Structure and function of the Ear Flashcards
List the 3 components of the external ear
1) Pinna (auricle)
2) External auditory meatus
3) Tympanic membrane
Label the image
What tube opens into the nasopharynx?
Eustachian tube
Which 2 parts of the ear are filled with air?
What can be said about the pressure across these parts and what structure maintains it?
The external and middle ear is filled with air.
The air pressure on the outside and inside is the same which maintained by the eushachian tube.
What 2 nerves are found in the internal ear?
The vestibulocochlear nerve and facial nerve.
What 2 ear structures arise from the first pharyngeal arch
Malleus and incus
What ear structure arises from the second pharyngeal arch
Stapes
Where does the Pinna arise from embryologically?
Pinna arises from six Hillocks of His, which is derived from pharyngeal arches 1+2
The first 3 hillocks of His = pharyngeal arch 1
The second 3 hillocks of His = pharyngeal arch 2
What 2 ear structures do the first pharyngeal pouch form?
The middle ear and Eustachian tube
What 2 ear structures do the first pharyngeal cleft form?
EAM and the tympanic membrane
What is the Pinna comprised of and what is its function?
Comprised of cartilage and skin and functions to collect and amplify sound
Label the image of the outer ear and briefly explain each structure you have labeled
Pinna is shaped like a bowl so sound is collected, and can then diverge down
The rim of the ear is the helix, and situated just in-front is the anti-helix
The Tragus is the bit of cartilage located in front of ear, and situated just in-front is the anti-tragus
Lobule: is determined by genes
Cocha: shape is designed to collect sound efficiently
What nerve innervation correlates to:
- Red triangles
- Blue dots
- Yellow area
- The rest
Red triangles: CN X (supplies most of the ear canal)
Blue dots: CN VII
Yellow: CN V
The rest are cervical nodes
Everything behind the are = cervical
Everything infront of the ear are = CN
Where nerve does most of the sensation to ear canal come from?
Why may using a cotton bud stimulate a cough?
CN X
The vagus nerve also supplies the larynx. Hence, stimulating this area with a cotton bud can elicit a cough reflex because it can stimulate the recurrent laryngeal nerve (branch of the vagus nerve)
What is the outer vs inner external auditory meatus made of?
What is the enitre canal lined by?
The outer 1/3 of the ear canal is cartilage
The inner 2/3 is made of bone (tympanic plate part of the temporal bone)
The entire tube is lined by normal hair bearing skin.
If you look into someones ear what can be seen?
What must be done in order to visualise this and why? (think direction of the EAM)
The ear drum and the bones of the ear
The EAM runs obliquely. Hence, when looking into an ear you have to pull the ear back.
What is function and composition of wax?
Wax is a good thing, it helps to clean out the dead skin cells within the ear
Cerumen (produced by ceremonious glands in the outer 1/3 of the ear) + Dead skin cells (migrate from the middle of the ear drum out) mix togther = to form wax and then move out of the ear
If part of the eardrum gets sucked inwards, what is the clinical implication?
The skin cells cannot migrate outwards leading to blockages
What structure is indicated by X?
The Tympanic membrane!!
What 6 structures comprise the middle ear?
- Tympanic membrane
- Ossicles/bones
- Mastoid
- Muscles
- Eustachian tube (Pharyngotympanic Tube)
- Mastoid air cells
The middle ear has a roof, a floor and anterior, posterior, medial and lateral walls
The ossicles within the middle ear project UP in what area?
The ossicle’s project upwards within the middle ear in an area called the epitympanic recess
This is a bulge within the middle ear located superior to the tympanic cavity, which lies next to the mastoid air cells. However, it cannot be seen as its hidden
Label the image of the Tempanic membrane
How can we tell if this is a R or L ear?
It is a Right ear because the light reflex is closest to the midline
What is the location and function of Mastoid air cells?
Mastoid air cells are located within the mastoid process of the temporal bone which is located behind the middle ear.
They are a collection of air-filled spaces contained within a cavity called the mastoid antrum. These function as a ‘buffer system‘ of air, releasing air into the tympanic cavity when the pressure is too low
What is the name of the ‘thin membrane’ located in the Tympanic Membrane
An absent light reflex may indicate what problem with this structure?
Pars flacida
Absent light reflex might suggest there is fluid accumulation behind the membrane
What are the two sections of the ear drum (tympanic membrane)
The bottom is called the Pars Tensa
The top 1/3ish is called the Pars Facida
What is the end of the handle of the malleus within the tympanic membrane called?
The umbo
What are the 3 layers of the Tympanic membrane in terms of CT/epithelium
Outer: stratified sqaumous epithelium
Middle: fibrous
Inner: mucous membrane
Describe the shape and angle of the tympanic membrane
Concave laterally
Lies obliquely
What is the sensory innervation to the outside vs inside of the Tympanic membrane
Outside: auriculotemporal (V3)
Inner: glossopharyngeal (IX)
In additon to an ear problem, what else must we consider if a patient has an ear ache?
Think about referred pain!
A variety of conditions can cause irritation of one of the nerves that provides sensation to the ear (CN V, VII, IX, X) and the nerves also supply other areas
Label the image of the Tympanic membrane
If we remove the eardrum and view the ear as a box, what structure is labeled above and below the black dotted line?
Above the line is the Epitympanic recess which you can’t see in real life.
Below the black dotted line is the Tympanic cavity and this is where the ear drum sits.
What 2 structures are located behind the mastoid process?
Located behind the mastoid process would be the brain and sigmoid sinus
What 2 structures would be found ABOVE the middle ear?
The middle cranial fossa and temporal lobe of the brain
What structure would be found BEHIND the middle ear?
The mastoid process which contains the mastoid air cells and opens into the mastoid antrum
What two structures would be found in the ANTERIOR wall of the middle ear?
The eustachain tube and the tensor tympani muscle
What is found below the FLOOR of the middle ear?
Internal Jugular Vein
What is found at the FRONT of the middle ear?
Internal Carotid Artery
What are the 2 openings from the inner ear to the middle ear:
What is the function of these?
1) Oval window (connects scala vestibuli to ME at stapes footplate)
2) Round window (connects scala tympani with middle ear)
Functions to transmit the sound waves from the tympanic membrane to the inner ear
What is the structure indicated by the box?
What surrounds this structure?
Promontory
This is the cochlea budging into the middle ear and is surrounded by a plexus of nerves arising from the glossopharyngeal nerve
What nerve travels through/ very close to the middle ear?
What are the 3 branches this nerve gives off?
The facial nerve (CN VII) enters via the IAM along with CN VIII.
3 branches within the middle ear:
- Greater petrosal nerve - supplies the eye (parasympathetic)
- Nerve to stapedius muscle - motor nerve
- Chorda Tympani - taste to the anterior 2/3 tongue. (Special sensory)
What is the Geniculate Ganglion?
This is a bulge of the facial nerve and where the facial nerve bends. The greater petrosal nerve is given off here.
What are the bones of the middle ear known as?
List the three bones and the function of these
The ossicles (smallest bones in the body)
1) Malleus: attached to the eardrum
2) Incus
3) Stapes (Stirup bone)
These bones function to translate mechanical energy into an electrical signal
Explain how vibration/sound is transmitted from the tympanic membrane to the inner ear?
Sound vibrations cause a movement in the tympanic membrane which then creates movement in the auditory ossicles:
vibration progresses from the malleus → incus → stapes
The stapes is connected to the oval window of the internal ear. The internal ear contains fluid
What is the function of the middle ear?
Convert sound waves in air of EAM to vibrations in fluid of inner ear
As most sound waves hitting inner ear fluid are reflected and not transmitted to inner ear, around 30dB of sound would be lost
List the two ways the middle ear overcomes this?
1) Relative size of tympanic membrane and oval window (14:1)
* allows the vibrations of the ear drum to be focused and condensed into a single area, so less sound energy is lost
2) Lever action of ossicles (x1.3)
* the ossicles are aligned which act as levers to increase the function of the middle ear
Togther these allow the 30dB sound to be gained
What are the 2 muscles of the middle ear
What is their attachment, innervation and function?
1) Tensor Tympani (V) attached to malleus
* loud noises causes tensor tympani to contract and pull in the ear drum. This ensures the ear drum does not vibrate too much and cause damage
2) Stapedius (VII) attached to stapes
* stops the stapes vibrating too much within the oval window, to prevent fluid to leaking out of the oval window
These both reduce vibration of ossicles in response to loud sounds
Describe the location of the Eustachian tube
From anterior wall of tympanic cavity
Passes down, forwards and medially to nasopharynx
Describe the composition of the anterior vs posterior Eustachian tube
Posterior 1/3 is bony
Anterior 2/3 cartilage
What is the function of the Eustachian tube?
Equalises pressure between middle ear and nasopharynx
During swallowing, yawning , chewing, valsalva we open the Eustachian tube which equalises pressure
What happens if we have a Blocked Eustachian tube?
What is the backup if the Eustachian tube fails?
We get negative pressure within the ear, which causes the ear drum to be sucked inwards. This can cause huge amounts of problems.
Mastoid air cells do the same thing as the eustahcian tube. They act as a back up in case the Eustachian tube isn’t functioning correctly.
List the 2 components of the Inner ear
State the function of each
1) Cochlea (hearing)
2) Vestibular apparatus (balance)
What bone does the inner ear sit within?
What structure runs below this bone?
The inner ear sits within the petrous temporal bone
The sigmoid sinus runs under the petrous temporal bone
List 2 functions of the Inner ear?
1) Convert mechanical signals (vibrations in fluid) to electrical signals → auditory pathway→ brain
2) Maintain balance
What 3 structures comprise the bony labyrinth of the the Inner ear
What is filled within this?
1) cochlea
2) vestibule
3) 3 semicircular canals
Filled with perilymph
What structure is found within the bony labyrinth of the Inner ear?
What 3 structures make up this stucture and what is it filled with?
The membranous labyrinth which is filled with endolymph and comprised of:
1) cochlear duct
2) utricle and saccule
3) semicircular ducts
Label the boxes shown of the cochlea
Bit going in is the Scala Vestibule
Bit going out is the Scala Tympani
Explain how sound is transmitted through the cochlea to the brain
1) vibration of stapes at oval window → vibrations of perilymph in scala vestibuli
2) vibrations transmitted to endolymph in cochlear duct and spiral organ of Corti on basilar membrane
3) Hair cells stimulated → impulses travel along CNVIII to brain
Label the image of the cochlea
What comprises the vestibular apparatus of the inner ear?
State the function of these
3 semicircular canals at right angles to each other: used for rotation of head
Utricle and Saccule: tells us the POSITION of the head (forward or back)
Describe the structure of the vestibular apparatus
Both ends of the semicircular canals (SCCs) open into utricle
One end of each canal has swellings - ampulla, which contains balance receptors
Balance receptors are stimulated by movement or change in position of head
What sensory structure is found inside the ampulla of the SCCs?
How is this stimulated and how are signals carried to the brain?
Cupula: Stimulated by starting/stopping of rotatory movements
1) Cupula is moved by by movement of endolymph
2) The Hair processes are bent which stimulates the hair cells
3) Impulses carried by vestibular branch of CNVIII to brain
What sensory structure is found inside the utricle and saccule (vestibule)?
How is this stimulated and how are signals carried to the brain?
Macula: stimulated by changes in position of head (eg.tilting)
1) The macula contains oliths (calcium carbonate crystals) which lay ontop of a gelatinous mass above hair cells
2) In response to movement, otoliths shift causing a change in weight distribution
3) This causes hair processes of hair cells to bend, thus stimulating them
4) Impulses carried by vestibular branch of CNVIII to brain
