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80 Cards in this Set
- Front
- Back
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What does the peripheral auditory system include?
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Outer ear, middle ear, inner ear, VIII cranial nerve
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What is the pinna/auricle? What’s it composed of?
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It’s the outermost and most visible part of the auditory system. It forms a cup around the entrance to the external auditory meatus/canal. Its composed of soft tissue and cartilage.
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What is the function of the auricle?
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To capture, funnel, direct sounds toward external auditory meatus.
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Label the major landmarks of the Auricle:
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Helix, antihelix, tragus, antitragus, scaphoid fossa, triangular fossa, concha, earlobe/lobule
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What is the External Auditory Meatus/Canal? Where is it located? What is the shape/size?
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It’s the outer ear canal, who’s opening is found within the squamous portion of the temporal bone. It’s an oval shaped opening, 5-9mm in diameter, 25-35mm in length. It’s S-shaped and leads to the tympanic membrane.
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What makes up the lateral (outer most) one-third of the external auditory canal? Medial (inner most)?
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Lateral 1/3rd is cartilaginous, and contains hair follicles, sebaceous (sweat and oil secreting) glands, and ceruminous (wax secreting) glands. Medial 2/3rd is osseous with no hair or glands.
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What is the function of the external ear canal?
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It directs sound toward eardrum.
Glandular secretions help to keep canal skin lining clean, supple, and avoid dryness. Along with hair, it helps protect eardrum from foreign objects . |
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What is the outer ear's mode of operation?
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Air vibration- Transmission
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The auricle and external ear canal amplify what frequency sounds to eardrum?
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Mid to higher frequency sounds.
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What are the resonant properties of the concha and ear canal?
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Concha resonance at 4500-5000 Hz
Ear canal resonance at 2500-3500 Hz |
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What structures are included in the middle ear?
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Tympanum and epitympanic recess, tympanic membrane, ossicular chain, middle ear muscles and ligament, Eustachian tube
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Describe the shape and dimensions of the tympanic cavity:
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Irregular shaped air-filled cavity.
Width/transverse: 2-4 mm Superior-inferior/vertical: 15 mm Anterior-posterior/front to back: 15 mm Capacity/volume: 1-2 cubic cm (cc) |
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What’s the lateral or membranous wall of the tympanic cavity?
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Most of it is made up by the eardrum/tympanic membrane
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What is the medial/labyrinthine wall?
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It’s a rounded prominence that projects into the middle ear. It’s part of the cochlea. It includes the round window (fenestra vestibuli), round window (fenestra rotunda) and houses the facial nerve (aqueduct of Fallopius).
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What is the posterior or mastoid wall?
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It has irregular shaped openings. It communicates with air spaces in the mastoid bone (along with superior wall). There is an opening there for the chorda tympani nerve (anterior portion of the tongue for taste). Pyramidal eminence (canal for the stapedius muscle)
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What is the anterior or carotid wall?
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It is separated from the carotoid canal by a thin plate of bone. It contains the cochleariform process, which the orifice for the canal that houses the tensor tympani muscle. It also has the orifice to the Eustachian tube.
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What is the Superior or tegmental wall?
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It is a thin wall that separates the tympanic cavity from the brain. It’s the wall that communicates with air spaces in the mastoid bone (along with the posterior wall).
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What is the interior fundus/floor wall?
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It separates the tympanic cavity from the jugular fossa, which houses the jugular vein.
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What is the Tympanic membrane?
What part of the ear is it considered? What is it's area? |
It’s a cone-shaped membrane that forms the boundary between the outer ear and the middle ear. It’s considered part of the ME. It is 55-90 cubic mm in area.
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What is the tympanic annulus?
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It’s a stiff cartilaginous ring at the periphery, which fits into the tympanic sulcus.
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What is the tympanic sulcus?
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A groove in the lateral wall
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What is the pars tensa?
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The part of the tympanic membrane that includes the middle ear. It’s the largest surface, and makes up 2/3-3/4 of eardrum. It’s most responsible for sound transmission/vibrating.
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What is the pars flaccida? Also know as what?
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It is also known as Shrapnell’s membrane. It is the posterior superior portion of the TM. It lacks fibrous middle layer and tympanic annulus. It does not fit into the tympanic sulcus.
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What is the umbo?
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Malleus, incus, stapes- ossicular chain.
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How are the ossicles held in place?
What are the joints called? |
They are held in place by a suspension system consisting of attatchment of malleus to the eardrum at umbo, and attachments to each other.
Malleus to incus= indudomalleolar/malleoincudal joint (double saddle type) Incus to stapes=incudostapedial joint (ball and socket type) |
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What is the tensor tympani muscle? Length?
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It connects to the manubrium of the malleus. It is innervated by cranial nerve V (trigeminal). It is contained within the cavity near the anterior wall of the middle ear tympanum. It is 25 mm in length.
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What is the stapedius?
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It connects to the head of the stapes. It is innervated by cranial nerve VII (facial). It is 6 mm in length and is the smallest muscle in the body. It is contained within the paramidal eminence, the cavity near posterior wall of the middle ear cavity.
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What is the function of the Eustachian tube?
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It connects the tympanum to the nasopharynx. It is 35 mm in adults, half as long in children. It equalizes pressure, aerates middle ear tissue, and drains middle ear fluids and secretions into nasopharynx.
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How is the Eustachian tube kept closed? Opened?
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Closed by actions of salpingopharyngeus and salpinggopalatius.
Open by levator palitini and tensor levi palitini during swallowing, yawning, talking etc. |
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Talk about acoustic reflex:
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Stiffening results in reduction of energy transmission of lower pitched/frequency sounds though in middle ear. It gives a 10-20 dB reduction for frequencies below 1000 Hz
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How much sound would be lost without middle ear?
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30 dB SPL
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What does the transformer action of the middle ear provide?
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Approximately 32.9 dB gain. It recaptures what is lost due to air-fluid impedance mismatch.
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What is the shape of the bony/osseous/perilymphatic labyrinth within the temporal bone?
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Snail-shaped/spiral canal is 35 mm long. There are 2 5/8 turns in humans.
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What is the modiolus?
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The inner pillar of bone in the coils
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What is the osseous spiral lamina?
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It is a thin spiral shelf of bone which projects from the modiolus and reaches half way toward the outer wall of the canal. It connects to the basilar membrane and Reisner’s membrane. It helps to divide the cochlea into 3 passages, except at apex. It is broadest at the basal end.
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What are the 3 canals of the cochlea?
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Scala vestibuli, Scala tympani, and Scala media
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What is the scala tympani and scala vestibuli filled with?
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Perilymph fluid, which is low in potassium and high in sodium
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What is the scala media filled with?
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Endolymph, which is high in potassium and low in sodium
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On the basilar membrane, where do low frequency sounds react? High frequency?
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Low frequencies at apex, high frequencies at the base
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Where are sensory hair cells located?
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On the upper surface of the basilar membrane and found along the entire length of the cochlear duct
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Describe inner hair cells:
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There is one row, following the entire length of the basilar membrane. There are 3500 pear shaped hair cells, each has 50-70 sterocillia in U or straight line pattern. They are greater in diameter than OHC.
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Describe outer hair cells:
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There are 3-4 rows, totaling 12,000-20,000 hair cells. They are cylindrical in shape and each of 150 sterocillia. The numbers increase from 58 at the apex to 150 at the vase and are lined in a W or V pattern. The tallest stereocilla are attached to the undersurface of the tectorial membrane.
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What is the function of the tunnel of corti?
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To separate the IHCs from the OHCs
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What is the function of the pillars of Corti?
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To separate the IHCs from the OHCs
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What about the pillars of Corti?
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They are between the OHCs and IHCs and are tilted to enclose the tunnel of corti.
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What are the IHCs supported by?
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A cup-like cell called a phalangeal cell
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What are OHCs supported by?
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Deiter's cell
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What is reticular lamina?
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It is made up of the tops of hair cells along with processes of the phalangeal and Deiter’s cells. It provides a source of support for the hair cells at their upper surfaces.
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What is the tectorial membrane?
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It juts into the scala media from the osseous spiral lamina. It attaches to the spiral limbus medially and connects laterally to Hensen’s cells (a very fragile net-like connection). It runs over the hair cells and has a gelatinous composition (90% water) to aid in bending.
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What is stria vascularis?
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It is attached to the vascular complex. It lies on top of the spiral ligament, and is the primary source of nutrients and oxygen to the scala media. It manufactures endolymph and eliminates waste products.
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What is the inner ear mode of function?
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Mechanical (at oval window, stapes moves in and out), hydrodynamic (celia bent from regular position, fluid displaced in oval window), electrochemical (occurs at neural level, neurotransmitters)
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Why doesn’t pressure get displaced via the helicotrema?
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If this happened, there would be no displacement of the basilar membrane.
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What are afferent neurons?
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They carry information to the central nervous system
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How do neurons enter the cochlea?
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Through the habenula perforata
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How are afferent neurons distributed between the IHCs and OHCs?
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90-95% are inner radial fibers. Each receives 20 radial fibers.
5-10% are outer spiral fibers. Each neural fiber innervates 10 OHCs |
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What are Efferent Neurons?
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They carry information away from the CNS. It runs parallel to the afferent system, extending from the cortex to the cochlea. They are less extensive than afferent neurons. There are 2 efferent fibers for every 100 afferent fibers. They are more extensive for OHCs than IHCs. OHC fibers directly synapse, IHC fibers only synapse with afferent neurons. Efferent system may have both inhibitory and excitatory influences on the afferent system.
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How many neurons are between the cochlea and auditory cortex?
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About 4, with VIII cranial nerve (auditory portion) being 1st -order neuron
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Where does the central auditory system begin?
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It begins at the brainstem, where the axonal extensions of CN VIII innervate neurons, which make up the cochlear nucleus.
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The axonal extensions of the CN VIII do what?
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Innervate neurons, which make up the cochlear nucleus.
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The brainstem is a juncture of what?
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Pons and the medulla.
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What can this juncture be referred to as?
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Cerebellopontine angle.
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The cochlear nerve fibers are tonotopic. Where are high and low frequency fibers bundled?
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High frequency fibers are on the outside/basal end.
Low frequency fibers are on the inside/ apex/apical end. |
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What is the “way station”?
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Ascending central auditory pathway involves multiple nuclei. It is a collection of specialized cell bodies. They include: The cochlear nucleus, superior olivary complex, lateral lemniscus, inferior colliculus, and medial geniculate body.
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What are the two ascending pathways from the cochlear nucleus?
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Ipsilateral: 1/3 of fibers from cochlear nucleus remain on the same side to ascend the superior olivary complex
Contralateral: 2/3 or fibers cross over/ decussate the brainstem to the other superior olivary complex. The trapezoid body is made up of the neural tracts that cross over. |
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Temporal lobes in each hemisphere are connected through the what?
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Corpus callosum
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T/F There are multiple neural tracts or relays?
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True!
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T/F Of the multiple neural tracts, all of them synapse in each of the major nuclei.
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False, not all of them synapse in each other, they can skip around.
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All neurons will synapse at the _____________ before going toward primary auditory cortex in the temporal lobe.
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Medial geniculate body.
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Where does the afferent/ascending pathway terminate?
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In the primary auditory cortex reception area, AKA Herschel’s gyrus (tranverse temporal gyrus)
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What are the two main segments comprise the efferent (centrifugal) or descending auditory pathways?
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Cortex and rostral brainstem system:
Made from the cortex fibers projects to neurons in the medial geniculate body and various other nuclei in the brainstem. The projections are also thought to descend to the sensory hair cell level. Very little is known about these systems. The Olivocochlear system (olivocochlear bundle): Made up of neurons, which make up medial and lateral superior olivary complex nuclei on both sides of the brainstem. Projections descend from the superior olivary complex to the organ of Corti. |
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What is the function of the afferent central auditory system?
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The afferent pathway is responsible for conveying information about the auditory signal from the peripheral auditory system, through the brainstem to the cortex. Each nucleus along the ascending pathway is tonotopically organized (using frequency cues). Each nucleus processes temporal/timing and intensity cues. The neurons in the primary auditory cortex also maintain a representation of the tonotopic organization (frequency map) of the basilar membrane.
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Where does the auditory system from both ears come together?
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Medial and lateral superior olivary complex nuclei. Analysis of timing/time of arribal and intensity difference between the two ears provide important cues for sound localization.
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What are binaural cues?
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Input from ipsilateral and contralateral cochlear nuclei.
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What are other binaural tasks?
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Binaural fusion, binaural interaction
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Where is language and speech processing mostly performed?
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In the left hemisphere
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What is the “right ear advantage”?
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When speech is directed to the right ear, contralateral pathway is stronger, so more neural input goes to the left hemisphere. When speech is directed to the left ear, contralateral pathway is stronger, so more neural input goes to the right hemisphere, then it must be delivered to the left hemisphere for decoding.
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Where does decoding of complex sounds with tonal quality (music) occur?
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Primarily in the right hemisphere
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What is the path of the efferent CANS? What is the function?
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The efferent pathways travel downward toward the nuclei. The pathway is believed to impact the afferent system in primarily an inhibitory way.
It modifies neural signals that are on their way to the auditory center in the brain. |
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What is the Olivocochlear bundle comprised of?
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Crossed bundle: most stimulate outer hair cells in the contralateral cochlea directly
Uncrossed bundle: most stimulate afferent neurons to the inner hair cells in the ipsilateral cochlea. |
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What is the function of the Olivocochlear bundle?
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It influences/inhibits the electromotility/mechanical action of the outer hair cells. It decreases the “amplifier” effect of the OHC on the IHC function. It also aids out perception and understanding of speech in adverse listening conditions (background noise).
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