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Essentials of Human AnatomyEssentials of Human Anatomy
Dr Fadel NaimAss. Prof. Faculty of Medicine
IUG
Special Senses
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Special Senses
• 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• chemoreceptors• respond to chemicals dissolved in liquids
Olfactory Organs• contain olfactory receptors and supporting epithelial cells
• cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum
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Olfactory Receptors
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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) and olfactory cortex (for interpretation)
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Olfactory Stimulation
• 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 Receptors
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Taste Sensations
Four Primary Taste Sensations• sweet – stimulated by carbohydrates• salty – stimulated by salts • sour – stimulated by acids• 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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Hearing
Ear – organ of hearing
Three Sections• External• Middle• Inner
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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
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Middle Ear
• tympanic cavity• air-filled space in temporal bone• auditory ossicles
• vibrate in response to tympanic membrane• malleus, incus, and stapes
• oval window • opening in wall of tympanic cavity• stapes vibrates against it to move fluids in inner ear
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Auditory Tube
• 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
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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
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Inner Ear
Three Parts of Labyrinths• cochlea
• functions in hearing• semicircular canals
• functions in equilibrium
• vestibule• functions in equilibrium
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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
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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
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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
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Auditory Pathway
To inferior colliculus of opposite side of midbrain
To thalamus
To auditory cortex
Cochlear branch of CN VIII
To cochlear nucleus of medulla
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Vestibular Complex:
• Semicircular canals with ampullae (mutually perpendicular)
• Saccule and utricle (= fill up vestibule)
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Two Receptor Organs:Two Receptor Organs: Maculae of Maculae of Vestibule (or: macula of saccule plus Vestibule (or: macula of saccule plus macula of utricle)macula of utricle)
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Macula
• responds to changes in head position• bending of hairs results in generation of nerve impulse
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Crista Ampullaris
•sensory organ of ampulla• hair cells and supporting cells• rapid turns of head or body stimulate hair cells
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Equilibrium
• Rotation of the head causes endolymph within the semicircular canal to push against the cupula covering the hair cells, resulting in bending of their stereocilia and the initiation of a nerve impulse.
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Equilibrium
Static Equilibrium• vestibule• sense position of head when body is not moving
Dynamic Equilibrium• semicircular canals• sense rotation and movement of head and body
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The Sense of Vision
• Visual receptors (photoreceptors) in the eyes to detect light, color, and movement.
• Accessory structures of the eye. – provide a superficial covering over its anterior exposed surface
(conjunctiva) – prevent foreign objects from coming into contact with the eye
(eyebrows, eyelashes, and eyelids) – keep the exposed surface moist, clean, and lubricated (lacrimal
glands)
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Lacrimal Apparatus
• lacrimal gland• lateral to eye• secretes tears
• canaliculi• collect tears
• lacrimal sac• collects from canaliculi
• nasolacrimal duct• collects from lacrimal sac• empties tears into nasal cavity
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Structure of the Eye
• hollow• spherical• wall has 3 layers• outer fibrous tunic• middle vascular tunic• inner nervous tunic
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Cavities and Chambers of the Eye
• The internal space of the eye is subdivided by the lens into two separate cavities. – anterior cavity – posterior cavity
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Cavities and Chambers of the Eye
• The anterior cavity is – the space anterior to the
lens and posterior to the cornea
• The iris of the eye subdivides the anterior cavity further into two chambers. – anterior chamber is between
the iris and cornea
– posterior chamber is between the lens and the iris
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Vitreous Humor
• Posterior cavity is posterior to the lens and anterior to the retina.
• Transparent, gelatinous vitreous body which completely fills the space between the lens and the retina.
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Optic Disc
• Optic disc lacks photoreceptors.• Called the blind spot because no image forms there.• Just lateral to the optic disc is a rounded, yellowish
region of the retina called the macula lutea containing a pit called the fovea centralis (the area of sharpest vision). – contains the highest proportion of cones and almost no rods
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Visual Pathways• Each optic nerve conducts
visual stimulus information. • At the optic chiasm, some
axons from the optic nerve decussate.
• The optic tract on each side then contains axons from both eyes.
• Visual stimulus information is processed by the thalamus and then interpreted by visual association areas in the cerebrum.
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Extrinsic Eye Muscles
Superior rectus• rotates eye up and medially
Inferior rectus• rotates eye down and medially
Medial rectus• rotates eye medially
Lateral rectus• rotates eye laterally
Superior oblique• rotates eye down and laterally
Inferior oblique• rotates eye up and laterally
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THE END