Ear Flashcards
Ear components:
- contains Vestibulocochlear organ
- functions in balance and hearing
- consists of external, middle and inner parts
Purpose of the ear:
Provides a mechanism for detection of sound waves and conversion to information that can be perceived by the CNS, also contains mechanism for balance and equilibrium
External ear is composed of:
Oval auricle (pinna) and the external acoustic meatus (EAM, auditory canal)
The auricle ______ and the EAM _____ to the tympanic membrane.
Collects the sound waves; conducts the sound waves to tympanic membrane
Tympanic membrane separates:
External and middle ear compartments
The auricle is:
A single elastic cartilage covered on both sides by hairy skin, the cartilage is prolonged medially where it is continuous with the cartilage of the EAM. The ear lobe contains no cartilage but has small blood vessels making it ideal for small blood samples
Sensory innervation for the auricle arises from:
C2, C3 - great auricular n. and lesser occipital n. and
V3 - auriculotemporal n.
Movement of the tympanic membrane (TM):
The TM is concave with a central depression (umbo) formed by the malleus - the cone of light can be seen radiated anteroinferiorly from the umbo.
TM moves in response to air vibrations that transverse the EAM –> TM moves against malleus –> vibrations transmitted via remaining auditory ossicles from middle –> inner ear
Sensory innervation for the external acoustic meatus comes from:
V3, VII, X.
The EAM extends from the auricle to the tympanic membrane, the outermost 1/3 of the EAM is cartilaginous and contains ceruminous glands for the production of ear wax - cerumen. The remaining inner part is bony. Where the EAM becomes bony, the diameter narrows - ISTHMUS - where foreign bodies - where foreign bodies become lodged in children
Innervation to the external part of the TM:
V3, VII, X - essentially the same as the EAM
Innervation to the internal part of the TM is by:
IX - Glossopharyngeal
Perforation of the TM occurs by:
Foreign bodies, infection, excessive pressure, or skull fracture - severe bleeding or cerebral spinal fluid drainage thru the TM and EAM is indicative of a skull fracture and illustrates the close proximity of the external and middle ear divisions to the meninges of the brain
Middle ear connected to nasopharynx by:
Auditory (eustachian) tube
Middle ear comprises:
A narrow cavity in the petrous portion of the temporal bone, connected anteriorly to the NASOPHARYNX by the AUDITORY (Eustachian) tube and posterosuperiorly to mastoid cells via the
Middle ear connected posterosuperiorly to mastoid cells via:
The mastoid antrum
The middle ear contains:
Auditory ossicles, stapedius and tensor tympani muscles, chorda tympani n, and tympanic plexus of nerves
Auditory ossicles located in:
Epitympanic recess
Tympanic cavity (shaped like a box):
- Roof forms the TEGMEN TYMPANI and separates the tympanic cavity from the dura on the floor of the middle cranial fossa
- Floor separates tympanic cavity from the internal jugular v.
- Lateral wall is formed by the tympanic membrane
- Medial wall separates the tympanic cavity from the inner ear
Contents of the tympanic cavity - MEDIAL WALL:
PWSF - the MEDIAL Piccolo Was So Fascinating
- Promontory - formed by the basal portion of the cochlea
- Windows - vestibular (oval) and cochlear (round) windows
- Stapes and stapedius m.
- Facial n.
Contents of tympanic cavity - LATERAL WALL
MICTT - My Itchy Cochlea Tickles Today
- Malleus
- Incus
- Chorda tympani nerve
- Tensor tympani muscle
- Tympanic membrane
On the medial wall, the _________ of CN _____ passes thru a hole in the floor of the tympanic cavity and spreads out across the round promontory as the TYMPANIC PLEXUS to provide ___ innervation to the middle ear.
Tympanic nerve; IX.
This plexus supplies sensory innervation to the middle ear.
What supplies sensory to the middle ear?
Tympanic plexus (comes from tympanic nerve of IX)
Tympanic n. also contains ________ axons that continue as the _________ n. (from IX), exiting the roof of the middle ear cavity.
Parasympathetic axons; lesser petrosal n.
The posterior (mastoid) wall has several openings including the:
Mastoid antrum (entrance to mastoid air cells) and the pyramid, (which transmits the tendon of the stapedius m (VII). to insert on the stapes)
The anterior (carotid) wall is related to ;
The internal carotid a. in the nearby carotid canal. This wall is narrow and has 2 openings.
The openings in the anterior (carotid) wall are:
Superior opening: transmits the TENSOR TYMPANI M.
Inferior opening: comprised by the opening of the AUDITORY TUBE - pharyngotympanic tube - pressure in ear
The auditory tube connects the _________ to the _____.
Nasopharynx to the middle ear. The wider end is toward the nasopharynx, the posterior 1/3 is bony (closer to tympanic cavity) and anterior 2/3 is cartilaginous. It is lined with mucuos membrane that is continuous with the middle ear and nasopharynx.
Function of the auditory tube:
Equalize pressure in the middle ear with atmospheric pressure. The cartilaginous part of the auditory tube is closed except during swallowing or yawning
What does swallowing/yawning cause in the auditory tube?
Contractions of the tensor veli palatini m. opens the tube to equalize pressure. Relieve middle ear pressure
Tubal tonsils:
Located near the pharyngeal orifice of the auditory tube providing a route for infections to spread to the middle ear. Mucus membrane swells closing off the already narrow passageway and lowering cavity air pressure. This prevents free movement of the tympanic membrane and results in diminished hearing during a middle ear infection (otitis media)
Infections of mastoid air cells can be transmitted via the _______ during otitis media
Mastoid antrum. Sometimes mastoidectomy is performed thru the posterior wall of the EAM - don’t damage VII
The 3 auditory ossicles - - form a chain across the tympanic cavity to connect the tympanic membrane to the:
Malleus, incus, and stapes; Vestibular (oval) window. The handle of the malleus is embedded within the tympanic membrane and moves when sounds wave vibrate the membrane
The stapes is embedded in the:
Oval window
2 muscles are connected to the auditory ossicles and function to reduce the intensity of sound waves to the inner ear - prevents damage (ATTENUATION REFLEX). 2 muscles:
- Tensor tympani (V3) - inserts into malleus and tenses the tympanic membrane which dampens vibrations
- Stapedius (VII) - inserts onto stapes and prevents excessive movement at the oval window
Paralysis in tensor tympani or stapedius (more common) results in:
Hyperacusia (sounds are excessively loud). The delay in attenuation reflex does not prevent damage from sudden loud sounds - explosions
THe attentuation reflex is better at suppressing __________ sounds and thus enables us to hear ___________ sounds.
Low-frequency sounds; high-frequency sounds. Ie hear a mating call in an environment of excessive low-frequency noises
Ostosclerosis:
Bony overgrowth around the stapes and oval window that stops the movement of the auditory ossicles and diminishes hearing
The inner ear contains:
Cochlea and vestibular apparatus, as well as vestibular and cochlear divisions of VIII embedded in the petrous portion of the temporal bone
Internal ear has bone cavities called the bony labyrinth. Cavities within this include:
Vestible, 3 semicircular canals, and cochlea
The bony labyrinth (includes vestible, 3 semicircular canals, and cochlea) is lined with ______ and filled with _______.
Periosteum; perilymph
Within the bony labyrinth is the membranous labyrinth, which consists of:
membranous ducts and sacs including the semicircular ducts, cochlear ducts, utricle, and saccule
The membranous labyrinth is filled with:
Endolymph
What is the organ of balance?
Vestibular apparatus
What does the vestibular apparatus consist of?
Semicircular canals, utricle, and saccule
**Linear and angular acceleration of the head
What is the organ of hearing?
Cochlea - detection of sound waves transferred to the internal ear via movements of the auditory ossicles against the oval (vestibular) window. The ear ossicles act as a series of levers to amplify sound waves thru air against a fluid-filled chamber
Stapes vibrations against the oval window produce the movement of:
Perilymph within a canal of the cochlea - scala vestibuli
Perilymph movement is transmitted to the central region of the cochlea -
Helicotrema, which communicates with the second canal of cochlea - scala tympani
Perilymph movements continue within the scala tympani until they reach:
Round (cochlear) window which is deflected into the middle ear cavity. This perilymph movement generates a traveling wave along the basilar membrane of the cochlear duct (filled with endolymph) to produce hair cell defelction with the Organ of Corti –> signals to brain via the cochlear portion of VIII
in what part of the ear do things get lodged?
- ISTHMUS - where foreign bodies - where foreign bodies become lodged in children
what is the function of ear wax (cerumen)
to protect the tympanic membrane
what forms the roof of the middle ear?
Roof forms the TEGMEN TYMPANI and separates the tympanic cavity from the dura on the floor of the middle cranial fossa
what is the purpose of the Tegem Tympani?
separates the tympanic cavity from the dura on the floor of the middle cranial fossa
what is the function of the floor of the middle ear?
Floor separates tympanic cavity from the internal jugular v.
what is the lateral wall of the middle ear formed by?
tympanic membrane
what is the purpose of the medial wall?
separates the tympanic cavity from the internal ear
