Special Senses

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created 7 years ago by winnieto89
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1

Eye

70% of body's sensory receptors are in the eye, cushion of fat for protection

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accessory structures include

eyebrows: sunshades
eyelids: nerve endings of follicles initiate blinking; tarsal glands: modified subaceous glands

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eyelid muscle that gives eyelid upper eyelid mobility

levator palpabrae superiorist

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conjunctiva

contacts sit here, transparent mucous membrane

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lacrimal apparatus

ducts that drain into nasal cavity

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lacrimal secretion (tears)

lysozyme, antibodies, mucus

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extrinsic eye muscle

6 muscles enable eyes to move

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layers of eyeball

1. fibrous
2. vascular
3. inner

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fibrous layer

outermost, dense, avascular, made up of sclera (white part, attachment site) and cornea (pain receptor, bends and focus light)

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vascular layer

middle pigmented layer with 3 regions

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choroid

dark pigment, vascularized

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ciliary body

secretes fluid, holds lens in position

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vascular layer of vascular layer

regulates light into eye (iris and pupil)
iris: color of eye
pupil: amt of light entering eye

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close vision

sphincter pupillae contract

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distant vision/dim light

dilator pupillae contract

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inner layer

retina: absorbs light and contains phagocytes and stores vitamin A

composed of photoreceptors, bipolar cells, and ganglion cells

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optic disc

blind spot; site where optic nerve leaves eye

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rods

dim lights, sensitive, hangs out in the periphery, blurry image

dark vision photoreceptors

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cones

bright light, high resolution, best vision at fovea centralis

red, green, yellow (color blindness in men on X chromosome)

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posterior

vitreous humor transmits light and holds neural layer firmly against pigmented layer

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anterior

aqueous humor supplies nutrients and oxygen to lens and removes waste

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glaucoma

blocked drainage of the aqueous humor can cause increased pressure and blindness

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lens

changes shape to precisely focus light on retina

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refraction

bending of light rays when light meets surface of different medium at oblique angle

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pathway of light entering eye

1. cornea
2. aqueous humor
3. lens
4. vitreous humor
5. neural layer of retina
6. photoreceptors

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rods and cones are

modified neurons and contains photopigments; can be destroyed by intense light

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how are visual pigments formed?

retinal combines with -opsins (proteins)

carrot: vitamin A

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rhodopsin

deep purple pigments

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transduction occurs in 3 steps

1. rhodopsin forms and gathers in the dark
2. pigment bleaching: light causes Rho to break down
3. Rho regenerated in outer segments

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light adaptation

move from darkness to bright light
pupils constrict and large amounts of pigments are broken down simultaneous to produce a glare

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dark adaptation

cones stop functionining and rhodopsin gathers in the dark and transducin returns to outer pigments

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visual pathway to brain

axons of retinal ganglion cells form optic nerve

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optic chiasma

part of the brain where the optic nerves (CN II) partially cross

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olfactory epithelium

olfactory receptors,supporting cells,basal cells

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how can we smell?

dissolved odorants bind to receptor proteins in olfactory cilium membranes

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taste buds

receptor organcs (10,000 on tongue papillae)
taste cells: gustatory epithelial cells and microvilli (receptors)

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how do we taste?

chemicals are dissolved in saliva and diffuse into the taste pore and contact gustatory hairs

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activation of taste receptors

binding of tastant depolarizes taste cell membrane and initiated NT release

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taste transduction

salty taste: Na influx
sour: H+ proton influx
G protein receptor (gustducin): sweet, bitter, umami

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three parts of ear

external: hearing
middle cavity: hearing only
internal: hearing and equilibrium

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external ear

auricle (lobe and rim)
external acoustic meatus (ear canal, earwax)
tympanic (eardrum)

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middle ear: tympanic cavity

small, air filled mucosa lined cavity
pharyngotympanic tube: ear pressure
ear ossicle: incus, malleous, stapes (vibrations to oval window)

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inner ear

filled with perilymph (similar to CSF)

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bony labryinth

3 regions:
vestibule
semicircular
cochlea

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vestibule

sacs respond to gravity and changes in head position

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semicircular

3 canals that have receptors, crista ampullaris, that respond to rotational movements of head

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cochlea

snail like in appearance, secretes endolymph

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sound

pressure disturbance

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higher frequency

higher pitch

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normal range of pitch

20-20,000 Hz

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normal range of volume

0-120 dB
<90 is dangerous

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Transmission of sound

1. sound waves vibrate to tympanic membrane
2. ossicles vibrate and increase pressure at oval window
3. cochlear fluid = nerve motion
4. pressure waves move through perilymph of scala vestibuli

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hair cells in ear

stereocilia bent by sound and opens mechanically gated channels and transmit impulses to the brain

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maculae

monitors position of the head in space and controls posture

responds to linear acceleration forces

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crista ampullares

sensory receptory for rotational acceleration