Neurophysiology: Vision- Pt 1

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Questions and Answers

What is the primary reason why animals have a wider peripheral vision than humans?

Because their visual fields of each eye completely overlap

Because they have a more efficient pupillary light reflex

Because they have more developed binocular vision

Because their visual fields of each eye do not completely overlap (correct)

Which nerve controls the lateral rectus muscle of the eye?

Olfactory nerve (facial nerve 1)

Trochlear nerve (facial nerve 4)

Abducens nerve (facial nerve 6) (correct)

Vestibulocochlear nerve (facial nerve 8)

What is the primary function of the area of centralis?

To regulate the pupillary light reflex

To enable binocular vision

To provide the greatest acuity (correct)

To provide peripheral vision

What type of vision do dogs have only in the area directly in front of them?

Binocular vision Signup and view all the answers

Which of the following is a characteristic of prey species' eyes?

They are laterally oriented, giving a wider view Signup and view all the answers

Choose the correct statement.

Monocular vision does not provide good depth perception Signup and view all the answers

Which nerve controls the superior oblique muscle of the eye?

Trochlear nerve (facial nerve 4) Signup and view all the answers

What is the main function of horizontal cells in the retina?

To transmit signals horizontally from the rods and cones to bipolar cells Signup and view all the answers

Which type of cells primarily transmit signals vertically from the rods, cones, and horizontal cells to ganglion and amacrine cells?

Bipolar cells Signup and view all the answers

What is the primary function of amacrine cells in the retina?

To transmit signals in two directions, either directly or horizontally from bipolar cells to ganglionic cells Signup and view all the answers

What is the primary neurotransmitter released by ganglionic cells in the retina?

Glutamate Signup and view all the answers

What is the primary purpose of the fovea in the retina?

To minimize image distortion Signup and view all the answers

What is unique about the structure of the fovea compared to the rest of the retina?

It has a higher concentration of cones Signup and view all the answers

What suspends the lens in the eye?

Suspensory ligaments Signup and view all the answers

Where is the lens located in the eye?

Behind the iris Signup and view all the answers

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

To change the curvature of the lens to focus on near or far objects Signup and view all the answers

What is the main purpose of the choroid in the eye?

To nourish the photoreceptors in the retina Signup and view all the answers

What is the term for the enlargement of the pupil in the dark?

Mydriasis Signup and view all the answers

What is the function of the tapetum lucidum in the eye?

To reflect light back onto the photoreceptors to enhance vision Signup and view all the answers

What type of muscle cells are found in the pupillary dilator muscles?

Smooth muscle cells Signup and view all the answers

What is the function of the iris in the eye?

To control the amount of light that enters the eye Signup and view all the answers

What is the term for the reduction of the pupil size in bright light?

Miosis Signup and view all the answers

What is the location of the tapetum lucidum in the eye?

In the choroid, behind the retina Signup and view all the answers

What is the result of pupillary sphincter muscle contraction?

Miosis Signup and view all the answers

What is the function of the optic nerve?

Carrying visual information from the eye to the brain Signup and view all the answers

What is the main function of rods in the retina?

Shades of grey and night vision Signup and view all the answers

What is the role of the outer segment in photoreceptors?

Photosensitive function Signup and view all the answers

What is the primary difference between rod cells and cone cells?

Rod cells are more sensitive to light, while cone cells are less sensitive Signup and view all the answers

What is the consequence of severe vitamin A deficiency?

Night blindness Signup and view all the answers

How many types of cone cells are present in primates?

3 Signup and view all the answers

What is the wavelength of the red sensitive pigment in cone cells?

570 nanometers Signup and view all the answers

What is the characteristic of most mammals in terms of color perception?

Dichromatic vision Signup and view all the answers

What is the proportion of rod cells in the retina?

95% Signup and view all the answers

Study Notes

Visual System

Vision is an integral part of neural function, and the eyes are an extension of the brain.
Animals have a wider peripheral vision than humans because their visual fields of each eye do not completely overlap.

Visual Field

The visual field is the spatial area seen with one eye.
The extent of overlap of the visual field depends on the anatomical placement of the eyes.
Prey species have laterally oriented eyes, giving them a wider view.
Dogs have binocular vision only in the area directly in front of them.
Monocular vision does not provide good depth perception.

Eye Structure

Fovea

The fovea is a minute area in the center of the retina, which is especially capable of acute and detailed vision.
In animals, it is called the "area centralis".
The fovea is composed almost entirely of cones, and their special long and slender bodies aid their detection in visual images.
The more cones present, the more colors that can be interpreted.

Lens

The lens is located behind the iris.
The lens is suspended by the suspensory ligaments, and these fibers are attached to the ciliary body.
The ciliary body is a muscular structure that helps with accommodation of the lens.

Choroid

The choroid consists of loose connective tissue with numerous vasculature and pigmented cells, and it serves a nutritive function.
Some diurnal animals have melanocytes that absorb light that has passed by the photoreceptors without stimulating them.
Nocturnal and most domestic mammals have a patch of reflective material that is called the "tapetum lucidum".

Iris

The iris is a diaphragm muscle that can contract/relax to control the rays of light that go into the eye via modification of the pupil diameter.
In the dark, pupils will dilate (mydriasis).
In the light, pupils will contract (miosis).
The iris has dilator and sphincter muscles.

Pupillary Dilator Muscles

The pupillary dilator muscles are radially arranged and oppose the action of the sphincter.
The pupillary dilator muscles are apart of the pigmented anterior epithelial cells, known as myoepithelial cells, which are composed of smooth muscle.
Its contraction results in pupillary dilation (mydriasis).

Pupillary Sphincter Muscles

Pupillary sphincter muscles are circularly arranged near the pupillary margin that are innervated by parasympathetic fibers.
Their contraction results in decreased pupillary size (miosis).

Eye Structure: Optic Nerve

The axons leaving the eye at the optic disk give rise to the optic nerve (cranial nerve 2).
There are more axons in both optic nerves than in all the dorsal roots of the spinal cord.

Photoreceptors (Rods and Cones)

There are about 130 million photoreceptor cells in the retina, which can either be cones or rods.
Rod and cone cells, each have an outer and inner segment.
The outer segment is the photosensitive region.
In cone cells, the outer segment is composed mainly of membranous invaginations.
In rod cells, the outer segment contains numerous flattened membranous sacs that are arranged like a stack of coins.
The membrane of these invaginations and sacs contains photopigments, which convert light stimulus to a receptor potential.

Rods

Rods are photochemical neurotransmitters that are responsible for the perception of shades of grey (black and white vision), making them essential for night vision.
Rod cells have rhodopsin, which has a low threshold of excitability.
Rhodopsin is easy to stimulate by low-intensity light.
Vitamin A is important for the formation of rhodopsin.

Cones

Cones are photochemical neurotransmitters that are responsible for the perception of color.
Cones have color pigments (or cone pigments), and they are less sensitive to light.
This lack of sensitivity means that cones require relative high-intensity light than rhodopsin.
Primates have the following 3 cone types: blue sensitive pigment (445 nanometers), green sensitive pigment (535 nanometers), and red sensitive pigment (570 nanometers).
These 3 types make up polychromatic vision.
The visual system mixes and contrasts the effects of each cone cell.

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Description

Learn about the visual system, its relation to the brain, and the differences in visual fields between humans and animals. Understand the concept of visual fields and how eye placement affects overlap.