L20 The Eye (Imported from Quizlet)

Detect prey, detect predators, detect mates, communicate

What does having vision allow us to do?

Third, visual

More than a ________ of the human neocortex is involved in analysing the ________ world

Electromagnetic, visible

Light is ___________________ radiation that is ________

Wavelength, frequency, amplitude

What 3 things does light have?

Distance between peaks or troughs

What is wavelength?

Number of waves per second

What is frequency?

Difference between wave peak and trough

What is amplitude?

Straight, rays, atoms, molecules

Electromagnetic light travels in ____________ lines, known as ______, until it interacts with ________ and ______________

Light rays interact in 3 ways

The speed of light differs between medium (e.g. slower through water than air, the greater the difference in speed in the two media the greater the angle of refraction)

Refraction occurs because ...?

Perpendicular

Refraction occurs towards a line that is ________________ to the border

Pupil, iris, cornea, sclera, extraocular muscles, optic nerve (cranial nerve II)

Name the 6 key components of the eye

Lets light inside the eye

What does the pupil do?

Contains muscles which control the amount of light entering the eye

What does the iris do?

Glassy, transparent covering of the pupil and iris that refracts light

Describe the cornea and its purpose

Continuous with cornea, forms the tough, protective wall of the eyeball to give it its shape

Describe the sclera and its purpose

Move the eyeball, controlled by oculomotor nerve (cranial nerve III)

What do extraocular muscles do and what are they controlled by?

Carries axons from retina to brain

What does the optic nerve (cranial nerve II) do?

Due to heavy pigment at back of the eye

Why does the pupil appear black?

Due to blood vessels on the surface of the retina

Reflected light appears bright red when light is shined, why?

This image shows the eye using an ophthalmoscope

Blood vessels and optic nerve, cannot sense light

What originates in the optic disk and what can't it sense?

Region of retina for central vision, devoid of large blood vessels to improve vision quality

Describe the macula, what is it devoid of and what does this entail?

Retina is thinnest here and is the area of higher visual acuity

Describe the fovea

To ensure that the area of interest in our visual field is focused on the fovea to give us the highest resolution image possible

Why do we move our eyes?

Sensory receptor cells and afferent neurons

What does the retina contain?

Zonal fibres, ciliary muscle

The lens is suspended by _______ ________ (ligaments) which are attached to the ___________ ___________, enabling stretching of the lens

Retina, fovea

Light rays must be focussed onto the ___________ (ideally the _______)

80, 20

Refraction occurs at the:

Cornea ~__%

Lens, remaining __%

Difference in refractive indices between the two media

The angle at which light hits the interface between these two media

The degree of refraction is determined by 2 things, what are they?

Speed, light, quicker, increased density

Refractive index is essentially a measure of ________ of ________ within it - so light moves ___________ through air (1.003) than the cornea (1.376) due to the ______________ ________ of the cornea

Air, water

Light arrives at the cornea through _____ but the cornea is mainly _________

Slowly, higher density

Light travels more _________ through water than air due to __________ __________ = refraction occurs

Focal distance

Distance from refractive surface to convergence of parallel light rays = ?

Almost parallel light rays

Cornea provides sufficient refraction to focus them on the retina

How does the lens accommodate distant objects?

Light rays are not parallel

Requires additional refraction to focus them on the retina

Provided by the flattening of the lens

How does the lens accommodate closer objects (<7m away)?

The refractive power to focus closer objects on the fovea

What does rounding of the lens increase and why is this done?

Elasticity, spherical

The lens has natural ____________ so if not stretched it will become more ___________

Emmetropic

Eye is ______________ when lens is flat and we are focussing a distant object

Eye is too short

Near objects are focussed behind the retina

Hyperopia is also referred to as farsightedness, describe this

Farsightedness

What kind of sight problem would this lens fix?

Eye is too long

Distant objects are focussed before retina

Too much refraction

Myopia is also known as near-sightedness, describe this

Near-sightedness

What kind of sight problem would this lens fix?

Cornea, fovea, retina, refraction

The _________ focuses most of the light on the _______ of the _______ due to the power of ______________

Accommodation of the lens, ciliary muscles

Closer objects require additional refraction, achieved by _________________ __ ____ _____ which is regulated by contraction and relaxation of the ____________ __________

Neural activity

What must the light focused on the retina be converted into?

Ganglion cells, bipolar cells

Light must pass through ____________ _____ and ___________ ______ before it reaches the photoreceptors

The pigmented epithelium

Light that passes all the way through the retina is absorbed by ...?

Layers are organised in reference to centre of the eye (i.e. photoreceptors are in the outer layer)

Cell bodies

What does the nuclear layer contain?

Synaptic connections

What occurs in plexiform layers?

Ganglion cells, amacrine cells, bipolar cells, horizontal cells, photoreceptors

What are the 5 cells of the retina?

Output from retina

What do ganglion cells do?

Modulate information transfer between GCs and BCs

What do amacrine cells do?

Connect photoreceptors to ganglion cells

What do bipolar cells do?

Modulate information transfer between photoreceptor and BCs

What do horizontal cells do?

Sensory transducers, both rods and cones

What are photoreceptors?

This image shows photoreceptors from the toad retina using scanning electron microscopy

Light-sensitive photopigments, light

Photoreceptors contain membranous disks which contain ______-___________ ______________ that absorb _______

Can't have high sensitivity and high resolution in single receptor

What is the duplicity theory?

True

There are separate systems for monochrome and colour (True or False)

Greater, higher, more

Rod photoreceptors have a _________ number of disks and a _________ photopigment concentration within each disk - meaning they are _____ likely to absorb photons

1000

Rods are ____ times more sensitive to light than cones

Vision in low light (scotopic) conditions (i.e. at night time)

What do rods enable?

Visual acuity/resolution

Rod photoreceptors have low _______ _______/_____________

92 million

There are ~__ _________ rods in each human retina

Fewer, lower

Cone photoreceptors have ________ disks so ________ photopigment concentration

During daylight (photopic) conditions

When are cone photoreceptors used?

Colour vision

What do cone photoreceptors enable?

Visual acuity/resolution, sensitivity

Cone photoreceptors have high __________ _____/___________ and lower _____________

5 million

There are ~_ _________ cones in the human retina

Intermediate

Rods and cones are used together in _______________ (mesopic) light conditions

The fovea

What contains most of the 5 million cones and no rods?

Low, low, high

The central retina has ____ convergence, _____ sensitivity and _____ resolution

High, high, low

The peripheral retina has ____ convergence, ____ sensitivity and _____ resolution

Sensitive, night vision

Rod photoreceptors are highly ___________ to light, allowing _______ _______

Photopigments, colour

Cone photoreceptors contain one of three ______________, enabling ________ perception during daylight

High, low, high resolution vision

The fovea contains a _____ concentration of cones, with a ____ convergence on retinal ganglion cells, making this area better for ______ ____________ _______