The Eye Flashcards
Which structures contribute to the shape of the eyeball?
- Sclera
- Aqeuous Humour
- Vitreous Humour
Which structures contribute to the optical function of the eye?
- Cornea
- Choroid
- Ciliary Body
- Suspensory Ligaments
- Iris
- Lens
Which structures contribute to the sensory function of the eye?
- Retina
- Macula
- Fovea
Physical features & function of Sclera?
- White fibrous coat
- Protects the inner parts of the eyeball and gives shape to the eyeball
Physical features & function of Aqueous Humour?
- Watery fluid
- Contributes to bulk of pressure in eyeball to keep it firm and maintain shape
- Allows nutrients to circulate
Physical features & function of Vitreous Humour?
- Jelly-like substance
- Contributes slightly to pressure in eyeball
- Holds retina flush against choroid to provide even surface
Physical features & function of Choroid?
- Contains black pigmentations & highly vascularised
- Reduce internal reflection of light and provides nourishment to the eye
Physical features & function of Ciliary Body?
- Circular band of smooth muscle
- Responsible for controlling thickness of lens
Physical features & function of Suspensory Ligaments?
- Fibrous structures attached to ciliary body and lens
- Responsible for holding lens in position and changing shape of lens
Physical features & function of Iris?
- Contains circular and radial muscles
- Controls the amount of light entering the eye
Physical features & function of Retina?
- Contains pigemented layer and neural layer consisting of photoreceptors and other neurones
- Receives and transmits visual input to brain
What is the role of photoreceptors?
Photoreceptors are stimulated by light
- Rods detect shape and movement
- Cones are able to distinguish colour
What is the difference between rods and cones?
Rods function much better in low light due to a pigment called visual purple than cones
What is the blind spot in the eye?
It is the area where neurones converge to form the optic nerve leading out of the eye
- Absence of rods and cones -> Images falling onto this area cannot be perceived
How are focused images created in the eye?
Light enters the eye -> Refracted by cornea, aqueous humour then lens -> brought to a focus on retina -> stimulates rods or cones depending on light -> produces nerve impulses
What happens to the final image in the eye?
It is vertically and laterally inverted
Outline the process when the eye is seeing a nearer object
- Contraction of circular muscles of the ciliary body
- Leads to release in tension of suspensory ligaments
- Lens become thicker and more convex
- Increases focusing power
- Greater convergence of light rays
Outline the process when the eye is seeing a far object
- Relaxation of circular muscles of ciliary body
- Increase in tension of suspensory ligaments, becomes taut
- Lens become thinner and less convex
- Focusing power decreases
- Lesser convergence of light rays
What is the pupil reflex?
It is the involuntary reflex arc that occurs as a result of changes in light intensity.
Outline the Pupil reflex pathway
Photoreceptors -> Sensory Neurone -> Relay Neurone (Brain) -> Motor Neurone -> Iris Muscles (Effector)
Outline the pupil reflex in bright light
- Photoreceptors in the retina detect the increase in light intensity
- Nerve impulses generated by the photoreceptors
- Transmitted through the sensory neurone out of optic nerve
- To relay neurone in the brain then motor neurone
- To the iris muscles
- Circular muscles of iris contract -> radial muscles relax
- Results in constriction of pupil so less light enters eye
Outline the pupil reflex in dim light
- Photoreceptors in the retina detect the decrease in light intensity
- Nerve impulses generated by photoreceptors
- Transmitted through sensory neurone out of optic nerve
- To relay neurone then motor neurone
- To the iris muscles
- Radial muscles contract while circular muslces relax
- Dilation of pupil to allow more light to enter eye
Physical features & function of Macula
- Yellow oval spot on retina containing nerves and blood vessels
- Processes sharp clear vision
Physical features & function of Fovea
- In center of macula
- Cones only, no rods
- Responsible for sharp colour vision
