Lesson 7: Hearing Flashcards
What is the difference between motor activity and motor control?
Motor activity: presence of movement - via corticospinal & corticobulbar tract
Motor control: quality of motor activity - via cerebellum & basal nuclei
How is intensity of sound measured? What can the human ear detect, and where is most language?
In decibels. 0dB-140dB, 60dB
How many decibels is painful? How many causes damage with time?
140dB is painful, and 90 causes damage with time
How is frequency of sound measured (pitch)?
Hertz
What are the two structures of the outer ear?
The pinna and the external auditory meatus
What is the purpose of the Eustachian tube? Where does it attach to?
From the middle ear to the nasopharynx. It equalizes middle-ear pressure with atmospheric pressure
What are the 3 ossicles?
Malleus, incus and stapes
What two muscles control the ossicles? What is their role?
The tensor tympani and stapedius. They protect the auditory mechanism from damage through the attenuation reflex
What is the bony labyrinth composed of?
Cochlea, vestibule and the semicircular canals.
What is the membranous labyrinth composed of?
The cochlear duct, the semicircular ducts, the saccule and the utricle - which are in the vestibule
How does the ear compensate for the discrepancy in size and consistency between the tympanic membrane (fluid) and the oval window (aid). What is the production of this restriction?
The stiffness of the ossicles. It results in restricted motion speed, and thus species can only hear frequencies within the ossicular motion limitations
What apparatus are responsible for equilibrium detection ?
The saccule, utricle, and the semicircular ducts
What is the primary receptor of hearing? Where is it located?
The organ of Corti, which is 3 rows of outer hairs and one row of inner hair cells, with stereocilia at their tips.
In the scala media, along the basilar membrane (bottom)
What is the difference in projection of outer hair cells vs inner hair cells?
IHCs: innervate the cochlear nerve
OHCs: project to the olivocochlear bundle
What is the structure of the cochlea? What are these parts filled with?
Scala vestibuli, cochlear duct (scala media), and scala tympani.
Vestibuli and tympani join in the back via the helicotrema, and are both filled with perilymph. The scala media is filled with endolymph
What is the primary receptor of equilibrium, and where are these located? What gel is it in?
The maculae (in the saccule and utricle), in the otolithic membrane The cristae ampullaris (in the tips of the semicircular ducts), in the cupula among endolymph
What is the site of maximum amplitude of high frequencies vs low frequencies?
Lower frequencies: near the helicotrema
Higher frequencies: near the oval window
How do sound waves in the tectorial membrane result in activation of the nerve?
The movement bends the ends of the cilia, which increases the cilia’s permeability to potassium ions - this depolarization results in the release of neurotransmitters to the cochlear nerve
What is the role of the spinal ganglia? Where are they located, and what are the types?
In the modiolus of the cochlea, they receive input from hair cells, and thus form the acoustic branch of the vestibulocochlear nerve. Type I responds to a select range of hair cells, whereas Type II synapses with 10+ hair cells
What cranial nerve is responsible for hearing? What number is it?
The vestibulocochlear nerve - CN VIII
How does the tympanic membrane work?
Vibration of the tympanic membrane, as received from the external auditory meatus, is converted to mechanical energy to the ossicles
How do the ossicles work?
They receive the mechanical energy from the tympanic membrane, which then is sent to the cochlea, where it becomes hydraulic energy
Where does hearing secondly synapse?
In the cochlear nuclear complex in the pons
What is the nature of the cochlear nuclear complex? Both in structure and in function
Dorsal and ventral cochlear nuclei
Low frequencies = surface of the cochlear nucleus
High frequencies = deeper in the nucleus
How does hearing ascend from the cochlear nuclear complex?
Trapezoid body - either crosses here or doesn’t
Then, either goes to superior olivary nucleus, or directly to lateral lemniscus
Then to the inf colliculus
What are the features of the superior olivary nucleus?
In the pons
Has binaural cells (lateral and medial superior olive)
This allows it to calculate differences in time and intensity
Where does the lateral lemniscus terminate?
the inferior colliculus of the tegmentum
Where does sound go from the inferior colliculus?
To the medial geniculate body
Info may cross here via the commissural fibres
Where does sound go from the MGB?
To the gyri of Heschl, for the primary auditory cortex, via the internal capsule
How are frequencies represented in the primary auditory cortex?
Higher f = posteromedial
Lower f = anterolateral
What damage causes conductive hearing loss? What causes sensorineural hearing loss? In terms of anatomy
Conductive: outer and middle ear
Sensorineural: cochlear hair cells (inner ear)
What is the difference in sound transmission with conductive vs sensorineural loss?
Conductive: interruption of sound transmission by air
Sensorineural: interruption of sound transmission equally by air and bone
What are the 3 symptoms of conductive hearing loss?
Fluctuating hearing loss
Softly spoken speech
Hearing well in noise
What are the 3 symptoms of sensorineural hearing loss, plus one that may occur?
Difficulty in hearing, particularly in noise
Speaking loudly
Loudness recruitment
Possibly: tinnitus
What is otosclerosis?
Abnormal bone growth near oval window = stapes are impeded
conductive hearing loss
What is otitis media?
Accumulation of fluid in the middle ear = Eustachian tube malfunction
What is Meniere disease? 3 symptoms
Excessive endolymph pressure in the membranous labyrinth
Progressive & fluctuating hearing loss, ringing in the ears, and vertigo
What is Prescbycusis? What causes it?
Degeneration of hair cells in the cochlear duct over time
Affects perception and discrimination of sound
What are the 3 symptoms of auditory nerve damage?
Preserved hearing sensitivity
reduced understanding of speech
difficulty hearing in noisy environments
What are the 2 main aspects of dysfunction of the central auditory system?
Near-normal sensitivity to auditory stimuli
Impaired processing
What occurs if there is damage to the cochlear nuclei?
Ipsilateral deafness
What happens with damage to the superior olivary nucleus?
Cannot identify and localize sound
What happens with damage to the lateral lemniscus (3)?
Impaired processing of speech in noise, cannot retain critical information from a conversation,
cannot identify sound source
What are 3 symptoms of damage to the MGB?
Impaired ability to incorporate attention in screening auditory info
Impaired ability to regulate information-processing speed
Inability to activate audition-triggered visceral functions
What is the left side of B21 and 22 responsible for?
nonverbal memory, musical and prosody interpretation, environmental sounds
What additional symptom comes with damage to the inferior colliculus compared with damage to the MGB?
Impaired self-awareness
What is the Rinne hearing test?
Tuning fork test
Testing bone conduction: on the mastoid process
Testing air condition: fork in front of ear
Positive: hear sound for longer by air than by bone
Negative: longer by bone
What is the meaning of a positive vs negative Rinne test?
Positive: normal hearing, or sensorineural (longer by air)
Negative: conductive loss (longer through bone)
What is the Weber hearing test?
Tuning fork on the scalp at the vertex
Unilateral –
Conductive: hear it in affected ear
Sensorineural: mainly in unaffected ear
(not for bilateral)
How does a pure tone audiometry work?
Audiometer generates pure tones at various Hz and dBs to detect hearing loss
What is hearing loss?
Amount of intensity (dB) of sound pressure above the normal sensitivity to perceive a frequency
What does tympanometry do? What does it show?
Changes the air pressure in the external auditory meatus
It shows if the tympanic membrane is impaired
Where are the primary receptors of the vestibular system? Where are they located?
Vestibular ganglia: in the utricle, saccule and semicircular canals
How does the info of the vestibulocochlear nerve split? Where does it do this?
In the pontocerebellar junction
The vestibular fibers go to the vestibular nuclear complex
The auditory nerve goes to the cochlear nuclear complex
What does disruption of the otolithic membrane in the utricle or saccule mean ?
Linear acceleration - gravity
What does disruption of the cupula in the semicircular ducts mean ?
Angular acceleration - head rotation
What is the first part of dynamic equilibrium, regarding static momentum?
Endolymph lags behind due to inertia, for 20 seconds. This results in static momentum, as the endolymph swings the cupula in the opposite direction of the head movement
What happens with bending of the cupula?
It communicates to the cristae ampularis, which then passes this info on to the vestibular ganglia. The ganglia are constantly active, but this changes the amount of firing
What is the second stage of dynamic equilibrium, regarding rotation in phase?
Endolymph starts moving in the right direction, and thus hair cells are no longer distorting
What is the third stage of dynamic equilibrium, regarding stopped rotation and anti-gravity movements?
The endolymph continues moving without the head moving, which bends the cristae
The adjustment of antigravity muscles forces the body to follow the head
How does motion sickness occur ?
Fluctuating movements of the otolithic membrane in the vestibule result in fluctuating activation of the maculae
What is the function of nystagmus ?
To maintain a stable, conjugate visual fixation point
What happens regarding nystagmus when warm water is put in the ear canals?
The eyes drift AWAY from the tested side, then snap back to the tested side quickly
What happens regarding nystagmus when cold water is put in the ear canals?
The eyes drift TOWARD the tested side, then snap to the untested side quickly
What is the doll’s eye test? What does it show?
Eyes correct for changes in head position
If the connection between the vestibular system and the medial longitudinal fasciculus is severely damaged
Done in unconscious patients
What is the caloric test? What does it test?
Water is put in the external ear that alters the temperature of the middle ear
This induces a current in the endolymph in the semicircular canals
This stimulates head rotation without moving the head
The eyes are monitored for nystagmus
