section 2, chapter 12: smell, taste, hearing

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section 2, chapter 12 Smell, Taste, and Hearing

• Sensory receptors are within large, complex sensory organs in the head

• Smell in olfactory organs

• Taste in taste buds

• Hearing and equilibrium in ears

• Sight in eyes

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Sense of Smell

• Olfactory receptors• Bipolar Chemoreceptors• Respond to chemicals (called odorants) dissolved in liquids

• Olfactory organs• Olfactory epithelium - contain olfactory receptors and supporting epithelial cells

• Cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

Olfactory Receptors

Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. The olfactory receptors pass through olfactory foramina in the cribriform plate and synapse with the olfactory bulb in the brain.

(b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae.

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Olfactory Nerve Pathways

• Once olfactory receptors are stimulated, nerve impulses travel through• •Olfactory nerves olfactory bulbs olfactory tracts

limbic system (for emotions) & olfactory cortex (for interpretation)

The limbic system, which is involved with emotions and memory is strongly effected by smell.

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Olfactory Stimulation

• Olfactory code• Hypothesis • Odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins

• Olfactory organs located high in the nasal cavity above the usual pathway of inhaled air• Olfactory receptors undergo sensory adaptation rapidly• Sense of smell drops by 50% within a second after stimulation

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Sense of Taste• Taste buds

• Organs of taste• Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx

• Taste receptors• Chemoreceptors• Taste cells – modified epithelial cells that function as receptors• Taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells

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Taste ReceptorsPapillae

(a)

(b)

Connectivetissue

Sensorynerve fibers

Epitheliumof tongue

Supportingcell

Tastepore

Taste hair

Taste cell

Taste buds

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Taste Sensations

• Four primary taste sensations• Sweet – stimulated by carbohydrates• Sour – stimulated by acids• Salty – stimulated by salts• Bitter – stimulated by many organic compounds

• Spicy foods activate pain receptors

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Taste Nerve Pathways

• Sensory impulses from taste receptors travel along:• Cranial nerves to… • Medulla oblongata to…• Thalamus to… • Gustatory cortex (for interpretation)

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Sense of Hearing

• Ear• Organ of hearing

• Three (3) sections:• External ear• Middle ear• Inner ear

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External Ear• Auricle

• Collects sounds waves• External auditory meatus

• Lined with ceruminous glands• Carries sound to tympanic membrane• Terminates with tympanic membrane

• Tympanic membrane • Vibrates in response to sound waves


Round window

PharynxAuditory tube

Auricle

Oval window (under stapes)

Cochlea

Malleus

Incus Stapes

External acousticmeatus

Semicircularcanals

Vestibulocochlearnerve

Tympanic cavity

Tympanicmembrane

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Middle EarCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Round window


Auricle


Cochlea

Malleus

Incus Stapes


Semicircularcanals


Tympanic cavity

Tympanicmembrane

• Tympanic cavity• Air-filled space intemporal bone

• Auditory ossicles• Vibrate in response to tympanic membrane• Malleus, incus and stapes• Hammer, anvil and stirrup

• Oval window • Opening in wall of tympanic cavity• Stapes vibrates against it to move fluids in inner ear

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Auditory Tube• Also known as the Eustachian tube • Connects middle ear to throat• Helps maintain equal pressure on both sides of tympanic membrane• Usually closed by valve-like flaps in throat


Round window


Auricle


Cochlea

Malleus

Incus Stapes


Semicircularcanals


Tympanic cavity

Tympanicmembrane

Inner Ear

• Complex system of labyrinths• Osseous labyrinth

• Bony canal in temporal bone• Filled with perilymph

• Membranous labyrinth• Tube within osseous labyrinth• Filled with endolymph

Cochlear nerve

Maculae

Utricle

(a)

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous labyrinth

Bony labyrinth

Vestibular nerve

Scalavestibuli (cut)

Scalatympani (cut)

Cochlearduct (cut)containingendolymph

VestibuleOvalwindow

Roundwindow

Semicircularcanals

Bony labyrinth(contains perilymph)

Membranous labyrinth(contains endolymph)


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Inner Ear• Three (3) parts of labyrinths:

• Cochlea• Functions in hearing

• Semicircular canals• Functions in equilibrium

• Vestibule• Functions in equilibrium

Cochlear nerve

Maculae

Utricle

(a)

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous labyrinth

Bony labyrinth

Vestibular nerve

Scalavestibuli (cut)

Scalatympani (cut)

Cochlearduct (cut)containingendolymph

VestibuleOvalwindow

Roundwindow

Semicircularcanals

Bony labyrinth(contains perilymph)

Membranous labyrinth(contains endolymph)


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Cochlea

• Scala vestibuli• Upper compartment• Leads from oval window to apex of spiral• Part of bony labyrinth

• Scala tympani• Lower compartment• Extends from apex of the cochlea to round window• Part of bony labyrinth

Stapes vibrating inoval window

Scala vestibulifilled with perilymph

Vestibularmembrane

Basilarmembrane

Scala tympanifilled withperilymph

Round window

Helicotrema

Membranouslabyrinth

Cochlear ductfilled with endolymph


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Cochlea

• Cochlear duct• Portion of membranous labyrinth in cochlea

• Vestibular membrane• Separates cochlear duct from scala vestibuli

• Basilar membrane• Separates cochlear duct from scala tympani

Spiral organ (organ of Corti)

Basilar membrane

(a)

Scala vestibuli(contains perilymph)Vestibular membrane

Cochlear duct(contains endolymph)

Scala tympani(contains perilymph)

Branch ofcochlearnerve


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Organ of Corti

• Group of hearing receptor cells (hair cells)• On upper surface of basilar membrane• Different frequencies of vibration move different parts of basilar membrane• Particular sound frequencies cause hairs of receptor cells to bend• Nerve impulse generated

Spiral organ (organ of Corti)

Hair cells

Basilar membrane

(a)

(b)

Scala vestibuli(contains perilymph)

Cochlear duct(contains endolymph)

Scala tympani(contains perilymph)

Branch ofcochlearnerve

Tectorialmembrane

Basilarmembrane

Supportingcells

Nervefibers

Branch ofcochlear nerve

Vestibular membrane


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Organ of Corti

Cochlear duct

Scala tympani Hair cells

(a)

(b)

Basilarmembrane

Tectorial membrane


a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited

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Auditory Nerve Pathways

Midbrain

Pons

Thalamus

Auditory cortex(temporal lobe)

Medial geniculatebody of thalamus

Superiorolivarynucleus

Medullaoblongata


Cochlearnuclei


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Summary of the Generation of Sensory Impulses from the Ear

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Sense of Equilibrium

• Static equilibrium• Vestibule• Senses position of head when body is not moving

• Dynamic Equilibrium• Semicircular canals• Senses rotation and movement of head and body

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Vestibule• Utricle

• Communicates with saccule and membranous portion of semicircular canals

• Saccule• Communicates with cochlear duct

• Macula• Hair cells of utricle and saccule

Saccule

UtricleCochlea

Maculae

Ampullae ofsemicircularcanals


Cochlearduct


Vestibule

Macula• Responds to changes in head position• Bending of hairs results in generation of nerve impulse

Hair cells

Sensory nerve fiber Supporting cells

Otoliths

(a) Head upright (b) Head bent forward

Maculaof utricle

Hairs ofhair cells bend

Gelatinousmaterial sags

Gravitationalforce


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Semicircular Canals• Three (3) canals at right angles• Ampulla

• Swelling of membranous labyrinth that communicates with the vestibule

• Crista ampullaris• Sensory organ of ampulla• Hair cells and supporting cells• Rapid turns of head or body stimulate hair cells

Saccule

Utricle Cochlea

Maculae

Ampullae ofsemicircularcanals


Cochlearduct


Vestibule

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Crista Ampullaris

Hair cell

Supporting cells

Sensory nerve fibers

Hairs

Cupula Cristaampullaris

(a) Head in still position

(b) Head rotating


(c)

Crista ampullaris

Semicircular canal

Endolymph

Ampulla


End of section 2, chapter 12

section 2, chapter 12: smell, taste, hearing

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