Lecture Human anatomy and physiology - Chapter 15: The special senses (part c)

Chapter 15 - The special senses (part c) provides knowledge of the chemical senses: taste and smell. This chapter focus describe the location, structure, and afferent pathways of taste and smell receptors, and explain how these receptors are activated.

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PowerPoint ® Lecture Slides

prepared by Janice Meeking, Mount Royal College

C H A P T E R

15

The Special Senses:

Part C

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Chemical Senses

in aqueous solution

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Sense of Smell

• The organ of smell—olfactory epithelium in the roof

of the nasal cavity

• Olfactory receptor cells—bipolar neurons with

radiating olfactory cilia

• Bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (cranial nerve I)

• Supporting cells surround and cushion olfactory

receptor cells

• Basal cells lie at the base of the epithelium

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Olfactory tract Olfactory bulb

(a)

Nasal conchae

Route of inhaled air Olfactory

epithelium

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Mitral cell (output cell)

Olfactory cilia

Olfactory bulb Glomeruli

Axon Olfactory receptor cell

Mucus

Route of inhaled air containing odor molecules

(b)

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Physiology of Smell

in the olfactory cilium membranes

produces cAMP as a second messenger

depolarization of the receptor membrane that then triggers an action potential

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Olfactory Pathway

cells in glomeruli of the olfactory bulbs

along the olfactory tracts to the:

• Olfactory cortex

• Hypothalamus, amygdala, and limbic system

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4

Adenylate cyclase converts ATP to cAMP.

5

cAMP opens a cation channel allowing

Na + and Ca 2+ influx and causing depolarization.

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Sense of Taste

• Found on the tongue

• On the tops of fungiform papillae

• On the side walls of foliate papillae and circumvallate (vallate) papillae

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(a) Taste buds are associated with fungiform,

foliate, and circumvallate (vallate) papillae.

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(b) Enlarged section of a

circumvallate papilla.

Taste bud

Circumvallate papilla

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Structure of a Taste Bud

• Basal cells—dynamic stem cells

• Gustatory cells—taste cells

• Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium

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Taste fibers

of cranial nerve

Connective tissue

Gustatory (taste) cells

Taste pore

Gustatory hair

Stratified squamous epithelium

of tongue

(c) Enlarged view of a taste bud.

Basal cells

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Taste Sensations

1 Sweet—sugars, saccharin, alcohol, and some amino acids

2 Sour—hydrogen ions

3 Salt—metal ions

4 Bitter—alkaloids such as quinine and nicotine

5 Umami—amino acids glutamate and aspartate

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Physiology of Taste

• Must be dissolved in saliva

• Must contact gustatory hairs

• Depolarizes the taste cell membrane, causing release of neurotransmitter

• Initiates a generator potential that elicits an

action potential

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Taste Transduction

cell depolarization by:

• Na+ influx in salty tastes (directly causes

depolarization)

• H+ in sour tastes (by opening cation channels)

• G protein gustducin in sweet, bitter, and

umami tastes (leads to release of Ca2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)

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Gustatory Pathway

taste buds to the solitary nucleus of the

medulla

there fibers branch to the:

• Gustatory cortex in the insula

• Hypothalamus and limbic system (appreciation

of taste)

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Gustatory cortex (in insula)

Thalamic nucleus (ventral posteromedial nucleus)

Pons

Solitary nucleus in medulla oblongata Facial nerve (VII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

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Influence of Other Sensations on Taste

nociceptors in the mouth also influence tastes

from taste

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The Ear: Hearing and Balance

1 External (outer) ear

2 Middle ear (tympanic cavity)

3 Internal (inner) ear

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The Ear: Hearing and Balance

hearing

hearing and equilibrium

• Respond to separate stimuli

• Are activated independently

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External acoustic meatus

Tympanic membrane

External ear

Middle ear

Internal ear (labyrinth)

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External Ear

• Helix (rim)

• Lobule (earlobe)

• Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands

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External Ear

• Boundary between external and middle ears

• Connective tissue membrane that vibrates in response to sound

• Transfers sound energy to the bones of the middle ear

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Middle Ear

temporal bone

• Flanked laterally by the eardrum

• Flanked medially by bony wall containing the oval (vestibular) and round (cochlear) windows

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Middle Ear

middle ear

the middle ear to the nasopharynx

• Equalizes pressure in the middle ear cavity

with the external air pressure

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Pharyngotympanic (auditory) tube

Cochlea

Cochlear nerve

Vestibular nerve

Oval window

(deep to stapes)

Round window

Incu (anvil)

Malleus (hammer)

Stapes (stirrup)

(b) Middle and internal ear

Vestibule

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Ear Ossicles

malleus, incus, and stapes

• Suspended by ligaments and joined by

synovial joints

• Transmit vibratory motion of the eardrum to the oval window

• Tensor tympani and stapedius muscles

contract reflexively in response to loud sounds

to prevent damage to the hearing receptors

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panic tube

Pharyngotym-Tensor tympani muscle

Tympanic membrane (medial view)

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Internal Ear

• Tortuous channels in the temporal bone

• Three parts: vestibule, semicircular canals, and cochlea

• Series of membranous sacs within the bony labyrinth

• Filled with a potassium-rich endolymph

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Facial nerve Vestibular nerve

Superior vestibular ganglion Inferior vestibular ganglion

Cochlear nerve Maculae Spiral organ (of Corti)

Cochlear duct

in cochlea

Round window

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Vestibule

• Central egg-shaped cavity of the bony labyrinth

1 Saccule is continuous with the cochlear duct

2 Utricle is continuous with the semicircular canals

• House equilibrium receptor regions (maculae)

• Respond to gravity and changes in the position of the head

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Semicircular Canals

that each define two-thirds of a circle

canal and communicate with the utricle

receptor region called the crista ampullaris

movements of the head

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Facial nerve Vestibular nerve

Superior vestibular ganglion Inferior vestibular ganglion

Cochlear nerve Maculae Spiral organ (of Corti)

Cochlear duct

in cochlea

Round window

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The Cochlea

• Extends from the vestibule

• Coils around a bony pillar (modiolus)

• Contains the cochlear duct, which houses the spiral organ (of Corti) and ends at the cochlear apex

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• Scala media (cochlear duct)—contains endolymph

• Scala tympani—terminates at the round window;

contains perilymph

• The scalae tympani and vestibuli are continuous with each other at the helicotrema (apex)

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• The bony spiral lamina

• The basilar membrane, which supports the organ of Corti

the organ of Corti to the brain

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Modiolus Cochlear nerve,

division of the vestibulocochlear nerve (VIII)

Cochlear duct (scala media)

Spiral ganglion Osseous spiral lamina Vestibular membrane

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Scala tympani (contains

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(c)

Outer hair cells

fibers

Basilar membrane

Fibers of cochlear nerve Supporting cells

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Inner hair cell

Outer hair cell

(d)

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