Special Senses (ch. 8)

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what are your special senses?
smell, taste, sight, hearing, equilibrium
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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)
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how many receptors are in the eye?
70% of all sensory receptors are in the eye
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what are the accessory structures of the eye?
extrinsic eye muscles, eyelids, conjunctiva, lacrimal apparatus
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eyelid
opens and closes to protect the eye

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meet at medial and lateral commissure (canthus)
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eyelashes
glands secrete different lubricants to moisture and protect eye

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2 types of glands
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tarsal glands
produce an oily secretion that lubricates the eye
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ciliary glands
located between the eyelashes
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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
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Lacrimal apparatus
lacrimal gland and ducts
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lacrimal gland
produces lacrimal fluid

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situated on lateral end of the eye
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lacrimal fluid
tears
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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
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tears contain
dilute salt solution

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mucus

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antibodies

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lysozyme (enzyme that destroys bacteria)
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function of tears
cleanses

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protect

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moisten

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lubricate the eye
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extrinsic eye muscles
6 muscles attach to the outer surface of the eye

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produce gross eye muscles
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lateral rectus
moves eye laterally

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cranial nerve VI -- abducens
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medial rectus
moves eye medially

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cranial nerve III -- oculomotor
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superior rectus
elevates eye and turns it medially

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cranial nerve III -- oculomotor
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inferior rectus
depresses eye and turns it medially

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cranial nerve III -- oculomotor
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inferior oblique
elevates eye and turns it laterally

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cranial nerve III -- oculomotor
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superior oblique
depresses eye and turns it laterally

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cranial nerve IV -- trochlear
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internal structures of the eyeball
layers/tunics

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humors and fluids

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lens
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how many layers form the wall of the eyeball?
3
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what are they three layers of the eyeball?
fibrous layer

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vascular layer

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sensory layer
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humors and fluids
fill the interior of the eyeball
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lens divides the eye. . .
into 2 chambers
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fibrous layer of the eyeball
sclera and cornea
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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
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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
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vascular layer
blood supply

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choroid

* ciliary body
* iris
* pupil
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choroid
a blood rich nutritive layer that contains pigment (prevents light from scattering)
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how is the choroid modified anteriorly?
into two smooth muscle structures

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ciliary body and iris
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ciliary body
attached to lens by a suspensory ligament called the ciliary zonule
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iris
regulates the amount of light entering the eye

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the pigmented layer that gives the eye color
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pupil
rounded opening in the iris

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while within iris, black part is the back of the retina
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sensory layer
photoreceptors

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retina and rods and cones
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how many layers does the retina contain?
2
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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)
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what are the photoreceptors?
rods and cones
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electrical signals pass from photoreceptors via __________
two neuron chain
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what are the two neurons in a two neuron chain?
bipolar cells and ganglion cells
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how do signals leave the retina to go to the brain?
via the optic nerve
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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
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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
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cones
allow for detailed color vision

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densest in the center of the retina

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fovea centralis
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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
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visual acuity
sharpest vision
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cone sensitivity
3 types of cones (RBG)

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each cone type is sensitive to different wavelengths of visible light
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what segments does the lens divide the eye into?

1. anterior segment
2. posterior segment
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anterior segment
aqueous segment

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anterior to the lens

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contains aqueous humor
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posterior segment
vitreous segment

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posterior to the lens

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contains vitreous humor
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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
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vitreous humor
gel-like substance

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prevents eye from collapsing

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helps maintain intraocular pressure
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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
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light must be focused to a point on the ___ for optimal vision
retina
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light is _______ by the cornea, aqueous humor, lens, and vitreous humor
bent/refracted
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the eye is set for _______
distant vision (over 20 ft away)
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accommodation
the lens must change shape to focus on closer objects (less than 20 ft away)
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image formed on the retina is a ________
real image
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real images are . . .
reversed L from R

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upside down

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smaller than the object
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optic nerve
bundles of axons that exit the back of the eye carrying impulses from the retina
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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
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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
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optic radiation
axons from the thalamus run to the occipital lobe

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synapse with cortical cells and vision interpretation (seeing) occurs
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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
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visual fields
overlap for each eye

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each eye sees a slightly different view
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binocular vision
results and provides depth perception
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depth perception
three-dimensional vision
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emmetropia
eye focuses images correctly on the retina (normal vision)
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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
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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
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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
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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)
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photopupillary reflex
bright light causes pupils to constrict
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accommodation pupillary reflex
viewing objects causes PUPILS to constrict
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how many senses does the ear house?
2 senses
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what are the two senses that the ear houses?
hearing and equilibrium (balance)
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what are the receptors in the ear?
mechanoreceptors
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how many areas is the ear divided into?
3
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what are the divisions of the ear?
external (outer) ear

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middle ear

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internal (inner) ear
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external (outer) ear
auricle (pinna)

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external acoustic meatus (auditory canal)

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only involved in collecting sound waves
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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)
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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)
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what are the two openings in the middle ear?
oval window and round window
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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
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what are the three bones in the middle ear?
the auditory ossicles are the malleus (hammer), incus (anvil), and stapes (stirrup)
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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
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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)
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what does the osseous labyrinth consist of?
cochlea

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vestibule

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semicircular canals
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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
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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
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high pitched sounds
disturb the short, stiff hairs/fibers of the basilar membrane

* receptor cells close to the oval window are stimulated
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low pitched sounds
disturb the long, floppy hairs/fibers of the basilar membrane

* specific hair cells further along the cochlea are affected
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equilibrium
2 types

* static
* dynamic
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equilibrium receptors
vestibular apparatus
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static equilibrium
balance concerned with changes in the position of the head
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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
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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
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dynamic equilibrium
sense that reports on the rotatory or angular movements of the head in space