Anatomy Unit 6 - Special Senses

General Senses of Touch

• Temperature

• Pressure

• Pain

Special Senses

• Smell 

• Taste

• Sight

• Hearing

• Equilibrium

The Eye and Vision

• 70 percent of all sensory receptors are in the eyes, only see 1/6^th of eye

• Each eye has over a million nerve fibers

• Protection for the eye

  • Most of the eye is enclosed in a bony orbit

  • A cushion of fat surrounds most of the eye

Eyelids

• Meet at medial and lateral canthus

Lacrimal Apparatus

keeps the surface of the eye moist

lacrimal gland

• produces lacrimal fluid 

Conjunctiva

• Membrane that lines the eyelids

• Connects to the surface of the eye

• Secretes mucus to lubricate the eye

Extrinsic Eye Muscles

• Muscles attach to the outer surface of the eye

• Produce eye movements

• Misplaced muscles result in a lazy eye

Wall of the Eye

• composed of three tunics (outer middle and inner)

Sclera and Cornea

• make up the 
  fibrous outer layer of the eye

Choroid

middle layer of the eye

Sensory tunic

(retina) inside layer of the eye

Sclera

• White connective tissue layer

• Seen anteriorly as the “white of the eye”

Cornea

• Transparent, central anterior portion

• Allows light to pass through

• Repairs itself easily

• The only human tissue that can be transplanted without fear of rejection

Middle Choroid Layer

• Blood-rich nutritive tunic

• Pigment prevents light from scattering

• Modified interiorly into two structures

Ciliary body

smooth muscle

Iris

Pigmented layer that gives eyes color

Pupil

rounded opening in the iris

Sensory Tunic (Retina)

• Contains receptor cells (photoreceptors)

  • Rods

  • Cones

Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve

Rods

• Most are found towards the edges of the retina

• Allow dim light vision and peripheral vision

Perception is all in gray tones

Cones

• 3 types detect different colors

  • Densest in the center of the retina

Fovea Centralis

• area of the retina with only cones (at the center of the macula)

Optic Disc (blind spot)

No photoreceptor cells, where the optic nerve connects to the eye.

Lens

• Biconvex crystal-like structure

• Held in place by the suspensory ligament attached to the ciliary body

Aqueous humor

• Watery fluid found in chamber between the lens and the cornea

• Similar to blood plasma

• Helps maintain intraocular pressure

• Provides nutrients for the lens and cornea

• Reabsorbed into venous blood

• Blocked drainage = glaucoma

Vitreous Humor

• Gel-like substance behind the lens

• Keeps the eye from collapsing

• Lasts a lifetime and is not replaced

Emmetropia

correct eye focus

Myopia

• Nearsightedness

  • Focus of light in front of the retina

  • Eyeball too long or lens too strong

  • Distant objects are blurry

Hyperopia

• Farsightedness

  • Focus of light beyond the retina

  • Short eyeball or lazy lens

  • Near objects are blurry

Astigmatism

Unequal curvatures in cornea & lens cause multiple focal points

Cochlea

Snail shell

Aqua-/ Aque-

water

Ante-

before/preceding

Post-

after/behind

vitre-

glass/clear

Optic/o-

sight/vision

Lacrim/o-

tear (duct)

Aur-

ear

Audi/o-

hearing

Tympan-

Drum

Semi-

Half

olfact-

smell