phys- the eye
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what are the protective mechanisms that help protect eyes from injury?
- Eyeball is sheltered by bony socket in which it is positioned
- ---Act like shutters to protect eye from environmental hazards
- ---Trap fine, airborne debris such as dust before it can fall into eye
- ---Continuously produced by lacrimal glands
- ---Lubricate, cleanse, bactericidal
- located on the superior lateral eyelid
- produce tears, which drain into the nasal cavity via the lacrimal ductfunction to moisten and lubricate the eye surface, and it has enzymes to kill bacteria (which thrive in warm, moist conditions)
light travels thru:
- pupil in iris,
- through vitreous humor,
- through axons, ganglion cells and bipolar cells,
- to photoreceptors next to pigmented layer
interior consists of what 2 fluid-filled cavities separated by the lens:
- posterior cavity
- anterior cavity
- Larger cavity between lens and retina
- Contains semifluid, jellylike substance = vitreous humor
- Important in maintaining the spherical shape of eyeball
- Anterior cavity between cornea and lens
- Contains clear, watery fluid = aqueous humor
- Carries nutrients for cornea and lens
- Produced by capillary network within ciliary body
function of the iris:
controls the amount of light entering the eye
iris contains what 2 sets of smooth muscle networks:
- Circular (or constrictor) muscle
- Radial (or dilator) muscle
Pigment in iris is responsible for:
what is the latest used for the basis of identity?
- varied flecks and lines
- they are unique for each individual
the pupil is the:
size is adjusted by:
- Round opening through which light enters the eye
- by variable contraction of the iris muscles to admit more or less light as needed
Divergent light rays reaching the eye from many directions must be:
bent to focus into a point on the retina to provide an accurate image
Convergence is needed to:
Therefore the refractive surfaces of the eye are:
- to bring an image to a focal point
When we look at an object, light rays gets focused on the retina.
The image on the retina happens after:
rods & cones in a particular area are excited
for the rod and cone to be excited, what has to happen:
light rays have to be bent and focused
The light rays are bent as they pass through:
the cornea and bent further as they pass through the lens and humors.
The Convex structures of the eye produce:
convergence of diverging light rays that reach eye
what are the 2 structures most important in eye’s refractive ability?
- ---Light rays pass through cornea and into interior of eye
- ---Contributes most extensively to eye’s total refractive ability
- ---Refractive ability remains constant because curvature never changes
- ---Refractive ability can be adjusted by changing curvature as needed for near or far vision
turning or bending of light
- Lens changes shape to facilitate focusing
- Shape change is dependent upon the suspensory ligaments
Strength of lens depends on its shape, which is regulated by:
Age related reduction in accommodation ability:
The ciliary body contains:
smooth muscle arranged in a circular fashion like a sphincter.
When the ciliary muscle is relaxed, the ligaments are:
and the lens is:
- Flat for viewing objects at some distance from the eye
When focusing on near objects, the sphincter-like ciliary muscle:
- Ciliary muscle contract
- ligaments relax
- lens becomes round
When focusing on far objects, the sphincter-like ciliary muscle:
- Ciliary muscle relax
- ligaments under tension
- lens if flattened
The eye must focus light rays from the environment on:
The rods and cones, the photoreceptors of the retina
The light energy must be transformed into:
Electrical signals to transmit the information to the CNS
Retina is the:
Receptor containing portion, is actually an extension of the CNS
Neural portion of the retina consists of what 3 layers of excitable cells:
- Outermost layer containing rods and cones
- Middle layer of bipolar cells
- Inner layer of ganglion cells
Which cells join to form the optic nerve?
Axons of ganglion cells
The optic nerve is the point on the retina where:
and what is this point called:
- Optic nerve leaves the optic disc
- Region is often called the blind spot bc no image can be detected here bc of the lack of rods and cones
- Pinhead-sized depression in exact center of retina
- Point of most distinct vision
- Has only cones
- Area immediately surrounding fovea
- Fairly high acuity
- Leading cause of blindness in western hemisphere
- “doughnut” vision
What type of cells do the photoreceptors have?
And how many parts do they consist of?
- Rod and cone cells
- Consists of 3 parts:
- Outer segment: Detects light stimulus
- Inner segment: Contains metabolic machinery of cell
- Synaptic terminal: Transmits signal generated in photoreceptor on light stimulation to next cells in visual pathway
Photopigments undergo chemical alterations when activated by light. When happens when photopigment becomes activated?
leads to a receptor potential in the photoreceptor that leads to generation of action potentials in the ganglion cells, which transmit the information to the brain for processing.
Photopigments consists of what 2 components?
- -Protein that is integral part of disc membrane
- -Derivative of vitamin A
- -Light-absorbing part of photopigment
Receptors ______ when stimulated.
Photoreceptors _______ on light absorption.
What is the cellular pathway of signaling after a photoreceptor gets activated?
Signals bipolar cells, which signal ganglion cells to generate (or not) APs: axons run on internal surface to optic nerve which runs to brain
What are the 4 different photopigments?
- Rod pigment
- ---Provide vision only in shades of gray
- ---Rhodopsin: Absorbs all visible wavelengths
- Cone pigments:
- ---Respond selectively to various wavelengths of light
- ---Make color vision possible
- -Red cones
- -Green cones
- -Blue cones
Location of gene for color blindness is on which chromosome?
- So it affects more boys than girls
Sensitivity of the eyes varies thru:
- Dark adaption
- Light adaption
What is dark adaption?
- Can gradually distinguish objects as you enter a dark area.
- Due to the regeneration of rod photopigments that had been broken down by previous light exposure.
What is light adaption?
- Can gradually distinguish objects as you enter an area with more light.
- Due to the rapid breakdown of cone photopigments
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