M22: Hearing and Vestibulation Flashcards
List the regions of the ear and explain the function of each region
External Ear: Funnels soundwaves to tympanic membrane which vibrates
—-> Soundwaves → Mechanical vibrations
Middle Ear: Ossicles transfer vibrations to oval window
Inner Ear: Vibrations in fluid triggers hair cells to depolarize
—-> Mechanical vibrations → Electrical signal
What are the anatomical structures in each region of the ear?
External ear
-Auricle = Elastic cartilage
—> large, fleshy structure on the lateral aspect of the head
—> Comes back to the same shape no matter how you bend it
- External acoustic meatus (ear canal)
—> Outer 1/3rd = cartilage
—> Inner 1/3rd = temporal bone
—-> Everything from the tympanic membrane to the auricle
-Cerumen (ear wax)
-Made up of specialized sweat glands and sebaceous glands
Middle ear
-Air-filled tympanic cavity inside temporal bone:
—> Made up of Tympanic membrane laterally
and Two windows (Superior oval window and Inferior round window) medially
-connected to the pharynx through the auditory (Eustachian) tube
—-> Contains an opening to the pharyngotympanic tube
-Auditory ossicles:
—> Malleus (hammer)
—-> Incus (anvil)
—–> Stapes (stirrup)
Inner ear
-Vestibule and Semicircular ducts
-Cochlea
-Divide into 2 regions (labyrinths):
—> Bony labyrinth
—–> Contains perilymph
—–> Composed of a series of canals embedded within the temporal bone
—–>Has two separate regions: Cochlea and Vestibule
—> Membranous labyrinth: Contains endolymph (inner fluid)
What are the functions of the anatomical structures in each region of the ear?
External ear
-Auricle
—> C-shaped curves of the auricle direct sound waves toward the external acoustic meatus
—–> Funnel and amplify sound into the meatus
—> Ridges of auricle aid in sound processing
—–>help pick up the location of the sound
- External acoustic meatus (ear canal)
—> Transfers soundwaves to tympanic membrane (eardrum)
-Cerumen (ear wax)
—> protects & lubricates skin – some defense
Middle ear
- Pharyngotympanic (Eustachian) tube allows pressure equalization on both sides of tympanic
membrane
- Must be equalized for eardrum (tympanic membrane) to function
- the tube is normally closed but will pop open when the muscles of the pharynx contract during swallowing or yawning
-Auditory ossicles:
–> Transfer mechanical vibrations to oval window
—> Malleus (hammer): attached to the tympanic membrane and articulates with the incus
—-> Incus (anvil): articulates with the stapes
—–> Stapes (stirrup): attached to the inner ear, where the sound waves will be transduced into a neural signal
Inner ear
-Vestibule and Semicircular ducts: Vestibulation (equilibrium) and balance
-Cochlea: Hearing
-Divide into 2 regions (labyrinths):
—> Bony labyrinth: contains cochlea for hearing and vestibule for equilibrium
—> Membranous labyrinth: where the gelatinous layers and specialized hair cells will be found that produce neural signals
Otitis Media
Infection of the middle ear
- Inflammation and fluid accumulation in the middle ear
- Causes inflammation and bulging of tympanic membrane
- Causes loss of hearing
Describe how sound is sensed and processed, using the anatomical structures found
in the cochlea.
- Tympanic Membrane
- Auditory Ossicles
- Oval Window
- Cochlea
—> 1. Scala vestibuli: contains fluid-filled (perilymph) tube, channel connected to oval window
—> 2. Scala tympani: channel connected to round, window contains perilymph, continuous with scala vestibuli,
—> 3. Cochlear Duct: central cavity of the cochlea that contains the sound-transducing neurons, contains endolymph (membranous labyrinth)
——-> Vestibular membrane: cochlear duct “roof”
——-> Basilar membrane: cochlear duct “floor”
———–> Supports spiral organ
———–> Moves up & down
——-> Spiral organ (of Corti): responsible for hearing
———–> Detects endolymph movement
———–> Thick sensory epithelium with hair cells (stereocilia)
—————> Synapse with cochlear nerve
—————> CN VIII
——-> Tectorial membrane: sits atop spiral organ
Overlying gelatinous mass the stereocilia are embedded Into
—————> Immobile
—————> When the pressure waves from the scala move the basilar membrane, the tectorial membrane slides across the
stereocilia
—————> Movement of the basilar membrane bends the stereocilia, depolarizing the hair cell membrane, triggering nerve impulses that travel down the afferent nerve fibers attached to the hair cells
Sound Wave Path Through the Ear
- Tympanic Membrane
- Auditory Ossicles
- Oval Window
- Scala vestibuli
- Cochlear duct
- Scala tympani
- Round window
- Sound waves vibrate tympanic membrane.
- Tympanic membrane vibrates ossicles.
- Vibration of stapes at the oval window creates waves in scala vestibuli.
- Waves in perilymph displace the endolymph and basilar membrane
- Hair cells vibrate against the tectorial membrane causing depolarization
and NT release - Information concerning the frequency and intensity of stimulation is
relayed to the CNS via the cochlear nerve.
High frequency sounds (e.g., -bird calls)
-Stimulates the spiral organ more proximal to the oval window
-Hair cells at the base of the cochlea are activated only by high frequencies
Low-frequency sounds (e.g., –deep thunder)
-Stimulates the spiral organ closer to the apex of the cochlea -helicotrema
-Hair cells at the apex of the cochlea are activated only by low frequencies
CNS Pathway: Audition
- Basilar membrane (of spiral organ)
- Cochlear part of CN VIII (vestibulocochlear nerve)
- Brainstem nuclei (Cochlear Nucleus) ← vestibulocochlear nerve synapse
- Inferior colliculi – (unconscious motor responses to sounds)
- Medial geniculate nucleus (thalamus)
- Primary auditory cortex
- Auditory association cortices
Explain how equilibrium sensations are sensed and processed using the anatomical structures of the vestibular complex.
Vestibulation: allow us to move around: do gymnastics, athletics, etc
Vestibule
- Utricle– horizontal movement
—-> composed of macula tissue
—-> contributes to controlling head and neck movements in response to vestibular signals
- Saccule– vertical movement
—-> composed of macula tissue
—-> contributes to controlling head and neck movements in response to vestibular signals
Semicircular canals/ducts
- contributes to controlling head and neck rotational movements in response to vestibular signals
—-> Anterior – sagittal rotation
—-> Posterior – coronal rotation
—-> Lateral–transverse rotation
Differentiate how the body senses acceleration/linear movement vs. rotational movement
Equilibrium: Orientation and Linear acceleration
- Vestibules contain macula (utricle and saccule covered in hair cells) which are specialized for sensing linear acceleration, such as when gravity acts on the tilting head, or if the head starts moving in a straight line
- The stereocilia and kinocilia are embedded in an Otolithic membrane (viscous gel, gelatinous layer covered in otoliths (calcium carbonate crystals))
- The otoliths push the gelatinous layer and bend the hair cells when the head moves. This affects NT release from the hair cells.
- It receives sensory information received about
orientation and linear acceleration.
Equilibrium: Rotation
-Rotational movement of the head is encoded by the hair cells in the base of the semicircular canals/ducts
-semicircular canals/ducts
—> Anterior - sagittal rotation
——> Detects rotation in the sagittal plane
——> Nodding “yes”, summersault, backflip
—> Posterior - coronal rotation
——> Detects rotation in the coronal plane
——> Tipping ear towards shoulder or a cartwheel
—> Lateral-transverse rotation
——> Detects rotation in the transverse plane
——> Shaking head “no” or spinning around
- Orientation for the anterior and posterior ducts are ~30-45 degrees off the cardinal plane of movement
- Ampulla: expanded region of each semicircular canal
—> the base of each semicircular canal, where it meets with the vestibule, connects to the ampulla (enlarged region)
—> Contains an elevated region covered by hair cells
—–> Hair cells respond to rotational movements, such as turning the head when saying no
Cupula: membrane that attaches to the top of the ampulla
—> overlying gelatinous dome that stereocilia and kinocilia are embedded into
—> As the head rotates in a plane parallel to the semicircular canal, the fluid lags, deflecting the cupula in the direction opposite to the head movement
Crista Ampullaris
Sensory organ of semicircular ducts
Describe the pathways vestibular and auditory senses take to reach their processing
centers in the brain.
-Sensory pathway for audition travels along the vestibulocochlear nerve, which synapses with neurons in the cochlear nuclei of the superior medulla
-Vestibular part of CN VIII
-Vestibular nuclei (medulla)
-Vestibular nuclei:
—> 1. Integrate sensory info concerning balance and equilibrium
—> 2. Relay info from the vestibular complex to the cerebellum
—> 3. Relay info from the vestibular complex to motor nuclei of the extraocular muscles of the eye
—> 4. Relay info from the vestibular complex to the cerebral cortex, providing a conscious sense of position and movement
—> 5. Send commands to other motor nuclei in the brainstem [(CN III, IV, VI, XI) eye, head, and neck movements] and spinal cord (reflex reactions to both limbs and trunk to regain balance)
