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Sensory input from the vestibular cochlear apparatus is transmitted to the brain via
- Vestibulocochlear nerve (CN VIII)
- (Balance and hearing)
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What determines the pitch of sound
Frequency of waves measured in Hz
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What determines the loudness of a wave and how is it measured
Amplitude measured in decibels
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10 Decibels is how large of an increase
10 Fold
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Safe exposure to sound is suggested to be what
85 dB for eight hours a day
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The external auditory meatus (external acoustic canal) has what covering it
Skin containing hair follicles, sebaceous glands, and modified sweat glands called ceruminous glands
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What do the ceruminous glands secrete
A waxy material called cerumen
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The external surface of the typanic membrane (eardrum) is covered by what
Thin epidermis derived from ectoderm
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The internal surface of the typanic membrane is composed of what type of cells, derived from where
Simple squamous/cuboidal epithelium derived from endoderm
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What lies between the internal and external surface of the typanic membrane
A thin layer of mesodermal elements (collagen, elastic fibers, fibroblasts)
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The middle ear is filled with
Air
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The middle ear communicates anteriorly with the pharynx via
Eustachian tube
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The ossicles connect the tympanic membrane to what
Oval window
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What bones make up the ossicles from lateral to medial
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What is the smallest bone in the body
Stapes, the size of a grain of rice
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What senses sound vibrations
Cochlea
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What senses head position (gravity)
Vestibule
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What senses head rotations
Semicircular canals
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What is used for balance
Vestibular apparatus (Vestibule + Semicircular canals)
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Bony Labyrinth
A series of spaces within the temporal bone covered by periosteum that houses the membranous labyrinth
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The membranous labyrinth is composed of
Continuous epithelium lined cavities of ectodermal origin
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What lies between the bony labyrinth and the membrane
Perilymph (similar to extracellular fluids)
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What is inside the membranous labyrinth
Endolymph, composed of low sodium and high potassium (like intercellular fluid)
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What is in the membranous labyrinth that detects hearing and balance
Hair cells
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What is the purpose of the Maculae of the vestibule
They detect vibrations from tilts of the head
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What does the maculae contain
Utricle and a Saccule (2 clumps total)
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What areas of the ear are hair cells found
- Organ of Corti
- Vestibule
- Semi circular canals
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How are the hair cells distributed in the semicircular canals
There are three clumps of hair, 1 per semicircular canal in the ampulla
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How do the hair cells in the semicircular canals and maculae differ from those in the cochlea
- Semicircular canals and maculae have one kinocilium and many stereocilia
- Cochlea have no Kinocilium in the adult hair cell
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How are the hair cells organized in the semicircular canals and maculae
- The one kinocilium has a 9+2 array of microtubules
- Many Stereocilia, each contain 50-100 actin arranged in rows the longest are next to the kinocilium
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Where is the longest stereocilia
Next to the Kinocilium
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How are the hair cells arranged in the Cochlea
3 rows in the outer layer and 1 row in the inner
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What hair cell sprouts first
Kinocilium, then the stereocilia surround them
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What are the two continuous tubes in the Cochlea that contain perilymph
- Scala vestibuli
- Scala tympani
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What lies between the scala vestibule and scala tympani in the cochlea
Cochlear duct/Scala media which contains endolymph
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What makes up the Organ of Corti
Tectorial membrane lying on the inner and outer hair cells which are imbedded in supporting cells all of which are sitting on a basilar membrane
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The outer hair cells in the Organ of Corti are positioned where and why
They are in the middle of the Basilar membrane where the movement stimulated by sound is the greatest
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Where are the inner hair cells situated and why
They lie close to the nerves, and they change the movement of the tectorial membrane into nerve impulses
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What is the tectorial membrane made up of
It is essentially a Glycoprotein rich secretion
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What happens for the hair cells to open channels allowing an influx of positive charge depolarizing them
When the rock to the side of the kinocilium due to sound waves, they pull on a thin filament at their tips and tug open the channels
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How many hair cells are present in the cochlea at birth
3500, they are not replaced
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Hair cells are not neurons but
They secrete neurotransmitters (Glutamate) that stimulate nerves
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Stria vascularis
- Found in the Scala media wall
- Vascularized epithelium containing ion and water transporting cells that give endolymph its unusual composition
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High frequency sounds selectively vibrate
The basilar membrane of the inner ear near the oval window
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Low frequencies are detected where
At the end of the basilar membrane
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Where is Endolymph stored
Endolymphatic sac and the Endolymphatic duct
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What does the endolymphatic sac attach to
One end to the Saccule and the other to the Utricle of the Vestibular apparatus
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What are the maculae
Clusters of hair cells in the saccule and utricle
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Otolith organs
- Saccule and Utricle
- These detect the force of gravity and tilts of the head
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How are the saccule and utricle oriented
- Saccule - Vertically
- Utricle - Horizontally
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Otoliths (Otoconia)
- Calcium carbonate crystals that cover the gelatinous membrane, which blankets the Stereocilia and Kinocilium
- They are like the rocks that force the gelatine towards the pull of gravity
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What causes the vestibular nerve fibers to depolarize
When the hair cells are bent towards the Kinocilium increasing the rate of firing
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What causes the vestibular nerve fibers to hyperpolarize
When the hair cells are bent away from the Kinocilium reducing the rate of firing
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What are the hair cells called in the semicircular canals
Cristae Ampullaris (found in only at the ends of the 3 semicircular canals in the ampulla)
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What is the function of the cristae ampullaris
To sense angular acceleration and deceleration
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Cupula
Gelatinous structure containing the hair cells in the Ampulla of the semicircular canals
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Otoliths are not found in the
Crista Ampullaris or Organ of Corti, but is in the Macula (Saccule & Utricle)
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What senses in the ear do not use Otoliths
- Sound (Organ of Corti)
- Head rotation (Ampulla)
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What connects the endolymph in the saccule to the cochlea
Ductus reuniens
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