Special Senses - Eye Flashcards
6 Senses
- Somatosensory system (pressure, warmth, vibration, limb position)
- Sight (Visual system)
- Hearing (Auditory system)
- Taste (Gustatory system)
- Smell (Olfactory system)
Components of the eye
- Vision is the dominant sense in humans
- Eye protected by orbit and cushion of fat
- Eyelids or palpebrae
- Blink
- Eyelashes
- Conjunctiva
- transparent mucous membrane
- Lacrimal apparatus
- Lacrimal gland: Responsible for tears (PNS) mucus, antibodies and lysozyme
- Nasolacrimal duct → nasal cavity
- Extrinsic Eye MusclesMovement
Fibrous Layer (Outer)
Sclera
The white of the eye
Fibrous Layer (Outer)
Cornea
Front of the eye (transparent)
Vascular layer
Choroid
- Dark: melanin containing cell
- Absorbs light
Vascular layer
Ciliary body
- Cilliary muscles
- Change thickness of Lens
Vascular layer
Iris
- Coloured part of eye
- Highly vascularised
- Pupil size controlled by muscles of the iris
- Light passes through pupil
Nervous tissue layer (inner most)
Retina
- Outer Pigmented retina
- Prevents light reflection
- Inner sensory retina
Anterior Segment / cavity
Anterior chamber
Chamber between cornea and iris
Anterior Segment / cavity
Posterior chamber
Chamber between iris and lens
Anterior Segment / cavity
Aqueous humor
- Watery liquid, replaced continuously
- Filtered through ciliary body and returned to blood via venoussynus
- Nutrients
- Refracts light
- Maintains pressure
Posterior segment/cavity
Vitreous humor
- Jellylike
- Maintains pressure and refracts
- Forms in embryo and doesn’t circulate
Vision
- The iris allows light into the eye
- Focused by the cornea, lens, and humors onto the retina
- The light striking the retina produces action potentials that are relayed to the brain via optic nerve
Retina
Outer thin pigmented layer
Melanocytes (prevent light scattering), contains melanin
Retina
Inner thicker neural/sensory layer
- Photoreceptors
- Rods
- Cones
- Bipolor cells
- Ganglion cells
Retina
Macula
- High-resolution, color vision (lots of rods and cones)
- Within this is the fovea
- Where light is most focused when the eye is looking directly at an object
- Highest density of cones
Retina
Optic disc
- Blood vessels enter the eye
- Axons from the retina meet, pass through the layers and exit the eye as the optic nerve
- No photoreceptors
Passage of Light through the eye
- Light passes through components of anterior cavity and is focused by lens and passes through vitreous humor
- Past/between axons, ganglion cells and bipolar cells, to
- photoreceptors next to pigmented layer
Glycoma
- large quantity of fluid (aqueous humour)
- Requires drainage so vision could be restored
Photoreceptors
Rod cells
- More sensitive to light - vision permitted in dim light
but only gray and fuzzy - Only black and white and not sharp
- Rhodopsin breaks down to opsin
Cone cells
- High acuity NEED bright light
- Colour vision
- 3 sub-types:
- blue, red and green light cones
- found in macula lutea,
- operate in bright light, colour vision
Photo Transduction
Retina takes light energy and converts it to electrical energy (in photoreceptors)
* Rods operate in dim light, numerous at periphery of
retina, fuzzy images
* Rhodopsin (1) = protein opsin loosely bound to pigment called retinal
* Light= retinal changes shape→ splits into opsin and retinal.
* Change in rhodopsin stimulates the rods, resulting in vision
* Generates a receptor potential → action potential in them attached
Neural pathway
- Optic nerve leaves eye enters brain at optic
chiasm - Some fibres cross to otherside of brain➔ then visual cortex in
occipital lobe
