Special Senses

Anatomy and Physiology

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

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

Inside View

When a doctor looks at the back of your eye, here's the view:

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

Ch. 8Day 2

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

Day 3 Taste and Smell

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!

Geographic tongue

Sweet – tip Salty – anterior

sides Sour – posterior

sides Bitter – back

BUT…

Taste Buds

Taste Buds Cont.Only slight differences in

locations of taste receptors.

Most taste buds respond to two or more types of taste.