Anatomy of Ear and Taste Flashcards
What part of the external ear collects soundwaves?
The pinna (auricle) = funnels soundwaves into the external acoustic meatus
What part of the pinna does the vagus nerve supply?
The inferior parts of the external auditory meatus and tympanic membrane
What are the nerves that supply the pinna?
Lesser occipital nerve (CN II, III), vagus nerve (CN X), auriculotemporal nerve (CN V3), greater auricular nerve (CN II, III)
What is the main function of the tympanic cavity?
To conduct soundwaves in the air towards the fluid-filled cavities of the inner ear
What kind of mechanism is the hearing of the tympanic cavity described as?
Bone conduction mechanism
Why do the ossicles of the tympanic cavity decrease in size as they go from lateral to medial?
Amplifies soundwaves
What facilitates and controls the movements of the ossicles?
The tympanic cavity
What is the tympanic cavity?
Air-filled cavity within the temporal bone
What are the names of the ossicles, from medial to lateral?
Stapes, incus, malleus
What does the footplate of the stapes connect with?
The oval window = connects middle ear with vestibule of inner ear
What do the synovial joints in the tympanic cavity allow for?
The smooth movement of the ossicles
What suspends the ossicles from the tegmen tympani (roof of cavity)?
Ligaments
What are both the tensor tympani and stapedius muscles part of?
The auditory reflex
What is the stapedius tendon attached to?
The pyramidal eminence of the tympanic cavity
Where does the tensor tympani run from?
Cartilaginous portion of Eustachian tube to the handle of the malleus
What is the function of the tensor tympani?
Dampens sound by reducing vibrations of tympanic membrane (reduces noise form chewing)
What nerve innervates the tensor tympani?
CN V3
Where does the stapedius muscle run from?
From pyramidal eminence to the neck of stapes
What is the function of the stapedius muscle?
Dampens sound by reducing vibrations of the stapes on the oval window
What is the innervation of stapedius?
CN VII
What facilitates ossicular movement?
Air in the tympanic cavity
What is the normal (and ideal) relationship between the atmospheric pressure and the pressure in the middle ear?
They are equal to each other
What impact can changes of atmospheric pressure have on the ossicles?
Can impact the vibrations of the ossicles
What is the function of the palate muscles?
Open the Eustachian tube to equalise pressure in the middle ear to the atmospheric pressure
What does an atmospheric pressure than that of the middle ear cause?
Makes the tympanic membrane push in
What does an atmospheric pressure less than that of the middle ear cause?
Makes the tympanic membrane push out
What can an unmatched atmospheric and middle ear pressure cause?
Reduced vibration of the ossicles and creates potential for barotrauma
What are the other names for the Eustachian tube?
Auditory tube, pharyngotympanic tube
Where does the Eustachian tube connect?
Connects anterior wall of middle ear cavity to the nasopharynx
What is the function of the Eustachian tube?
To equalise middle ear pressure to that of the atmosphere
How can otitis media arise?
Bacteria/virus uses Eustachian tube to move from pharynx/tonsils into middle ear
Why can tonsillitis and pharyngitis mimic otalgia?
The tonsils and the middle ear are both innervated by CN IX
What gives sensory innervation to the nasopharynx and oropharynx?
Mostly CN IX
What nerve provides sensory innervation to the laryngopharynx?
Mostly CN X
Where do the general sensory axons from the tympanic plexus pass down?
Eustachian tube
What conveys general sensation to the tympanic cavity mucosa?
CN IX via the tympanic plexus
What is the outflow of the tympanic branch of CN IX?
Goes to tympanic plexus overlying the promontory, then to lesser petrosal nerve (autonomic nerve supply to parotid gland)
What kind of nerve fibres are in the tympanic branch of CN IX?
General sensory and pre-ganglionic parasympathetic axons
What is the mastoid antrum continuous with?
The tympanic cavity (lined with mucosa)
Where is the opening (aditus) of the mastoid antrum?
Located in the posterior wall of the epitympanic recess
What can mastoiditis lead to?
Osteomyelitis
What can the mastoid be used to gain surgical access to?
The tympanic cavity
What structure is at risk of damage in mastoid antrum surgery?
The facial nerve = mastoid is closely related to facial canal
What forms the promontory of the inner ear?
Cupula of the cochlea
Where is the otic capsule located?
Located in the temporal bone
What is different about the bone that makes up the otic capsule?
The bone is denser than the rest of the temporal bone = otic capsule bone is fully developed at birth
What surrounds the otic capsule?
Less dense membrane of the mastoid part of the temporal bone
What are the two labyrinths that make up the otic capsule?
Bony labyrinth and the membranous labyrinth
What is the bony labyrinth?
Cavity of the otic capsule = filled with perilymph (similar to extracellular fluid)
Where is the membranous labyrinth located?
Suspended within the bony labyrinth of the otic capsule = filled with endolymph (similar to intracellular fluid)
What are the roles of the different sections of the ear in hearing?
External ear collects soundwaves, middle ear conducts, cochlear apparatus of inner ear converts soundwaves
What do soundwaves do to the tympanic membrane?
Make the tympanic membrane vibrate = vibrations are transmitted through ossicles
Where do the vibrations of the ossicles caused by soundwaves spread to?
The footplates vibrates into the oval window = vibration of stapes creates pressure wave in perilymph
What do the pressure waves in the perilymph cause?
Hair cells in the cochlea are moved = APs stimulated and conveyed to the brain by the cochlear nerve
Which cranial nerve supplies the cochlear nerve?
CN VIII
What happens to pressure waves once they have stimulated APs in the cochlea?
They descend and become vibrations again
What does the round window of the cochlea do to pressure waves?
Dampens them
What detects auditory stimuli in the cochlear apparatus?
Receptor hair cells in the organ of Corti
Where is the organ of Corti located?
On the basilar membrane of the cochlear duct
What is the cochlear canal divided into?
The scala vestibuli and the scala tympani
Which ligaments suspends the cochlear duct and divides the cochlear canal into two?
The spiral ligament
What areas of the ear would cause conductive hearing loss?
The middle or external ear
What area of the ear would cause sensorineural hearing loss?
The inner ear
What is the vestibular apparatus responsible for?
Balance and perception of head movement
What detects movement of endolymph in response to head movement?
Hair cells of vestibular apparatus = clusters of hair cells in regions of membranous labyrinth (maculae, ampulla of ducts)
What are the three semi-circular canals of the vestibular apparatus?
Posterior, lateral and anterior
What detects angular movement change?
Semi-circular ducts
What detects linear movement change?
Utricle detects horizontal movement and saccule detects vertical movement
Where do the semi-circular canals connect with?
The vestibule
What are the parts of the bony labyrinth?
Vestibule, semi-circular canals and the cochlear
What are the parts of the membranous labyrinth?
Semi-circular ducts, saccule and utricle, cochlear duct
Where are the saccule and the utricle located?
Within the vestibule
How are the three semi-circular canals orientated to each other?
At right angles to each other (form 2/3 of a circle) = anterior is in sagittal plane, lateral is in axial plane, posterior is in coronal plane
What do the ampullae of the semi-circular canals have?
Internal crests with hair cell clusters
What does head movement do?
Moves hair cells relative to the endolymph causing depolarisation
What structures flow through the internal acoustic meatus?
CN VII, CN VIII, labyrinthine artery and veins
What is the labyrinthine artery a branch of?
Inferior cerebellar artery = from circle of Willis
What are the modalities of the facial nerve?
Parasympathetic secretomotor supply, special sensation of taste, somatic motor, general sensory
What are some structures supplied by the facial nerve?
Lacrimal gland, minor glands of nasal cavity/palate/nasopharynx, anterior 2/3 of tongue, sublingual and submandibular glands, muscles of facial expression
What would be some signs of facial nerve dysfunction?
Parasympathetic = dry eyes, mouth or mucosa Motor = facial paralysis
What is the course of the cranial portion of the facial nerve?
Leaves brain stem at pontomedullary junction from the cerebellopalatine angle and enters internal acoustic meatus
What cranial nerves are contained within the cerebellopalatine angle?
CN VII and CN VIII
What is the course of the temporal portion of the facial nerve?
Travels through temporal bone in close relationship to middle ear, leaves temporal bone through stylomastoid foramen
What are the temporal branches of the facial nerve?
Nerve to stapedius, greater petrosal nerve
What kind of nerve fibres are within the greater petrosal nerve?
Pre-ganglionic parasympathetic axons
What is the course of the extratemporal portion of the facial nerve?
Courses towards and through the parotid gland, splits into six branches
What is the course of the chorda tympani of the facial nerve?
Leaves tympanic cavity via petrotympanic fissure, courses between incus and malleus, branches from facial nerve in facial canal
Where does the chorda tympani innervate?
Conveys taste to anterior 2/3 of tongue, pre-ganglionic parasympathetic fibres to submandibular ganglion
What nerve gives general sensation to the anterior 2/3 of the tongue?
Lingual nerve = CN V3
What nerves join together to give secretomotor supply to the submandibular and sublingual glands?
The chorda tympani (CN VII) and the lingual nerve ( CN V3) = submandibular ganglion
What kind of fibres does the geniculate ganglion have?
Sensory from CN VII
What fibres are in the pterygopalatine ganglion?
Parasympathetic = innervated by greater petrosal nerve (CN VII)
What innervates the posterior 1/3 (vertical) of the tongue?
Taste and general sensation by CN IX
Which part of the tongue is within the oral cavity?
The anterior 2/3
What innervates the anterior 2/3 of the tongue?
General sensory by CN V3, taste by CN VII
Which papillae do not have taste buds?
Filiforme taste buds = responsible for touch and temperature sensation
Which gland should produce earwax?
Ceruminous and sebaceous glands
What is the umbo?
Shallow cone like depression in the tympanic membrane
Where is the cone of light of the tympanic membrane located?
Anteroinferiorly from the umbo
What’s is the flaccid part of the tympanic membrane called?
Pars flaccida = superior to attachment of malleus
What is present in the pars tensa that is absent in the pars flaccida?
Radial and circular fibres
Where is the epitympanic recess located?
Space superior to to the tympanic membrane
What is the role of the tegmen tympani?
Separates tympanic cavity from the dura on the floor of the middle cranial fossa
What is the anteroinferior relation of the mastoid antrum?
The facial canal
