Ch. 10 Special Senses: The EyeHuman Body Structure and Function

Mrs. Clayton

Objectives:

•Describe the different sensory organs in the body

• Label and describe parts of the sensory organs: eye

• Trace the pathways through the eye

•Describe common disorders of the eye

•Define the key words that relate to the chapter

Special Senses

• Organs and receptors associated with touch, vision, hearing, smell, and taste

• Receive stimuli and transmit impulses to the brain for interpretation

• Sight, hearing and smell are distance senses- bring information from far away

• Touch and taste can only give information

about things that you actually come in

contact with

Special Senses: The Eye

•A tender sphere about 1 inch in diameter

•Protected by the orbital socket, eyebrows, eyelids, and eyelashes

Special Senses: The Eye• Tears help fight bacterial

infections, cleanse and moisten the eyes on a continuous basis

• lacrimal glands secrete tears

• Located under the upper lid of each eye

Special Senses: The Eye

• Tears are released (crying) through our lacrimal duct (tear duct) in the inner canthus

• Excess tears go to the nasal lacrimal duct and drain into the nose

https://youtu.be/Ajhj1lwTsR8

Special Senses: The Eye

• The wall of the eye is made up of 3 layers with special functions

1. Sclera

2. Choroid

3. Retina

Special Senses: The Eye

•Sclera- outermost layer of the eye; the “white” of the eye•Tough, fibrous capsule that maintains shape and protects•Muscles responsible for moving the eye are attached to the sclera. These are known as extrinsic muscles

Special Senses: The Eye• Extrinsic muscles of the eye:

• Superior rectus- rolls upward

• Inferior rectus- rolls downward

• Lateral rectus- rolls laterally; away from nose

• Medial rectus- rolls medially; toward the nose

• Superior oblique- rolls on its axis; cornea downward and laterally

• Inferior oblique- rolls on its axis; cornea upward and laterally

Special Senses: The Eye

Special Senses: The Eye

•Cornea- circular clear area in the center of the sclera; “the window” of the eye

•Transparent- allows light rays to pass

•Pain and touch receptors

• Injury could cause scarring or impaired vision

Special Senses: The Eye

•Choroid- middle layer of the eye•Contains blood vessels and non-reflective pigments• Deep, dark red-purple in color•This darkness helps prevent light reflection within the eye

Special Senses: The Eye

•Pupil- circular opening in the front of the choroid coat

•Entry of light into the eye

•Appears black bc light rays entering the eye are absorbed

Special Senses: The Eye

•Iris- colored, muscular layer surrounding the pupil

•Blue, green, brown, black (or combo)

•Eye color is related to the amount of melanin in the iris

Special Senses: The Eye

•Lens- located behind the iris and pupil

•Focuses images on the retina

•Ciliary body- ligaments that hold the lens in place

•Controls the shape of the lens for vision at near and far distances. This is called accommodation

Special Senses: The Eye

• Retina- innermost (3rd) layer of the eye

•Does not extend to the front portion of the eye

•Where light rays from an object form an image

•Once focused, it travels by the optic nerve to the occipital lobe

• If light rays aren’t focused correctly the image is not sharp- thus the need for contacts or glasses

Special Senses: The Eye

• https://youtu.be/YcedXDN6a88

Disorders of the Eye:

•Conjunctivitis- inflammation of conjunctival membranes (pink eye)

-redness, pain, swelling, discharge

-Highly contagious, spreads rapidly

- If bacterial, use of antibiotic drops

Disorders of the Eye:

•Glaucoma- excessive intraocular pressure causing destruction of the retina and hardening of optic nerve

-Mild aching, loss of peripheral vision, and a halo around lights

Disorders of the Eye:

•Cataract- lens of the eye gradually becomes cloudy

-Painless, gradual blurring and loss of vision

-Pupil will appear milky white

Disorders of the Eye:

•Sty (hordeolum)- tiny abscess at the base of an eyelash

-Caused from inflammation of a sebaceous gland

-Red, painful, swollen

Disorders of the Eye:

•Hyperopia (farsightedness)- eyeball is shorter than normal; difficulty seeing objects up close

•Myopia (nearsightedness)- eyeball is elongated; difficulty seeing objects far away

•Diplopia- double vision

•Strabismus- crossed eyes