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UNIT 3: SENSE ORGANS – NOSE AND EARS
• Chemical senses•Sense of hearing and balance
Campbell et.al, 2010 – CHAPTER 50
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1. SENSE OF SMELLReceptor cells of smell are OLFACTORY
CELLSOlfactory cells are located within
olfactory epithelium high in the roof of the nasal cavity.
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SENSE OF SMELL
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PERCEPTION OF SMELLThe gas molecules in the air dissolves
in the mucus of the nasal cavity.It stimulates the microvilli of olfactory
cells.This cause an impulse to be send from
olfactory cell through the sensory nerve fibers, to the olfactory bulb in the temporal lobe of the cerebrum.
Smell is integrated and perceived.
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PERCEPTION OF SMELL
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2. THE SENSE OF HEARING AND BALANCE
The ear has two sensory functions: Hearing and Balance.
The sensory receptors for both of these is located in the inner ear, and each consist of hair cells and cillia which are sensitive to mechanical stimulation. They are called machanoreceptors.
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THE HUMAN EAR
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FUNCTIONS OF
DIFFERENT PARTS OF THE EAR
OUTER EARMIDDLE EAR
INNER EAR
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THE OUTER EARPinna – Concentrate sound waves in the
direction of the external auditory canal.External Auditory canal – Transport sound waves from the pinna to the
tympanic membrane. - Contain fine hairs and cerumin glands that
secrete cerumin (earwax) to help guard the ear against foreign material and insects. (smell)
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THE OUTER EARTympanic membrane – A thin membrane that covers the opening
between the inner- and middle ear.- Converts soundwaves into vibrations.
(starts to vibrate)
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MIDDLE EAR3 Bony ossicles e.g.: (start to vibrate):
- Malleus – transmit vibration to incus- Incus – transmit vibrations to stapes- Stapes – transmit vibrations to oval
window (fenestra ovalis)Oval window – start to vibrate and cause
waves in liquid (perilymph) in cochlea.Eustachian tube – Equalize the pressure
between the atmosphere and the inside of the ear. (Connected with the pharynx).
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MIDDLE EAR
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INNER EAR
Cochlea: - Snail shaped canal.- Divided in 3 canals separated by membranes1. Vestibular canal (scale vestibuli) – top canal, filled with perilymph. Receives vibration from oval window, form waves in perilymph, causes Reissner membrane to form waves.
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2. Cochlear canal (Scala media) – middle canal, filled with endolymph.
Form waves in endolymph, that causes Basilar membrane to wave up and
down. Contains the receptor cells for hearing:
Organ of Corti - which pushes the stereocilia against the tectorial
membrane, causes an impulse which is send through the cochlear nerves to the temporal lobe of the brain for integration.
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3. Tympanic canal (Scala tympani)– bottom canal, filled with perilymph. Form
waves which are carried to the round window (fenestra rotunda).
Round Window: absorb excess sound waves to prevent echoing in the ear.
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COCHLEACross section
through cochleaCochlear unrolled
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3. INNER EAR: SEMI CIRCULAR CANALS
Contain machanorecepters (cristae) – detect rotational or angular movement of the head.
Cristae- located in the ampulla (enlarged base of semi circular canals)in the endolymph found in the semi circular canals.
- Consist of hair cells, supporting cells, stereocillia imbedded in a gelatin capsule called cupula, and nerve fibers.
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INNER EAR: SEMI CIRCULAR CANALS
Movement of the head causes the endolymph to move around in the
ampulla, the cupula moves, bending the stereocilia, causing an impulse send through the
vestibular nerve to the cerebellum of the brain for integration.
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CRISTAE
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4. INNER EAR: UTRICULUS AND
SACCULUSEnlarged area below the semi circular canals.Contain mechanoreceptors (macula) – that
detects straight line movement of the head in any direction – gravitational equilibrium.
Macula: Consist of hair cells with stereocilia embedded
in a gelatin membrane called otolithic membrane with otoliths (crystals) ontop, supporting cells and vestibular nerves.
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4. INNER EAR: UTRICULUS AND
SACCULUSIf a person stops suddenly, the endolymph in the utriculus and
sacculus move around, the otolithic membrane moves, bending the stereocilia, which sends an impulse through the
vestibular nerves to the cerebellum of the brain to maintain
balance.
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MACULA FOUND IN SACCULUS AND UTRICULUS
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PROCESS OF HEARING
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PROCESS OF HEARING
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PROCESS OF HEARING
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Fig. 50-8
Hair cell bundle froma bullfrog; the longestcilia shown areabout 8 µm (SEM).
Auditorycanal
EustachiantubePinna
Tympanicmembrane
Ovalwindow
Roundwindow
Stapes
Cochlea
Tectorialmembrane
IncusMalleus
Semicircularcanals
Auditory nerveto brain
Skullbone
Outer earMiddle
ear Inner ear
Cochlearduct
Vestibularcanal
Bone
Tympaniccanal
Auditorynerve
Organ of Corti
To auditorynerve
Axons ofsensory neurons
Basilarmembrane
Hair cells
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SENSE OF BALANCE
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Fig. 50-11
Vestibular nerve
Semicircular canals
Saccule
Utricle Body movement
Hairs
Cupula
Flow of fluid
Axons
Haircells
Vestibule