Eye physiology (topic 1 of exam 1)

cornea

transparent layered tissue that acts as barrier to environmental factors while allowing light to pass through

iris/pupil

a muscle control diaphragm that controls the amount of light that enters the eye

lens

changes size to control the focal plane of the light entering the eye

ciliary body /zonule

Muscle and ligaments that control lens’ shape and size

Trabecular meshwork/Schlemm’s canal

controls the amount aqueous humor within the eye

• Important for controlling eye pressure

sclera

hard outer surface of the eye made of connective tissue and extracellular matrix

choroid

vascular structure for nutritional support

Retina pigment epithelium (RPE)

specialized epithelium tissue for aiding photoreceptor protein turnover

retina

light sensitive tissue and image processing circuit

macula/fovea

central retina for high-resolution and color vision

Optic nerve

the only nerve connection between the retina and the brain

photoreceptors

light-sensitive neuron in the back of eye

Rods – highly sensitive to light, night vision

Cones – color-sensitive, central vision, daylight only

what are the two types of photoreceptors?

horizontal cells

inhibitory interneurons; provide feedback to photoreceptors; light-adaptation

bipolar cells

connect outer retina to inner retina

amacrine cells

inhibitory interneurons; aid in visual feature detection such as motion and edge detection

retinal ganglion cells

connect the retina to the brain

6

how many extraocular muscles control eye movement?

• In-use all the time - Eye movements occur during sleep
• Need to make fast, coordinated movements
• Fast, fatigue-resistant
• More innervation, more blood vessels

what 4 characteristics make extraocular muscles different than skeletal muscles?

• Superior rectus
• Inferior rectus
• Lateral rectus
• Medial rectus
• Superior oblique
• Inferior oblique

what are the 6 major extraocular muscles?

superior rectus

which muscle moves the eye:

• up
• up-medial

Superior oblique

which muscle moves the eye:

• up
• up-lateral

inferior rectus

which muscle moves the eye:

• down
• down-medial

inferior oblique

which muscle moves the eye:

• down
• down-lateral

lateral rectus

which muscle moves the eye: lateral

medial rectus

which muscle moves the eye: medial

optic nerve (sensory)

CN II is:

oculomotor nerve (motor)

CN III is:

trochlear nerve (motor)

CN IV is:

abducent nerve (motor)

CN VI is:

Origin: Oculomotor nucleus
Innervates: superior rectus, medial rectus,
inferior rectus, inferior oblique

*nothing lateral; only oblique is inferior

what is the origin and innervation of Oculomotor nerve (III)?

Origin: Trochlear nucleus
Innervates: Superior oblique

what is the origin and innervation of the Trochlear nerve (IV)

Origin: Abducens nucleus
Innervates: lateral rectus

what is the origin and innervation of the Abducens nerve (VI)