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The Eye - Coggle Diagram
The Eye
Structure and Function
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Blind spot
- A small area on the retina where the optic nerve leaves the eye
- No light-sensitive cells are present, so any image falling here is not seen
Ciliary Body
- Contains the ciliary muscle, which is attached to the lens
- The ciliary muscle changes the shape of the lens to allow for focusing at different distances
Cornea
- A transparent tissue that covers the front of the eye
- It refracts (bends) light more than any other part of the eye
Iris
- A muscular layer that contains circular and radial muscles
- It controls the size of the pupil and the amount of light entering the eye
- Also contains a pigment that absorbs light
Lens
- A transparent biconcave structure that refracts light passing through the eye
- It can change shape to adjust the degree of refraction and focus light
Optic Nerve
- A bundle of sensory nerve fibres that transmit visual signals from the eye to the brain
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Sclera
- The tough, opaque outer covering of the eyeball
- It protects the eyeball against mechanical damage and provides attachment points for eye muscles
Conjunctiva
- A thin, transparent membrane that protects the cornea against damage
- Tears lubricate the surface of the conjunctiva
Rods and Cones
Structure
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Rods and cones synapse with bipolar neurons, which then synapse with ganglion cells
Differences
Rods are more numerous and evenly distributed throughout the retina, while cones are concentrated in the fovea
Rods are very sensitive and operate in dim light, while cones operate only in bright light
Rods are insensitive to colour and provide monochromatic vision, while cones are sensitive to red, green, or blue light and provide colour vision
Rods have poor resolution and visual acuity, while cones have good resolution and high acuity
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Main features
Light control
- The iris controls the size of the pupil to regulate the amount of light entering the eye
- The circular and radial muscles in the iris work antagonistically to adjust the size of the pupil
Focusing
- The lens changes shape to focus light rays and allow clear vision at different distances
- The ciliary muscles attached to the lens control its shape and adjust the degree of refraction
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Accommodation
Focusing Light
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The cornea provides most of the refraction, but the lens can adjust the degree of refraction
Lens Adjustment
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For distant objects, the ciliary body relaxes, causing the lens to become thinner and less converging
For near objects, the ciliary body contracts, causing the lens to become thicker and more converging
Reflex Actions
- Accommodation and the control of light entering the eye are reflex actions
- They are automatic responses and not under voluntary control
Structure of the Retina
Layers
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Rods and cones form a layer inside the choroid, followed by a layer of bipolar neurons
Beyond the bipolar neurons, there is a layer of ganglion cells
The axons of ganglion cells form the optic nerve, which carries visual signals to the brain
Inverted Arrangement
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Light has to pass through the neurons before reaching the rods and cones, which can compromise light detection
The blind spot is where the optic nerve leaves the eye, and no light-sensitive cells are present
Retinal Convergence
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Cones synapse individually with bipolar neurons, providing higher visual acuity
Binocular Vision
Advantages
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The visual fields of both eyes overlap, allowing for accurate judgment of distance and depth perception
Binocular vision provides larger visual field, better visual acuity, and stereoscopic vision
Predatory Species
Predatory species, like humans and foxes, have eyes positioned at the front of their head for binocular vision
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Prey Species
Prey species, like rabbits, have laterally placed eyes on the side of their head
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Adjustment of Pupil Size
Iris Muscles
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The circular muscle constricts the pupil, while the radial muscles dilate the pupil
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