The Auditory System Flashcards
What is the external ear made up of
Pinna (auricle)
External auditory meatus
Tympanic membrane
What does the external ear do
Conducts sound waves to middle ear
What is the middle ear made up of
Tympanic cavity
Ossicles (malleus, incus, stapes) -small bones
What does the middle ear do
Conducts sound waves to inner ear
What is the inner ear made up of
Cochlear and vestibular system
Vestibulocochlear nerve
What does the inner ear do
Hearing and equilibrium (balance)
How is the pinna Innervated
Mandibular trivision of the trigeminal nerve and cervical nerve 2+3
What is the pinna
External ear
Elastic cartilage covered with skin
Sound waves pass into the eternal auditory meatus
What 3 parts of the external ear helps to funnel sounds into the ear canal
Tragus, helix and concha
How is the external auditory meatus (ear canal) Innervated
Auriculotemporal nerve and the vagus nerve
External auditory meatus
-canal that conducts sounds to the tympanic membrane
-2-3cm long
-cartilaginous lateral third
-skin continuous with skin of pinna
-skin is continuous with external layer of tympanic membrane which is at the distal end of external auditory meatus
Does the external auditory meatus have a slight s bend true or false
True and it needs to be straightened in order to use an otoscope
What produces cérumen (earwax)
Sebaceous and ceruminous glands
What is the tympanic membrane
External ear
Ear drum
What is the tympanic membrane (eardrum)
-oval thin and semi transparent membrane
-1cm diameter
-mucous membrane internally (columnar epithelium)
-laterally concave
What does the tympanic membrane seperate
External auditory meatus form the tympanic cavity
Where does the tympanic membrane conduct sound waves to
Auditory ossicles
The tympanic membrane is covered with skin externally. What kind of tissue is this
Stratified squamous epithelium
How is the central Umbro formed
Handle of malleus
What kinds of fibres does the Tense part inferior to lateral handle of malleus have
Has radial and circular fibres
What kind of fibres does the flaccid part superior to handle of malleus (eardrum) have
Thin and lacks fibres
How is the tympanic membrane Innervated
Glossopharyngeal nerve
What are the two parts of the tympanic cavity
- tympanic cavity proper medial to the tympanic membrane
-epitympanic recess supero- medial to the tympanic membrane
What does the tympanic cavity contain
-the auditory ossicles (malleus, incus, stapes)
-tensor tympani and stapedius muscles
-chords tympani (branch of the facial nerve)
-tympanic nerve plexus
What is the tympanic cavity in communication with
The nasopharynx via the Eustachian tube
The mastoid air cells vis the aditus and mastoid antrum
What part of the ear is the tympanic cavity
Middle ear
Tympanic cavity walls
-tegmetal wall
-jugular wall
-membranous wall
-labryinthine wall
-mastoid wall
-carotid wall
Tegmetal wall
Roof
-formed by Tegan tympani, a thin plate of bone
-seperates tympanic cavity from middle cranial fossa and brain
Jugular wall
Floor
-formed from bone
-seperates tympanic cavity from superior bulb of internal jugular vein
Membranous wall
Lateral wall
-formed from tympanic membrane and lateral bony wall of epitympanic recess
-seperates tymapnic cavity from external ear
Labryinthine wall
Medial wall
-formed from lateral wall of vestibule (including oval window) and initial turn (including round window) of the cochlear
-seperates tympanic cavity from inner ear
Mastoid wall
Posterior wall
-aditus links tympanic cavity to the antrum which in turn communicates with the mastoid air cells
-facial nerve canal is between the antrum and the posterior wall of the tympanic cavity
-mastoid antrum and air cells are within the mastoid process
-lined with mucous membrane that is continuous with lining of tympanic cavity
-tegmen tympani seperates antrum from middle cranial fossa
Carotid wall
Anterior wall
-contains openings of the pharyngotympanic tube and the canal for the tensor tympani
-seperates tympanic cavity from the carotid canal (and internal carotid artery)
Ossicles
-middle ear
-three bones, incus, malleus and stapes
-transmit sounds from the tympanic membrane to the cochlear
-increase the force of sound waves
-maintain the frequency of the sound waves
Malleus
(Part of the ossicles in the middle ear)
-handle of malleus is embedded in the tympanic membrane
-neck lies against the flaccid part of the tympanic membrane
-head in epitympanic recess and is in contact with incus
Incus
(Part of the ossicles in the middle ear)
-body of incus (anvil) is in epitympanic recess and articulates with the malleus
-long limb articulates with stapes
-short limb is connected by a ligament to the posterior of the tympanic cavity
Stapes
(Part of the ossicles in the middle ear)
-stapes (stirrup) is the smallest ossicle
-has two limbs and a base
-base fits into the oval window of the medial wall
-transmits sound waves to cochlear
What are the 2 muscles in the tympanic cavity
Tensor tympania and stapedius
Reduce vibrations when contracted to protect against loud noises
Tensor tympani muscle origin
-has origin on cartilaginous part of eustachin tube, greater wind of sphenoid and temporal bone
Tensor tympani muscle insertion
Handle of malleus and tenses tympanic membrane
How is the tensor tympani muscle Innervated
By a mandibule nerve
Origin of the stapedius muscle
Inside pyramidal eminence of posterior wall
Insertion of the stapedius muscle
Inserts onto neck of stapes and pulls it posteriorly and tilts its base in the oval window
How is the stapedius muscle Innervated
By a branch of the facial nerve VIII
Hyperacusis
Distorted and aching sounds due to stapedius paralysis
What is the pharyngotympanic also known as
Eustachian tube
What does the pharyngotympanic tube communicate with
Nasopharynx
What does the pharyngotympanic tube do
Equalises pressure between middle and external ears
Pharyngotympanic tube
-posters latéral third is bony and the remainder is cartilaginous
-exits through foramen lacerum
-Lined with mucous membrane
-walls normally in contact but can be open by contracting tensor veil palatini lavator veil palatini eg yawning or swallowing
What does the vestibulocochlear organ do
-involved in the reception of sound and the maintenance of equilibrium (balance)
-vestibulocochlear organ is contained within the otic cavity in the inner ear
Where is the octic cavity
-in a region of dense bone located in the petrous part of the temporal bone
-therefore inferior to the middle cranial fossa
What are the tunnels called that the octic cavity contains
The bony labyrinth
What is the bony labyrinth
-fluid filled space
-the fluid is called perilymph
What is suspended inside the bony labyrinth
Membranous labyrinth
This also contains fluid: endolymph (lots of potassium but less sodium)
Branches of bony labyrinth are called…
Canals
Branches of membranous labyrinth are…
Ducts
What is the bony labryinth comprised of
Vestibule, cochlea, semicircular canals
What is the membranous labyrinth comprised of
Utricle and saccule, semicircular ducts, scala media
What does the spiral ligament in the octic cavity do
Secures scala media within the cochlear canal
Otherwise secured by filaments through the perilymph
Cochlea
-shell shaped
-first (basal) turn produces the medial (labryinthine) wall of the tympanic cavity
-first turn is punctured by the round window
-round window is covered by the secondary tympanic membrane
-cochlear canal starts at vestibule and make 2.5 turns around the modiolus
-cochlear canal contrains scala media
Scala media (cochlear duct)
-spiral tube, blind at one end
-triangular in cross section
-also called cochlear duct
-supported by spiral ligament superficially and bony spiral lamina deeply
What are the 2 compartments that the bony labyrinth of cochlear are separated into
Scala vestibule and Scala tympani
What is the roof of the Scala media formed by
Vestibular membrane
What is the floor of Scala media formed by
Basilar membrane
Transmission of sound waves
- Pressure waves in perilymph pass from oval to round windows
- Ascend to apex via scala vestibuli.
- Pass back to first turn via scala tympani
- Reach round window and secondary tympanic membrane.
- Waves dissipated into air of middle ear.
- Sounds that we can hear take a short cut
- They move vestibular membrane
- Then the endolymph
- Then the basilar membrane
Where is the organ of corti
- situated on basilar membrane
-lies under gelatinous tectorial membrane
What happens in the organ of corti
- Sound waves move basilar membrane
- This in turn bends the hairs (receptor) cells in relation to tectorial membrane where their ends are embedded
- Hairs move up and down.
- Mechanically gated ion channels open and close
- Therefore, movement of hairs converted into receptor potential.
- Movement of hairs: mechanically gated ion channels open and close
- Receptor potential converted into an action potential in cochlear nerd neurons.
- Nerve impulses transmitted to brain via spiral ganglion and cochlear division of CN VIII
How are frequencies determined
- Volume determined from amplitude of basilar membrane oscillation.
- Low frequency (pitch) sounds travel further than those of higher frequencies
- <50 Hz cause movements of entire basilar membrane
- Excites hair cells near apex
- Basilar membrane varies in thickness and width along its length
- This is where high frequency sounds are detected (20000Hz) (base of cochlear)
- It Is thin and wide at the apex this is where low frequency sounds are detected
- Two ears- stereoscopic sound
Where are high frequencies detected
Base of the cochlear
Where are low frequency sounds detected
Apex Where it is thin and wide
What does the internal acoustic meatus do
-the internal acoustic meatus transmits the vestibulocochlear nerve (CNVIII) from the cranial cavity to the middle ear
-it also transmits blood vessels and the facial nerve (CN VII)
Neural pathways of hearing
- Fibres of cochlear divisor of CN VIII pass to cochlear nucleus of medulla
- Synapse with neurones that pass to the inferior colliculi of midbrain.
- These neurones project to the thalamus
- This sense axons to auditory cortex of temporal lobe: perceived as sound.
What are the two kinds of hearing loss
Conductive or sensorineural
Conductive hearing loss
- Conductive hearing loss results from problems in the external and middle ears:
- External auditory meatus (stenosis)
- Tympanic membrane (perforation)
- Tympanic cavity (fluid retention)
- Auditory ossicles (inflammation, scarring)
Sensorineural hearing loss
- Sensorineural hearing loss results form problems with the inner ear or neurological pathway:
- Cochlea (cochlear ossificans)
- Cochlear nerve
- Cortical connections
- Brain stem
What are the 3 semicircular canals
Anterior, posterior and lateral
Semicircular canals
- actually deserve 2/3 of a Circle
-at right angles to each other therefore one in each plane so are important for balance
-semi circular ducts inside each canal
What are semi circular ducts
Communicate with the utricle
Each have ampulla at one end
Semi circular ducts ampullae
- Ampullae contain a sensory area, the ampullary crest
- Crests contain hair cells
- Sense movement of endolymph cause by movements of the head in that plane
Anterior duct
Anterior detects rotational movement inn the sagittal plane
Posterior duct
Posterior detects rotational movement in the coronal plane
Lateral duct
Lateral detects rotational movement in the transverse plane
What does the inertia of the endolymph do
Cause hairs in cupola to bend
Vestibule of the bony labyrinth
- An oval chamber about 5mm long
- Contains utricle and saccule of membranous labyrinth.
- Lateral wall has an oval window
- Baseplate of the stapes sits in the oval window
- Communicates with: the cochlear anteriorly, the semi circular canals posteriorly and the posterior cranial fossa via the aqueduct of the vestibule.
Vestibular labyrinth
- Comprised of two sacs, the utricle and saccule
- Joined by utriosaccular duct.
- Utricle is continuous with the semicircular ducts
- Saccule is continuous with the cochlear duct via the ducts reuniens
- Both utricle and contain sensory epithelium- maculae
Hair cells
Hair cells
- Hair cells of maculae involved in equilibrium
- Hair cells of macule are Innervated by vestibular division of the vestibulocochlear nerve (CN VIII)
Maculae
- Macula of the utricle is in its floor, parallel with the cranial base.
- Macula of the saccule is place vertically against its medial wall.
- Saccule: detects vertical linear motion and tilting of the head out of the horizontal (transverse) plane
- Utricle: detects horizontal linear motion (in the transverse plane) and tilting of the head out of the verticle plane
