10-26. receptors are exteroceptors because respond to chemicals in external environment ...

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Receptors are exteroceptors because respond to chemicals in external environment

Interoceptors respond to chemicals in internal environment

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Detects sweet, sour, salty, bitter, & amino acids (umami)

Taste receptor cells are modified epithelial cells◦ 50-100 are in each

taste bud Each bud can

respond to all categories of tastants

Fig 10.7

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Salty & sour do not have receptors; act by passing through channels

Fig 10.8

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Sweet & bitter have receptors; act thru G-proteins

Fig10.8

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Olfactory apparatus consists of receptor cells, supporting cells, & basal cells ◦ Receptor cells are

bipolar neurons that send axons to olfactory bulb

◦ Basal cells are stem cells that produce new receptor cells every 1-2 months

◦ Supporting cells contain detoxifying enzymes

Fig 10.9

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Odor molecules bind to receptors & act through G-proteins

Olfactory receptor gene family is huge

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Sound waves funneled by pinna (auricle) into external auditory meatus

External auditory meatus channels sound waves to tympanic membrane

Fig 10.1710-47

Malleus (hammer) is attached to tympanic membrane◦ Carries vibrations to incus (anvil)◦ Stapes (stirrup) receives vibrations from incus, transmits to

oval window

Fig 10.18

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Stapedius muscle, attached to stapes, provides protection from loud noises ◦ Can contract & dampen large vibrations◦ Prevents nerve damage in cochlea

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Fig 10.18

Consists of a tube wound 3 turns & tapered so looks like snail shell

Fig 10.19

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Tube is divided into 3 fluid-filled chambers◦ Scala

vestibuli, cochlear duct, scala tympani

Fig 10.19

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Oval window attached to scala vestibuli (at base of cochlea)

Vibrations at oval window induce pressure waves in perilymph fluid of scala vestibuli

Scalas vestibuli & tympani are continuous at apex◦ So waves in vestibuli pass to tympani & displace

round window (at base of cochlea) Necessary because fluids are incompressible & waves would

not be possible without round window

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Low frequencies can travel all way thru vestibuli & back in tympani

As frequencies increase they travel less before passing directly thru vestibular & basilar membranes to tympani

Fig 10.20

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High frequencies produce maximum stimulation of Spiral Organ closer to base of cochlea & lower frequencies stimulate closer to apex

Fig 10.2010-55

Is where sound is transduced

Sensory hair cells located on the basilar membrane ◦ 1 row of inner cells

extend length of basilar membrane

◦ Multiple rows of outer hair cells are embedded in tectorial membrane

Fig 10.22

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Pressure waves moving thru cochlear duct create shearing forces between basilar & tectorial membranes, moving & bending stereocilia◦ Causing ion channels to open, depolarizing hair cells◦ The greater the displacement, the greater the amount

of NT released & APs produced

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Info from 8th nerve goes to medulla, then to inferior colliculus, then to thalamus, & on to auditory cortex

Fig 10.23

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Neurons in different regions of cochlea stimulate neurons in corresponding areas of auditory cortex◦ Each area of

cortex represents different part of cochlea & thus a different pitch

Fig 10.24

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Conduction deafness occurs when transmission of sound waves to oval window is impaired◦ Impacts all frequencies◦ Helped by hearing aids

Sensorineural (perceptive) deafness is impaired transmission of nerve impulses◦ Often impacts some pitches more than others◦ Helped by cochlear implants

Which stimulate fibers of 8th in response to sounds

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Provides sense of equilibrium◦ =orientation to

gravity Vestibular

apparatus & cochlea form inner ear

V. apparatus consists of otolith organs (utricle & saccule) & semicircular canals

Fig 10.11 10-35

Provide information about rotational acceleration

Project in 3 different planes

Each contains a semicircular duct

At base is crista ampullaris where sensory hair cells are located

Fig 10.12

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Utricle and saccule provide info about linear acceleration

Semicircular canals, oriented in 3 planes, give sense of angular acceleration

Fig 10.12

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Hair cells are receptors for equilibrium◦ Each contains 20-50 hair-like extensions called

stereocilia 1 of these is a kinocilium Fig 10.13

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When stereocilia are bent toward kinocilium, hair cell depolarizes & releases NT that stimulates 8th nerve

When bent away from kinocilium, hair cell hyperpolarizes◦ In this way, frequency of APs in hair cells carries information

about movement Fig 10.13

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Have a macula containing hair cells◦ Hair cells embedded in gelatinous otolithic membrane

Which contains calcium carbonate crystals (=otoliths) that resist change in movement

Fig 10.14

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Utricle sensitive to horizontal acceleration◦ Hairs pushed

backward during forward acceleration

Saccule sensitive to vertical acceleration

Hairs pushed upward when person descends

Fig 10.14

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Provide information about rotational acceleration

Project in 3 different planes

Each contains a semicircular duct

At base is crista ampullaris where sensory hair cells are located

Fig 10.12

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Hair cell processes are embedded in cupula of crista ampullaris

When endolymph moves cupula moves◦ Sensory processes

bend in opposite direction of angular acceleration

Fig 10.15

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Fig 10.16

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Vestibular nystagmus is involuntary oscillations of eyes that occurs when spinning person stops ◦ Eyes continue to move in direction opposite to spin,

then jerk rapidly back to midline Vertigo is loss of equilibrium

◦ Natural response of vestibular apparatus◦ Pathologically, may be caused by anything that alters

firing rate of 8th nerve Often caused by viral infection

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