Anatomy of the Eye in Animals

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Questions and Answers

What is the function of the tapetum lucidum in nocturnal and domestic mammals?

To enhance dark-adapted vision under dim light

What type of muscle is the pupillary dilator muscle?

Smooth muscle

What is the function of the suspensory ligaments in the eye?

To suspend the lens and aid in accommodation

What is the function of the vitreous humor in the eye?

To give the eye its spherical shape Signup and view all the answers

What is the term for the constriction of the pupil?

Miosis Signup and view all the answers

What type of cells are found in the vitreous humor?

Phagocytic cells Signup and view all the answers

What is the function of the ciliary body in the eye?

To aid in accommodation of the lens Signup and view all the answers

What is the structure that lies behind the vitreous humor in the eye?

Retina Signup and view all the answers

What is the main difference between the outer segment of cone cells and rod cells?

Cone cells have membranous invaginations, while rod cells have flattened membranous sacs. Signup and view all the answers

What is the role of vitamin A in the retina?

It is important for the formation of rhodopsin. Signup and view all the answers

What is the main function of rod cells?

To detect low-intensity light. Signup and view all the answers

How many types of cones are present in primates?

3 Signup and view all the answers

Describe the pathway of visual signals from the retina to the visual cortex.

Retina, optic nerve, optic chiasm, optic tract, thalamus, visual cortex Signup and view all the answers

What is the term for the ability to detect different wavelengths of light?

Polychromatic vision. Signup and view all the answers

What is the result of severe vitamin A deficiency?

Night blindness. Signup and view all the answers

How many types of cells make up the retina?

5 Signup and view all the answers

What is the primary function of the retina in the eye?

To transform light into electrical activity of neurons Signup and view all the answers

What is the point where axons of the retina ganglion cell layer leave the eye on their way to the brain?

Optic disc or blind spot Signup and view all the answers

What is the structure that arises from the axons leaving the eye at the optic disc?

Optic nerve Signup and view all the answers

Which of the following statements is true?

The pupillary sphincter muscle is circularly arranged, and is innervated by parasympathetic nerves Signup and view all the answers

What is the function of the blood vessels in the retina?

To provide nutrition to the retina together with vessels of the choroid Signup and view all the answers

What is the structure that surrounds the optic nerve in some animals?

Tapetum Signup and view all the answers

Where do the arteries and veins enter the retina?

At the optic disc Signup and view all the answers

What is the comparison between the number of axons in the optic nerves and the dorsal roots of the spinal cord?

There are more axons in the optic nerves Signup and view all the answers

What happens to cGMP in the dark?

It accumulates and binds to ligand-gated Na/Ca ion channels Signup and view all the answers

What is the role of the antipoter in rod cells?

To transport calcium ions out of the cell Signup and view all the answers

What is the ratio of rod cells to ganglion cells?

Hundreds of rod cells to one ganglion cell Signup and view all the answers

Which part of the retina provides the highest visual acuity?

Area centralis Signup and view all the answers

What is the role of phosphodiesterase 6 (PDE6) in rod cells?

To convert cGMP to 5'-GMP Signup and view all the answers

What is the equivalent of the film in a photographic camera in the eye?

Retina Signup and view all the answers

What happens to the light as it passes through the eye?

It is refracted by a sequence of transparent media Signup and view all the answers

What is the effect of the activation of rhodopsin by light?

It leads to the activation of PDE6 Signup and view all the answers

Where is the lens located in relation to the aqueous humor and the vitreous humor?

Between the posterior surface of the lens and the vitreous humor Signup and view all the answers

What is the purpose of the lens in the eye?

To converge the light rays to a focal point on the retina Signup and view all the answers

What is unique about the central retina in most mammals?

It has the highest visual acuity Signup and view all the answers

What happens to the light rays as they approach the eye?

They get closer together and then cross over Signup and view all the answers

What is the nature of the images formed on the retina?

Real, inverted, and smaller than the object Signup and view all the answers

What happens to the images formed on the retina?

They are transformed into nerve impulses by cones and rods Signup and view all the answers

Where do the optic nerve fibers terminate for visual perception?

Lateral geniculate nucleus, optic radiation, and occipital lobe Signup and view all the answers

Where do the optic nerve fibers terminate for visual reflexes?

Pretectal nucleus, rostral colliculus, and tectospinal tract Signup and view all the answers

Regarding image formation, the fibers terminate in the midbrain for visual perception or thalamus for visual reflex; respectively.

False Signup and view all the answers

Photoreceptors and ganglion cells communicate via receptor potential rather than action potential.

True Signup and view all the answers

Which of the following statements regarding the area centralis is false?

All the above Signup and view all the answers

In order to perceive light, ganglion cells must be __________ (activated)

Depolarized Signup and view all the answers

Match to the correct retinal layer

Photoreceptor cells = Synapse with bipolar and horizontal cells Amacrine cells = Most are inhibitory interneurons that transmit signals in two directions Bipolar cells = Retinal interneurons that transmit signals vertically from the rods, cones and horizontal cells to ganglion and amacrine cells Ganglion = Projection neurons that transmit output from the retina through the optic nerve into the brain. Signup and view all the answers

Match the following neurotransmitter(s) to the correct cell of the retina

Horizontal cells = GABA Ganglion cells = Glutamate Amacrine cells = GABA or Glycine Bipolar cells = Glutamate Signup and view all the answers

Match the correct order of the cells of the retina

Photoreceptor cells, horizontal cells, bipolar cells, amacrine cells and ganglion cells Signup and view all the answers

In the DARK: photoreceptor cells are ___ and release (neurotransmitter), which activates bipolar cells. Bipolar cells then inhibit _ cells which doesn’t allow the optic nerve to perceive no light.

Depolarized, glutamate, ganglion Signup and view all the answers

The activation of light activates and this leads to activation of the G protein _. Activated split away and activate ____

Rhodopsin, transducin, transducin PDE6 Signup and view all the answers

After PDE6 is activated, it hydrolizes to . This causes the to close; thus leading to _. This depolarization/hyperpolarization does not release ______ (neurotransmitter).

cGMP to 5’GMP, Na/Ca channels, hyperpolarization, hyperpolarization, glutamate Signup and view all the answers

Study Notes

Fundus and Tapetum

Choroidal vessels are visible throughout the fundus.
In some diurnal animals, melanocytes absorb light that has passed by photoreceptors without stimulating them.
Nocturnal and most domestic mammals have a reflective material called tapetum lucidum, which enhances dark-adapted vision under dim light.

Iris and Pupil

The iris controls the amount of light that passes through the pupil.
In the dark, the pupil will dilate (mydriasis).
In the light, the pupil will contract (miosis).
The iris contains dilator and sphincter muscles.
Pupillary dilator muscle:
- Radially arranged
- Opposes the action of the sphincter
- Contraction results in pupillary dilation (mydriasis)
- Dilation reflects the general state of sympathetic tone (e.g., pain, fear, anger)
Pupillary sphincter muscle:
- Circularly arranged near the pupillary margin
- Contraction results in decreased pupillary size (miosis)
- Innervated by parasympathetic fibers

Lens and Accommodation

Behind the iris is the lens.
The lens is suspended by suspensory ligaments.
These fibers are attached to the ciliary body.
The ciliary body is a muscular structure near the base of the iris.
The ciliary body helps with accommodation of the lens.
Increase or decrease in tension on the lens makes the lens curvature more or less convex.
This allows the lens to focus on near or far objects.

Vitreous Humor and Retina

Behind the lens is a chamber filled with vitreous humor.
Vitreous humor is a gelatinous fluid.
It gives the spherical shape of the eye.
Contains phagocytic cells.
Behind the vitreous humor lies the retina.
The retina is where light is transformed into electrical activity of neurons.

Optic Disc and Optic Nerve

The retina is interrupted at a point where axons of the retina ganglion cell layer leave the eye on their way to the brain – optic disc or blind spot.
The axons leaving the eye at the optic disc give rise to the optic nerve (CN II).
There are more axons in both optic nerves than in all the dorsal roots of the spinal cord.

Photoreceptor Cells

There are about 130 million photoreceptor cells in the retina.
There are two types of photoreceptor cells: cone cells and rod cells.
Each type consists of two portions: outer segment and inner segment.
Outer segment is the photosensitive region.
Inner segment is the metabolic region of the photoreceptor.
Rod cells have rhodopsin, which is responsible for the perception of shades of gray.
Rhodopsin has a low threshold of excitability, making it easy to stimulate by low-intensity light.
Rod cells are essential for night vision.
Cone cells have color pigments or cone pigments, which are responsible for the perception of color.
There are three different types of cones in primates, each with a different type of color pigment.
Most mammals have only two types of cones (dichromatic).

Visual System

Color is the brain's interpretation of differences in the wavelengths of light.
The visual system involves the activation of rhodopsin, leading to the activation of a G protein, transducin, and the hydrolysis of cGMP to 5'-GMP.
This leads to hyperpolarization, reducing the release of glutamate, and ultimately, the excitation of bipolar cells.
The ratio of rods to cone photoreceptor cells, as well as the ratio of photoreceptors cells to ganglion cells, affects the acuity of visual images.
The area centralis provides the highest visual acuity in the retina.

Eye and Camera

The eye is optically equivalent to the usual photographic camera.
The eye catches the light reflected by the objects and guides its passage until the image is formed.
The lens works by converging the light rays to a certain focal point on the retina.
The images formed on the retina are real, inverted, and smaller than the object.

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