Ear Flashcards
What are the three chambers of the ear?
External, middle, internal ear
What does the auricle/pinna do?
Collects and amplifies sound
What is the structure of external acoustic meatus?
Lateral one third is elastic cartilage, medial two thirds is bone, covered with skin
What does skin of lateral wall of external ear contain?
Hair follicles, sebaceous glands, ceruminous glands
How is cerumen made?
Secretions from apocrine ceruminous glands mix with secretions from the sebaceous glands and desquamated cells
What important factor does cerumen have?
Antimicrobial properties with lubricating properties
What is the middle ear known as?
Tympanic cavity
What is middle ear lined with?
Simple cuboidal epithelium
What does the internal ear do?
Auditory sensory receptors convert sound energy to electrical impulses
What do sensory receptors of vestibular system provide?
Responses to gravity movements of the head, maintain balance and equilibrium to help coordinate movements of head and eyes
What is main function of middle ear?
Convert sound waves arriving from external ear into mechanical vibrations that are transmitted to internal ear
What three components does the middle ear consist of?
Three auditory ossicles, Malleus, Incus, Stapes
Muscles attached to ossicles
Round window
Oval window
Auditory/Eustachian tube
What does auditory/eustachian tube do?
Connects middle ear to pharynx, vents middle ear by equalizing pressure of middle ear with atmospheric pressure
What is auditory/eustachian tube lined with?
Ciliated pseudostratified columnar epithelium
What is important clinical feature of auditory/eustachian tube?
Route for spread of infection from pharynx to middle ear- Otitis Media
Mastoiditis- System of air cells extends into mastoid portion of temporal bone from middle ear, epithelial lining of air cells is continuous with tympanic cavity, this continuation allows infections from middle ear to spread to mastoid air cells called Mastoiditis
What does tympanic membrane do?
Separates middle ear from external acoustic meatus, transmits sound waves to the ossicles of middle ear
What are the layers of tympanic membrane?
Skin of external auditory canal, lined with simple squamous keratinized epithelium, fibers arranged radially
Epithelial lining on internal surface of low simple cuboidal, fibers arranged circularly
What are the two labyrinth compartments of internal ear?
Bony labyrinth
Membranous labyrinth
What are the three fluid filled spaces of the internal ear?
Endolymphatic space-endolymph
Perilymphatic space-perilymph
Cortilymphatic space-cortilymph
Where is endolymph found?
In membranous labyrinth
Where is perilymph found?
In between bony and membranous labyrinth
Where is cortilymph found?
In inner tunnel and out tunnel of Corti
What is composition of perilymph and cortilymph?
Exrtacellular fluid, high Na and low K
What is composition of endolymph?
Intracellular like fluid, high K and low Na
What is the vestibule?
Small chamber located in center of bony labyrinth, houses saccule and utricle, also contains round and oval windows
What do the semicircular canals open into?
Vestibule
How many orifices does the semicircular canals have opening into vestibule?
5
How many ampulla is located in semicircular canals?
3, one in each
What degree are semicircular canals arranged with eachother?
90 degree angles
How many turns does cochlea have?
2.75 - 60% of people
Range is 2.5-3
What is central spongy bone in cochlear called?
Modiolus
What ganglion lies in the modiolus?
Sensory spiral ganglion, cell bodies of auditory nerve
What system are the membranous semicircular ducts, utricle, and saccule components of?
Vestibular system
What system is the membranous cochlear duct a component of?
Auditory system
Where are sensory hair cells located?
6 regions of the membranous labyrinth
3 in crista ampullaris of semicircular canals
2 in macula of saccule and utricle
1 in organ of corti
What is the function of crista ampullaris?
Detect angular acceleration, movement of head in all directions, balance/equilibrium
What is function of maculae?
Detect linear acceleration, position of head, balance/equilibrium
What is function of organ of Corti?
Hearing receptor
What are maculae and where are they found?
Sensory thickenings of epithelium, Saccule and Utricle
What nerve innervates maculae?
Vestibular nerve
What cells does maculae consist of?
Hair cells types 1 and 2, supporting cells, afferent and efferent nerve ending
What is the membrane that overlies the stereocilia of cells in maculae?
Otolithic membrane, gelatinous membrane of glycosaminoglycans
What does otolithic membrane contain on top of it?
Otoconia, crystals of calcium carbonate and proteins
Describe type 1 hair cells
Round bottom, flask shaped, surrounded by afferent nerve that engulfs entire cell, few efferent nerves
Describe type 2 hair cells
Cylindrical, afferent nerve that only covers base, few efferent nerves
What are hair cells considered?
Transducers, convert mechanical energy into electrical energy
What important feature do both types of hair cells have ?
Stereocilia varying in size, one kenocilium in the back row
What is kinocilia?
Single true cilium, 9+2 arrangement
What is imaginary line in the middle of the maculae?
Striola
What direction do hair cell cilia face in the utricle?
Towards the striola midline
What direction do hair cell cilia face in the saccule?
Away from the striola midline
When in anatomical position, what direction are the hair cells of utricle facing?
Nearly horizontal with the stereocilia oriented vertically
When in anatomical position, what direction are the hair cells of saccule facing?
Vertical with the stereocilia oriented horizontally
What is the crista ampullaris?
A sensory receptor for the angular movements of the head
Where are crista ampullaris located?
In the ampulla of the semicircular ducts
What cells does the crista ampullaris have?
Hair cells with stereocilia, type 1 and 2
Supporting cells
What is the gelatinous protein polysaccharide mass attached to the hair cells?
Cupula, projects into lumen, surrounded by endolymph
Does the endolymph move at the same speed of turning your head in the crista ampullaris, or in the same direction?
No, crista is attached to bony labyrinth, it will be swayed by lagging endolymph in opposite direction to the movement of head
What are the three divisions of the cochlear canal?
Scala vestibuli
Scala media (cochlear duct)
Scala tympani
Where does scala vestibuli begin?
Oval window
Where does scala tympani end?
Round window
What is the helicotrema?
Small channel located at the apex of the cochlear, where scala tympani and scala vestibuli communicate through
What lumen is the scala media continuous with?
Saccule
Where is the organ of corti housed?
Scala media
What is the roof of scala media?
Reissners membrane/vestibular membrane
What is the floor of scala media?
Basilar membrane
What is the frequency at the narrow base of basilar membrane?
High frequency
What is the frequency at the wider apex of basilar membrane?
Low frequency
What is the lateral wall of the scala media?
Stria vascularis
What is stria vascularis made of?
Three types of cells, rich network of capillaries
What is main function of stria vascularis ?
Secrete endolymph
What does stria vascularis sit on?
Spiral ligament
What is menieres disease?
Displacement of the vestibular membrane due to over abundance of the endolymph in scala media
What cells does spiral organ of corti hold?
Inner and outer hair cells, inner and outer phalangeal cells, inner and outer pillar cells
How many rows do inner hair cells form in organ of corti?
One row
How many rows do outer hair cells form in organ of corti?
3-5 rows
What is special about the stereocilia connection to each other?
Hold tiplinks, when stereocilia are moved, the tiplinks open and let K into the cell, depolarization takes place
What are outer hair cells of organ of corti supplied with?
Efferent nerves
What is special about outer hair cells in organ of corti?
Able to contract, act as motor units that amplify the movement of basilar membrane in response to stimulus
Also able to produce sounds known as otoaucoustic emissions, tests neonates for hearing defects
Do inner phalangeal cells completely surround the inner hair cells in organ of corti?
Yes
What is important feature of outer phalangeal cells in organ of corti?
Sends apical processes towards the endolymphatic space, flattening at the apical end and form a complete plate surrounding the apex, called apical cuticular plate
What is importance of apical cuticular plate?
Apical ends are bound together by tight junctions, forms the RETICULAR LAMINA/MEMBRANE, this ensures that the endolymph and corticolymph dont mix
What do the inner pillar cells of the organ of corti rest on?
Tympanic lip of the spiral lamina
What do the outer pillar cells of the organ of corti rest on?
Basilar membrane
Where is the inner tunnel of corti located?
In between 2 sets of the pillar cells, filled with cortilymph
What is the tectorial membrane attached to medially?
Modiolus
What is the lateral free edge of the tectorial membrane attached to?
Extends over and attaches to stereocilia of inner and outer hair cells
What is the tectorial membrane made of?
Type 2,5,9 collagen embedded in amorphous ground substance, contains glycoproteins similar to those in otolithic membrane
What is the effect of tectorial and basilar membrane vibrating together when sound vibrations enter the ear?
Shearing effect of both membranes distorts the stereocilia of the hair cells, apical membrane of hair cells depolarize and results in neurotransmitter release and action potential in bipolar neurons of spiral ganglia
