Lecture 4 Ear Flashcards
What are the 3 parts of the ear
External
Middle
Inner
Describe the external ear
- Receives sound waves
- Pinna and the ear canal
- Tympanic membrane separates it from middle ear
Describe the middle ear and its functions
- Transmits sound waves from air to bone
- Amplifies by bone to bone
- Transmits sound to inner ear
- Air-filled cavity that connects with the pharynx through the eustachian tube
What part of the ear connects with the eustachian tube
Middle ear
It opens transiently to allow middle ear pressure to equilibrate with atmospheric pressure during chewing, swallowing and yawning
Describe the inner ear and its function
- Sound waves converted to nerve impulses
- Transmitted to CNS via acoustic nerve (CNVIII)
- Vestibular organs
What are the 2 parts of the external ear canal
Lateral 1.]/3rd made of skin and cartilage
Medial 2/3rd made of skin and bone (no hairs or cilia)- doesn’t produce wax
Where does skin in the externally ear grow from and where is it shed
Umbo of the tympanic membrane outwards
Shed in the lateral 1/3rd of canal
Name the features of the tympanic membrane
Pars flaccida Posterior fold Umbo Annulus Pars tensa Cone of light Manubrium of malleus Incus
What is the contents of the middle ear
- Ossicular chain
- Oval window
- Round window
- Facial nerve (usually covered in bone)
- Chorda tympani
- Eustacian tube opening
- Includes mastoid air cells
Name the Ossicles
Malleus
Incus
Stapes
What is the function of the ossicles
Conduct sound waves from tympanic membrane to inner ear via oval window
Amplification
What can disrupt the ossicles function
Trauma or bony sclerosis (Ostosclerosis)
Describe the process of sound in air being converted to nerve impulses
- Directs sound into canal
- TM vibrates
- Ossicular chain vibrates
- Transmitted to oval window of Cochlea
- This is detected by hair cells in organ of corti
- Converted into nerve impulses
- Transmitted to brainstem (junction of pons and medulla) by CN VIII
What is the function of the middle ear
Transduce vibration into nervous impulses
What are the most important relations to middle ear
Middle cranial fossa
Internal carotid artery
Sigmoid sinus and internal jugular vein
Nasopharynx
What does the Eustachian tube connect
The middle ear to the nasopharynx
What are the functions of the eustachian tube
Pressure equalisation
Mucus drainage
What causes fluid in the middle ear
Eustachian tube dysfunction which causes negative pressure to draw into the middle ear and mucus remains
What is acute Otitis Media
Infection of lining of middl earned can be bacterial or viral
What is the cause and presentation of acute Otitis media
Respiratory infections via Eustachian tube
Bulging red tympanic membrane
Pus in middle ear
Very painful
What is a complication of pus in the middle ear causes by otitis media
Mastoitis and pus in mastoid air cells
What is the cause of Otitis Media with Effusion
Eustachian tube not opening causing negative pressure and fluid to be drawn into middle ear
Why does fluid in the ear lead to hearing loss
Fluid filled ear limits mobility of ossicular chain
Why is Otitis media with effusion common in children
Narrow, horizontal Eustachian tube
Large adenoids at opening
What is the management of Otitis Media with Effusion
Monitor for 3 months
If no improvement Grommets can be inserted
What is Cholesteatoma
It is when negative pressure sucks in tympanic membrane causing a retraction pocket which enlarges and forms a large keratin ball in middle ear that can destroy and invade structures
What structures can result in complications with Otitis Media and Cholesteatoma
- Meninges
- Middle cranial fossa
- Facial nerve
- Mastoid cavity
- Inner ear
- Sigmoid sinus/internal jugular vein
What is the 6 segments of the facial nerve CNVII within the ear
Intracranial Metal segment Labyrinthe segment Tympanic segment Mastoid segment Extratemporal segment
What muscles of the face do the facial nerves supply motor function
Motor supply to:
Stapedius
Posterior belly of digastric
Stylohyoid
What part of the tongue does the facial nerve supply taste to
Anterior 2/3rds of tongue from Chorda tympani
What are the 5 branches of the facial nerve
Temporal Zygomatic Buccal Marginal Mandibular Cervical
Whats the difference between UMN and LMN palsy
UMN is caused by strokes, SDH or tumour and forehead is unaffected
LMN is cased by acute otitis media, cholesteatoma and forehead is affected as well as ipsilateral side
What is the contents of the Cochclear
Organ of Corti
Bony and membranous labyrinth
Bony-perilymph
Membranous- endolymph
What is the contents od the peripheral vestibular apparatus
Utricle
Saccule
Semilunar canals
What nerve supplies the Inner ear
Vestibularcochlear nerve (CN VIII)
What is the purpose of semilunar canals
responsible for detecting head rotation and maintaining balance
What is the purpose of Vestibule-ocular reflex
This is what is responsible for your ability to fix your vision on an object even when your head is moving
What is the function of the Saccule
Detects linear acceleration in vertical plane
What is the function of the Utricle
Detects linear accelerate
What innervates the sensation to the middle ear
• Tympanic branch of glossopharyngeal nerve (CN IX) AKA Jacobsons nerve.
What nerve innervates the sensation to posterior half of EAC
Auricular branch of vagus nerve (CN X)
What nerve innervates the anterior half of EAC
Facial nerve
What nerve innervates the pinna
Mandibular branch of the trigeminal nerve
