018 Clinical anatomy of the ear Flashcards
what 3 parts is the ear split into?
external middle and inner
what embryology gives rise to the ear?
- otic placodes (ectodermal) and the 1st pharyngeal pouch
what is the external/outer ear split into?
the auricle/pinna and external acoustic meatus
what is the function of the auricle/pinna?
to collect and channel soundwaves towards the external acoustic meatus
assists in determining direction of sound
what is the structure of the auricle/pinna?
mostly a cartilaginous framework other than the lobule
- elastic fibrocartilage (mobile) with lots of eminence and depressions to help channel soundwaves e.g. helix, concha, tragus…
what is the blood supply and drainage to the outer ear?
external carotid artery branches of auricular arteries and superficial temporal artery and also some occipital arteries
drainage = pterygoid venous plexus of the infratemporal fossa –> external jugular vein and maxillary vein
what is the musculature of the auricle?
- intrinsic muscles between the cartilage to change shape of the auricle (more in animals)
- extrinsic muscles from scalp to the auricle to position it
- both innervated by the facial nerve
what is the innervation of the auricle?
- upper anterior quadrant of ear = trigeminal nerve, mandibular division, auriculotemporal branch
- the remainder of ear = facial nerve across the whole ear and vagus nerve across the concha and ear canal
- also spinal nerves C2,3 via the lesser occipital nerve (C2) and great auricular nerve (C2,3)
what is the lymphatic drainage of the outer ear?
- preauricular, parotid, mastoid posterior auricular, and superficial temporal lymph nodes into superficial and deep cervical lymph nodes
what is the clinical relevance of stimulating the auricular branch of the vagus nerve in the ear?
stimulating the auricular branch in the ear causes a cough reflex as it is stimulating the vagus nerve
what is the structure of the external auditory meatus?
- bony-cartilaginous, tubular component of the external ear
- about 4 cm in length when measured from the tragus
- the medial/inner two-thirds of the canal is osseous (bone), while the lateral/outer third is cartilaginous.
- S-shaped tubular structure
- The external acoustic meatus is occluded medially by the tympanic membrane
what is the tympanic membrane?
- where the external acoustic meatus ends
- double layered covered with skin on the outside and mucous membrane on the inside
- partially translucent, so structures of middle ear can be seen
what is the structure of the tympanic membrane?
- double layered covered with skin on the outside and mucous membrane on the inside
- partially translucent, so structures of middle ear can be seen, mallulous connects to the membrane at the umbo (centre)
- connected to surrounding temporal bone by a fibrocartilaginous ring
- pars flaccida, superior part is more vascularised and more opaque
- pars tensa, inferior part is not vascularised and more translucent
- healthy membrane is concave on the external surface
what is the clinical relevance of the tympanic membrane?
- perforation of tympanic membrane
- middle ear infection (ottis media) can cause pus and fluid to build up, increasing pressure and can burst the tympanic membrane (ear drum)
what is the clinical relevance of the auricle (rugby)?
- auricular haematoma
- due to trauma, blood may collect between cartilage and the overlying perichondrium
- disrupts the vascular supply to the cartilage of pinna which can cause deformity = cauliflower ear, if not drained quickly
what is the innervation of the external acoustic meatus?
vagus nerve and mandibular division of the trigeminal nerve
what are the 2 parts of the middle ear?
tympanic cavity = medial to tympanic membrane, contains majority of bones in middle ear, communicates with pharynx via the auditory/eustachian tube
epitympanic cavity = superior, in space above malleus and incus, near mastoid air cells
what is the structure of the middle ear?
- air-filled space in the temporal bone with the tympanic membrane on its lateral wall and oval and round windows on its medial wall
- connects to the pharynx via the auditory/eustachian/pharyngotympanic tube
- connects to the mastoid antrum posteriorly
- contains 3 ear ossicles (bones), malleus, incus and stapes
what are the 3 ossicles/bones in the tympanic cavity?
malleolus, incus, stapes
what is a?
pharyngotympanic/auditory/eustachian tube
what is b?
lesser petrosal nerve (branch of facial nerve)
what is c?
branch from internal carotid plexus
what is d?
sympathetic plexus
what is e?
internal carotid artery
what is f?
chorda tympani nerve (branch of facial nerve)
what is g?
tympanic branch of the glossopharyngeal nerve
what is h?
internal jugular vein
what is i?
round window
what is j?
facial nerve
what is k?
oval window
what is j?
aditus/opening to mastoid antrum
what do the auditory ossicles connect?
the tympanic membrane and the oval window of the internal ear
describe the structure of the malleus
- largest most lateral ossicle
- handle attaches to the tympanic membrane
- head lies in the epitympanic recess where is articulates with incus
describe the structure of the incus
- middle ossicle
- body articulates with malleus
- short limb attaches to the posterior wall
- long limb attaches to stapes
describe the structure of the stapes
- smallest most medial ossicle, stirrup-shaped
- head articulates with incus
- base joins to oval window of the inner ear
what are the 2 muscles in the middle ear?
- stapedius = stabilizes the stapes and dampens its vibrations (CNVII)
- tensor tympani = dampens sound vibrations from the tympanic membrane (CNViii), attaches to malleus
what is the acoustic reflex?
the stapedius and tensor tympani contract and dampen vibrations when there is a loud sound to prevent damage (e.g. your own voice)
what is the purpose of the ossicles?
concentrates the vibrations from the tympanic membrane to the inner ear
- the diameter of the tympanic membrane to the oval window is about 20 times smaller, so decreased area = increased force of vibrations
what is the mastoid antrum?
- posterior to epitympanic recess
- a collection of air-filled spaces (air sinus) in the mastoid process / petrous part of the temporal bone
- used as a buffer system of air, when tympanic cavity pressure is low, it releases air into it
- the mastoid process does not develop until 2 years old
- innervated by glossopharyngeal
- respiratory epithelium mucosa
what is the location/structure of the auditory/eustachian tube?
- tube that connects the middle ear to the pharynx
- accompanied by tensor tympani canal for the tensor tympani muscle
- bony and cartilaginous (shorter in children than adults)
- mucosa innervated by the glossopharyngeal nerve
what is the function of the auditory/eustachian tube?
- important in pressure equalisation of tympanic membrane/ external acoustic meatus
- opens when swallowing and yawning ( think about going on a plane and yawning to pop ears)
what is the blood supply to the middle ear?
external carotid artery –> maxillary artery branches e.g. tympanic artery,and middle meningeal artery and stylomastoid artery
what is the lymph drainage of the middle ear?
-parotid, submandibular nodes into superficial and deep cervical nodes
what is the clinical relevance of the middle ear?
- otitis media (middle ear infection)
- common in children due to shorter auditory tube, spreading infection from the pharynx to the ear
- can lead to ear pain, hearing loss and the tympanic membrane will be convex (rather than concave)
what are the complications of otitis media?
- permanent loss of hearing due to damage of ossicles or tympanic membrane
- can spread to mastoid air cells causing mastoiditis which can spread into the brain causing meningitis
what is the blood supply to the inner ear?
- vertebral arteries –> basilary artery –> labyrinthine artery = cochlear branch and vestibular branch which supply the membranous labyrinth
- bony labyrinth is supplied by anterior tympanic branch from maxillary artery, petrosal branch from middle meningeal artery and stylomastoid artery from posterior auricular artery (of external carotid)
where is the location of the inner ear?
within the petrous part of the temporal bone
- between the middle ear and internal acoustic meatus
what are the 2 components of the inner ear?
- bony labyrinth
- membranous labyrinth
what parts is bony labyrinth made up of?
cochlea, vestibule and 3 semi circular canals
what are the 2 openings connecting the middle and inner ear?
- oval window (between middle ear and vestibule)
- round window (separated middle ear from scala tympani (part of cochlear duct))
what is membranous labyrinth made up of?
- lies within bony labyrinth surrounded by perilymph
- consists of cochlear duct, semi-circular ducts, utricle and saccule
- filled with endolymph
what is the structure of the vestibule?
central part of bony labyrinth
- connects semicircular canals to the cochlea
- separated from the middle ear by oval window
- 2 parts of membranous labyrinth inside, saccule and utricle
what is the structure of the cochlea?
- connects to the vestibule
- central axis is called modiolus and the cochlea twists around this to form a cone shape
- spiral lamina extends outwards from modiolus as a ledge of bone, attaches to cochlear duct, creating 2 perilymph filled chambers above and below:
- scala vestibule = superior to cochlear duct, continuous with vestibule
- scala tympani = inferior to cochlear duct, terminates at round window
helicotrema = where scala vestibule and tympani meet
what are the 2 perilymph-filled chambers in the cochlea?
scala vestibule (above cochlear duct)
scala tympani (below cochlear duct)
what is the helicotrema?
where the scala vestibule and tympani meet
describe the structure of semicircular canals
3 semi-circular canals = anterior, lateral, posterior
- contain semicircular ducts, responsible for balance
- connect the ducts to the utricle and vestibule
- situated superoposterior to vestibule, right angles to each other
- ampule = swelling at one end of the canal
- the walls of the ampullae contain cristae ampullaris, ridge of sensory cells which detect movement of endolymph in the canals
what is the significance of the semicircular canals being at right angles to each other?
enables detection of deceleration and acceleration of the endolymph in all directions, so helps balance movement and assist eye tracking when moving
what is the structure of the cochlea duct?
located within the bony scaffolding of the cochlea
- held in place by spiral lamina, between the scala vestibule and tympani
- triangular shape
- lateral wall = spiral ligament
- roof = vestibular membrane ( of scala vestibuli)
- floor = basilar membrane ( of scala tympani)
- filled with endolymph, produced in the stria vascularis of the duct wall
- organ of Corti is inside the duct ( hearing) on the basilar membrane
what is the organ of Corti?
- specialised organ of hearing in the cochlear duct
- on the basilar membrane which is narrower and stiffer at the base of the cochlea and wider at apex
what is the function of the organ of Corti?
- on the basilar membrane in the cochlear duct
- inner and outer hairs sit on the basilar membrane which slopes together to form a triangular tunnel of Corti
- hairs are called stereocilia
- vibrations from soundwaves move the hairs at different magnitudes depending on pitch of sound
- impulses from hair cells are carried towards spiral ganglion in the modiolus which pass onto cochlear nerve to translate to the brain to hear
- different frequencies displace the basilar membrane at different locations - high frequencies = close to base at cochlea (more stiff and narrow), low close to apex
- the longer the cochlea the lower frequencies can be heard
where are the saccule and utricle found?
in the vestibule in the inner ear
what is the structure of the saccule and utricle?
- utricle = larger, receives from semicircular ducts
- saccule = globular, receives from cochlear duct
- both contain specialised neuroepithelium with cilia sensitive to gravity
- both have maculae (thickenings)
- their cilia are embedded in a gelatinous otolithic membrane containing otoliths
- filled with endolymph which drains into endolymphatic duct
how are the saccule and utricle involved in balance?
- moving the head alters movements of the otoliths in relation to gravity
- this then deflects the cilia which trigger the neural firing via the vestibular nerve to move the body to maintain balance
- detect gravity, linear acceleration and thus sense of orientation and balance
describe the function of semicircular ducts
- upon movement in head, endolymph changes speed/direction
- sensory receptors in the ampullae of the ducts (thickening) detect this change and send signals to the brain via the vestibular nerve
- helps maintain balance and orientation
describe the structure of semicircular ducts
- within semi-circular canals in the inner ear
- filled with endolymph
- thickenings called ampullae each have projections called ampullary crests
- ampullary crests signal angular acceleration rather than static balance
- covered with gelatinous doe-shaped capula
- capula blocks flow of endolymph around the canal but drag and currents of endolymph press up against it and draws capula to the side
- stereocilia on ampullary crest in capula which detect movement
describe the pathway of soundwaves to the brain
- sound vibration collects on the auricle and is channeled into the external acoustic meatus
- vibrations transmit through the tympanic membrane and through into the ossicles which transmit vibrations to the oval window to the inner ear (stapedius and tensor tympani muscle can dampen excess vibrations here)
- in inner ear, vibrations cause waves of movement of perilymph into the cochlea up and down through scala vestibule and scala tympani to the cochlea duct
- cochlea duct contains organ of Corti on the basilar membrane which contains lots of hair cells/stereocilia
- these hairs are displaced by waves of perilymph causing firing of neurones via the cochlear nerve translating the sound waves to the brain via electrical signals
what are the sensory receptors for balance in the ear?
- the macula of the utricle and saccule
- crista in the ampulla of semicircular ducts
what does the utricle respond to?
- linear acceleration in a horizontal plane and sideways head tilts
what does the saccule respond to?
- linear acceleration in the verticle plane
what do the semicircular ducts respond to?
rotational movement in any direction
