BIO 281 CH 8: special senses

Eyebrows

shades eyes from sunlight, prevent perspiration from eyes

Eyelids

protects from foreign objects and prevent drying

Conjunctiva

produces lubricating & cleansing fluid

what cranial nerve controls accessory structures of the eye? (ex. eyebrows, eyelid, conjunctiva)

cranial nerve 7

Lacrimal Gland

exocrine gland, secretes tears (mucus, antibodies, antibacterial enzymes protecting eyes from infection) to moisten eyes

3 layers of eye tissue

- fibrous tunic
- vascular tunic
- sensory tunic

Fibrous Tunic

- outermost layer
- connective tissue w/ min. blood vessels
2 regions = sclera and cornea

Vascular Tunic (uvea)

- middle layer
- thin connective tissue w/ numerous capillaries

Sensory Tunic (retina)

- innermost layer
- 2 layers of tissue - outer pigment layer, inner neural layer
- 2 types of photoreceptors: rods and cones (colors)

anterior layers of the eye

cornea and cillary body

posterior layers of the eye

sclera, choroids, retina

cornea function

light transmission & refraction

Ciliary body

Iris: accommodation, controls light intensity

Sclera

protection (outer layer)

Choroids

blood supply, pigment prevents reflection (middle layer)

Retina

(inner layer): photoreception & impulse transmission

Pathway of light

cornea → aqueous humor → lens → vitreous humor → retina

refraction

Bending of light

Lens must ___ to focus on ___ objects

thicken; close

Superior rectus:

Lens ___ for distant vision

flattens

Lens ___ for close vision

bulges

In close vision, ciliary muscle ___, lens ligaments ___, lens more ___.

contracts; relax; convex

In distant vision, ciliary muscle ___, lens ligaments ___, lens more ___.

relax; contracts; concave

superior rectus muscle

rotates eye up and in

inferior rectus muscle

rotates eye down and in

medial rectus muscle

rotates eye inward

lateral rectus muscle

rotates eye out

superior oblique muscle

rotates eye down and out

inferior oblique muscle

rotates eye up and out