Exam 7 - Ear Flashcards
The ear is divided into three main regions:
External ear, which collects sound waves and funnels them inward
Middle ear, which conveys sound vibrations to the oval window
Internal (inner) ear, which contains the receptors for hearing and for equilibrium
which collects sound waves and funnels them inward
External ear
which conveys sound vibrations to the oval window
Middle ear
which contains the receptors for hearing and for equilibrium
Internal (inner) ear
The external ear consists of the
Auricle
External auditory canal
Eardrum
The rim of the auricle is the
helix
The inferior portion is the
lobule
________ lies in the temporal bone, and leads to the eardrum
The external auditory canal
The eardrum has a covering of
epidermis
___ ____ are specialized sebaceous (oil) glands that secrete earwax (cerumen), which in combination with hairs that are present helps prevent dust and foreign objects from entering the ear
Ceruminous glands
The ___ is a small pointed eminence projecting backward over the meatus
tragus
The ____ is opposite the tragus
antitragus
Regionally are the mastoid process posterior to the lobule, and the __ __ __ anterior to the tragus
superficial temporal artery
The middle ear is a small air-filled cavity in the…
…temporal bone
The middle ear
It is separated from the external ear by the eardrum, and from…
the inner ear by the oval window and the round window
WHERE IS THE SITE OF TRANSDUCTION FROM LECTURE 1 ????
HE said it was important in lecture so I threw it in here as a reminder… find the answer in JB’s cards
The middle ear contains the ____ ____ :
They transmit vibratory motions of the eardrum to the oval window
auditory ossicles
The ossicles are named for their shapes:
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
(hammer)
Malleus
(anvil)
Incus
(stirrup)
Stapes
Auditory ossicles:
The handle of the ____ is secured to the internal surface of the eardrum
The incus articulates with the….
The base of the stapes fits into the __ ___
malleus
…malleus laterally and the stapes medially
oval window
The handle of the malleus is secured to the…
… internal surface of the eardrum
The incus articulates with the ___ laterally and the ____ medially
malleus laterally and the stapes medially
The base of the ___ fits into the oval window
stapes
What can be seen on the tympanic membrane with an otoscope?
The handle and lateral process of the malleus, and the long limb of the incus produce bulges that can be seen when viewing the tympanic membrane using an otoscope
Muscles of the middle ear
Two small skeletal muscles attach to the ossicles:
Tensor tympani muscle
Stapedius muscle
Tensor tympani muscle
Arises from the wall of the auditory tube and inserts into….
Limits movement and increases tension on the eardrum to….
Innervated by…
….the handle of the malleus
prevent damage from loud noises
…. the trigeminal nerve (V)
Stapedius muscle
Originates from ?
Dampens ?
Innervated by ?
____ skeletal muscle in the body
Originates from the posterior wall of the middle ear cavity and inserts into the stapes
Dampens large vibrations of the stapes due to loud noises
Innervated by the facial nerve (VII)
Smallest skeletal muscle in the body
slide 13 otoscopic view
slide 13 otoscopic view
slide 14
slide 14
An ear exam includes bilateral otoscopic inspection of both tympanic membranes. A normal tympanic membrane is
pearly gray and translucent
The cone of light is a reflection from the otoscope’s illuminator. Termed the __ __, it is visible radiating ____ in a healthy ear, and can provide orientation
light reflex
anteroinferiorly
Also called the auditory tube, or the pharyngotympanic tube
Consists of both bone and cartilage
Connects the middle ear with the nasopharynx
Eustachian tube
Eustachian tube
Also called the ?
Consists of?
Connects the middle ear with the ?
Also called the auditory tube, or the pharyngotympanic tube
Consists of both bone and cartilage
Connects the middle ear with the nasopharynx
It is normally closed, but opens upon swallowing and yawning
Equalizes the pressure in the middle ear with the atmosphere
Without equalization, the ear would not be as effective, and pain or vertigo could also develop
Eustachian tube
The Eustachian tube is also a route that pathogens may take from the…
…nose and throat to the middle ear
The inner ear is also called the…
Two main divisions?
…labyrinth
Bony labyrinth (outer) Membranous labyrinth (inner
The bony labyrinth is a series of cavities in the petrous portion of the temporal bone comprising three areas
Semicircular canals
Vestibule
Cochlea
The ___ ___ is a series of sacs and tubes inside the bony labyrinth, which has the same general form as the bony labyrinth
membranous labyrinth
Cross-sectional representation of semicircular canal and contained semicircular duct
slide 21 of membranosu labryrinth
Fluids in the inner ear?
Perilymph
Endolymph
Chemically similar to cerebrospinal fluid
Surrounds the membranous labyrinth
Perilymph
Within the membranous labyrinth
Has a high level of potassium ions (K+) which plays a role in generation of auditory signals
Endolymph
slide 23 image
23
is the oval central portion of the bony labyrinth
Vestibule
Part of the membranous labyrinth is within the vestibule, and is composed of two sacs,
the utricle and saccule, connected by a duct
The vestibule also contains the
oval window (vestibular window)
The semicircular canals are three bony structures
At approximately right angles to each other
Named according to position:
Anterior (oriented vertically)
Posterior (oriented vertically)
Lateral (oriented horizontally)
Semicircular canals :
A swollen enlargement called the
ampulla is at one end of each canal
Semicircular canals :
Parts of the membranous labyrinth that are inside the semicircular canals are called
semicircular ducts; they connect to the utricle of the vestibule
they connect to the utricle of the vestibule
semicircular ducts
Caused by an increased amount of endolymph, which enlarges the membranous labyrinth
Symptoms include fluctuating hearing loss (due to distortion of the basilar membrane), roaring tinnitus (ringing in the ears), whirling vertigo (dizziness)
The hearing may be lost over a number of years
Ménière’s disease
The vestibular branch of the vestibulocochlear nerve (cranial nerve VIII) consists of three nerves:
utricular, saccular, and ampullary
The nerves synapse with receptors for equilibrium
They have both first-order sensory neurons and motor neurons:
Sensory neurons carry sensory information from the receptors
Motor neurons carry feedback signals to the receptors to modify their sensitivity
Cell bodies of the sensory neurons are located in the
vestibular ganglia
Cell bodies of the motor neurons are in the pons, and project to the
semicircular canals, saccule, and utricle
The cochlea is a bony spiral canal
Its central supporting core is called the
modiolus
The cochlea has a Y-shaped partition that forms three channels:
Scala media (AKA cochlear duct) in the forks of the Y
Scala vestibuli, on one side, ending at the oval window
Scala tympani, the other side, ending at the round window
The scala vestibuli and scala tympani contain
Scala vestibuli and scala tympani are separated by the stem of the “Y” except at the apex of the cochlea, where there is an opening called the…
perilymph
…helicotrema (“the hole in the spiral”) that joins them
The ___ opens into the vestibule (hence its name)
scala vestibuli
The _____ (AKA scala media) is between the wings of the “Y”
cochlear duct
The scala media is a continuation of the membranous labyrinth into the cochlea
Membranes contain the perilymph within the different scalae:
Vestibular membrane of the scala vestibuli
Basilar membrane of the scala tympani
The ____ (AKA organ of Corti) is on the basilar membrane, within the cochlear duct
It contains hair cells, which are the receptors for hearing
spiral organ
It contains hair cells, which are the receptors for hearing
spiral organ (AKA organ of Corti)
Hair cells of the spiral organ are in two groups:
Inner hair cells, arranged in a single row
Outer hair cells, arranged in three rows
A hair bundle is at the apical tip of each hair cell
Stereocilia comprise the “hairs” but they are actually…
…long microvilli
Inner and outer hair cells synapse with both first-order sensory neurons and with motor neurons from the
cochlear branch of the vestibulocochlear nerve (cranial nerve VIII)
Cell bodies of sensory neurons are in the
spiral ganglion of the cochlea
The afferent fibers from the cochlea are myelinated dendrites of bipolar cells of the spiral ganglion. These bipolar neurons are the only neurons that have
a myelin sheath surrounding the cell body
Cell bodies of motor neurons are in the ___, and project to hair cells of the spiral organ
pons
The __ ___ projects over the hair cells, and is in contact with them
tectorial membrane
Alternating high and low pressure regions of a medium (generally air)
Frequency = pitch
Amplitude = volume = intensity
Sympathetic vibrations
Sound
Human hearing
Frequency range
Most acute 500 to 5000 Hertz (cps)
Audible range 20 to 20,000 Hz
Threshold defined as 0 dB at 1000 Hz, which is the point at which an average young adult can just distinguish sound from silence
Normal conversation is 60 dB
OSHA requires hearing plan when occupational noise levels exceed 90 dB
Rock concert and headphones produce >110 dB
Amplitude
STEPS IN HEARING
- Sounds are directed into the external auditory canal by the auricle
- Sound waves strike the eardrum, causing it to vibrate in sympathy
- The vibrations are transmitted through the auditory ossicles, and somewhat magnified due to the mechanical relationships of the ossicles
- The stapes vibrates, transmitting movements to the oval window, amplifying the energy due to differences between surface areas of eardrum and oval window
- Oval window moves in and out, setting up fluid pressure waves in the perilymph
- Pressure waves are transmitted from scala vestibuli to the scala tympani
- Pressure waves deform the walls of the scala vestibuli and scala tympani pushing the vestibular membrane back and forth
7a. Pressure waves from the scala vestibuli and scala tympani create pressure waves in the endolymph inside the scala media (cochlear duct) - Pressure waves in the endolymph cause the basilar membrane to vibrate, moving the hair cells of the spiral organ against the tectorial membrane
- Pressure waves cause vibration of the secondary tympanic membrane in the round window (no physiological consequence—fluid is incompressible)
Hair cells transduce mechanical vibrations into electrical signals by means of
mechanically gated ion channels
of differing heights comprise the hair bundles at the apex of each hair cell
Stereocilia
The tips of shorter stereocilia are connected by a __ __ __ to its taller stereocilium neighbor
tip link protein
A mechanically-gated ion channel called a __ ___ is associated with the tip link proteins
transduction channel
As stereocilia bend in the direction of the taller stereocilium to which they are connected, the tip links tug on
the transduction channels and open them
Steps in hearing
The open channels allow ___ in the endolymph to enter the cell
cations
Cations enter and produce a __ __ __, which spreads along the membrane
depolarizing receptor potential
Bending the stereocilia in the opposite direction closes transduction channels, allows repolarization, and
reduces neurotransmitter release from the hair cells
Cell bodies of the first-order sensory neurons are in the spiral ganglia, and their axons comprise the
cochlear branch of the vestibulocochlear nerve
Axons of the cochlear branch synapse with neurons in the cochlear nuclei in the
medulla oblongata (on the same side—no decussation up to this point)
Some axons from the cochlear nuclei decussate in the medulla and ascend in the lateral lemniscus on the opposite side, where they terminate in the
inferior colliculus of the midbrain
Other axons from the cochlear nuclei end in the __ ___ __ in the pons on each side. These also ascend in the lateral lemniscus tracts on both sides, and end in the inferior colliculi
superior olivary nucleus
Slight differences in the timing of nerve impulses arriving from each ear at the superior olivary nuclei enable us to
determine the direction of sounds
Other axons from the cochlear nuclei end in the superior olivary nucleus in the pons on each side. These also ascend in the __ and end in
lateral lemniscus tracts on both sides, and end in the inferior colliculi
From each inferior colliculus, nerve impulses are conveyed to the ___________________, then to the primary auditory area of the cerebral cortex
medial geniculate nucleus of the thalamus
From each inferior colliculus, nerve impulses are conveyed to the medial geniculate nucleus of the thalamus, then to the
primary auditory area of the cerebral cortex
may be caused by allergy, high or low blood pressure (blood circulation problems), a tumor, diabetes, thyroid problems, injury to the head or neck, as well as a variety of medications including anti-inflammatory medicines, antibiotics, sedatives, antidepressants, and aspirin
Tinnitus
The exact mechanism that causes tinnitus is not known. Younger people tend to have tinnitus as a result of exposure to loud noise. Older people who experience tinnitus often have a certain amount of hearing impairment related to the natural aging process
cool
Exceptionally loud noises damage stereocilia, causing them to mistakenly continue sending sound information to the auditory nerve as they move randomly in a state of irritation.
Sometimes tips of some stereocilia break off
Ringing is temporary because the tips grow back within about 24 hours
Unlike many other forms of tinnitus, this form has a known cause
Ringing due to loud noises
Deafness is significant or total hearing loss
Two broad types:
Sensorineural deafness, due to damage or disease of the sensorineural pathway (hair cells, cochlear branch of cranial nerve VIII)
Conduction deafness (conductive deafness), caused by impairment of mechanisms in the external and middle ear (otosclerosis (deposition of new bone around the oval window)), impacted cerumen, eardrum injury, stiffening of the joints of the auditory ossicles
due to damage or disease of the sensorineural pathway (hair cells, cochlear branch of cranial nerve VIII)
Sensorineural deafness,
caused by impairment of mechanisms in the external and middle ear (otosclerosis (deposition of new bone around the oval window)), impacted cerumen, eardrum injury, stiffening of the joints of the auditory ossicles
Conduction deafness (conductive deafness),
Exposure to loud noises damages hair cells of the cochlea
Continued exposure to high-intensity sounds is a cause of deafness
Noise-induced deafness
The cochlea has the ability to produce sounds, which are termed
otoacoustic emissions
They are usually inaudible, but can be picked up by a sensitive microphone next to the eardrum
Cause by vibrations of the outer hair cells in response to signals from motor neurons and to sound waves
otoacoustic emissions
Otoacoustic emissions
The vibrations of the outer hair cells set up a traveling wave that goes back toward the ____, causing the eardrum to vibrate
stapes
This provides a fast, inexpensive, noninvasive way to screen newborns for hearing defects, since in deaf babies ______ are not produced, or are greatly reduced in size
otoacoustic emissions
Equilibrium
Two types of equilibrium (balance) exist
Static equilibrium—the maintenance of the position of the body (mainly the head) relative to the force of gravity
Dynamic equilibrium—maintenance of body position (mainly the head) in response to sudden movements
the maintenance of the position of the body (mainly the head) relative to the force of gravity
Static equilibrium—
maintenance of body position (mainly the head) in response to sudden movements
Dynamic equilibrium—
Dynamic equilibrium
_____ is a complex of strange eye movements that occurs during and immediately after rotational movement
Nystagmus can be accompanied by vertigo
Vestibular nystagmus
Equilibrium pathway
Cell bodies of the first-order sensory neurons are in the __ __, and their axons comprise the…
vestibular ganglia
…and their axons comprise the vestibular branch of the vestibulocochlear nerve
Equilibrium pathway
Most of the axons of the vestibular branch synapse with neurons in the vestibular nuclei in the….
…medulla oblongata (on the same side—no decussation up to this point)
Equilibrium pathway
Most of the axons of the vestibular branch synapse with neurons in the vestibular nuclei in the….
…medulla oblongata (on the same side—no decussation up to this point)
Equilibrium pathway
The remaining axons enter the cerebellum through the….
The ___ and ____ are connected by bidirectional pathways
….inferior cerebellar peduncles.
The cerebellum and vestibular nuclei are connected by bidirectional pathways
Equilibrium pathway
The remaining axons enter the cerebellum through the….
The ___ and ____ are connected by bidirectional pathways
….inferior cerebellar peduncles.
The cerebellum and vestibular nuclei are connected by bidirectional pathways
Equilibrium pathway
The vestibular nuclei integrate information from…
vestibular, visual, and somatic receptors, then send commands via a number of nuclei and tracts:
Equilibrium pathway
The vestibular nuclei integrate information from…
vestibular, visual, and somatic receptors, then send commands via a number of nuclei and tracts:
Motion sickness
Appears to be due to sensory input mismatch:
Within a moving vehicle the immediate frame of reference (the vehicle) is
stationary according to visual inputs
Motion sickness
Appears to be due to sensory input mismatch:
A discrepancy arises when . . .
The surroundings are moving according to visual input
The vehicle is moving according to vestibular inputs (acceleration, deceleration, tilting, etc.)
Motion sickness
Appears to be due to sensory input mismatch:
The brain receives conflicting information, and its “confusion” causes
motion sickness
The receptor organs for equilibrium are called the vestibular apparatus, and include
Saccule
Utricle
Semicircular ducts (within the semicircular canals)
Walls of the utricle and saccule contain a small region called a ___?
___ it’s horizontal in utricle
vertical in the saccule
macula
Macula is horizontal in the utricle
Macula is nearly vertical in the saccule
The maculae consist of two kinds of cells:
Hair cells, which are sensory receptors
Supporting cells, which produce a gelatinous glycoprotein layer called the otolithic membrane, that rests on the hair cells
Hair cells are composed of hair bundles, having two types of hairs
Stereocilia (actually microvilli)
Kinocilium
One kinocilium per bundle
A true cilium
Longer than the longest stereocilia of the bundle
The stereocilia are connected by
tip links (same as in the cochlea)
A layer of calcium carbonate crystals, called ___, extends over the surface of the otolithic membrane
otoliths
Physiology of static equilibrium
When the head is tilted or accelerates, inertia causes the otolithic membrane to
slide over the hair cells, bending the hair bundles
Physiology of static equilibrium
Bending the hair bundles in one direction stretches the tip links, opening the mechanically-gated transduction channels, and producing
depolarizing receptor potentials and release of neurotransmitter
Physiology of static equilibrium
Bending the hair bundles in the other direction closes the __ and produces what?
transduction channels and produces repolarization
Physiology of static equilibrium
The maculae respond only to changes in ?
They adapt ___ ?
They do not report on unchanging head positions
The maculae respond only to changes in acceleration or velocity of head movement
They adapt quickly
They do not report on unchanging head positions
Dynamic equilibrium
The three semicircular ducts plus the saccule and utricle function in dynamic equilibrium (there are also visual and proprioceptor inputs, but these are not located in the
inner ear, so they are not generally discussed)
Dynamic equilibrium
Within the ampulla (dilated portion) of each duct is a small elevation called a crista (crista ampullaris)
Each crista contains
Hair cells
Supporting cells
Cupula, a mass of gelatinous material
Dynamic equilibrium
When the head moves the endolymph within the ampulla lags behind due to ___
This causes?
inertia
This causes the hair cells to bend, producing receptor potentials
Dynamic equilibrium
Receptor potentials lead to nerve impulses that pass along the
vestibular branch of the vestibulocochlear nerve (cranial nerve VIII)
Dynamic equilibrium
If the body continues to rotate at a constant rate, the endolymph eventually __ causing what?
If the body stops suddenly….
catches up, and stimulation of the hair cells ends
If the body stops suddenly, the endolymph keeps moving
