Week 2 Lecture 6: Hearing and Equilibrium Flashcards
What senses is the ear responsible for?
Hearing and equilibrium
What does the external ear consist of?
The pinna, ear canal, and tympanic membrane (or eardrum)
Where is the middle ear located and what is it connected to?
The middle ear is after the eardrum and connected to the pharynx via the Eustachian tube
What sensors does the inner ear contain and what senses do they correspond to?
The cochlea (hearing) and the vestibular apparatus (equilibrium)
What is sound?
Pressure waves, at the peaks of the waves pressure is high and at the troughs pressure is low
What is frequency?
The number of wave peaks per second
What is frequency perceived as?
Pitch, low frequencies are low-pitched sounds, high frequencies are high-pitched sounds
What is the measurement of frequency?
Hertz (Hz), waves per second
What is the frequency range humans can hear?
16 to 20,000 Hz, 10 octaves
What frequency range is aquity highest?
1000-3000 Hz
What is amplitude?
The pressure difference between peaks and troughs
How does amplitude play a factor in our perception of sound?
It determines our perception loudness, the larger the amplitude, the louder the sound
What does also loudness depend on?
Frequency, if a sound is beyond the range of human hearing it won’t be perceived no matter how loud it is
What do sound waves do to the eardrum
Vibrates the eardrum
What bones carry the vibrations from the eardrum through the middle ear to the oval window?
The ossicles, the eardrum vibrates the malleus which move the incus which moves the stapes which pushes against the oval window.
What is the oval window?
A membrane between the middle ear and the inner ear (cochlea)
What does the cochlea contain?
Receptor cells
What are the vestibular and tympanic ducts?
The vestibular and tympanic ducts are lateral ducts of the cochlea.
What do the vestibular and tympanic ducts contain?
Perilymph, a fluid similar to plasma
Where do the vestibular and tympanic duct communicate?
At the helicotrema
What is the cochlear duct?
The medial duct of the cochlea
What does the cochlear duct contain?
Endolymph, a fluid similar to intracellular fluid AND the organ of Corti
What happens when the oval window vibrate?
Creates waves in the perilymph which shakes the cochlear duct
What happens after the cochlear duct vibrates?
The wave energy eventually exits back into the middle ear via the round window
Where is the organ of Corti located?
It sits on the basilar membrane and under the tectorial membrane
What does the organ of Corti contain?
Auditory receptor cells (mechanoreceptors) called hair cells
Are hair cells neurons?
No, they are epithelial cells (20,00 per cochlea)
What does each hair cell have?
Stereocilla, 50-100 stiff hairs that extend into tectorial membrane
What happen to stereocilla when there are waves in the perilymph?
They bend when waves in the perilymph deform the basilar and tectorial membrane
When does the hair cell excite its primary sensory neuron (depolarizes/releases transmitter)?
When its cilia bends toward the longest cilium
When does the hair cell releases less transmitter (hyperpolarizes)?
When its cilia bend away from its longest cilium
How does the basilar membrane respond to different frequencies at different points?
High frequencies displace the basilar membrane at its stiff, narrow end near the oval window while low frequencies displace the basilar membrane and its wide, flexible end near the helicotrema
What does the pattern of membrane motion reveal to the brain?
Pitch
What is the pathway of auditory information?
Auditory nerve, cochlear nuclei in the medulla (crossing over), midbrain, medial geniculate nucleus of the thalamus and the auditory cortex
Where is the primary auditory cortex (A1) located?
Temporal lobe
What does the brain localize sounds based on?
Loudness and timing, if a sound is louder in the right ear it coming from the right side or if a sound reached the right ear before the left ear it is coming from the right side
What are the different types of hearing loss?
Conductive, sensorineural and central
What is conductive hearing loss?
Sounds cannot be conducted through external or middle ear
What is sensorineural hearing loss?
Damage to the hair cells or elsewhere in the inner ear, most common in elderly (presbycusis) since hair cells cannot be replaced and are lost with age
What is central hearing loss?
Damage to cortex or to the pathway between cochlea and cortex, patients usually have trouble interpreting/recognizing sounds
What is the Rinne test?
Tuning fork is held against the mastoid bone and then beside the ear. If the sound is louder through the bone rather than beside the ear, there is conductive loss
What is the Weber Test?
A tunic fork is held to the middle of the patient’s forehead. If the sound is louder in the good ear there is sensorineural loss. If it is louder in the bad ear ear there is conductive loss (doesn’t have to pass through ear canal)
What are the utricle and saccule?
Parts of the vestibular apparatus that contain hair cells that are activated when the head tilts relative to gravity
What are semicircular canals?
Part of the vestibular apparatus, fluid-filled hoops that detect head rotation
Where vestibular pathways project?
Mainly to the cerebellum, vestibular hair cells activate primary sensory neurons of the vestibular nerve (cranial nerve 8) which either pass directly to the cerebellum or synapse in the medulla and proceed to the cerebellum or the thalamus (cortex)
