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ANP1106 > Lecture 5 - Vision > Flashcards

Lecture 5 - Vision Flashcards

1
Q

What are the accessory Structures of the Eye?

A

Eyebrows
Eyelids
Conjuctiva
Lacrimal Apparatus
Extrinsic Eye Muscles

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2
Q

Describe the Conjunctiva

A

Transparent mucosa membrane that produces a lubricating mucosa secretion

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3
Q

Palpebral Conjunctiva

A

Membrane that lines underside of the eyelid

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4
Q

Bulbar Conjunctiva

A

The membrane that covers the white of the eyes (NOT THE CORNEA)
- bloodshot eyes are due to small
blood vessels found in this
membrane

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5
Q

Conjunctival Sac

A

Space between palpebral and bulbar conjunctiva
- this is the area where the contact
lens rests

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6
Q

Describe the Lacrimal Apparatus Step 1

A

The lacrimal gland produces and secretes tears

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7
Q

How many extrinsic eye muscle and their functions

A

6 traplike muscles that
- originate from bony orbit and inserted on eyeball
Enable eye to follow moving objects, maintain shape of eyeball and hold it in oribit

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8
Q

What are the motor inputs of the eye (3)

A

III. Oculomotor
IV. Trochlear
VI. Abducens

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9
Q

What are the 3 wall layers of the eyeball

A
  1. fibrous layer
  2. Vascular layer
  3. Inner layer
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10
Q

What is the internal Cavity of the Eye filled with

A

Humors Fluid

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11
Q

What separates the internal cavity of the eyeball into anterior and posterior

A

Lens

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12
Q

What muscle causes the eye to constrict?

A

Spinchter pupillae muscle
- causes it to contract and the pupil to constrict

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13
Q

What muscle causes the pupil to dilate?

A

Dilator pupillae muscle contracts and pupil dialtes

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14
Q

Name the 2 muscles of the Iris

A

The Spinchter Pupillae
The Dilator Pupillae

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15
Q

How does the eye focus on Distant and Close Vision?

A

The cillary muscle and the cillary zone focus an imahe by change the shape of the lens
- they are arranged sphincterlilke around the lens
- cillary muscle contraction loosens the ciliary zone fibers and relaxation tightens them

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16
Q

Explain how the eye focuses on distance

A

Ciliary muscle is relaxed, pulling on ciliary zonule and the lens are stretched flat

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17
Q

Myopia

A

Nearsightedness
Eyeball is too long, so focal pointy is in the front of the retina

Corrected with a concave lens

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18
Q

Explain Focusing for Close Vision

A

Requires eyes to make active adjustments using three muscles simultaneously
Accommodation of the lens
- changing lens shape to increase
refraction
Constriction of pupils
- constriction of the pupils to prevent most divergent light rays from entering eye - mediated by the parasympathetic nervous system
Convergence of the eyeballs
- medial rotation of eyeballs causes convergence of eyes towards object being viewed - controlled by the somatic motor neuron innervaytion on medial eye muscle movement

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19
Q

Hyperopia

A

Farsightedness
Eyeball is too short, so focal point is behind retina
corrected with convex lens

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20
Q

Optic Disc

A

found in the retina -
Site where optic nerve leaves the eye
It lacks photoreceptors (blind spot)

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21
Q

Describe the Pigmented Layer of the Retina

A

Single-cell-thick lining next to choroid
Extend anteriorly, covering ciliary body and iris
Function:
Absorbs light and prevents its scattering
Phagocytizes photoreceptors cell fragments
Stores vitamin A

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22
Q

Describe the Neural layer of the Retina

A

Composed of 3 types of neurons:
1. Photoreceptors
2. Bipolar cells
3. ganglion Cells
Signals spread from photoreceptors to bipolar cells to ganglion cells

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23
Q

Describe the Rods in the Retina

A

Dim light, peripheral vision receptors
more numerous and more sensitive to light than cones
No colour vision or sharp images
Numbers are greatest at the periphery

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24
Q

Describes the cones of the Retina

A

Vision receptors for bright light
High resolution colour vision

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25
Photoreceptors of the Retina
(rods and cones) are modified neurons that resemble upside-down epithelial cells and consist of a cell body, synaptic terminal and two segments
26
Outer Segment (Photoreceptor)
light-receiving region that contains visual pigments (photopigments) that change shape as they absorb light
27
Inner Segment (photoreceptors)
joins cell body is connected via cilium to outer segment and top cell body via outer fiber
28
Phototranduction
pigment captures photon of light energy, which is converted into a graded receptor potential
29
Rhodopsin
Visual pigment of the eye Deep purple pigment of the rod, arraned in the outter segment
30
3 steps of rhodopsin
1. pigment synthesis 2. pigment bleacking 3. pigment regeneration
31
Retinal
key light absorbing molecule that combine with one of four proteins called opsin to form visual pigments - synthesized from vitamin A
32
How many opsins are rhodopsin (found in rods only)
4
33
How many opsins are found in cones and what are they?
3 Red Blue Green
34
Can more than one cone be triggered at a time
yes cone wavelength overlap which allows us to see a variety of hues ex: yellow light stimulates red and green cones - but if more red are triggered we seen green
35
Retinal Isomer
Different 3-D forms Bent: 11-cis0retinal Straight - all-trans-retinal conversion of bent to straight initiates reactions that lead to electrical impulses along the optic nerve
36
Formation and Breakdown of Rhodispin
(1) pigment synthesis: 11-cis-retinal (ben) derived from Vitamin A is comboined with opsin to form rhodopsin (2) Pigment Bleaching: light absorption by rhodopsin triggers a rapid series of steps in which retinal changes shape (11cis to all-trans) and eventually release opsin (3) Pigment Regeneration: enzymes slowly convert all-trans to its 11-cis form in cells of the pigmented layer - requiring ATP
37
5 events of Phototransduction
(1) retinal absorbs light and changes shape. Visual pigment activated (2) Visual pigment activates transducin (G-Protein) (3)Transducin activates photodiestrase (4)Converts cGMP into GMO causing cGMP levels to fall (5)cGMP levels fall, cGMP-gated cations channels close, resulting in hyperpolarization
38
Signal Tranmission of the Retina
(1) cGMP-gation channels open allowing cation influx. Photoreceptors depolarize (2) Volatge-gated Ca+ channels open in synaptic terminals (3) Neurotransmitter is released continuously (4) Neurotransmitter causes IPSP in bipolar cell - hyperpolarization results (5) Hyperpolarization closes voltage-gated Ca+ channels inhibiting neurtranmitter release (6) No EPSPs occur in ganglion cell (7) No action potential occurs along the optic nerve
39
How is information processed in the Retina
Photoreceptors and bipolar cells generate only graded potentials (EPSP and IPSP) (NOT APS) when light hyper polarizes photoreceptor cells they stop release inhibitory neurotransmitters glutamate to bipolar cells Bipolar cells (no longer inhibited) depolarize, release neurtranmitter onto ganglio cells Ganglion cells generate APs tranmitted in optic never to the brain
40
Light and Dark Adaptation
Rhidopsibn is so sensitive that bleaching occurs even in starlight - rods are virtually nonfunctional Cones respons to bright light and adctivation of rods and cones depends on light adaptation dark adaptation
41
Light Adaptation
when moving from darkness into bright light we see glare - both rods and cones are strongly stimulated - large amount of pigment are broken down instantaneously = glare pupils restrict Visual acuity improves over 5-10 minutes - rod system turns odd, transducins move to the inner segment retinal sensitivity decreases cones and neurons rapidly adapt
42
Dark Adaptation
When moving from bright light into darkness, we see blackness because cones stop functioning in low intesity lihgt bright light bleached rod pigments, so thet are still turned off pupils dilate rhodospin accumulate in dark, so retinal sensitivity starts to increase - transducin return to out segment - sensitvity increases within 20-30 minutes
43
Visual Pathway to the Brain
axons of retinal ganglion cells form the optic nerve medial fibers from each eye cross over at the optic chiasma then continue on as optic tracts - each tract contains fibers from lateral (temporal) aspect of the eye oin the same side and medial (nasal) aspect of the opposite eye - each carries information from the same half of the visual field fibers of the optic tract contine on to lateral geniculate nuclei of the thalamus thalamic neurons form optic radiation which projects to primary visual correct in occipital lobes (where conscious perception of visual images occurs) other optic tract fibers send branches to the midbrain ending in superior colliculi (controls extrinsic eye movement) - a small subset of ganglion cells in retina contain melanospin which porjects to pretectal nuclei (puilary reflex) and surachiasmaytic nucleus of hypothalamus
44
Explain Depth Perception
Both eyes view the same image from slightly different angles, visual cortex fuses these slightly different images, resulting in a three dimensional image, which leads to depth perception and requires input from both eyes
45
What is the purpose of accessory structures of the eye?
To protect the eye and aid in eye function
46
Describe step 2 of the Lacrimal Apparatus
Tears enter the conjunctival sac via the excretory ducts of the lacrimal gland
47
Describe step 3 of the lacrimal apparatus
Tears flow down and across the eyeball
48
Describe Step 4 of the lacrimal apparatus
Tears enter the lacrimal canaliculi at openings called lacrimal puncta
49
Describe step 5 of the lacrimal appartus
Tears drain into lacrimal sac
50
Describe step 6 of the lacrimal appartus
From the lacrimal sac tears empty via nasolacrimal duct into the inferior meatus of the nasal cavity
51
Parasympathetic fibers contract ciliary muscles for close vision True or False
True
52
The optic nerve leaves the eye at the posterior opening of the _____
Choroid
53
The vestibular nuclei controls
Extrinsic eye muscles
54
Describe the Sclera
The white of the eye and is an anchoring site for extrinsic eye muscles
55
What is astigmatism?
Defective curvature of the cornea or lens of the eye that leads to blurry images
56
Light becomes visible at:
400-700nm
57
Describe the pupillary light reflex
Fast contraction of the inner muscle of the iris in response to excess light
58
What is the function of the ciliary zonule?
Help hold lens in an upright position
59
What is Strabismus
Crossed-eyes
60
The fibrous layer of the eye is dense avascular CT and split into what 2 parts
1. Sclera 2. Cornea
61
What is the function of the cornea?
To allow light to enter the eye
62
What are the muscles that help us look side to side
the medial and lateral rectus muscles

ANP1106 (10 decks)

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