The ear, hearing and balance - Topic 10 Flashcards
What is the visible outer part of the ear called?
The auricle
or
The pinna
what is the outer folded edge of the auricle called?
Helix
Which structure is designed as a funnel to channel soundwaves into the ear canal.
Pinna
or
Auricle
What is the deep depression leading into the ear canal called?
Concha cava
What is the small flap of skin anterior tothe ear canal called?
tragus
Together the _____ and the ____ ____ comprise the external ear.
- Auricle
2. Ear canal
The s-shaped ear canal runs from the auricle to the ____ ____.
tympanic membrane (ear drum)
The ear canal has two means of trapping potentially harmful organisms before they can enter deep into the ear canal. What are they?
- small hairs lining the canal.
2. cells that produce cerumen (ear wax)
What is the physical boundary between the external ear and the middle ear?
tympanic membrane
When sound waves traveling down the ear canal hit the tympanic membrane, what does it do?
Vibrates.
The middle ear is divided into 2 cavities by the ossicles. What are the 2 cavities filled with?
Air
Most lateral bone in the middle ear?
Malleus
What is the communication point between the middle and inner ear?
The oval window.
Which of the ossicles rests against the oval window?
Stapes
Between the tympanic membrane and the inner ear, 3 bones extend. What are their names?
- malleus
- incus
- Stapes
What can happen if too much pressure builds up in the inner ear?
Damage to the ossicles
The cavity above the ossicles is called…?
The Epitympanic recess
What is the cavity below the ossicles called?
The tympanic cavity
The most medial ossicle?
Stapes
Tube linking nasal cavity and middle ear called?
Pharyngotympanic tuble
This bone attaches to the tympanic membrane.
Malleus
Ossicle in the middle of the other two.
Incus
The organ for sensing hearing. Shell like structure:
Cochlea
Structures in the inner ear located close to the cochlea. Similar structure to cochlea, but sense equilibrium.
semicircular canals
Nerve that brings special sensory information about equilibrium from semicircular canals, and sound from cochlear:
CN VIII Vestibulocochlear
External opening in the temporal bone = external opening into the ear canal.
External auditory meatus
OR
External acoustic meatus
There are 2 major aspects of the temporal bone.
1, Squamous part (outer flattened section)
2. petrous part (inside the skull, thickened section visible from superior view of skull floor)
Bone located on the lower lateral aspect of the skull, and partly fills the floor of the skull.
Temporal bone
The mastoid process of the temporal bone is usually filled with a network of hollow spaces called what?
*Mastoid air cells (or mastoid sinuses).
Structures of the inner ear are embedded deep in which bone?
Temporal bone
What is the purpose of the mastoid sinuses?
*reduce skull weight.
*Help equalise middle ear pressure
(direct communication between middle ear and mastoid air cells via opening in the wall of the middle ear. But infections in inner ear can also spread to the mastoid air cells.)
Opening between the petrous part of temporal bone and the inside of the skull.
Internal auditoriy meatus
or
Internal acoustic meatus
What passes through the internal auditory meatus?
- CN VIII Vestibulocochlear nerve traveling from the inner ear to the brain.
- CN VII Facial Nerve (on its way to the face - exits skull through stylomastoid foramen)
Name the ossicles:
- Malleus
- Incus
- Stapes
Air filled space with a chain of 3 bones strung across it?
Middle ear
The ossicular chain extends from the medial surface of the _____ _____ to the _____ _____.
- tympanic membrane
2. oval window.
The oval window opens from the middle ear into the ____ ____.
inner ear
What fits nicely into the oval window?
The footplate of the stapes.
What is the inner ear filled with?
Fluid
Apart from the oval window, there is another opening between the middle and inner ear called, what?
The round window.
What is the secondary tympanic membrane?
The membrane across the round window, dividing the air filled space of the middle ear from the fluid filled space of the inner ear.
What helps excess sound waves to escape from the inner ear and helps to prevent damage to the delicate structures of the inner ear?
The secondary tympanic membrane sealing the space across the round window.
Opening below the stapes and oval window in a diagram of the middle ear.
round window
How many tiny muscles in the middle ear?
2
How many muscles act on the ossicles? What are they called?
2
- Stapedius muscle
- Tensor tympani
Muscle between the posterior wall of the middle ear and stapes. Contraction stiffens the stapes and limits its movement (vibration) in response to sound waves.
Stapedius muscle
This muscle attaches to the malleus and partly to the pharyngotypmanic tube, sphenoid bone and temporal bone.
Tensor tympani
This muscle is about 25mm long. When it contracts it stiffens the malleus, limiting its movement.
Tensor tympani
Why are the tensor tympani and stapedius muscle important?
Excessive sound waves can damage the delicate structures of the inner ear. These 2 muscles can reduce sound conductivity by limiting the movements of the ossicles.
Why are the tensor tympani and stapedius muscle important?
Excessive sound waves can damage the delicate structures of the inner ear. These 2 muscles contract reflexively and reduce sound conductivity by limiting the movements of the ossicles.
What is the sound attenuation reflex?
An involuntary muscle contraction that occurs in the middle ear in response to high-intensity sound stimulus.
This stiffens the ossicles, limiting the transmission of sound waves via the tympanic membrane to the inner ear.
Structure between the cochea and the semicircular canal?
Vestibule
Which nerve innervates the stapedius muscle?
CN VII Facial nerve
Other names for the sound attenuation reflex?
- Acoustic reflex
- Stapedius reflex
- MEM (middle-ear muscles) reflex
- auditory reflex
The inner ear is comprised of 2 major parts. Name them:
- Cochlea
- semicircular canals
(vestibule between them is actually part of the equilibrium system, although sound waves do pass through the vestibule to reach the cochlea)
Which part of the inner ear houses the oval window that communicates with the middle ear?
The vestibule
The cochea is formed by a hollow bone called…?
Bony labyrinth
Inside the bony labyrinth is a tube of membrane called the…?
Membranous labyrinth
The turns of the bony labyrinth centre around a bony core called the…?
the modiolus
What is the modiolus of the ear?
The modiolus is a conical shaped central axis in the cochlea. It consists of spongy bone and the cochlea turns approximately 2.5 times around it.
How many turns does the bony labyrinth have?
about 2 1/2
The very end tip of the cochlea is called…?
The helicotrema (apex)
Both the bony labyrinth and the membranous labyrinth contain what?
Fluid
What is perilymph and what does it do?
The fluid filling the bony labyrinth. Similar constitution to other body fluids like CSF and extracellular tissue fluid. Assists in transmission of sound waves by fluid movement.
Opening between the middle and inner ear at the beginning of the scala vestibuli of the cochlea?
Oval window
Which way does the cochlea coil?
Outside to inside, anticlockwise, from oval window to helicotrema.
What is endolymph?
Comprised of specialised concentrations of ions such as sodium and potassium ions that are important in enabling activation of nerve action potentials in response to sound wave stimulation.
Opening between the middle and inner ear at the beginning of the scala tympani of the cochlea?
Round window.
What is the space extending from the oval window to the helicotrema, and filled with perilymph, called?
The Scala vestibuli
What is the space extending from the round window to the helicotrema, and filled with perilymph, called?
The scala tympani
What is the space in the membranous labyrinth which is filled with endolymph, called?
the Scala media
What is suspended within the membranous labyrinth and surrounded by endolymph?
The Spiral organ
The lower membrane of the membranous labyrinth is called? (Forms the roof of the scala tympani)
Basilar membrane
The upper membrane of the membranous labyrinth is called? (Forms the floor of the scala vestibuli)
Vestibular membrane
Found within the membranous labyrinth, the third membrane is called the…?
Tectorial membrane
Suspended within the scala media and bathed with endolymph, the third cochlear membrane is called the…?
Tectorial membrane
The cells involved in transmitting hearing information to the brain rest on the basilar but the hairs on the top of these cells are embedded in the _______ ______, above.
Tectorial membrane
Dendritic nerve endings carry sound information from the hairs cells to the brain via the….?
Vestibulocochlear nerve (CN VIII).
There are 2 types of cells resting on the basilar membrane. What are the cells called?
- support cells
2. hair cells
Distortion of the basilar membrane causes part of the sensory cells embedded in it to move. But part of these sensory cells are embedded in the tectorial membrane and can’t move. Which part of this sensory cell is the moving part, and which part is the part that is held stationary by its attachment to the tectorial membrane?
Sensory cells are Hair Cells.
Tiny hairs at the top of the hair cells are embedded in the tectorial membrane and held stationary.
The cell body of the hair cells, below the tiny hairs, is attached to the basilar membrane and moves when it moves. The cell body bends relative to the hair cells at the top of it.
How is sound information converted into an electrical signal which is transmitted to the brain by CN XIII vestibulocochlear nerve?
Oval window -> Scala vestibuli -> via thin vestibular membrane -> scala media -> distortion of basilar membrane -> support cells and hair cells move, but hairs of hair cell are embedded in tectorial membrane, so hairs of hair cells stay stationary but cell body of hair cells bend in relation to the hairs -> mechanical signal that causes ion channels in cell membrane to open -> Ion flow from Endolymph fluid into hair cell body -> electrical potential occurs -> electrical signal transmitted to dendritic nerve endings at the base of the hair cell body -> to brain via CN VIII Vestibulocochlear nerve.
Which sensory cells attached to the basilar membrane, detect sound waves and transfer them to dendritic nerve endings at the base of their cells?
Hair cells
Electrical signals generated in the hair cell body when endolymph fluid enters the hair cell body, are transmitted to CN XIII vestibulocochlear nerve via….?
Dendritic nerve endings attached to the base of the hair cell.
The vestibulocochear nerve is comprised of 2 special sensory nerves which combine with each other to form CN XIII just after they pass through the internal auditory meatus into the skull. What 2 special sensory nerves?
- Vestibular nerve
2. Cochlear nerve
Which special sensory nerve carries auditory information from the cochlea in the inner ear, through the internal auditory meatus before combining with another nerve to form CN XIII Vestibulocochlear nerve?
Cochlear nerve.
Which special sensory nerve carries information about balance from the semicircular canals in the inner ear, through the internal auditory meatus before combining with another nerve to form CN XIII Vestibulocochlear nerve?
Vestibular nerve.
What is the Spiral Ganglion?
Ganglion in which cell bodies of dentrites attaching to base of hair cells in the cochlea are found. Axons coming from this ganglion form the Cochlear nerve.
CN XIII, the Vestibulocochlear nerve, attaches to the brain where?
At the brainstem near the juncture between the pons and medulla oblongata
What is another name for the
Cochlear ganglion?
Spiral Ganglion
What is the vestibular ganglion?
Ganglion in which cell bodies of dendritic
nerve endings coming from the semicircular canals are found. Axons from these neurons then form the vestibular nerve.
Oval window opens from the middle ear into the _____, and sound waves pass through it to reach the cochlea.
Vestibule
There are 2 key parts to the system for sensing movement and balance. What are they?
- Vestibule - senses static movement
* Semicircular canals - sense kinetic (active) head movements
The vestibule contains 2 structures inside the bone, which sense static position. What are they?
- Utricle (hairs at right angles to the skull base)
* Saccule (hairs parallel to skull base)
What are the specialised patch of cells inside the vestibular structures that sense static position called?
Macula
- Utricular macula
- Saccular macula
What are the two types of cells found in the macula of the structures of the vestibule?
*Support cells
* Hair cells
(just like in the cochlea)
In the cochlea, hairs on the end of the hair cells are embedded in the tectorial membrane. In the utricle and saccule they are embedded in…. what?
A gelatinous matrix containing otoliths.
What are otoliths?
little crystals or stones in the gelatinous matrix in the macula of the utricle and saccule.
Why are otoliths present in the gelatinous matrix?
They make the matrix more dense and can contribute to movement of the matrix that stimulates the hair cells.
What is static movement?
movement of our whole selves when we are not moving ourselves, ie traveling in a car or in a lift.
How is static movement detected?
Movement makes the gelatinous matrix, aided by the oticles, move -> bends the hair cells embedded in the matrix -> body of hair cells held stationary by the support cells, so doesn’t move. -> Bending of hair of hair cells relative to body of hair cells -> Lets in endolymph fluid which activates an electrical potential that is transmitted to the dendritic nerve endings - > via vestibular ganglion -> vestibular nerve -> combines with cochlear nerve just through inner auditory meatus -> CN VIII Vestibulocochlear nerve
The gelatinous matrix in the utricule and saccule will only move with forward/backward movement of the head in relation to gravity. True or false?
False!
True for the utricle, as the hairs are perpendicular to the space of the skull, so the matrix is parallel to the base of the skull and the horizon. Forward/backward motion will move it. But the Saccule hairs are parallel to the base of the skull and the matrix is a right angles to the base of the skull. Vertical Up and down movement will bend these hairs, not horizontal movement.
There are ___ semicircular canals all arranged at right angles to one another. Each corresponds to one of the body ____. What are the planes?
3 (bony canals) body planes * Sagittal * Coronal * Horizontal
Nodding our head as if saying yes is movement detected by which semicircular canal?
Superior semicircular canal
sagittal plane movement
Which semicircular canal would detect this movement: Shaking our head as if saying no?
Horizontal semicircular canal (transverse/horizontal plane movement)
Tilting our head, bringing our ear down to our shoulders is movement detected by which semicircular canal?
Posterior semicircular canal
coronal plane movement
What is the bony labyrinth?
The rigid, bony outer wall of the inner ear in the temporal bone.
The bony labyrinth consists of 3 parts. What are they?
- Vestibule
- Semicircular canals
- Cochlea
What is the otic capsule?
Another name for the bony labyrinth. Also: osseous labyrinth.
What is found in the expanded base of each semicircular canal?
A specialised structure responsible for detecting movement in one plane.
What are the hairs of the hair cells in the base of the semicircular canals embedded in?
Cupula - a gel-like membrane.
Surrounding the cupula on all sides, and flowing through the entire semicircular canal, is which fluid?
Endolymph
Why doesn’t the cupula contain otoliths?
The otoliths are there to respond to changes in gravity. But in the semicircular canals, it is movement of the endolymph that pushes on the cupula and moves the hairs on the hair cells. The cupula is not required to respond to gravity.
Audition
hearing
The ear acts as an energy transducer, in that it converts acoustic energy (____ ____) into electrochemical energy (_____ _____ ______) for the brain to interpret as sound.
- Sound waves
2. nerve action potentials
The inner ear is located in the ____ part of the temporal bone.
petrous
External auditory meatus (EAM)
Ear canal
Ear drum
tympanic membrane
Cavity of middle ear:
Tympanic Cavity
The tympanic membrane is covered with thin ____ externally, and the ____ _______ of the middle ear internally.
- skin
2. mucous membrane
The tympanic membrane has a shallow central depression called the ____ which is the attachment point of the malleus.
umbo
The middle ear is an air-filled space separated into two parts. what are they?
- Tympanic cavity (directly internal to the tympanic membrane)
- epitympanic recess (superior to the tympanic membrane)
The middle ear connects with which sinuses?
Mastoid cells (which are sinuses in the mastoid process of the temporal bone)
What are the contents of the middle ear?
- Ossicles
- Stapedius and Tensor Tympani muscles
- Chorda Tympani (branch of CN VII Facial nerve)
- Tympanic plexus of nerves
What is covered by the secondary tympanic membrane?
The round window
Where is the opening in the middle ear that connects with the mastoid air cells?
Posterior wall (mastoid wall)
Where is the connection between the tympanic cavity and the nasopharynx?
Anteriorly, in the tympanic part of the middle ear
Name 2 functions of the ossicles.
- Deliver sound vibrations to the fluid of the inner ear
* help limit damage to the inner ear by tensing in response to excessively strong vibrations
Which 2 muscles dampen the movement of the ossicles?
- Tensor tympani
* Stapedius
This muscle attaches to the malleus, sphenoid bone and temporal bone and the auditory tube.
Tensor tympani
Which nerve innervates the tensor tympani?
CN V3 Mandibular branch of Trigeminal nerve
This muscle attaches to the stapes and the posterior wall of the middle ear. It rotates the stapes posteriorly.
Stapedius
Which nerve innervates the stapedius?
CN VII Facial nerve
What is the sound attenuation reflex?
Stapedius and Tensor tympani stiffen the ossicles, reducing the strength of signal reaching the inner ear, thus protecting it from damage. Only works for lower frequency sounds.
Describe the pathway of sounds to the point where they are received by the brain.
Auricle captures from environment -> EAM -> Tympanic membrane (vibrates) -> Ossicles vibrate -> Oval window vibrates -> fluid in inner ear vibrates -> deformation of basilar membrane -> Hair cells (sensory receptors) in basilar membrane send action potentions in response to the deformation -> Nerve impulses via vestibulocochlear nerve -> Auditory cortex of the temporal lobe
What is the osseous labyrinth?
(bony labyrinth) - series of tunnels and chambers located in petrous part of the Temporal bone. 3 parts - vestibule, semicircular canals, cochlea
What is the osseous labyrinth filled with?
Perilymph
Name the parts of the bony labyrinth:
- Vesibule
- Semicircular canals
- Cochlea
What is suspended within the bony labyrinth by perilymph?
Membranous labyrinth
What does the membranous labyrinth contain?
Endolymph
The entry way to the inner ear, located between the cochlea and the semicircular canals:
Vestibule
Which structures in the vestibule are involved in balance?
- Utricle
2. Saccule
What is on the lateral wall of the vestibule?
The oval window
Name the semicircular canals:
- Anterior canal
- Posterior canal
- lateral canal
What planes are the semicircular canals arranged in? What movements can they sense?
- Sagittal, coronal and horizontal (at 90* to each other)
2. Nodding, rotating, tilting (ear to shoulder)
Each semicircular canal opens onto the _____.
vestibule
Within the semicircular canals are…. what?
The semicircular canals of the membranous labyrinth
What is the modiolus made of ?
Finely perforated bone. (fibres of CN VIII pass through these perforations to hair cells within the cochlea)
What is the modiolus?
The core of the cochlea. (Made of finely perforated bone).
What is the osseous spiral lamina?
A bony shelf projecting from the modiolus. The scala media (cochlear duct) is attached by the osseous spiral lamina
Which structure houses the organ of hearing?
The scala media (cochlear duct)
The osseous spiral lamina divides the bony labyrinth into 2 incomplete chambers and attaches the scala media between them. What are the chambers called?
- Scala tympani
* Scala vestibuli
What do the scala tympani and the scala vestibuli contain?
Perilymph
The osseous labyrinth has 3 openings. Name them:
- Round window (scala tympani to middle ear. Sound exit)
- Oval window (scala vestibuli to middle ear. Sound entry)
- Cochlear aqueduct (scala tympani to cranial cavity)
This structure can be considered as a series of fluid filled sacs and ducts suspended within the bony labyrinth
Membranous labyrinth
What is the membranous labyrinth filled with?
Endolymph
The membranous labyrinth is involved in both ____ and _____ and has _____ parts.
- hearing
- balance
- three
Where are the utricle and saccule located? What is their function?
- The vesibule
2. Static balance
Name the 3 parts of the membranous labyrinth:
- Utricle and saccule (found in the vestibule. Static balance)
- three semicircular ducts (found in the semicircular canals. Dynamic balance)
- Cochlear duct [scala media] (in cochlea. Hearing)
The cochlear duct (scala media) is located in the cochlea between the __ _____ and the _____ _____.
- scala tympani
2. scala vestibuli
Vestibular membrane. Another name?
Reissner’s membrane
Reissner’s membrane?
Vestibular membrane
What forms the roof of the scala media (cochlear duct)?
Reissner’s membrane (vestibular membrane)
What forms the floor of the scala media?
Basilar membrane and outer edge of osseous spiral laminal
Where is the Spiral organ of Corti located? What is it?
- on the Basilar membrane (floor of the Scala media)
2. receptor for auditory stimuli
Describe the spiral organ of Corti:
Comprised of Hair cells that rest on the surface of the basilar membrane. Their tips are embedded in the Tectorial membrane. The bases of the hair cells connect to dendrites of sensory neurons (cell bodies are in the spiral (cochlear) ganglion.
The tips of hair cells of the organ of Corti are embedded in the tectorial membrane and have limited movement capacity. True or False?
True
The bony labyrinth is filled with perilymph, but the membranous labyrinth is filled with what?
Endolymph
How does the spiral organ of Corti work?
sound waves in perilymph move Basilar membrane -> Hair cells embedded in Basilar membrane move -> Tips of hair cells embedded in tectorial membrane don’t move much so hair cells bend -> Bending causes hair cells to release a neurotransmitter that causes activation of attached sensory nerve cells -> transmitted to brain
Vibration of perilymph in the scala ____ displaces the basilar membrane.
vestibuli
Short sound waves/high pitch means displacement of Basilar membrane _____ to the oval window.
Close
Long sound waves/low pitch means displacement of basilar membrane ____ ____ _____ the oval window.
Further away from
Vibrations of the perilymph in the scala vestibuli then the endolymph in the cochlea duct are transferred to the perilymph of the ____ _____.
scala tympani
Vibrations in the perilymph of the scala tympani are transferred to the ____ ____ where they are _____ (protects from pressure build-up and dissipates the sound waves)
- round window
2. dampened
If the Primary Auditory cortex in only one hemisphere is damaged, will hearing be effected?
No. Neural auditory pathway consists of crossed and uncrossed pathways.
Sensory nerves from the spiral ganglion terminate where?
Cochlear (spiral) nucleus in the brainstem. From there they are relayed to thalamus and then to the primary auditory cortex.
The inner ear has two systems for regulating balance. What systems?
- Static system
* Dynamic system
The static system for regulating balance consists of what?
- Utricle
* Saccule
What is the static system of balance?
Position of the head relative to gravity and linear acceleration/deceleration
What are the specialised epithelia that consist of hair cells and supporting cells, found within the utricle and saccule?
Maculae
The hair cells in the utricle and saccule are embedded in a gelatinous mass containing what?
Otoliths (little stones)
What is the ampulla?
The expanded base of each semicircular canal, containing the crista ampullaris (specialised epithelium similar to the maculae in the utricle and saccule)
What does the Crista Ampullaris in the ampulla of the semicircular canals consist of?
A ridge with a curved gelatinous mass, the CUPULA. Hair cells are embedded in the cupula.
How is dynamic balance detected?
Endolymph within the semicircular canals has intertia, and doesn’t move at the same rate as the canals when the head moves. This different rate of movement causes the displacement of the hair cells and creates action potentials.
