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sense organs Flashcards

1
Q

Where are the eyes located, and what is their form?

A

A: The two eyes are located in deep sockets or orbits on the front side of the head. Each eye is in the form of a ball.

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2
Q

How do the eyes rotate?

A

A: The eyes rotate with the help of six muscles.

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3
Q

What is the role of eyelids?

A

A:
The upper movable and the lower eyelids protect the outer, front surface of the eyes.
They can shut out light.

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4
Q

What do eyelashes do?

A

A: Each eyelid carries outwardly curved eyelashes which prevent larger particles from falling into the eye.

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5
Q

What is the function of eyebrows?

A

A: Eyebrows prevent raindrops or trickling perspiration from getting into the eyes.

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6
Q

What are tear glands and where are they located?

A

A: Tear glands, also called lacrimal glands, are located at the upper sideward portion of the orbit.

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7
Q

How do tear glands function?

A

A:
6-12 ducts of the gland secrete liquid over the front surface of the eye.
The movement of the eyelids (blinking) spreads this liquid, which mainly serves as a lubricant.

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8
Q

What are the other functions of tears?

A

A:
Tears keep the front surface of the eye clean by washing away dust particles.
They have an antiseptic property due to the enzyme lysozyme, which kills germs.

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9
Q

What is the role of tear ducts?

A

A: Tear ducts drain off the liquid into a sac lying at the inner angle of the eye. A nasolacrimal duct conducts the secretion into the nasal cavity.

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10
Q

What is conjunctiva?

A

A: Conjunctiva is a thin membrane covering the entire front part of the eye and is continuous at the inner lining of the eyelids.

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11
Q

What happens to the conjunctiva over the cornea?

A

A: Over the cornea, it is reduced to a single layer of transparent epithelium.

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12
Q

What is the sclerotic layer, and where is it visible?

A

A:
The sclerotic layer is made of tough, fibrous tissues and is white in color.
The white portion of the front of the eye is the sclerotic layer, visible through the conjunctiva.

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13
Q

What is the cornea?

A

A: The sclerotic layer bulges out and becomes transparent in the front region, forming the cornea, which covers the colored part of the eye.

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14
Q

What happens if the cornea turns opaque?

A

A: If the cornea turns opaque (white and non-functional), it can be replaced by a healthy cornea from a donated eye.

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15
Q

What is the choroid layer?

A

A:
The choroid layer is richly supplied with blood vessels for providing nourishment to the eye.
It contains a dark black pigment, melanin, which prevents light rays from reflecting and scattering inside the eye.

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16
Q

What is the ciliary body?

A

A:
The ciliary body is an expansion of the choroid in the front of the eye.
It contains circular muscles that alter the shape of the lens.

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17
Q

What is the iris?

A

A: The iris, an extension of the choroid, particularly covers the lens and leaves a circular opening in the center called the pupil.

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18
Q

What does the color of the iris indicate?

A

A: The blue, brown, or black color of the eye refers to the color of the iris.

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19
Q

What does the pupil do?

A

A: The pupil regulates the amount of light entering the eye by widening or constricting.

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20
Q

What is the retina?

A

A: The retina is the innermost layer of the eye, sensitive to light.

21
Q
A
22
Q

What are rod cells?

A

A:
Rod cells are sensitive to dim light and contain the pigment rhodopsin or visual purple.
They do not respond to color.

23
Q

What are cone cells?

A

A:
Cone cells are sensitive to bright light and responsible for color vision.
They contain the pigment iodopsin or visual violet.

24
Q

Where are cone cells concentrated?

A

A: Cone cells are mostly confined to the yellow spot, the area of best vision and color perception.

25
Q

What is the yellow spot?

A

A:
The yellow spot (macula lutea) lies at the back of the eye on the horizontal axis of the eyeball.
It is the region of brightest vision and color perception.

26
Q

What is the blind spot?

A

A:
The blind spot is lateral to the yellow spot.
It contains no sensory cells, making it a point of no vision.

27
Q

What is the lens?

A

A: The lens is a transparent, flexible, biconvex crystalline body located just behind the pupil.

28
Q

What is the suspensory ligament?

A

A: The lens is collectively held in position by fibers called the suspensory ligament, which attaches to the ciliary body.

29
Q

What does the ciliary body do for the lens?

A

A: The ciliary body contains muscles that contract and relax to change the shape of the lens for viewing objects at different distances.

30
Q

Compare rods and cones in terms of number.

A

A: Rods are more numerous, while cones are less numerous.

31
Q

Compare the location of rods and cones.

A

A: Rods are mostly at the periphery of the retina, while cones are mostly located at the center

32
Q

Compare the sensitivity of rods and cones.

A

A: Rods are very sensitive to dim light, while cones are stimulated only by bright light.

33
Q

Compare the function of rods and cones.

A

A:
Rods respond to most wavelengths of visible light except red.
Cones allow color perception due to three types of cones, each responsible for different wavelengths.

34
Q

What is the structure of the lens in the eye?

A

The lens is a transparent, flexible, biconvex crystalline body located just behind the pupil. It contains transparent lens fibers, long, thin cells that have lost their nuclei.

35
Q

How is the lens held in place?

A

Held by suspensory ligaments attached to the ciliary body.
The ciliary body is part of the choroid layer and located at the junction of the choroid and iris.

36
Q

Where is the ciliary body located, and what is its role?

A

A:

The ciliary body lies at the junction of the choroid and the iris and is part of the choroid.
It contains muscles that, upon contraction and relaxation, change the shape of the lens, enabling it to focus on objects at different distances.

37
Q

How does the lens divide the inner cavity of the eyeball?

A

A:
The lens, along with the suspending structures, divides the inner cavity into two chambers:

Aqueous Chamber: In front of the lens.
Vitreous Chamber: Behind the lens.

38
Q

What is the aqueous chamber, and what does it contain?

A

A:

The aqueous chamber lies between the lens and the cornea.
It is filled with a clear, watery liquid called aqueous humor (aqueous = watery, humor = fluid).

39
Q

What are the functions of aqueous humor?

A

Keeps the lens moist.
Protects the lens from physical shock.

40
Q

What is the vitreous chamber, and what does it contain?

A

A:

The vitreous chamber is the largest cavity of the eyeball, located behind the lens.
It is filled with a transparent, jelly-like thicker fluid called vitreous humor (vitreous = glassy, humor = fluid).

41
Q

What are the functions of vitreous humor?

A

A:

Helps in maintaining the shape of the eyeball.
Protects the retina.

42
Q

How do light rays enter the eye?

A

A:
Light rays from the object enter the eyes through the transparent structures: conjunctiva, cornea, aqueous humor, lens, and vitreous humor.

43
Q

How is the image focused in the eye?

A

A:

The curvature of the cornea converges the light rays to some extent.
The lens further converges them to form a real, inverted image on the retina.

44
Q

How are nerve impulses transmitted from the retina to the brain?

A

A:
The light energy of the image causes chemical changes in the sensitive cells (rods and cones). These changes generate nerve impulses, which travel through the optic nerve to the brain’s visual area.

45
Q

How does the brain interpret visual information?

A

A:
The brain interprets the upright position of objects, even though the image formed in the eye is inverted.

46
Q

What is accommodation in the eye, and how is it achieved?

A

A:

Accommodation is the process of focusing the lens to see objects at different distances.
For distance vision, the lens is flattened and thinner.
For near vision (less than 6 meters), the lens becomes more convex or rounded.
These changes are brought about by the ciliary muscles.

47
Q

What is dark adaptation, and what causes it?

A

A:
Dark adaptation occurs when moving from a bright area to a dark room, such as a cinema hall. Causes:

Regeneration of rhodopsin (pigment in rods) broken down in bright light.
Dilation of pupils, allowing more light into the eyes.

48
Q

What happens during light adaptation?

A

A:
When moving from a dark room to a bright area, there is a dazzling effect initially. Causes:

Bleaching of rhodopsin, reducing sensitivity of rods.
Constriction of pupils, reducing light entry.

49
Q

How does the eye perceive color?

A

A:

Cones in the retina are responsible for color vision and are stimulated only in bright light.
Rods function in dim light and do not detect color.

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