Special Senses - Eyes And Vision Flashcards
Photoreceptors
70% of all sensory receptors are in the eyes
Protection for the eye?
- Most eyes are enclosed in a bony orbit
- A cushion of fat surrounds most of the eye
- eyebrows and eyelids protect eye by blocking debris, excess light, sweat, and spreading moisture (from tears) over the surface of the eye
- Eyelids and eyelashes? - structure
Ciliary glands - located between eyelashes and trap dust
Tarsal glands lubricate eye (oily substance) by helping prevent evaporation of tears
- Conjunctiva? - structure
Clear membrane that covers white part of eye. Does not cover the cornea and secretes mucus to lubricate eye so that eyelid can slide smoothly
- Extrinsic eye muscles
Sex muscles attached to outer surface of eye. Produce eye movements
What each eye muscle does
Lateral rectus (VI) - moves eye laterally (toward head)
Medial rectus - moves eye medially (toward nose)
Superior rectus - elevates eye and turns it medially (up and slightly inward)
Inferior rectus - depresses eye and turns it medially (down and slightly inward)
Superior oblique (IV) - elevates eye and turns it laterally (up and slightly outward)
Inferior oblique - depresses eye and turns it laterally (down and slightly outward)
- Lacrimal apparatus? - structure
Lacrimal gland - produces tears (lacrimal fluid)
Lacrimal canals - drain tears from eyes to lacrimal sac
Lacrimal sac - provides passage of tears towards nasal cavity
Nasolacrimal duct - empties tears into nasal cavity
Function of lacrimal apparatus?
Protects, moistens and lubricates eye. Provides nutrients and oxygen to conjunctiva. Reduces friction and removes debris
Properties of lacrimal fluid
Dilute salt solution. Contains antibodies and lysozyme (enzyme helping to defend against infection)
3 layers forming wall of eyeball?
- Sclera layer (white of the eye plus cornea) - outside fibrous layer
- Choroid layer - middle vascular layer
- Retina layer - inside sensory layer
- Sclera (outside layer)
Attachment site for external eye muscles. White connective tissue layer holding contents of eye
- Sclera - cornea?
Allows light to pass through and repairs itself easily. Only human tissue that can be transplanted without fear of rejection (avascular)
- Choroid (middle layer)
- Blood rich layer at the back of eye
- lens and ciliary body
What is the iris?
- Pigmented layer that gives eye colour
- regulates amount of light entering the eye by controlling size of pupils (dilates when its dark, constricts to reduce amount of light when its bright)
- smooth muscle: dilates (SNS) and constricts (PNS)
Ciliary body?
- Smooth muscle attached to lens
- produces humor, a fluid that fills space between lens and cornea
- supports lens and holds it in place
- Retina (inside layer)
- contains photoreceptors (stimulated by light). Includes rods and cons (convert light into electrical signals that can be interpreted by brain)
- signals leave retina to brain via optic nerve
- optic disc (blind spot which we are not aware of) is where optic nerve leaves the eyeball
Rods?
Allow dim light vision and peripheral vision (part of vision outside centre of gaze)
Three type of cones
- S cones (short wavelength cones) - blue
- M cones (medium wavelength cones) - green
- L cones (long wavelength cones) - red
Lens?
Focus light rays onto the retina - prone to cataracts (clouding of lens inside eye, leading to decreased vision)
How lens work
Light must focus on retina for vision. Eye is set for distance vision (over 20 ft away). The lens must change shape to focus for closer objects
Shape of lens can contribute to poor eyesight (blurred vision)
Chambers of eye
- Anterior (aqueous segment) - anterior to lens. Contains aqueous humor
- Posterior (vitreous segment) - posterior to lens. Contains vitreous humor
