What is the primary issue for individuals with Protanopia?

Absence of the red cone opsin Signup and view all the answers

Which color vision deficiency is associated with the absence of the blue cone opsin?

Tritanopia Signup and view all the answers

How does visual acuity change in individuals with Tritanopia?

It is unaffected Signup and view all the answers

Which condition involves a mutation leading to less pronounced deficits in color vision?

Tritanopia Signup and view all the answers

What is true color blindness known as?

Achromatopsia Signup and view all the answers

What separate condition involves the absence of the green cone opsin?

Deuteranopia Signup and view all the answers

Which of the following groups suffers from color vision deficiency due to mutations in the green cone opsin?

6% of males Signup and view all the answers

What common characteristic do Protanopia and Deuteranopia share?

Both involve absent cone opsins Signup and view all the answers

What is the primary role of cone cells in the human eye?

They are essential for color vision. Signup and view all the answers

Which part of the eye is primarily responsible for focusing light?

The lens Signup and view all the answers

What is the main function of the rod cells in the eye?

To detect low light levels. Signup and view all the answers

What structure controls the amount of light entering the eye?

The pupil Signup and view all the answers

Where are the photoreceptor cells located within the eye?

On the retina Signup and view all the answers

Why are rod cells described as being 100 times more sensitive than cone cells?

They enable vision in dim lighting. Signup and view all the answers

What structure of the eye acts as a protective mucous membrane?

The conjunctiva Signup and view all the answers

What is the primary difference between sensation and perception?

Sensation refers to the detection and transduction of stimuli. Signup and view all the answers

What part of the eye does the optic disk correspond to?

Where blood vessels enter and exit Signup and view all the answers

What role do sensory neurons play in sensation?

They detect specific physical stimuli and convert them to membrane potential changes. Signup and view all the answers

Which type of sensory neuron is responsible for vision?

Photoreceptors Signup and view all the answers

How do photoreceptors generate a change in membrane potential?

By changing the shape of retinal which activates metabotropic receptors. Signup and view all the answers

What is true about the action potentials in sensory neurons?

Some sensory neurons do not involve action potentials but still release neurotransmitter. Signup and view all the answers

Which characteristic do opsins have in photoreceptor cells?

They bind molecules of light to change shape. Signup and view all the answers

Which of the following is NOT a category of physical stimuli detected by sensory neurons?

Presence of magnetic fields Signup and view all the answers

What effect does depolarization have on sensory neurons that do not have action potentials?

It leads to a greater release of neurotransmitter. Signup and view all the answers

What causes the blind spot in the eye?

Absence of photoreceptors Signup and view all the answers

What type of eye movement occurs when tracking a moving object?

Pursuit movements Signup and view all the answers

What is the arrangement of cells in the fovea compared to the rest of the retina?

Equal number of all cell types Signup and view all the answers

Which eye movements are described as rapid and jerky?

Saccadic movements Signup and view all the answers

What must light pass through before reaching the opsin proteins in photoreceptor cells?

Retinal ganglion cells Signup and view all the answers

How do extraocular muscles function in relation to the eye?

They rotate the eye and stabilize its position. Signup and view all the answers

What visual acuity ratio indicates normal vision in the fovea?

20/20 Signup and view all the answers

What is the primary reason for the placement of opsin proteins in the retina?

Due to an evolutionary arrangement Signup and view all the answers

Study Notes

Sensation vs. Perception

Sensation is how the nervous system detects stimuli and converts them into signals.
Perception is the conscious experience and interpretation of sensory information.

Sensory Neurons

Specialized cells that detect specific physical events.
Sensory neurons can detect:
- Molecules (smell, taste, nausea, pain)
- Physical pressure (touch, stretch, vibration, acceleration, gravity, balance, hearing, thirst, pain)
- Temperature (heat, cold, pain)
- pH (sour taste, suffocation, pain)
- Electromagnetic radiation (light)
Some animals have additional senses like detecting electric and magnetic fields, humidity, and water pressure.

Sensory Transduction

Sensory neurons have specialized receptors that convert sensory stimuli into changes in membrane potential.
Sensory neurons can take many shapes and sizes.
Many sensory neurons do not have axons or action potentials.
These neurons release neurotransmitter in a graded fashion based on their membrane potential.

Photoreceptors

Photoreceptor cells are responsible for vision.
These cells convert light energy into changes in membrane potential, affecting neurotransmitter release.
They lack action potentials.

Opsins

Light-sensitive proteins.
Opsins in photoreceptor cells are metabotropic receptors.
They bind a molecule of retinal which changes shape in response to light.
This shape change activates the metabotropic receptor.

Retinal

A small molecule synthesized from vitamin A.
It attaches to opsin proteins.
Retinal absorbs electromagnetic energy of light.
The two configurations of retinal:
- cis-retinal (inactive)
- trans-retinal (active)

Neural Transduction of Light

light + retinal molecule + opsin protein = activation
Activation launches a g protein signaling cascade, changing the photoreceptor cell's membrane potential and affecting neurotransmitter release.

Types of Photoreceptor Cells

4 types contribute to vision:
- Red cone cells (red cone opsin)
- Green cone cells (green cone opsin)
- Blue cone cells (blue cone opsin)
- Rod cells (rhodopsin opsin)
Each opsin is sensitive to different wavelengths of light.
Rod cells, the last to evolve, are 100 times more sensitive to light than cone cells.

Visible Light

Electromagnetic radiation with wavelengths between 380-760 nm.
Detected by 4 photoreceptor cell types: 1 rod cell and 3 cone cells.

Cone Photoreceptors/Trichromatic Coding

Blue cone opsins are most sensitive to short wavelengths.
Green cone opsins are most sensitive to medium wavelengths.
Red cone opsins are most sensitive to long wavelengths.
These opsins allow for color vision.

Color Vision Deficiency

Protanopia: Absence of the red cone opsin (1% of males), difficulty distinguishing colors in the green-yellow-red spectrum, visual acuity is normal.
Deuteranopia: Absence of the green cone opsin (1% of males), difficulty distinguishing colors in the green-yellow-red spectrum, visual acuity is normal.
Tritanopia: Absence of the blue cone opsin (1% of the population), blue cone cells don't compensate, visual acuity is not affected.

Achromatopsia

True color blindness.
Caused by mutations in the g protein signaling cascade used by all cone opsins.

Anatomy of the Eye

Conjunctiva: Mucous membrane lining the eyelid.
Cornea: Outer, front layer of the eye, focuses incoming light.
Sclera: Opaque, does not permit light entry.
Iris: Ring of muscle, controls pupil size and light entering the eye.
Lens: Transparent layers, changes shape for focusing near and far objects (accommodation).
Retina: Inner lining of the eye containing photoreceptor cells.
Vitreous humor: Clear, gelatinous fluid behind the lens.
Fovea: Central region of the retina, primarily contains cone cells, sharpest visual acuity (20/20 vision).
Periphery: Outer area of the retina, contains only rod cells.
Optic disk: Where blood vessels enter/exit the eye and the optic nerve exits, contains no photoreceptors, creating a blind spot.

Eye Movements

Orbits: Bony sockets in the skull that hold the eyes.
Saccadic eye movements: Rapid, jerky shifts in gaze.
Pursuit movements: Smooth, slow eye movements when focusing on a moving object.
Extraocular muscles: Muscles attached to the sclera, rotate the eye and hold it in place.

Organization of the Retina

Visual information travels: Photoreceptor cells -> Bipolar cells -> Retinal ganglion cells -> Brain.
Light passes through all retinal layers to reach the photoreceptor cells.

Retina Fovea vs. Periphery

Fovea: Equal number of photoreceptor cells, bipolar cells, and retinal ganglion cells, no information compression, high visual acuity.
Periphery: Information compression, lower visual acuity.

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