Special Senses (ch. 8)

what are your special senses?

smell, taste, sight, hearing, equilibrium

what are your special sense receptors?

large, complex sensory organs (eye and ear)

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localized clusters of receptors (taste buds and olfactory epithelium)

how many receptors are in the eye?

70% of all sensory receptors are in the eye

what are the accessory structures of the eye?

extrinsic eye muscles, eyelids, conjunctiva, lacrimal apparatus

eyelid

opens and closes to protect the eye

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meet at medial and lateral commissure (canthus)

eyelashes

glands secrete different lubricants to moisture and protect eye

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2 types of glands

tarsal glands

produce an oily secretion that lubricates the eye

ciliary glands

located between the eyelashes

conjunctiva

membrane that lines the eyelid and eyeball

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connects with the transparent cornea

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secretes mucus to lubricate the eye and keep it moist

Lacrimal apparatus

lacrimal gland and ducts

lacrimal gland

produces lacrimal fluid

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situated on lateral end of the eye

lacrimal fluid

tears

path of tears

tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity

tears contain

dilute salt solution

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mucus

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antibodies

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lysozyme (enzyme that destroys bacteria)

function of tears

cleanses

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protect

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moisten

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lubricate the eye

extrinsic eye muscles

6 muscles attach to the outer surface of the eye

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produce gross eye muscles

lateral rectus

moves eye laterally

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cranial nerve VI -- abducens

medial rectus

moves eye medially

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cranial nerve III -- oculomotor

superior rectus

elevates eye and turns it medially

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cranial nerve III -- oculomotor

inferior rectus

depresses eye and turns it medially

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cranial nerve III -- oculomotor

inferior oblique

elevates eye and turns it laterally

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cranial nerve III -- oculomotor

superior oblique

depresses eye and turns it laterally

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cranial nerve IV -- trochlear

internal structures of the eyeball

layers/tunics

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humors and fluids

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lens

how many layers form the wall of the eyeball?

3

what are they three layers of the eyeball?

fibrous layer

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vascular layer

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sensory layer

humors and fluids

fill the interior of the eyeball

lens divides the eye. . .

into 2 chambers

fibrous layer of the eyeball

sclera and cornea

sclera

white connective tissue layer

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seen anteriorly as the white of the eye

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holds structure of the eye

cornea

1st area where light enters the eye

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transparent, central anterior portion

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allows for light to pass through

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repairs itself easily

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the only human tissues that can be transplanted without fear or rejection due to lack of blood vessels

vascular layer

blood supply

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choroid

* ciliary body
* iris
* pupil

choroid

a blood rich nutritive layer that contains pigment (prevents light from scattering)

how is the choroid modified anteriorly?

into two smooth muscle structures

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ciliary body and iris

ciliary body

attached to lens by a suspensory ligament called the ciliary zonule

iris

regulates the amount of light entering the eye

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the pigmented layer that gives the eye color

pupil

rounded opening in the iris

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while within iris, black part is the back of the retina

sensory layer

photoreceptors

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retina and rods and cones

how many layers does the retina contain?

2

what are the two layers of the retina?

1. outer pigmented layer absorbs light and prevents it from scattering
2. inner neural layer contains receptor cells (photoreceptors)

what are the photoreceptors?

rods and cones

electrical signals pass from photoreceptors via __________

two neuron chain

what are the two neurons in a two neuron chain?

bipolar cells and ganglion cells

how do signals leave the retina to go to the brain?

via the optic nerve

optic disk

the blind spot

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where the optic nerve leave the eyeball

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cannot see images focused on the optic disc because it lacks rods and cones

rods

most are found toward the edges of the retina

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allow vision in dim light and peripheral vision

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all perception is in gray tones

cones

allow for detailed color vision

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densest in the center of the retina

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fovea centralis

fovea centralis

lateral to the blind spot

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area of the retina with only cones

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visual acuity is here

visual acuity

sharpest vision

cone sensitivity

3 types of cones (RBG)

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each cone type is sensitive to different wavelengths of visible light

what segments does the lens divide the eye into?

1. anterior segment
2. posterior segment

anterior segment

aqueous segment

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anterior to the lens

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contains aqueous humor

posterior segment

vitreous segment

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posterior to the lens

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contains vitreous humor

aqueous humor

watery fluid found between the lens and cornea

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similar to blood plasma

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helps maintain intraocular pressure

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provides nutrients for the lens and cornea

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reabsorbed into venous blood through the sclera venous canal/canal of schlemm

vitreous humor

gel-like substance

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prevents eye from collapsing

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helps maintain intraocular pressure

ophthalmoscope

instrument used to illuminate the interior of the eyeball and fundus (posterior wall)

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can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina

light must be focused to a point on the ___ for optimal vision

retina

light is _______ by the cornea, aqueous humor, lens, and vitreous humor

bent/refracted

the eye is set for _______

distant vision (over 20 ft away)

accommodation

the lens must change shape to focus on closer objects (less than 20 ft away)

image formed on the retina is a ________

real image

real images are . . .

reversed L from R

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upside down

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smaller than the object

optic nerve

bundles of axons that exit the back of the eye carrying impulses from the retina

optic chiasma

location where the optic nerves cross

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fibers from the medial side of each eye cross over to the opposite side of the brain

optic tracts

contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye

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synapse with neurons in the thalamus

optic radiation

axons from the thalamus run to the occipital lobe

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synapse with cortical cells and vision interpretation (seeing) occurs

pathway of impulses from the retina to the point of visual interpretation

1. optic nerve
2. optic chiasma
3. optic tract
4. thalamus
5. optic radiation
6. visual cortex in occipital lobe of the brain

visual fields

overlap for each eye

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each eye sees a slightly different view

binocular vision

results and provides depth perception

depth perception

three-dimensional vision

emmetropia

eye focuses images correctly on the retina (normal vision)

myopia

nearsightedness

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distant objects appear blurry

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light from those objects fails to reach the retina and are focused in front of it

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results from having an eyeball that is too long

hyperopia

farsightedness

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near objects appear blurry, whereas distant objects are clear

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distant objects are focused behind the retina

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results from an eyeball that is too short or from a lazy lens

astigmatism

images are blurry

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results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens

convergence

reflexive movement of the eyes medially when we focus on a close object (going cross eyed when a pen is brought to your nose)

photopupillary reflex

bright light causes pupils to constrict

accommodation pupillary reflex

viewing objects causes PUPILS to constrict

how many senses does the ear house?

2 senses

what are the two senses that the ear houses?

hearing and equilibrium (balance)

what are the receptors in the ear?

mechanoreceptors

how many areas is the ear divided into?

3

what are the divisions of the ear?

external (outer) ear

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middle ear

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internal (inner) ear

external (outer) ear

auricle (pinna)

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external acoustic meatus (auditory canal)

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only involved in collecting sound waves

external acoustic meatus (auditory canal)

narrow chamber in the temporal bone

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lined with skin and ceruminous (earwax) glands

* glands secrete cerumen (earwax)
* cerumen traps foreign objects and repels insects

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ends at the tympanic membrane (eardrum)

middle ear cavity (tympanic cavity)

air-filled mucosa-lined cavity within the temporal bone

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involved in sense of hearing

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located btwn tympanic membrane and by a bony wall with two openings

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pharyngotympanic tube

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3 bones (ossicles)

what are the two openings in the middle ear?

oval window and round window

pharyngotympanic tube

aka auditory tube

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links the middle ear cavity with the throat

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equalizes pressure in the middle ear cavity so the eardrum can vibrate

what are the three bones in the middle ear?

the auditory ossicles are the malleus (hammer), incus (anvil), and stapes (stirrup)

function of the auditory ossicles

transmit and amplify vibrations from the tympanic membrane to fluids of the inner ear

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vibrations travel from the hammer→anvil→stirrup→oval window of the inner ear

internal (inner) ear

includes sense organs for hearing and balance

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bony labyrinth/osseous labyrinth

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filled with perilymph (bony labyrinth)

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filled with endolymph (membranous labyrinth)

what does the osseous labyrinth consist of?

cochlea

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vestibule

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semicircular canals

spiral of corti

located within the cochlear duct

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receptors= hair cells on basilar membrane

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gel-like tectorial membrane is capable of bending hair cells

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cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

pathways of vibrations from the sound waves

1. auricle (pinna)
2. external acoustic meatus (auditory canal)
3. Tympanic membrane
4. ossicles amplify the sound waves
5. oval window
6. basilar membrane in the spiral organ of corti
7. hair cells of the tectorial membrane are bent when the basilar membrane vibrates against it
8. an AP starts in the cochlear nerve (cranial nerve VIII)
9. impulse travels to the auditory cortex in the temporal lobe

high pitched sounds

disturb the short, stiff hairs/fibers of the basilar membrane

* receptor cells close to the oval window are stimulated

low pitched sounds

disturb the long, floppy hairs/fibers of the basilar membrane

* specific hair cells further along the cochlea are affected

equilibrium

2 types

* static
* dynamic

equilibrium receptors

vestibular apparatus

static equilibrium

balance concerned with changes in the position of the head

maculae

receptors in the vestibule

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report on position of the head

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help us keep our head erect

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send info via vestibular nerve to the cerebellum of the brain

anatomy of the maculate

hair cells are embedded in the otolithic membrane, otoliths float in a gel around hair cells, movements cause otoliths to roll and bend hair cells

dynamic equilibrium

sense that reports on the rotatory or angular movements of the head in space