A4 - ear Flashcards
what is the ear divided into?
external, middle and inner ear
what separates the external and middle ear?
tympanic membrane
what joins the middle ear to the nasopharynx?
pharyngotympanic tube
where is much of the ear housed?
in the petrous part of the temporal bone
what does the lobule of the auricle consist of?
fibrous tissue, fat and blood vessels
what is the arterial supply to the auricle derived mainly from?
the posterior auricular and superficial temporal arteries (branches of the external carotid artery?
what is the function of the auricle?
capture and direct sound waves towards the external auditory meatus
what is the only part of the auricle not supported by cartilage?
lobule
what divides the 2 crura of the auricle?
the anti helix
what forms the skeleton of the external ear?
elastic cartilage
describe the external auditory meatus
= a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane
- the walls of the external 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone
- the ceruminous and sebaceous glands in the subcutaneous tissue of the cartilaginous part of the meatus produce cerumen (earwax)
describe the tympanic membrane
- lies at the distal end of the external acoustic meatus
- it is a connective tissue structure, covered with skin on the outside and a mucous membrane on the inside
- the membrane is connected to the surrounding temporal bone by a fibrocartilaginous ring
what attaches to the inner surface of the membrane at a point called the umbo of the tympanic membrane?
the handle of malleus
describe the tympanic membrane superior to the lateral process of the malleus
the membrane is thin and is called the pars flaccida — lacks the radial and circular fibres present in the remainder of the membrane (pars tensa)
what does the pars tensa of the tympanic membrane form?
the lateral walls of the superior recess of the tympanic cavity
the parts of the tympanic membrane moving away from the lateral process are called the what?
the anterior and posterior malleolar folds
label the tympanic membrane
what innervates the skin of the auricle?
greater auricular nerve (branch of cervical plexus) and the lesser occipital nerve (branch of cervical plexus)
what innervates the skin of the auricle and the external auditory meatus?
auriculotemporal nerve
what is the auriculotemporal nerve a branch of?
mandibular division of CN V
what innervates the deeper aspect of the auricle and external auditory meatus?
branches of facial and vagus nerves
what 2 nerves provide sensory innervation to the external ear?
greater auricular (C2,3) and auriculotemporal (branch of V3) nerves
coughing when cleaning the ears is due to stimulation of what?
the auricular branch of the vagus nerve (vagus nerve responsible for cough reflex)
lymphatics of external ear
superficial parotid, mastoid, upper deep cervical and superficial cervical nodes
what are the 2 parts of the middle ear? describe them
- tympanic cavity — located medially to the tympanic membrane. contains the ossicles. they transmit sound vibrations through the middle ear
- epitympanic recess — a small space superior to the tympanic cavity, which lies next to the mastoid air cells. the malleus and incus partially extend upwards into the epitympanic recess
what 2 things is the tympanic cavity connected to? how?
- nasopharynx by pharyngotympanic tube
- mastoid cells by mastoid antrum
what is the tympanic cavity lined with?
mucous membrane that is continuous with the lining of the phayngotympoanic tube, mastoid cells and mastoid antrum
what are the contents of the middle ear?
- auditory ossicles
- stapedius and tensor tympani muscles
- chorda tympani nerve, a branch of CN VII
- tympanic plexus of nerves
what forms the roof of the middle ear?
a thin bone from the petrous part of the temporal bone called tegmen tympani
what does the roof of the middle ear separate the middle ear from?
the middle cranial fossa
describe the floor of the middle ear
known as the jugular wall, it consist of a thin layer of bone, which separates the middle ear from the IVJ
describe the lateral wall of the middle ear
made up of the tympanic membrane and the lateral wall of the epitympanic recess
describe the medial wall of the middle ear. what does it contain?
- formed by the lateral wall of the internal ear
- it contains a prominent bulge, produced by the facial nerve as it travels nearby
describe the anterior wall of the middle ear
a thin bony plate with 2 openings; for the auditory tube and the tensor tympani muscle
what does the anterior wall separate the middle ear from?
the internal carotid artery
describe the posterior wall of the middle ear
- aka mastoid wall
- it consists of a bony partition between the tympanic cavity and the mastoid air cells
- superiorly, there is a hole in this partition, allowing the two areas to communicate. This hole is known as the aditus to the mastoid antrum.
- posterior wall provides the attachment of the stapedius muscle and opens into mastoid antrum
what do the ossicles link?
the tympanic membrane to the oval window of the internal ear
describe the malleus
- largest and most lateral. attaches to tympanic membrane via the handle of malleus
- head of the malleus lies in the epitympanic recess, where it articulates with the next auditory ossicle, the incus
describe the incus
consists of a body and 2 limbs. body articulates with malleus, the short limb attaches to the posterior wall of the middle ear, and the long limb joins the last of the ossicles via the lenticular process, the stapes
describe the stapes
the smallest bone in the body. it joins the incus to the oval window of the inner ear. it is stirrup-shaped, with a head, 2 limbs and a base. the head articulates with the incus and the base joins the oval window
label
describe the mastoid air cells — where are they, how are they connected to the middle ear, function
- located posterior to epitympanic recess
- they are a collection of air-filled spaces in the mastoid process of the temporal bone
- the air cells are contained within a cavity called the mastoid antrum
- the mastoid antrum communicates with the middle ear via the aditus to mastoid antrum
- they act as a buffer system of air — releasing air into the tympanic cavity when the pressure is too low
what are the 2 muscles of the middle ear?
tensor tympani and stapedius
what is the function of the muscles in the middle ear?
- have a protective function
- contract in response to loud noise, inhibiting the vibrations of the auditory ossicles, and reducing the transmission of sound to the inner ear = acoustic reflex
origin, insertion and innervation of tensor tympani
O - auditory tube and greater wing of the sphenoid bone
I - handle of malleus
innervation - mandibular nerve (CN V3)
what does the stapedius muscle attach to and what is its innervation?
- attaches to stapes
- facial nerve
where does the pharyngotympanic tube open?
posterior to the inferior nasal meatus
function of the pharyngotympanic tube
to equalise the pressure of the middle ear to that of the external auditory meatus
why are middle ear infections more common in children than adults?
the pharyngotympanic tube (pathway for an upper resp infection to spread) is straighter and shorter
describe how the pharyngotympanic tube is opened?
- because the walls of the cartilaginous part of the tube are normally in apposition, the tube must be actively opened — this is done by a combination of the expanding girth of the belly of the levator veli palatine as it contracts longitudinally, pushing against one wall and the tensor veli palatini pulling on the other
- because these are muscles of the soft palate, this act is commonly associated with activities such as yawning and swallowing
opened by contraction of tensor veli palatini
what wall does the auditor tube extend from?
the anterior wall
what are the 2 main functions of the internal ear?
- convert mechanical signals from the middle ear into electrical signals, which can transfer information to the auditory pathway in the brain
- to maintain balance by detecting position and motion
where is the internal ear located?
in the petrous part of the temporal bone
what does the internal ear lie between?
the middle ear and internal acoustic meatus
what are the 2 components of the internal ear?
bony labyrinth and membranous labyrinth
what does the bony labyrinth consist of?
cochlea, vestibule, 3 semi-circular canals
what are the structures of the bony labyrinth lined with and what do they contain?
- lined with periosteum
- contain a fluid called perilymph
where is the membranous labyrinth?
lies within the bony labyrinth
how is the membranous labyrinth suspended in the bony labyrinth?
by either delicate filaments or by the substantial spiral ligament — it doesn’t float
what does the membranous labyrinth consist of?
cochlear duct, semi-circular ducts, utricle and saccule
what are the structures of the membranous labyrinth filled with?
endolymph
what are the 2 openings of the inner ear into the middle ear?
oval window and round window — both covered by membranes
where does the oval window lie?
between the middle ear and the vestibule
what does the round window separate?
separates the middle ear from the scala tympani (part of the cochlear duct). it is closed by a secondary tympanic membrane
describe the vestibule of the bony labyrinth
- central part
- separated from the middle ear by the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-circular canals
- 2 parts of the membranous labyrinth are located within the vestibule — the saccule + utricle
what does the cochlea house?
cochlear duct of the membranous labyrinth
the cochlea twists itself around a central portion of bone called the ____?
modiolus
what does the modiolus contain?
- contains canals for blood vessels and or distribution of the branches of the cochlear nerve
- branches from the cochlear portion of the vestibulocochlear (CIII) nerve are found at the base of the modiolus
extending outwards from the modiolus is a ledge of bone known as _____?
spiral lamina
describe the spiral lamina
- extends outwards from modiolus
- attaches to the cochlear duct
- holds cochlear duct in position
the presence of the cochlear duct creates 2 chambers filled with what?
perilymph
describe the 2 perilymph-filled chambers above and below the cochlear duct
- scala vestibuli — superior to duct. continuous with vestibule
- scala tympani — inferior to duct. terminates at round window
describe the semi-circular canals
- 3 — anterior, lateral and posterior
- communicate with the vestibule of the bony labyrinth
- contain semi-circular ducts = responsible for balance
- the canals are situated superoposterior to the vestibule, at right angles to each other
- they have a swelling at one end known as the ampulla
what are the organs of balance (vestibular apparatus)?
the semi-circular ducts, saccule and utricle
describe the cochlear duct
- within bony scaffolding of cochlea
- held in place by the spiral lamina
- the presence of the duct creates 2 canals above and below it = scala vestibuli + scala tympani respectively
- cochlear duct can be described as having a triangular shape
describe the lateral wall of the cochlear duct
formed by thickened periosteum, known as the spiral ligament
describe the roof of the cochlear duct
formed by Reissner’s membrane (vestibular membrane) — separates the cochlear duct from scala vestibuli
describe the floor of the cochlear duct
formed by the basilar membrane — separates the cochlear duct from the scala tympani
describe the basilar membrane
- forms floor of cochlear duct
- separates the duct from the scala tympani
- houses the epithelial cells of hearing — the spiral organ of corti
- it is overlaid by the gelatinous tectorial membrane
what do scala tympani and vestibuli contain?
perilymph
the tips of hair cells (in spiral organ of corti) are embedded in what?
tectorial membrane
what innervates the hair cells of the spiral organ?
cochlear nerve (the cochlear division of CN VIII)
what are the utricle and saccule?
2 membranous sacs located in the vestibule
the saccule and utricle are the organs of balance which detect movement or acceleration of the head in what planes?
vertical — saccule
horizontal — utricle
what do the utricle and saccule receive? which is larger?
- utricle is larger, receiving the 3 semi-circular ducts
- saccule is globular in shape, and receives the cochlear duct
endolymph drains from the saccule and utricle into what?
the endolymphatic duct
describe the endolymphatic duct
- the duct travels through the vestibular aqueduct to the posterior aspect of the petrous part of the temporal bone
- here the duct expands to a sac where endolymph can be secreted and absorbed
arterial supply of bony labyrinth
- anterior tympanic branch (from maxillary artery)
- petrosal branch (from middle meningeal artery)
- stylomastoid branch (from posterior auricular artery)
arterial supply of membranous labyrinth
labyrinthine artery (branch of inferior cerebellar artery, or occasionally the basilar)
divides into 3 branches:
- cochlear branch — supplies cochlear duct
- vestibular branches x2 — supplies the vestibular apparatus
venous drainage of inner ear?
labyrinthine vein —> sigmoid sinus or inferior petrosal sinus
innervation of inner ear?
CN VIII = vestibulocochlear nerve
- enters the inner ear via the internal auditory meatus where it divides into the vestibular nerve (balance) and the cochlear nerve (hearing)
what else passes through the internal auditory meatus?
facial nerve CN VII
describe Meniere’s disease
label A-J
A = auricle
B = external auditory meatus
C = tympanic membrane
D = incus
E = round window
F = vestibule
G = semicircular canals
H = vestibulocochlear nerve
I = cochlea
J = pharyngotympanic tube
what is the channel that ends at the round window?
scala tympani
what is the function of the vestibule?
contains utricle and saccule which are receptors for static equilibrium
where does the vestibulocochlear nerve terminate?
in the vestibulocochlear nucleus in the brainstem
basilar vs tectorial membrane
The key difference between basilar and tectorial membrane is that basilar membrane is the membrane that forms the floor of the cochlear duct, on which the cochlear hair cells lie embedded, while tectorial membrane is the fibrous sheet overlying the apical surface of the cochlear hair cells
describe the auriculotemporal nerve (anatomy)
branch of V3
runs with superficial temporal artery and vein
innervation of auricle in full
Which nerve provides sensory innervation to the internal surface of the tympanic membrane?
CN IX
describe the course of the facial nerve
Within the temporal bone the facial nerve gives off three main branches. what are they?
greater petrosal, nerve to stapedius and chorda tympani
Arises from the facial nerve as it descends behind the pyramid, contains motor fibres. what is this describing?
nerve to stapedius
greater petrosal nerve : Arises at the _______ ganglion, contains ________ ________ fibres which pass to __________ ganglion.
Arises at the geniculate ganglion, contains preganglionic parasympathetic fibres which pass to pterygopalatine ganglion
Arises just above the __________ foramen, contains ________ _________ fibres that pass to the __________ ganglion and sensory fibres for taste from the anterior two-thirds of tongue. what is this describing? chorda tympani
stylomastoid foramen
preganglionic parasympathetic
submandibular
Which structure on the medial wall of the middle ear is formed by the basal turn of the cochlear?
promontory
Which structure separates the scala vestibuli from the middle ear?
oval window
