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Secondary 3 Biology > the human eye > Flashcards

the human eye Flashcards

1
Q

describe the human eye?

A
  • each eyeball lies in a hollow in the skull called the orbit
  • each eyeball is attached to the skull by rectus muscles which control eye movement
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2
Q

what are the parts of the eye that can be seen?

A
  • iris
  • conjunctiva
  • pupil
  • eyelash
  • upper eyelid
  • lower eyelid
  • sclera
  • conjunctiva
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3
Q

what is the function of the iris?

A
  • circular sheet of muscles
  • contains pigment that gives eyes colour
  • has two sets of involuntary muscles, circular and radial muscles
  • control the amount of light entering the eye
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4
Q

what is the function of the pupil?

A
  • hole in the centre of the iris

- allows light to enter eye

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5
Q

what is the function of the sclera/scelrotic coat

A
  • tough, white outer covering of eyeball
  • continuous with cornea
  • protects eyeball from machenical damage
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6
Q

what is the function of the conjunctiva?

A
  • thin, transparent, mucous membrane covering scelra in front of it
  • secretes mucus to keep front of eyeball moist
  • continuous with skin of eyelids
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7
Q

what is the function of eyelashes?

A
  • shield eye from dust particles
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8
Q

what is the function of eyelids?

A
  • protect cornea from mechanical damage
  • squint to prevent excessive light from entering eye and damaging light sensitive retina
  • blinking spreads tears over cornea and conjunctiva and wipes dust particles off cornea
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9
Q

what is the function of tear glands?

A
  • secretes tears that:
  • wash away dust particles
  • keep cornea moist for atmospheric oxygen to dissolve. Dissolved oxygen diffuses into cornea
  • lubricates conjunctiva, helping to reduce friction when eyelids move
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10
Q

name the parts of the internal eye?

A
  • ciliary body
  • superior rectus muscle
  • choriod
  • scelera
  • foreal yellow spot
  • blind spot
  • vitreous chamber
  • retina
  • inferior rectus muscle
  • lens
  • aqueous chamber
  • cornea
  • iris
  • suspensory ligament
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11
Q

what is the function of the cornea?

A
  • transparent layer, continuous with sclera
  • refracts or bends light rays into eyes
  • causes most refraction of light that occurs in eye
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12
Q

what is the function of the aqeous chamber?

A
  • space between cornea and lens
  • filled with aqueous humour, a transparent water fluid
  • keeps front of eyeball firm, and helps to refract light into the pupil
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13
Q

what is the function of the lens?

A
  • transparent, circular and biconvex structure. Elastic

- changes shape and thickness to focus light onto retina

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14
Q

what is the function of the ciliary body?

A
  • contains ciliary muscles

- controls curvature or thickness of lens

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15
Q

what is the function of the suspensory ligament?

A
  • connective tissue, attaches edge of lens to ciliary body

- transmits force from ciliary muscles to the attached lens

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16
Q

what is the function of vitreous chamber?

A
  • space behind lens, filled with vitreous humour, a transparent, jelly-like substances
  • keeps eyeball firm and helps to refract light onto retina
17
Q

what is the function of the retina?

A
  • innermost layer of eyeball
  • light-sensitive, contains photoreceptors
  • site whre images are formed
18
Q

what is the function of the forea/yellow spot?

A
  • small depression in retina
  • site where images are normally focused
  • enables detailed colour vision in bright light
19
Q

what is the function of the blindspot?

A
  • region where optic nerve leaves eye

- not sensitive to light

20
Q

what is the function of the choriod?

A
  • middle layer of eyeball between retina and sclera
  • pigmented black to prevent internal reflection of light
  • contains blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste products
21
Q

what is the function of the optic nerve?

A
  • transmits nerve impulses to brain when photoreceptors in retina are stimulated
22
Q

what are the photoreceptors in the retina?

A
  • consists of rods and cones

- connected to nerve endings from optic nerve

23
Q

what is the function of cones?

A
  • enable us to see colours in bright light
  • red, green and blue cones
  • each cone contains different pigments which absorbs light of differing wavelengths
  • do not work well in dim light
24
Q

what is the function of rods?

A
  • enable us to see in dim light, but only in black and white
  • more senstivie than cones
  • sensitive to dim light because they contain the pigment visual purple which is bleached in bright light
  • visual purplse must be reformed to see in dim light again
  • takes awhile to reform + requires vitamin A
25
Q

what is pupil reflex?

A
  • reflex action
  • pupil changes size due to change in light intensity
  • eyelids may come closer to screen off part of the light if it is too bright
  • prevents excessive light from damaging retina
26
Q

describe the pathway of the neurones?

A

change in light intensity –> photoreceptors in retina are stimulated and generate nerve impulses –> nerve impulses transmitted along sensory neurone in optic nerve to brain –> nerve impulses transmitted across a synhapse to relay neurone in brain –> nerve impulses transmitted across another synapse to motor neurone and to effector

27
Q

how does the iris control the amount of light entering the eye in bright light?

A
  • circular muscles of iris contract
  • the radial muscles of iris relax
  • pupil becomes smaller or constricts
    this reduces amount of light entering eye
28
Q

how does the iris control the amount of light entering the eye in dim light?

A
  • circular muscles of iris relax
  • radial muscles of iris contract
  • pupil dilates. This includes the amount of light entering the eye
29
Q

how do we see?

A
  1. light rays are refracted through cornea and the aqueous humour onto the lens
  2. lens cause further refraction and rays are brought to a focus on the retina
  3. image on retina stimulates either rod or cones, depending on light intensity
    - image formed on retina is:
    * upside down
    * laterally inverted
    * diminished
    - nerve impulses produce when light falls on rod/come. Transmitted via optic nerve to brain, which interpret impulses so object is seenat right size
30
Q

define focusing?

A

adjustment of lens of the eye so that clear images of objects at different distances are formed on retina

31
Q

what happens when focusing on distant object (>7m)

A
  1. ciliary muscles relax, pulling on the suspensory ligament
  2. suspensory ligament becomes taut, pulling on edge of lens
  3. lens become thinner and less convex, increases focal length
  4. light rays from distanct object are sharply focused on retina
  5. photoreceptors stimulated
  6. nerve impulses produce are transmitted by optic nerve to brain. Brain interprets impulses and person sees the object
32
Q

what happens when focusing on nearby object?

A
  1. ciliary muscles contract, relaxing their pull on on suspensory ligaments
  2. suspensory ligaments slacken, relaxing their pull on the lens
  3. the lengs, being elastic, becomes thicken and more convex, decreases focal length
  4. light rays from near objects are sharply focused on retina
  5. photoreceptors stimulated
  6. nerve impulses produced are transmitted by optic nerve to brain. Brain interprets the impulses and person sees the object

Secondary 3 Biology (13 decks)

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