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Introduction Senses are classified in two major groups:
A. Special – senses of smell, taste, sight, hearing, and balance
B. General – touch, pressure, pain, temperature, itch, and proprioception (position of the body and its various parts)
Anatomy of the Eye Adult eye is sphere – 1 inch in diameter Accessory structures: extrinsic eye
muscles, eyelids, conjunctiva, lacrimal apparatus
Eyes protected by eyelids Corners are:
Medial canthusLateral canthus
Anatomy of the Eye Cont. Meibomian glands – sebacious glands
produce oily secretions - lubricates eye Ciliary gland – modified sweat gland-
between eyelashes Conjunctiva – membrane - lines eyelid;
covers part of outer surface Conjunctivitis –red eyes, irritation, Pink
eye –bacteria or virus – highly contagious
Anatomy of the Eye Cont. Lacrimal apparatus – gland and ducts
drain lacrimal secretions into nasal cavity
Lacrimal glands –Tears flush eyeball
Lysozyme – enzyme that destroys bacteria
Internal Structure of Eye Eye is hollow
sphere wall composed of
three tunics or coats
Interior filled with fluid called humors – maintains shape of eye
Tunics of Eyes1. Sclera – outermost tunic –
protection – white of eyeA. cornea – transparent –
light enters –no blood vessels -can be transplanted–not a tunic
A. Ciliary body – smooth muscle structure
– lens and iris are attached
B. Iris – pigmented portion – eye color
-has muscles to regulate light.
C. Pupil - in iris – light passes
2. Choroid – middle tunic – blood rich and dark pigment
Tunics of the Eye cont.
Pupil Close Vision and Bright light –
circular muscles contract and pupil constricts allowing less light in
Distant Vision and Dim light – radial fibers contract enlarges pupil (dilate) allows more light in
Tunics of the Eye Cont. 3. Retina – innermost tunic – contains
millions of receptor cells –rods and conesRods and cones -photoreceptors
– nerve impulses transmitted to optic nerve Rods - see gray and peripheral vision Cones - allows us to see color
no rods or cones on optic nerve where it leaves the eye –called blind spot or optic disk
Visual problemsNight blindness – vit A deficiency –
deteriorates neural retina – rods
Color blindness – lacks one or more cones – common red-green – sex linked trait – found on X chromosomes – most always in males
Cont. Cataracts – vision is hazy – cause blindness –
surgically remove lens Glaucoma – pressure within eye – build up of
aqueous humor – causes pain, blindness in older people
Myopia – nearsightedness – distant objects blurry – eyeball too long
Emmetropia – good vision Hyperopia – farsightedness – eyeball too short –
distant objects are clear - p. 283
Eye Muscles Six muscles control the movements
of eye.
Lateral rectus - moves eye laterally
Medial rectus - moves eye medially
Superior rectus - elevates eye Inferior rectus - depresses eye Inferior oblique - rotates eye Superior oblique - rotates eye
The Ear – External Ear Auricle – fleshy part-
external ear Auricle opens into
external auditory meatus –leads to eardrum
Auricle directs sound waves toward external auditory meatus
External Ear Cont. Meatus lined with hairs and ceruminous
glands – EAR WAX
Eardrum – called tympanic membrane – thin membrane, separates external from middle ear. Sound waves cause eardrum to vibrate.
Middle Ear The middle ear contains three auditory ossicles –
ear bones Malleus – hammer Incus – anvil Stapes – stirrup
Eustachian tube – enables equalization of air pressure b/w outside and middle ear cavity. Changing altitude causes pain. swallow, yawn, chew, or hold nose to force air
out of lungs
Inner Ear
Tunnels called bony labyrinth – maze – has fluid called perilymph
Inner ear has three parts
Cochlea – hearing Vestibule – between
Cochlea & Semicircular canal
Semicircular Canal- balance
Steps involved in Hearing – Test Question Sound waves collected by auricle and
conducted through external auditory meatus to tympanic membrane, causing vibrations
Vibrating tympanic membrane causes malleus, incus, and stapes to vibrate
Steps involved in hearing Cont. Vibration of stapes produces vibration in
perilymph of scala vestibuli Causes vibration in cochlea Vibration detected by hair cells which induce
action potential in cochlear neurons Action potentials conducted to CNS Perceived as SOUND by cerebral cortex
Taste and Smell Chemoreceptors –taste
and olfaction(smell)
Taste buds – 10,000 on tongue – few on soft palate and cheeks
Papillae – peglike– where taste buds are on tongue
Four basic types – sweet, sour, bitter, salty
Factors that affect taste – olfactory– congestion – temperature - texture
The Tongue Dorsal surface
covered with small projections, or papillae.
4 types of papillae: Fungiform Filiform Circumvallate Foliate
FYIOlder adults often prefer highly
seasoned foods. (Why??)Mid-40s – diminished ability to
taste and smell (fewer receptor cells)
Half of people over 80 have poor taste and cannot smell at all.
Geographic TongueSome papillae fall off
–Map-like, geographic appearance
–Only symptom in most cases
Sometimes painful
–Sensitivity to hot and spicy foods
No cure – heals by itself
No known cause
–Can happen to anyone!
Taste Buds Cont.Only slight differences in
locations of taste receptors.
Most taste buds respond to two or more types of taste.