Anatomy and Physiology 2

The Special SensesSmellTasteSightHearingThese allow us to

experience and interpret the world around us

Anatomy of the EyeA sphere that is

about 1in in diameter

Only about 1/6 of the eye is seen and rest is protected

The eye is protected by bone, eyelids and eyelashes

Anatomy of the EyeThere are several

glands and ducts around the eyeTarsal glands:

lubricate the eyeLacrimal gland:

produce tearsNasolacrimal duct:

empties tears into the nasal cavity

Anatomy of the EyeEye muscles

Lateral rectus: moves laterally

Medial rectus: moves medially

Superior rectus: elevates Inferior rectus:

depressesInferior oblique: elevates

and turns laterallySuperior oblique :

depresses and turns laterally

Anatomy of the EyeStructures:

Sclera: the “white of the eye:

Cornea: where light enters

Lens: focuses the light that enters through the cornea

Iris: the pigmented part of the eye

Pupil: controls the amount of light that enters the eye

Retina: responds to the light

Anatomy of the EyeStructure:

Retina continued: Contains rods and

cones which are called photoreceptors

Cones allow us to see colors

Rods allow us to see in dim light and use our peripheral vision

Optic nerve: transfers information to the optic cortex of the brain

How we seeWhen light passes

through cornea and lens the light is bent or refracted as they move through the aqueous humor

The image is then projected on the retina upside down

That information is then carried to the optic nerve and process by the brain

Eye ProblemsMyopic eye (nearsighted):

distant objects appear blurry, results of an eyeball that is too long

Hyperopic eye (farsighted): close objects appear blurry, results from a too short eye

Astigmatism: the cornea has an unusual curve to it

Conjunctivitis: bacteria or viral infection of the conjunctive (membrane that covers the eye)

Anatomy of the EarOuter ear:

Pinna or auricle what is typically called the ear

External acoustic meatus: a narrow chamber carved into the temporal bone Lined with

ceruminous glands that produce earwax or cerumen

Anatomy of the EarMiddle Ear

Ear drum: vibrates in response to sound waves

Ossicles: the three smallest bones in the body Incus (anvil), malleus

(hammer) and stapes (stirrup)

Vibrations trigger the coordinated movements of these bones

Anatomy of the EarInner Ear

Bony labyrinth Cochlea Vestibule Semicircular canals

Vestibular apparatus (responsible for equilibrium)

Equilibrium Static equilibrium

Static = at restProvides information on

which way is up or down

Helps maintain posture and balance when standing upright

Dynamic equilibriumProvides information for

angular movements (e.g. twirling, spinning. Etc.)

How We HearThe auricle works to

capture as much sound waves as possible

The waves travel through the ear until they reach the cochlear duct

Hair follicles move in response to the vibrations

Once the follicles are triggered they send the impulse to the cochlear nerve

Hearing and Equilibrium Deficits

Deafness is defined as hearing loss of any degreeConduction deafness =

problems in the earSensorineural deafness =

problems in the cochlear nerve or brain

Vertigo is the sense of falling or spinningUsually result in nausea

and difficulty in maintaining balance

Chemical Senses: SmellThe nose contains

thousands of olfactory receptors that can respond to thousands of different smells

The olfactory receptors lead to the olfactory nerve, which leads to the olfactory cortex in the brain (here the smells are “identified”)

Chemical Senses: SmellThe olfactory cortex

of the brain is tied to the emotional part of the brain, thus many smells with trigger memories and emotions

The receptors are quickly triggered, but also quickly adapt to smells

Chemical Senses: TasteTaste buds are the

receptors for tasteThe tongue contains

about 10,000 taste budsThe small peg like

projections on the tongue are called papillae

The papillae contain tiny hairs that are linked to 3 nerves that carry the information to the brain

Chemical Senses: Taste5 basic taste sensations:

Sweet = responds to sugars, saccharine and certain amino acids

Sour: responds to acidsBitter: responds to

alkaloidsSalty: responds to

metal ionsUmami: recently

discovered to respond to food additives

Chemical Senses: TasteHistorically, each taste

on the tongue had “it’s own part”, but only slight differences have been found between the parts

Typically, cravings are linked to deficits in the body, but like smell the taste part of the brain is close to the emotionally part of the brain

Developmental AspectsAll special senses are

functional at birth; however, vision is the only one not fully functional

Newborns see only in gray tones and cannot see much further that a foot in front of them

It takes until about 5 years of age to have fully functioning vision

The lens will continue to grow throughout life causing “old vision”

Hearing is very important to language development

Smell and taste also developmentally important