Audiology Lesson 1 Flashcards
What are the 3 Parts of the ear?
The outer ear - external auditory canal and tympanic membrane
The middle ear - Tympanic cavity and mastoid air cells
The inner ear - Cochlear system and vestibular system
Describe the auricle and it’s main functions
The Auricle is the outside part of the ear, composed of: The Helix, antihelix, tragus,the lobule, and concha
Main functions are:
- localization for body
- Selective reinforcement of most important frequencies
- Amplification of around 10dB
Fully describe the external auditory canal and structures found nearby
The lateral 1/3 is cartilaginous and has ceruminous glads for cerumen (earwax) production
The median 2/3 is bony canal
Altogether it is 2.5 cm long
The canal amplifies frequencies between 2 - 4 kHz (most common in daily life)
It is near the TMJ therefore when inflamed - ear pain is experienced.
It is connected by Santorini fissures to the parotid gland - allowing infections / tumours to spread.
The mastoid process is found posteriorly (where the facial nerve runs
Fully describe the structure and function of the tympanic membrane
It is made of the pars flaccida and pars tensa
Pars tensa is made of 3 layers :
Outer layer (keratinized squamous stratified epithelium),
Inner layer (simple cuboidal epithelium)
Middle layer (lamina propria - fibrous - these fibres form the annulus which attaches the tympanic membrane)
Pars flaccida- triangular portion in superior part - involved in disventilation pathologies
Functions of the tympanic membrane
- Part of the sound conduction system
- Gathers sound like a microphone
- Provides a sonic shield to the round window
Loss of TM leads to maximum -35dB hearing loss
Fully detail all the walls of the tympanic cavity (middle ear) and what they connect with
Lateral wall - tympanic membrane
Superior wall - Tegmen tympani (close to middle cranial fossa)
Inferior wall - close to jugular vein
Anterior wall - Eustation tube, Tensor tympani muscle (CN 5) and near carotid artery
Posterior wall - connection with Mastoid cells - Aditus to Antrum, 3rd portion of the facial nerve, Stapedius muscle
Medial Wall - Promontory (basal turn of the cochlea), Round window and Oval window, 2nd portion of facial nerve, Jacobson nerve (CN 9 branch) which innervates tympanic cavity
Describe the 3 spaces the tympanic cavity is divided into
The Epi-tympanium - superior portion (Tegmen tympani, head of malleus, body and short process of incus)
The Meso-tympanium - Malleus and long process of the incus, opening of the eustation tube and stapes with chorda typmani
The Hypotympanium - close to jugular vein
Discuss the functions of the Tympanic-ossicular system
Works as: - Impedance transformer - Is a Type II lever - Provides and amplification of 90X (If completely destroyed the hearing loss would be -60dB maximum)
Describe the structure and function of the Eustachion tube (and mastoid process)
Links the nasopharynx to the middle ear. The first 1/3rd is bony canal - rest is cartilage. The isthmus is the narrowest part and it is opened and closed by the Tensor tympani and tensor levator palatini muscles
Functions:
- Ventilates the tympanic cavity
- Equalizes pressure between tympanic membrane and atmosphere
- Drains middle ear, and is a barrier from ascending infections
Mastoid process
Composed of air cells (biggest is antrum) which communicate with tympanic cavity - works as air reservoire
Fully describe the structure of the inner ear
Inner ear is made of the body labyrinth and membranous labyrinth
Bony -filled with perilymph (high Na+, low K+)
Membranous - filled with endolymph (high K+, low Na+)
Potential difference of -80mV between the two
Perilymph connects with liquor - hence meningitis can spread to inner ear to cause deafness. The anatomical links are the:
cochlear aqueduct
vestibular aqueduct
fundus of the inner ear canal
Cochlear is arranged spirally with 2.5 turns around a central structure called modiulus. The spiral ganglion is found within the modiulus and is composed of bipolar neurons of CN 8
The organ of Corti is the is the sensory system of the ear. It is supported by the basilar membrane.
The basilar membrane, The vestibular membrane and the Spiral lamina divide the 3 areas of the cochlea
- Scala Vestibuli (top)
- Scala Media / Cochlea duct
- Scala Tympani (bottom)
The scala media is filled with endolymph, the other 2 are filled with periplymph
The scala vestibuli and tympani communicate with each other at the apex - at the Helicotrema
Describe how sound transmission works and the tonotropic arrangement of the ear
The stapes transmits sound waves into the oval window which travel into the scala vestibuli, all the way to the apex then down the scala tympani.
On top of the organ of corti is the Tentorial membrane. As sound waves move - the relative movement between the T. membrane and the basilar membrane make the cilia of the hair cells on the organ of corti move. The inner hair cells transduce this movement into nerve impulses (interpreted as sounds)
The inner hair cells (1 row, type 1 hair cells)
The outer hair cells (3 rows, type 2 hair cells)
The outer hair cells recieve little innervation and only increase the sensitivity of the cochlea. Normal ears would ring upon stimulation of outer hair cells
Tonotopic arrangement
High frequencies are received near the base
Low frequencies are received near the apex
Describe how we visualize the ear in the clinic and the 4 part division of the tympanic membrane
Otoscope
Endoscope
Microscope
Draw a line along the manubrium of the malleus and another line perpendicular to it to divide the tympanic membrane into 4
Post. Sup. - manubrium of malleus
Post. Inf - round window
Ant. Sup. - Eustachian tube, tensor tympani canal and tensor tympani muscle
Ant. Inf - nothing, therefore the best place if you need to inject drugs
