Ear Flashcards
What are the main divisions of the ear and their function?
External ear - collects sounds waves and directs them towards the middle ear, tympanic membrane converts sound waves into mechanical vibrations
Middle Ear (Tympanic cavity) - amplifies mechanical vibration and transmits vibrations to fluid in internal ear
Internal Ear - Converts fluid vibration to nerve impulse to detect sound, orientation, and acceleration of head, vestibulocochlear nerve (CN VIII)
What are the parts of the external ear?
Auricle
External Acoustic Meatus
Tympanic Membrane
What is the auricle?
Lined by thin skin with hair follicles, sweat and sebaceous glands
Overlies a core of elastic cartilage
What is the external acoustic meatus?
Lateral 1/3 elastic cartilage and medial 2/3 is temporal bone
Line with thin skin but lacks sweat glands
Ceruminous glands present - modified sweat glands that secrete cerumen (wax)
What is the tympanic membrane?
Lined externally by skin from ectoderm and continuous with that of external acoustic meatus
Lined internally by simple cuboidal epithelium and continuous with mucous membrane of the middle ear cavity. Derived endoderm
What are the parts of the middle ear?
Ossicles:
Malleus
Incus
Stapes
Epithelium
What is the malleus?
Hammer
Attached to tympanic membrane
Tensor tympani muscle pulls on malleus to increase tension of the tympanic membrane, preventing vibration
What is the incus?
Anvil
What is the stapes?
Stirrup
Smallest of the ear ossicles
Transmits mechanical vibration to oval window, causing vibrations in fluid of internal ear
Staepedius muscle - dampens movement of the stapes on the oval window
What is the attenuation reflex?
Staepedius and tensor tympani limit movement of ossicles to protect the internal ear from damaging loud sounds
Describe the epithelium of the middle ear
Lined with simple cuboidal to pseudostratified columnar epithelium
Mucous glands (goblet cells) are present deep within the tympanic cavity in the vicinity of the auditory tube
Auditory tube allows communication between tympanic cavity and nasopharynx
What are the parts of the internal ear?
Bony Labyrinth - space within temporal bone and filled with perilymph, semicircular canals, vestibule, cochlea
Membranous Labyrinth - sacs suspended within bony labyrinth, filled with endolymph, vestibular labyrinth, cochlear labyrinth
What is in the vestibular labyrinth of the membranous labyrinth?
Saccule and utricle - sensory organ the macula
Semicircular ducts - sensory organ is crista ampullaris
Sensory cells
What are the characteristics and functions of the macula?
Detects linear acceleration - horizontal and vertical movements
Within utricle and saccule
Macula of utricle (horizontal acceleration) and saccule (vertical acceleration) are at right angles with each other
Structure - hair cells with sterocilia embedded within otolithic membrane and surrounded by supporting cells
Otolithic membrane - gelatinous sheet with small crystals (otoconia) lining surface and inertia of otoconia causes lag between movement of head and otolithic membrane, deflecting stereocilia
What is the crista ampullaris in the semicircular ducts?
Located in the ampulla of semicircular ducts
Sense angular/rotational movements of the head
Orientated 90 degrees to long axis of the semicircular canal
Structure: Stereocilia of hair cells embedded in cupula, which is gelatinous cap over sensory epithelium.
Hair cells surrounded by supporting cells
Rotational movement of head in the plane of a particular semicircular canal causes deflection of the cupula and stereocilia in the opposite direction of movement
What are the sensory cells within the vestibular labyrinth?
Vestibular hair cells consist of a single true cilium (kinocilium) and many sterocilia
stereocilia are asymmetrical with longest adjacent to kinocilium to sense directionality and directionality of movement indicated by deflection towards or away from kinocilium
Type I hair cells - rounded base, surrounded by afferent nerve
Type II hair cells - cylindrical base, afferent nerve does not surround base
What is the cochlear labyrinth of the membranous labyrinth?
Cochlear duct divides the cochlea into 3 chambers:
- Scala Vestibuli
- Scala tympani
- Scala Media
What is the Scala Vestibuli of the cochlear labyrinth?
Separated from cochlear duct by the vestibular membrane
Communicates with tympanic cavity through oval window
Filled with perilymph
What is the scala tympani of the cochlear labyrinth?
Separated from cochlear duct by basilar membrane
Basilar membrane - attaches to osseous spiral lamina, supports spiral organ of corti
Ends at the round window on medial wall of the tympanic cavity
Filled with perilymph
Scala vestibuli and scala tympani are continuous at the ____
Helicotrema (apex of the cochlea)
What is the scala media?
Within the cochlear duct itself
Filled with endolymph
Stria vascularis in outer wall produces endolymph
Spiral ligament attaches cochlear duct to outer wall of cochlea and supports basilar membrane
Tectorial membrane overlies spiral organ of corti, hair cells embedded within it, and spiral limbus secretes and anchors tectorial membrane to medial wall of cochlea
Ends at the helicotrema - tip of spiral cochlea
What is the Spiral Organ of Corti, the sensory organ of the scala media?
Organ of hearing
Contains sensory cells:
Hair cells - inner and outer with stereocilia embedded within tectorial membrane, no kinocilium, do not detect directionality
Inner hair cells - form one row and completely surrounded by inner phalangeal cells
Outer hair cells - form 3-4 rows, only partially surrounded by outer phalangeal cells
Supporting cells:
Phalangeal cells - inner and outer, support hair cells
Pillar cells - inner and outer, form tunnel of Corti
How is sound perceived?
- Sound waves vibrate tympanic membrane
- Tympanic membrane moves ossicles and amplifies vibrations
- Movement of stapes in oval window produces waves in perilymph of scala vestibuli
- Fluid waves vibrate basilar membrane deflecting stereocilia of hair cells - pitch detected based on width of basilar membrane
- Vibrations dissipate through round window into tympanic cavity
What is vertigo?
Otoconia usually from utricle, become dislodged and falls into the ampulla of a semicircular canal
Stimulates hair cells of crista ampullaris when head is moved
Produces erroneous sensation of spinning with movements of the head
