Ear Flashcards
Divisions of the Ear
External Ear, Middle Ear, Internal Ear
External Ear
Auricle (aka Pinna, visible portion of external ear) consists of elastic cartilage covered with skin. Its function is to collect sound waves and pass them to external auditory meatus. Consists of Helix, Lobule, Tragus, External Acoustic Meatus, and Tympanic membrane
Helix
Outer rim of the visible external ear
Lobule
Inferior fleshy portion of the visible external ear. Consists of fibrofatty tissue
Tragus
Portion of the visible external ear, elevation anterior to the meatus
External Auditory
Extends from auricle to the tympanic membrane. Approx 1.25 inches in length. Canal is lined with skin, which contains modified sweat glands (Ceruminous glands) which produce waxy material. Lateral 1/3 of canal is cartilaginous, medial 2/3rds is bony.
Nerve supply to the External Acoustic Meatus
Auriculotemporal Nerve and Vagus Nerve
Blood Supply to External Acoustic Meatus
Deep auricular branch of maxillary artery
Ceruminous Glands
Modified sweat glands in the skin of the external acoustic meatus that produce waxy material
Tympanic Membrane
Approx 1cm in diameter; separates the external ear from the middle ear. Placed obliquely at the medial end of the external auditory meatus. The membrane is a a connective tissue membrane lined on the outside with skin and on the inside with mucus membrane. Biconcave in shape with a depression in the center (the Umbo) which serves for attachment of the handle of the malleus.
Umbo
Central depression of TM; serves as point of attachment for Malleus
Quadrants of the tympanic membrane
Anterosuperior, anteroinferior (shows very bright on examination, ergo refered to as cone of light), posteroinferior, posterosuperior
Nerve supply of Tympanic Membrane
Auriculotemporal nerve (to external side) and tympanic branch of glossopharyngeal nerve (to internal surface)
Middle Ear
Cavity of the middle ear is known as the Tympanic cavity and is shaped like a biconcave lens. The cavity is found in the petrous portion of the temporal bone (along with the internal ear) and is lined with mucous membrane. Boundaries of the tympanic cavity include: roof, floor, posterior wall, lateral wall, medial wall, interior wall, and anterior wall. The tympanic cavity itself includes the eustachian tube (aka auditory tube), the ossicles (malleus, incus, stapes), stapedius and tensor tympani, and nerves (chorda tympani and tympanic plexus).
Roof of the Tympanic Cavity
Formed by thin layer of temporal bone called Tegman Tympani
Tegman Tympani
Thin layer of temporal bone forming the roof of the tympanic cavity
Floor of the tympanic cavity
Lies above the carotid canal and the beginning of the internal jugular vein
Posterior wall of the tympanic cavity
Provides entrance to mastoid air cells and entrance of the stapedius muscle to attach to the neck of the stapes and the chorda tympani
Lateral wall of the tympanic cavity
It’s the tympanic membrane!
Medial wall of the tympanic cavity
Separates tympanic cavity from inner ear. Consists of: tympanic plexus, oval window, round window
Tympanic Plexus
Tympanic nerve (branch of CN IX) divides into branches which form the tympanic plexus. Found in the medial wall of the tympanic cavity. Provides innervation to the mucosa of the middle ear, along with autonomic parasympathetic fibers that eventually innervate parotid (lesser petrosal)
Oval Window
AKA Fenestra Vestibuli. Covered by the footplate of the stapes
Round Window
Fenestra Cochleae. Inferior to the oval window. Usually closed by a membrane
Anterior Wall
Separates tympanic cavity from carotid canal. Has an opening for the eustachian tube.
Eustachian Tube
Aka auditory tube. Part bony, part cartilaginous. Extends from/opens into nasopharynx to/from middle ear (1.5 inches long). Muscles serve to open and close tube. Tube functions to equalize pressure on each side of the tympanic membrane. Cartilage part of the tube remains closed normally; opened by the action of the tensor villi palatini and salpingopharyngeal muscle.
Ossicles of the middle ear
Malleus, incus, stapes. Work together to conduct vibrations from the tympanic membrane to the oval window (propogate from external ear to inner ear). Two muscles are attached to the ossicles: tensor tympani and stapedius
Malleus
Tensor tympani attaches at the handle of the mallus. Handle of the malleus attached to the umbo of the tympanic membrane
Incus
Intermediate bone: articulates between the malleus and the stapes
Stapes
Foot bone of stapes fits in the oval window: serves to connect the middle to the inner ear.
Tensor Tympani
Attaches to the malleus. Innervated by CNV3 (mandibular)
Stapedius Muscle
Attached to neck of stapes. Innervated by CNVII. Smallest voluntary muscle in the body (Fun fact!)
Inner Ear
Located in petrous portion of temporal bone (along with tympanic cavity). Consists of an vestibular and auditory portion. Also refered to as the labyrinth due to its complicated series of canals. The labyrinth consists of two main divisions: bony labyrinth and membranous labyrinth.
Bony labyrinth
Series of canals of inner ear that exist in bone (petrous bone) and contain fluid (perilymph) similar to CSF. Divided into three areas: Vestibule, cochlea, and semicircular canals
Vestibule
Smal oval cavity which communicates anteriorly with the cochlea and posteriorly with semicircular canals. Oval window is in its lateral wall
Cochlea
Bony snail like structure about 5mm in height. Coiled 2.25 times around a central structure known as the modiolus
Modiolus
Central structure around which the cochlea coils
Semicircular canals
There are 3 semicircular canals in the bony labyrinth. Each forms 2/3rds of a circle and communicate with the vestibule
Membranous labyrinth
The membranous labyrinth is a membranous duct system that is located WITHIN the bony labyrinth. The membranous labyrinth contains a watery fluid known as endolymph (DIFFERENT FROM PERILYMPH, RESEMBLES INTRACELLULAR FLUID). The membranous labyrinth consists of a cochlear duct, three semicircular ducts and two small sacs (utricle and saccule)
Perilymph
Fluid of the bony labyrinth. Resembles CSF
Endolymph
Fluid of the membranous labyrinth. Resembles ICF
