Hearing & Equilibrium
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Cochlea consits of:
- Cochlear duct - Contains Endoplymph
- Scala Vestibuli & S Tympani: Contain Perilymph
- Basilar Membrane with hair cells
- Cross section through cochlea
Organ of corti:
The Tip Link.....
Inner hair cells.....
Each stereocilium is attached by its tip to the next one via the Extracellular protein bridge called a tip link.
The Tip Link.....is attached to a mechanically gated transduction chan. which allows K+ from endolymph into cell.
1000 inner hair cells are connected to the cochlear nerve.
What are the two senses transduced by the ear?
Audition & Equilibrium
Movement of molecules in a medium cause:
- Compression = Increased pressure
- Rarefaction= Decreased Pressure
The higher the frequency.......
The higher the pitch
What is Pitch or cycles per second measured in?
hZ or Cycles per second.
What do we hear best at?
1000 - 4000 Hz
What is the inverse of tone?
- Pitch is the inverse of tone
- also is equal to time between waves
What is intensity or Loudness measured in?
Measured in decibels (dB) where 1 dB is just barely audible.
Every 10 decibels indicate a tenfold increase in sound intensity.
Loudness of the brain is dependent upon.....
# of action potentials
Transmission & Transduction of soundwaves to the hair cells.
EXTERNAL EAR: --> MIDDLE EAR -- INNER EAR
- EXTERNAL EAR:
- Pinna - Collects sound and amplifies it some
- External auditory meatus
- Tympanic membrane (vibrates)
- MIDDLE EAR (In temporal bone):
- Cavity filled w/ air due to Eustachian tube
- Ossicles:Transmit vibrations from tymp. Mem to Oval window. (malleus Incus Stapes)
- Stapedius&Tensor Tympani(protct earofloud)
- Purpose of Ossicles = Amplification of sound
- INNER EAR:
- Pathway from stapes to hair cells
- Oval window movement causes perilymph in the scala vestibuli goes to vestibular membrane & Helicotrema
Pressure waves push vestibular membrane which pushes endoplymph
Endolymph then pushes against the basilar membrane causing it to vibrate
Movement of the Basilar membrane moves the hair cells. The micro villi and sterocillia are stuck in the gelatinous tectorial membrane so they bend.
Why is the Middle ear filled with air?
Due to Eustachian Tube
Vibrations from tympanic membrane to the oval window
Are for amplification of wound
What muscles protect the ear from overly loud noises?
Where are they located?
- Tensor Tympani
Located: Ossicles/Middle ear
INNER EAR:Pathway from stapes to hair
- Oval window movement causes perilymph in the scala vestibuli goes
- to vestibular membrane & HelicotremaPressure waves push vestibular
- membrane which pushes endoplymphEndolymph then pushes against the
- basilar membrane causing it to vibrateMovement of the Basilar membrane moves the hair cells. The micro villi and sterocillia are stuck in the gelatinous tectorial membrane so they bend
MIDDLE EAR PATHWAY (In temporal bone):Cavity filled w/ air due to _______________
- Eustachian Tube
- Ossicles:Transmit vibrations from tymp. Mem to Oval window. (malleus
- Incus Stapes)Stapedius&Tensor Tympani(protct earofloud)Purpose of
- Ossicles = Amplification of sound
Physiology of hearing at the hair cells:
- Fibers R attached to ion Channels in the PM
- Whn sterCil&Bas.Mem R neutral 10% ionC open
- WhenSterCil R deflected towards tallest sterCIl
- NON-SELECTIVE CATION CHAN PULLED OPEN
- -K+ gates open & depolarize cell
- - ^ of + opens Volt. Gated Ca2+ causing ----cell to release neurotransmitter
- This creates a receptor potential in hair cells which causes release of GLUTAMATE which stimulates 10 primary sensory neurons of the 8th cranial nerve.
Whn sterCil&Bas.Mem R neutral ___ ionC open
WhenSterCil R deflected towards tallest sterCIl
NON-SELECTIVE CATION CHAN PULLED OPEN
Fibers R attached to ______ _____ in the PM
AUditory Neural Pathway
NEED TO FINISH
- Neuron to Hair Cell
- Nerve cell fiber of 8th cranial nerve
- Spiral Ganglion in the Modiolus
- (Most cross over in Medulla)
Place a tuning fork handle on midsagital suture after hitting it.
Place tuning fork handle on mastoid process after hitting it.
What is the propper term called for ringing in the ear?
Conduction --> Nerve (something wrong w/ neural pathway) --> Central (Damage in temporal lobe)
What are the 2 types of balancing?
Static Equilibrium: Totally still
Dynamic Equilibrium: Keeping balance while moving
How many parts does the Vestibular Apparatus have? What are they? What does the structure consist of?
- 2 parts --> Semicircular Canals & Ampullae
- Sensory part called a CRISTA which contains gelatinous mass called CUPULA in the AMPULA
of hair cells imbeded in CUPULA
are bent when we move
Fuctions of Vestibular Apparatus:
Detect angular movement in 3 planes.
- Superior Semicircular Canal: Senses Pitch
- Post Semicircular Canal: roll or ear 2 shoulder
- Lateral Semicircular Canal: senses yaw
Superior Semicircular Canal:
Post Semicircular Canal:
Roll or ear to shoulder
Lateral Semicircular Canal:
What does acceleration in the Vestibular duct do?
Bends hair cells because fluid in the semicircular ducts is not attached and displays inertia/
Anatomy of Utricle & Saccule
These otolith organs contain endolymph
Endolymph is secreted constantly like CSF
- Has sensory hair cells imbeded in Otolith membrane which contains calcium carbonate crystals in a gelatinous matrix.
- -Hair cells have sterocilia & 1long kinocilium
- -Whole thing called Macula
Functions of Utricle & Saccule
Detect linear movement & head position
Utricle has verticle hairs that bend backwards when we move fwd or when you tilt head.
Saccule stereocilia R horizontal & they move when we jump up and down or going flying to landing.
Uses of Vestibular System
Control Eye Movement Muscles
Keeps Balanced & maintains upright position
Sense position and acceleration of body
Nystagmus: you spin around and when u stop ur eyes keep jerking in that direction and then suddenly jerk back
you spin around and when u stop ur eyes keep jerking in that direction and then suddenly jerk back
Projects primarily to cerebellum.
Can be caused by?
- Dizziness, with illusion of spinning
- Caused by unexpected input from vestibular system
- Can be caused by stroke, irritation from infection, loose calcium carbonate particles in semicircular canals, excess alcohol, spinning.
Unequal pressure in the ducts
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