Special Senses

• Eye


  Organ of vision

  Transmits visual stimuli to the brain for interpretation
• Eye orbit


  Where eyeball is located. It has a cushion of fat that surrounds and protects the eyes
• Eyelids


  Two movable structures that protect the eye from foreign bodies, distribute tears that lubricate the surface of the eye, and limit the amount of light entering the eye.
• Upper eyelid


  Larger, more mobile, and contains tarsal plates
• Tarsal plates


  Located in the upper eyelid made up of connective tissue and contains meibomian glands
• Meibomian glands


  Secrete an oily substance that lubricate the eyelid.
• Lateral (outer) canthus and medial (inner) canthus


  Two points where eyelids join at.
• Medial (inner) canthus


  Contains Puncta and Caruncle.

  Puncta: Two small openings that allow the drainage of tears into the lacrimal system

  Caruncle: Small, fleshy mass that contains sebaceous glands
• Palpebral fissure


  White space between open eyelids
• Limbus


  Point where the sclera meets cornea
• Eyelashes


  Stiff hair curving outward along the margins of the eyelids that filter dust and dirt from entering the eyes
• Conjunctiva


  Thin, transparent continuous membrane that allows for inspection of underlying tissue and protects the eye from foreign bodies.

  Divided into two portion: Palpebral and Bulbar
• Palpebral Conjunctiva 


  Lines the inside of the eyelids
• Bulbar Conjunctiva


  Covers most of the anterior eye, merging with the cornea at the limbus.
• Lacrimal apparatus


  Consists of glands and ducts that lubricate the eye.
• Lacrimal Gland


  Located in the upper outer corner of the orbital cavity just above the eye. Produces tears.
• Flow of tear

  Lacrimal Gland - produces tears - tears are washed across the eyes - drained in the puncta - empties in the lacrimal canals - chanelled into the nasolacrimal sac (through nasolacrimal ducts) - drained in the nasal meatus
• Extraocular muscles


  Six muscles attached to the outer surface of each eyeball.

  Four Rectus Muscles: Superior, inferior, lateral, and medial

  Two Oblique Muscles: Superior and inferior
• CN IV: Trochlear 


  CN that innervates superior oblique
• CN VI: Abducens


  CN that innervates lateral rectus
• Cranial nerves that supply the innervation of the eye muscles

  CN III (Oculomotor): Lifting eyelids / movement of eyes

  CN IV (Trochlear): Vertical / medial gaze

  CN VI (Abducens): Lateral gaze
• Binocular vision 


  Each muscle coordinates with a muscle in the opposite eye. This allows for parallel movement of the eyes, thus _____ in humans
• Eyeball


  Round, bony hollow formed by the different bones of the skull, composed of three layers:

  External: Sclera and Cornea

  Middle: Iris, Cilliary body, Lens, Choroid

  Innermost: Retina, Optic dics, Vessels
• Sclera


  White part of the eye that physically supports the internal structures of the eyes.
• Cornea


  Window of the eye

  Permits the entrance of light, and is well supplied with nerve endings making it responsive to touch and pain.
• Corneal Reflex


  Stimulation of the blinking of the eyes that can be stimulated with a wisp of cotton. It is supported by the CN V: Trigeminal and CN VII: Facial.
• Ciliary body

  Consists of muscle tissue that controls the thickness of the lens which must be adapted to focus on objects near and far away.
• Iris


  Circular disc of muscle that determines eye color. Muscles in here adjust to control the pupil's size, to control the amount of light entering the eye.
• Constricted pupil size 


  Lesser light enters the eyes and accommodate for near vision
• Dilated pupil 


  More light enters the eyes needed for far vision. Happens in times of darkness as the amount of light is limited.
• Pupil 


  Center aperture of the iris. Admit light that travels over the visual pathways.
• Lens


  Biconvex, transparent, avascular, encapsulated structure located posterior to the iris. Functions to refract (bend) light rays onto the Retina.

  Bulges: To focus on close objects

  Flattens: To focus on far objects
• Choroid layer


  Contains the vascularity necessary to provide nourishment to the inner aspect of the eye. It prevents light from reflecting internally.
• Retina


  Innermost layer of the eye. It receives visual stimuli and send it to the brain. Consists of photoreceptors that are sensitive to light: rods and cones

  Rods: Highly sensitive to light, regulate black and white vision, and function in dim light

  Cones: Function in bright light and is sensitive to color.
• Optic discs


  Cream-colored circular area located on the retina where optic nerve (CN II) is connected and enters the eyeball. Normally round or oval in shape.
• Physiologic cup 


  Smaller circular area that appears to be slightly depressed. Approx. 1/3 the size of the optic disc
• Fovea Centralis


  Retinal depressions surrounded by macula.
• Macula


  Reddish spot inside the eye that appears darker than the rest of the fundus.
• Fovea Centralis and Macular Area


  Form the the are of the highest visual resolution and color vision highly concentrated with cones.
• Eyeball chambers


  Maintain eye structure, protect against injury, and transmit light rays