Physiology of Ear Flashcards
State the basic functions of the external, middle and inner ear
External: collect sound
Middle: amplify sound
Inner: sound transduction
What does sound “frequency” dictate? What frequency of sound can humans perceive?
Frequency = pitch of sound
Humans perceive between 20 and 20,000 Hz
What does sound “amplitude” dictate?
Amplitude = intensity/loudness of sound
How does the auricle/pinna of the external ear aid sound collection?
Concave cartilaginous structure directs sound into the ear canal
The inner ?/3 of the ear canal is embedded in the temporal bone
The inner 2/3 of the ear canal is embedded in the temporal bone
Where does airborne sound travel towards in the ear canal?
Towards the tympanic membrane (eardrum)
What is the function of the tympanic membrane (eardrum)?
Separates external + middle ear
Transmits airborne sound from external ear to middle ear through vibration
Protects middle ear structures
Where (anatomically) is the middle ear cavity located?
Mastoid process of temporal bone
List the main structures of the middle ear
Tympanic membrane Malleus Incus Stapes Oval window Eustachian tube
What makes up the ossicular chain?
Incus
Malleus
Stapes
The malleus is attached to the tympanic membrane. True/False?
True
At how many decibels does the ossicular chain amplify sound?
25 decibels, depending on frequency of sound transmitted
What is meant by “impedance matching” of sound in the middle ear?
When sound in air strikes fluid, there is a loss of sound energy and thus intensity which would be detected by a listener;
to compensate, the middle ear concentrates sound on the small SA of the stapes to result in proportional amplification (SA eardrum 21x greater than stapes), thus overcoming loss of decibels due to liquid interface
What is the function of the Eustachian tube?
Air pressure equaliser + ventilator for middle ear mucosa
At rest, the Eustachian tube is closed. True/False?
True
Which muscles open the Eustachian tube?
Tensor veli palatini
Levator palatine
What are the two openings from the middle ear to cochlea (inner ear)?
Oval window
Round window
What are the 2 main components of the inner ear?
Cochlea
Vestibular system
What is the collective term for the cochlea + vestibular system?
Otic capsule
What is the fluid system that suspends the otic capsule?
Perilymph (connected to cerebrospinal fluid)
The perilymph system is located within the membranous labyrinth of the inner ear. What are the 6 specialised receptor organs found within the membranous labyrinth?
Organ of Corti
Maculae of utricle + saccule
Cristae of the 3 semicircular canals
What 3 chambers make up the cochlea?
Scala vestibuli
Scala tympani
Scala media
The scala media is filled with endolymph/perilymph and the scala tympani + vestibuli are filled with endolymph/perilymph
The scala media is filled with endolymph and the scala tympani + vestibuli are filled with perilymph
What is the function of the Organ of Corti?
Sensory organ for hearing
Contains hair cells that convert mechanical bending force (caused by sound waves) into electrical impulses
Outline the process of hearing sound!
- Sound wave enters inner ear via oval window
- Transmitted through cochlear fluid
- Basilar membrane deflects in response to waves in inner ear
- Motion of basilar membrane bends hair cells resulting in sound transduction into electrical impulse
- CN VIII carries impulse from Organ of Corti to brainstem
The basilar membrane is “tonotopically organised” - what does this mean?
Each part responds to specific sound frequency
Apex = curly part of cochlea = low frequency
Base = high frequency
Where is the auditory cortex in the brain located (where electrical sound impulses arrive)?
Superior temporal gyrus, Broadmann area 41/42
List the central pathways for sound (ECOLI)
Eighth cranial nerve Cochlear nucleus Olivary complex Lateral lemniscus Inferior colliculus
What is the function of the vestibular system?
Maintain balance regardless of head position or gravity in conjunction with eye movement + somatosensory input
What are the 5 specialised receptor organs within the membranous labyrinth of the inner ear related to balance?
Maculae of utricle + saccule
Cristae of the 3 semicircular canals
What is another term for the utricle + saccule?
Otolith organs
Outline the function of the maculae of the otolith organs
Sensory part with upward-projecting cilia covered in gelatinous mass + calcium carbonate
Brain perceives linear movement due to firing of cilia when head is tilted
What is the degree of orientation of the otolith organs?
360’
Outline the function of the cristae of the semicircular canals
Sensory part with hair cells embedded in a cupula that depolarise/hyperpolarise depending on fluid inertia created by head angulation
What is the degree of orientation between the semicircular canals?
90’
