Special Senses (III)

Vision

tear function

cleanse and lubricate the eye surface, deliver oxygen and nutrients to the conjunctiva, and protect from infection

tear path

1. lacrimal gland

2. ducts ~12

3. lacrimal punctum

4. lacrimal canaliculus

5. lacrimal sac

6. nasolacrimal duct

7. inferior meatus of nasal cavity

8. nostril

fibrous tunic

outermost, with the sclera and the cornea

vascular tunic

middle layer, with the iris, ciliary body, and choroid

neural tunic

inner layer with the retina

path of light through the eye

1. cornea

2. pupil

3. lens

4. vitreous body

5. retina

cornea

it is a transparent membrane that protects the eye, it allows light to enter the eye, contains stem cells for regeneration after injury

cornea refraction

as light passes through the eye, the cornea and lens bend and focus it on the retina

pupil

aperture through which light enters the eye

iris

adjustable diaphragm that controls pupil diameter, thus the amount of light entering - it enlarges and shrinks depending on how much light is entering the eye

sympathetic activation

dim light, dilator pupillae muscle contracts, pupil dilates (increases)

parasympathetic activation

bright light, sphincter pupillae muscle contracts: pupil constricts (decreases)

lens

clear, biconvex, and flexible structure works like the lens in a camera, shortening and lengthening its width in order to focus light rays, suspended within the eye by the suspensory ligaments

ciliary muscles

control lens shape

zonules

suspensory ligaments

ciliary process

produces aqueous humor

aqueous humor

supply nutrients to the avascular structures of the eye, cornea, and lens. it maintains intraocular pressure within its physiological range

anterior chamber

it is transparent fluid found in the anterior portion of the eye

trabecular meshwork

while an equal amount flows out through the trabecular meshwork in the drainage angle

vitreous body

gel-like substance: light can pass through and reach the retina, maintains round shape of eye

retina

back surface of the eye, it receives the image that the cornea focuses through the lens and transforms this image into electrical impulses that are carried by the optic nerve to the brain

blind spot

The exact place where the optic nerve leaves the rear of the eye. it doesn’t contain photoreceptors: blind spot in the visual field

rhodopsin

visual pigment

scotopic (night) vision

rods - specialized to absorb light

photopic (day) vision & trichromatic (color) vision

cones - visual pigment: photopsin

trichromatic vision

3 colors: red, blue, and green

short wavelengths

blue

medium wavelength

green

long wavelength

red

phototransduction

The conversion of light energy into the electrical energy of an action potential

visual projection pathway

optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, and occipital lobe