General senses of touch Temperature Pressure Pain

 Smell  Taste  Sight  Hearing  Equilibrium

 70% of all sensory receptors are in the eyes  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 and eyelashes ◦ lubricates the eye  Conjunctiva (part of eye that is affected by pink eye or conjuctivitis) ◦ Membrane that lines the eyelids ◦ Connects to the surface of the eye ◦ Secretes mucus to lubricate eye

 Functions: ◦ Protects, moistens, and lubricates the eye ◦ Empties into the nasal cavity  Properties of lacrimal fluid ◦ Dilute salt solution (tears) ◦ Contains antibodies and lysosomes Extrinsic eye Muscles ◦ 6 muscles attach to outer surface of eye ◦ Produces eye movement

 Fibrous layer ◦ Outside layer  Vascular layer ◦ Middle layer  Sensory layer ◦ Inside layer

 Sclera ◦ White connective tissue layer ◦ Seen anteriorly as the “white of the eye”  Cornea ◦ Transparent, central anterior portion ◦ Allows for light to pass through ◦ Repairs itself easily ◦ The only human tissue that can be transplanted without fear of rejection

 Choroid is a blood-rich nutritive layer in the posterior of the eye ◦ Pigment prevents light from scattering  Modified anteriorly into 2 structures ◦ Ciliary body-smooth muscle attached to lens ◦ Iris-regulates amount of light entering eye  Pigmented layer that give eye color  Pupil- rounded opening in the iris

 Retina contains 2 layers ◦ Outer pigmented layer ◦ Inner neural layer  Contains receptor cells (rods, cones)  Signals pass from photoreceptors via a 2- neuron chain  Signals leave the retina toward the brain through the optic nerve  Optic disc (blind spot) where optic nerve leaves eyeball ◦ Cannot see images focused on the optic disc

 Rods ◦ Most are found towards the edges of the retina ◦ Allow dim light vision and peripheral vision ◦ All perception is in gray tones  Cones ◦ Three types of cones ◦ Different cones are sensitive to different wavelengths ◦ Color blindness is the result of the lack of one cone type  No photoreceptor cells are at the optic disc or blind spot

 Biconvex crystal-like structure  Held in place by a suspensory ligament attached to the ciliary body  Cataracts result when the lens becomes hard and opaque with age ◦ Vision becomes hazy and distorted ◦ Eventually causes blindness in affected eye

 Found in anterior segment  Watery fluid found between lens and cornea  Similar to blood plasma  Helps maintain intraocular pressure  Provides nutrients for the lens and cornea  Reabsorbed into venous blood through the scleral venous sinus or canal of Schlemm

 Gel-like substance posterior to the lens  Prevents the eye from collapsing  Helps maintain intraocular pressure

 Emmetropia- eye focuses images correctly on the retina  Myopia-nearsighted ◦ Eyeball is too long, distant objects appear blurry, light from objects fails to reach the retina and are focused in front of it  Hyperopia-farsighted ◦ Eyeball is too short, near objects are blurry, distant objects are focused behind the retina  Astigmatism-images are blurry, light focuses as lines, not points due to unequal curves of the cornea or lens

 Night blindness ◦ Inhibited rod function that hinders the ability to see at night  Color blindness ◦ Genetic condition that result in the inability to see certain colors  Cataracts ◦ Lens becomes hard and opaque  Glaucoma ◦ Increasing pressure within the eye  Hemianopia ◦ Loss of the same side of the visual field of both eyes, damage to visual cortex on only 1 side.

 Controls 2 senses ◦ Hearing ◦ Equilibrium ◦ Ear is divided into 3 areas  External (outer) ear-Hearing  Middle Ear-hearing  Inner Ear-hearing and balance

 Opening from the auditory canal is covered by a tympanic membrane (eardrum)  There are 3 bones (ossicles)in the middle ear: ◦ Vibrations from eardrum move the malleus -> incus->stapes ◦ Worksheet Label the parts of the ear

 There are 4 sensations of taste ◦ Sweet (sugars) ◦ Sour ( acids ) ◦ Bitter ( alkaloids ) ◦ Salty ( metal ions )  Impulses are governed by several cranial nerves because taste buds are found in different areas ◦ Facial nerve ◦ Glossopharyngeal nerve ◦ Vagus nerve

 Formed early in embryonic development  Eyes are outgrowths of the brain  All special senses are functional at birth

 Cross eyes- results from unequal pulls by the external eye muscles in babies  Ophthalmia neonatoroum- conjunctivitis resulting from mother having gonorrhea, baby’s eyelids are swollen and pus is produced.