The mammalian eye

By Sze Nga CHAN Cecilia

Content1. Structure and function of eye2. Properties in focusing an image3. Features of retina4. Structure of rod cells and cone cells5. Role of rod cells and cone cells6. Sensitivity of vision7. Acuity of vision8. Effect on rhodopsin

Features and Functions Layers1. Sclera

-tough layer-form the transparent cornea -transparent conjunctiva covers the cornea-transmission-Refraction

2. Choroid-rich in blood vessels-black in color-prevent internal reflection of light

3. Retina-photoreceptive-contains rod cells and cone cells

Features and Functions1. Aqueous humour

-behind the cornea-a clear salt solution

2. Vitreous humour-behind the lens-jelly-like dark solution

3. Fovea- contains most of the rod cells and cone cells- light rays are focused onto it

4. Blind spot-the connection point of optic nerve-no rod cells or cone cells can be found

How to adjust the amount of light goes into the eye?

Strong light-circular muscle contracts-radial muscle relaxes-pupil becomes smaller -less light rays enter the eye

Iris is a muscular diaphragm surrounding the pupil

How to adjust the amount of light goes into the eye?

Weak light-circular muscle relaxes-radial muscle contracts-pupil becomes dilate- more light rays enter the eye

http://www.youtube.com/watch?v=JadaWSDxBYk&feature=related

How to adjust the focus point?

A near target-ciliary muscles contract-suspensory ligament slack-lens more rounded shape(more convex)-light focused on retina

How to adjust the focus point?

A far target-ciliary muscles relax-pull the suspensory ligament taut-lens flat (pull in)- light focused on retina

Features of retinaThree main layers

Photoreceptorrod cells and cone cells

Bipolar neurones

Sensory neurones

Rod cells and Cone cells

Feature Rod cells Cone cells

Distribution -Evenly throughout the retina-absent from the fovea

-mainly found in the fovea

Sensitivity to light -very sensitive to light, can operate in dim intensities-insensitive to colour

-sensitive to bright light , can operate in high light intensities only-sensitive to red, green, blue light

Visual acuity (details) -produce poorly resolved images

-produce high-resolved images

Light-sensitive pigments

-rhodopsin -three types of iodopsin (red, green, blue)

Synapse with bipolar neurone

Group of rod cells synapse with one bipolar synapse

Each cone cell synapse individually with a single bipolar synapse

Effect on rhodopsin

1. Light energy is absorbed by retinal

2. Rhodpsin separate to retinal and opsin

3. Opsin causes the closure of Na channel

4. Less inhibitory neurotransmitter is released

5. Less inhibition of bipolar neurons

6. Depolarisation7. Action potential 8. Optic nerve

Reformation of rhodopsinCatalystATPTrans-retinal + opsin rhodopsin

In iodopsin in cone cells, the same reaction happen

but it breaks less easily and reforms more slowly

Exam question

Toop ticn e rve

The diagram shows the distribution of rods and cones in the retina of a human eye. Using information in the diagram, explain how:

(i) rod cells enable us to see in conditions of low light intensity;

(ii) cone cells enable us to distinguish between objects close together.

Several rod cells to each neuron / bipolar cell/each synapse/convergenceprinciple of additive effect of light striking several rod cells/(spatial)summation;

Each cone connects to a single neurone/no convergence;brain receiving information from each cone cell individually

Reference http://www.virtualmedicalcentre.com/uploads/VMC/Di

seaseImages/2133_eye_anatomy_label_v2_700.jpg http://upload.wikimedia.org/wikipedia/commons/2/2e/

Mona_Lisa_detail_eyes.jpg http://thebrain.mcgill.ca/flash/d/d_02/d_02_m/d_02_m

_vis/d_02_m_vis_1a.jpg http://www.sapdesignguild.org/editions/edition9/imag

es/accomodation.png http://www.insightseyecare.net/EyeEducation/retinaN

euronalLayers.jpg http://cas.bellarmine.edu/tietjen/Laboratories/Eye07.g

if http://4.bp.blogspot.com/_GrFZK0cwrtk/SCXHEojGp5I/

AAAAAAAAAB8/7y0hnATxxFg/s400/6a00d41423ae593c7f00d41422a3576a47-320pi.jpg

http://images.ifguk.co.uk/products/609/609-large1.jpg All information obtained in the internet on 18th

April,2010

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Good luck in EXAM!